The mammalian genome encodes 49 proteins that possess a PX (phox-homology) domain, responsible for membrane attachment to organelles of the secretory and endocytic system via binding of phosphoinositide lipids. The PX domain proteins, most of which are classified as SNXs (sorting nexins), constitute an extremely diverse family of molecules that play varied roles in membrane trafficking, cell signalling, membrane remodelling and organelle motility. In the present review, we present an overview of the family, incorporating recent functional and structural insights, and propose an updated classification of the proteins into distinct subfamilies on the basis of these insights. Almost all PX domain proteins bind PtdIns3P and are recruited to early endosomal membranes. Although other specificities and localizations have been reported for a select few family members, the molecular basis for binding to other lipids is still not clear. The PX domain is also emerging as an important protein–protein interaction domain, binding endocytic and exocytic machinery, transmembrane proteins and many other molecules. A comprehensive survey of the molecular interactions governed by PX proteins highlights the functional diversity of the family as trafficking cargo adaptors and membrane-associated scaffolds regulating cell signalling. Finally, we examine the mounting evidence linking PX proteins to different disorders, in particular focusing on their emerging importance in both pathogen invasion and amyloid production in Alzheimer's disease.

INTRODUCTION

Eukaryotic cells contain numerous membrane-bound organelles involved in secretion and endocytosis. Transmembrane proteins, lipids and other critical cargo molecules must be selectively sorted and transported between these compartments via membrane trafficking processes, involving either vesicular or tubulovesicular carriers or compartmental maturation and fusion events. Furthermore, it is now apparent that endocytic compartments are also critical platforms for the regulation of cell signalling, well beyond the traditional function of controlling receptor degradation [1,2]. The mammalian Phox-homology (PX) domain-containing molecules constitute a large family of at least 49 proteins. They are predominantly found in the endosomal system, but also localize to other cellular compartments and regulate diverse trafficking and signalling processes in the cell. The PX domain is a membrane recruitment module that binds to PtdInsP lipids (phosphoinositides) on the cytoplasmic leaflets of different organelles, similar in function to other lipid-binding domains such as the PH (pleckstrin homology), FYVE (Fab1p/YOTB/Vac1p/EEA1) and ENTH (epsin N-terminal homology) domains. This association defines the cellular localization of the different PX proteins and hence is critical to their function. The present review summarizes recent progress in defining the structural and functional properties of the PX domain-containing proteins, and presents an update of some previously ambiguous structural classifications of the proteins. We provide a survey of the diverse biomolecular interactions that are regulated by these molecules, demonstrating their central functions as both cargo adaptors in cell trafficking and scaffolds regulating signal transduction, and discuss some of the recent work on previously poorly characterized PX domain-containing protein families. Finally, we highlight the emerging roles of PX proteins in disease.

THE PX DOMAIN

Structure of the PX domain and binding to the endosomal lipid marker PtdIns3P

The PX domain is a globular fold approximately 110 residues in length, composed of three β-strands followed by three α-helices (Figure 1). Specific features of this protein fold are a long proline-rich loop between helices α1 and α2, and an electropositive basic pocket that is involved in direct binding of negatively charged phosphate groups of phosphoinositides [3]. In addition several studies have highlighted the role of adjacent hydrophobic residues in membrane penetration in at least some PX domains, and an additional positively charged surface patch, which is able to associate weakly with other anionic lipids, such as phosphatidylserine [48].

Structure of the PX domain

Figure 1
Structure of the PX domain

(A) Ribbon and surface structures of a representative PX domain from p40phox in complex with PtdIns3P (PDB code 1H6H). Key determinants of the interaction are the arginine side chain electrostatic association with the 3-phosphate (ArgP3), stacking of the inositol ring with the tyrosine (or phenylalanine) side chain immediately downstream from the conserved arginine residue (Tyrinositol), contact of a lysine side chain with the 1-phosphate (LysP1), and hydrogen bonds of the 4- and 5-hydroxy groups to a second arginine side chain (Arg4,5-hydroxyl). The polyproline loop also forms a steric block of potential 5-phosphate groups in the binding pocket. The PtdIns3P headgroup is located within a deep positively charged pocket. The consensus PX domain-binding sequence is shown below. See also Supplementary Movie S1 at http://www.BiochemJ.org/bj/441/bj4410039add.htm. (B) Structure of the human SNX5 PX domain [22] overlaid with the human PX domain of SNX9 within the SNX9 PX-BAR assembly [18]. The SNX9 protein is coloured in grey, whereas SNX5 is coloured dark blue to light blue (N- to C-terminal). Bound PtdIns3P molecules are shown as spheres, with carbon atoms coloured green. A schematic membrane is indicated with a curvature that follows the curvature of the SNX9 PX-BAR assembly. The SNX5 helical insertion, indicated by the broken red circle, will clearly form steric interactions with the membrane environment in this orientation. SNX5 is only shown aligned with one subunit of the PX-BAR dimer for clarity.

Figure 1
Structure of the PX domain

(A) Ribbon and surface structures of a representative PX domain from p40phox in complex with PtdIns3P (PDB code 1H6H). Key determinants of the interaction are the arginine side chain electrostatic association with the 3-phosphate (ArgP3), stacking of the inositol ring with the tyrosine (or phenylalanine) side chain immediately downstream from the conserved arginine residue (Tyrinositol), contact of a lysine side chain with the 1-phosphate (LysP1), and hydrogen bonds of the 4- and 5-hydroxy groups to a second arginine side chain (Arg4,5-hydroxyl). The polyproline loop also forms a steric block of potential 5-phosphate groups in the binding pocket. The PtdIns3P headgroup is located within a deep positively charged pocket. The consensus PX domain-binding sequence is shown below. See also Supplementary Movie S1 at http://www.BiochemJ.org/bj/441/bj4410039add.htm. (B) Structure of the human SNX5 PX domain [22] overlaid with the human PX domain of SNX9 within the SNX9 PX-BAR assembly [18]. The SNX9 protein is coloured in grey, whereas SNX5 is coloured dark blue to light blue (N- to C-terminal). Bound PtdIns3P molecules are shown as spheres, with carbon atoms coloured green. A schematic membrane is indicated with a curvature that follows the curvature of the SNX9 PX-BAR assembly. The SNX5 helical insertion, indicated by the broken red circle, will clearly form steric interactions with the membrane environment in this orientation. SNX5 is only shown aligned with one subunit of the PX-BAR dimer for clarity.

A survey of the known structures of mammalian and yeast PX proteins, their localization and lipid binding in vitro reveals a number of insights into the PX domain phosphoinositide specificity (Figure 1, and Supplementary Movie S1, Table S1 and Figure S1 at http://www.BiochemJ.org/bj/441/bj4410039add.htm). A global assessment of Saccharomyces cerevisiae PX domain molecules demonstrated an almost absolute PtdIns3P specificity [9], and a review of the literature presents an overwhelming consensus that mammalian PX domains also show a preference for PtdIns3P (see Supplementary Table S1). PtdIns3P is primarily found on early endosomal limiting membranes and therefore most commonly directs PX protein recruitment to PtdIns3P-enriched endosomal organelles. It should be noted, however, that distinct pools of PtdIns3P can be found in other compartments, such as the plasma membrane, being often generated during specific signalling processes [10]. Currently there are 27 structures of mammalian PX domains available in the PDB (from 14 different proteins), but only two have been solved in complex with PtdIns3P: p40phox (PDB code 1H6H) and SNX9 (sorting nexin 9; PDB code 2RAK). There are five known structures of yeast PX domains, with one structure of Grd19p/Snx3p in complex with PtdIns3P (PDB code 1OCU). In addition, the binding of PtdIns3P to the SNX17 and SNX22 PX domains has been analysed using NMR and restrained computational docking approaches [11,12]. These studies reveal the key determinants for PtdIns3P binding (Figure 1 and Supplementary Table S1) [3]. Each moiety of the PtdIns3P headgroup interacts with a specific and strictly conserved side chain of the PX domain. The defining 3-phosphate forms electrostatic bonds with a conserved arginine side chain. The inositol group forms a key stacking interaction with a conserved tyrosine residue (or in some cases phenylalanine) immediately one residue downstream of the conserved arginine. The 4- and 5-hydroxy groups of the inositol form hydrogen bonds with a conserved arginine side chain, which helps orient the PtdIns3P in the binding pocket and also sterically precludes binding of 4- or 5-phosphorylated lipids. In most cases, the polyproline loop also creates a steric boundary against incoming 5-phosphate groups, although this loop is inherently flexible and may be able to alter its conformation. Finally, the 1-phosphate is co-ordinated by a conserved lysine side chain, which is immediately downstream of the polyproline loop. The necessary consensus sequence in PX domains for PtdIns3P binding is thus R[Y/F]x23–30Kx13–23R.

Apart from lipid binding by the PX domain, a very important additional factor is the contribution of associated domains and other molecular interactions that drive and enhance membrane attachment through ‘coincidence detection’ [13]. Thus membrane attachment specificity may be controlled not only by the PX domain, but also by combination with domains that associate independently with membrane lipids [e.g. BAR (Bin/amphiphysin/Rvs), FERM (band4.1/ezrin/radixin/moesin) and PH domains] or bind to other membrane-associated proteins such as Rabs or cargo molecules.

Do PX domains bind other phosphoinositides?

PtdIns3P is the most common phosphoinositide bound by PX domains; however, many other phosphoinositide interactions have been reported, suggesting a diverse role in membrane trafficking or signalling at different cellular compartments (Supplementary Table S1). Typical reported affinities (Kd values) in vitro are of the order of 0.1–10 μM, but vary wildly from nanomolar to millimolar values depending on the PX domain studied and sometimes even for the same PX domain. Assessing the phosphoinositide binding of PX domain proteins is complicated by the range of different methods used and the relative reliability of these methods [14,15]. Despite the wide variety of other phosphoinositide specificities reported, there is still no conclusive structural indication of how these interactions occur. Indeed, a naïve analysis of the available structural data predicts that other phosphoinositides apart from PtdIns3P will not be able to associate with PX domains, unless their binding mode is significantly different from that demonstrated for PtdIns3P (Supplementary Table S1 and Figure S1). In most cases there are steric considerations that preclude the association of 4- and 5-phosphate groups, and where this is not the case there are no obvious determinants for specific coordination of these phosphates as might be expected.

This lack of a clear mechanistic basis for binding of alternative phosphoinositides to PtdIns3P suggests that cases where other specificities are reported could merit further scrutiny, and we have selected two cases to illustrate this point. SNX9 has been reported to have a functional preference for PtdIns(4,5)P2 in liposome-binding assays and in vitro assays for stimulation of dynamin and N-WASP [neuronal WASP (Wiskott–Aldrich syndrome protein)] activities, but it can associate with all other phosphoinositide lipids, including PtdIns3P [1621]. This liposome association, however, requires co-operation of the SNX9 C-terminal BAR domain, thus clouding the PX domain specificity [18,20]. The structure of SNX9 was determined by crystallography in the presence of PtdIns3P (PDB code 2RAK), but notably, despite soaking with other phosphoinositide lipids, none were observed to bind the PX domain [18]. Furthermore, additional biochemical data shows that mutation of the PX domain abrogates binding of the PX-BAR unit of SNX9 to PtdIns3P- but not PtdIns(4,5)P2-containing liposomes [18]. This suggests that the SNX9 PX domain is specific for PtdIns3P, whereas the binding of PtdIns(4,5)P2 is mediated primarily by the SNX9 BAR domain.

SNX5, and its related homologues SNX6 and SNX32 have an unusual PX domain with a large conserved insertion following the polyproline loop [3]. The structure of the SNX5 PX domain shows that this insertion forms an extended helix–turn–helix structure [22] (PDB code 3HPC). The authors used NMR to map the binding of different phosphoinositides and suggested that PtdIns(4,5)P2 binds to a site overlapping the approximate location where PtdIns3P binds other PX domains. However, their data shows that the affinity is extremely weak (Kd>400 μM). It also contradicts previous studies from their own group [23] and perhaps, more importantly, does not explain cell localization data showing that SNX5 is only membrane-associated in the presence of SNX1 [24]. As the structure of SNX5 reveals that it lacks both conserved residues required for phosphoinositide binding and an identifiable binding pocket for PtdIns(4,5)P2, the specificity of SNX5 certainly merits closer scrutiny. In conclusion, although mammalian PX domains have been reported to have specificities for phosphoinositides other than PtdIns3P, a detailed structural explanation is required to understand precisely how they are associated.

The PX domain as a protein-interaction module

Studies of the PX domain have almost exclusively focused on its ability to bind phosphoinositides, but there is accumulating evidence that the PX domain can also act as a protein-scaffolding device. We have surveyed all reported protein–protein interactions of PX domain-containing molecules, and a number of these occur directly via the PX domain itself (Supplementary Table S2 at http://www.BiochemJ.org/bj/441/bj4410039add.htm). Compared with the detailed molecular understanding we now have of PtdIns3P binding, how PX domains control protein–protein interactions remains very poorly understood. One common feature of PX domains is the presence of a polyproline loop between helices α1 and α2, which may potentially be involved in interactions with SH3 (Src homology 3) domains. Indeed both intramolecular and intermolecular SH3 domain binding has been observed. An example of the former is the binding of C-terminal SH3 domains of p47phox to the p47phox PX domain [25], an interaction that regulates its activation [26]. An example of an intermolecular association is the binding of the PLCγ1 (phospholipase Cγ1) SH3 domain to the polyproline loop of the PLD1 (phospholipase D1) and PLD2 PX domains, important in EGF (epidermal growth factor) signalling [27]. Given the importance of the dynamic remodelling of the polyproline loop on PtdIns3P binding, this also suggests a possible role for protein–protein interactions in regulating membrane association [28].

A number of other direct protein–protein interactions involving PX domains have also been reported. The PX domains of PLD1 and PLD2 have been found to bind to the GTPase domain of dynamin and are able to act as GAPs (GTPase-activating proteins) affecting dynamin-mediated endocytosis [29]. PLD1 and PLD2 PX domains are also able to associate with the exocytic SM (Sec/Munc) protein Munc18-1, and this association potently inhibits the phospholipase activity of the proteins [30]. The PX domains of a number of PX proteins, including SNX1, SNX2, SNX4 and SNX6, can associate with the cytoplasmic tails of members of the TGF-β (transforming growth factor β) receptor family [31]. The functional significance of these interactions have not been well characterized, but overexpression of SNX6 was found to downregulate TGF-β signalling. The SNX2 PX domain was also found to bind to the DEAD-box helicase Abstrakt [32], although again the functional importance of this interaction is not clear. The vesicle coat protein clathrin can bind to several PX domains through a novel inverted clathrin box sequence, including SNX1, SNX2, SNX3 and SNX4 [33]. The SNX6 PX domain can drive association with the oncogene Pim-1, resulting in SNX6 phosphorylation and nuclear translocation [34], although once more the role of this nuclear localization remains a mystery. Intriguingly, the SNX9 PX domain is able to bind to and stimulate phosphoinositide kinases, implying that a positive feedback mechanism between phosphoinositide generation and effector binding may be involved in SNX9-mediated endocytosis and signalling [16,19]. A final example of PX domain protein interactions involves the binding of SNX20 to the cytoplasmic tail of the transmembrane cell-surface protein PSGL-1 (P-selectin glycoprotein ligand 1), discussed below in more detail [35].

Taken together, the evidence is substantial that PX domains act not only as lipid recognition modules, but play a key role in protein–protein interactions, and it will be of major interest to determine the molecular details of how these interactions occur. There is an obvious parallel here between the PX domain and the PTB (phosphotyrosine binding)/PH domains [36]. Like the PX domain, these are small modules of approximately 120 amino acids that bind to different phosphoinositides and are found in a number of different endocytic adaptors and signalling molecules. In addition, they are known to associate directly with other proteins, typically via short peptide motifs. A similar understanding of the protein-binding partners of the PX domain will allow us to discern common features governing their association, will lead to the identification of other interacting molecules, and will drive the design of specific mutants aimed at dissecting the functional importance of PX domain protein recruitment.

THE MAMMALIAN PX PROTEIN FAMILY – AN UPDATE

There are currently 49 known proteins that contain a PX domain encoded in the human genome. Most of these are modular proteins containing one or more additional domains with diverse functions, including membrane remodelling, phosphoinositide kinase activity, phospholipase activity, protein–protein interaction and numerous other functions both known and unknown. We have revisited recent catalogues of the PX domain proteins [3,3740], and in Table 1 and Figure 2 we propose a modified classification based not only on sequence homology or known domains, but also on the presence of conserved structural elements defined by careful analysis of secondary-structure predictions. This reveals that in some cases proteins have been misclassified and in other cases there is strong evidence for the presence of conserved domains not previously characterized. The classification of PX proteins into related structural subfamilies provides an important basis for considering both the common and distinct functions of these diverse proteins. Some of these subfamilies contain many members, such as the PX-BAR and PX-only families, whereas others contain only a single member. The majority of PX domain proteins have been named SNXs [3,37]. This terminology was originally used by Kurten et al. [41], after identification of SNX1, and later this nomenclature was refined to refer to proteins that have greater than 50% sequence similarity to SNX1 in the PX domain [42,43]. A difficulty with this nomenclature arises from the fact that the classification of PX proteins as SNXs remains somewhat arbitrary. As just one example, it is not obvious why TC-GAP (TC10/cdc42 GAP) should also have the name SNX26, whereas GC-GAP (GAB/cdc42 GAP) does not have an SNX moniker. Therefore we propose that current common names for these proteins remain in place, but that a new SNX name is assigned for any future molecules identified for the PX family (e.g. C6ORF145, which we have named SNX34; see below).

Table 1
Subfamilies of mammalian PX proteins on the basis of domain architecture
Subfamily Member(s) Notes 
PX-BAR SNX1, SNX2, SNX4, SNX5, SNX6, SNX7, SNX8, SNX30, SNX32 Each protein has a C-terminal BAR domain involved in membrane tubulation. Several also have N-terminal extended sequences, thought to be involved in protein–protein interactions (e.g. SNX1 and SNX2) 
SH3-PX-BAR SNX9 (SH3PX1), SNX18, SNX33 These molecules are very similar in architecture to the PX-BAR proteins, except that they have an N-terminal SH3 domain that binds to polyproline sequences and an intervening low-complexity region containing AP2- and clathrin-binding motifs 
PX-SH3 SH3PXD2A (SH3MD1, FISH), SH3PXD2B, SNX28 (NOXO1), p47phox (NCF1), p40phox (NCF4) SNX28, p47phox and p40phox are components of the NADPH oxidase complex. The PX-SH3 proteins have various numbers of SH3 domains C-terminal to the PX domain (from 1 to 5) 
PX-SH3-GAP SNX26 (TC-GAP), PX-RICS (GC-GAP, p250GAP) The PX-SH3-GAP proteins have very long extended C-terminal domains with no identified structural motifs 
PX-FERM SNX17, SNX27, SNX31 The FERM domain has all three modules of a typical FERM domain (F1, F2 and F3), except that the F2 module is significantly smaller. SNX27 contains an additional N-terminal PDZ domain 
PXA-RGS-PX-PXC SNX13, SNX14, SNX19, SNX25 Each PXA-RGS-PX-PXC protein possesses two N-terminal hydrophobic stretches predicted to form transmembrane helices. Each PXA-RGS-PX-PXC protein possesses an RGS domain, except for SNX19 
PX-serine/threonine kinase PXK, RPK118 (RPS6KC1), SGK3 (CISK) PXK and RPK118 are predicted to have non-catalytic serine/threonine-kinase domains. RPK118 may also possess an MIT domain 
PI3K-PX PI3K-C2α, PI3K-C2β, PI3K-C2γ These are type II PI3K enzymes with multiple domains, including Ras-binding domains, C2 domains, a PI3K domain and a PI3KC2 homology domain of unknown structure and function 
PX-PH-PLD PLD1, PLD2 These proteins have two separate membrane-recruitment domains (PX and PH) coupled to a PLD domain 
PX-PXB SNX20 (SLIC-1), SNX21 SNX20 and SNX21 are highly homologous and share a conserved helical domain (PXB) of ~140 residues downstream of the PX domain. The PXB domain may be composed of up to three TPR helical repeats 
PX-only SNX3, SNX10, SNX11, SNX12, SNX22, SNX24, SNX29, HS1BP3 These proteins have been annotated as having no identified domains outside of the PX domain [3,37]. In all cases, the proteins possess short extra sequences without predicted secondary structure. The C-terminal tail of HS1BP3 is a proline-rich region 
Kinesin-PX SNX23 (KIF16B) SNX23 is a member of the kinesin family of microtubule motors. It includes an N-terminal kinesin motor domain, a putative forkhead association (FHA) domain and a central coiled-coil dimerization domain 
PX-MIT SNX15 SNX15 includes a C-terminal MIT domain 
PX-LRR-IRAS IRAS (nischarin) IRAS is a large protein ~1504 residues in length. Apart from the N-terminal PX domain, IRAS has a predicted leucine-rich repeat region from approximately residues 220 to 397, and secondary structure predictions indicate that the C-terminal region from approximately residue 570 onwards is composed of one or more structural domains with mixed α/β topologies. 
PX-SNX16 SNX16 SNX16 possesses significant predicted helical structure from between approximately residues 220 and 310 downstream of the PX domain 
SNX29-PX SNX29 SNX29 possesses significant predicted helical structure between approximately residues 80 and 250 upstream of the PX domain 
PX-SNX34 SNX34 (C6ORF145) SNX34 has not been annotated previously and was identified in the present study via bioinformatics searches. It potentially contains a small C-terminal β-sheet domain between approximately residues 160 and 230 
Subfamily Member(s) Notes 
PX-BAR SNX1, SNX2, SNX4, SNX5, SNX6, SNX7, SNX8, SNX30, SNX32 Each protein has a C-terminal BAR domain involved in membrane tubulation. Several also have N-terminal extended sequences, thought to be involved in protein–protein interactions (e.g. SNX1 and SNX2) 
SH3-PX-BAR SNX9 (SH3PX1), SNX18, SNX33 These molecules are very similar in architecture to the PX-BAR proteins, except that they have an N-terminal SH3 domain that binds to polyproline sequences and an intervening low-complexity region containing AP2- and clathrin-binding motifs 
PX-SH3 SH3PXD2A (SH3MD1, FISH), SH3PXD2B, SNX28 (NOXO1), p47phox (NCF1), p40phox (NCF4) SNX28, p47phox and p40phox are components of the NADPH oxidase complex. The PX-SH3 proteins have various numbers of SH3 domains C-terminal to the PX domain (from 1 to 5) 
PX-SH3-GAP SNX26 (TC-GAP), PX-RICS (GC-GAP, p250GAP) The PX-SH3-GAP proteins have very long extended C-terminal domains with no identified structural motifs 
PX-FERM SNX17, SNX27, SNX31 The FERM domain has all three modules of a typical FERM domain (F1, F2 and F3), except that the F2 module is significantly smaller. SNX27 contains an additional N-terminal PDZ domain 
PXA-RGS-PX-PXC SNX13, SNX14, SNX19, SNX25 Each PXA-RGS-PX-PXC protein possesses two N-terminal hydrophobic stretches predicted to form transmembrane helices. Each PXA-RGS-PX-PXC protein possesses an RGS domain, except for SNX19 
PX-serine/threonine kinase PXK, RPK118 (RPS6KC1), SGK3 (CISK) PXK and RPK118 are predicted to have non-catalytic serine/threonine-kinase domains. RPK118 may also possess an MIT domain 
PI3K-PX PI3K-C2α, PI3K-C2β, PI3K-C2γ These are type II PI3K enzymes with multiple domains, including Ras-binding domains, C2 domains, a PI3K domain and a PI3KC2 homology domain of unknown structure and function 
PX-PH-PLD PLD1, PLD2 These proteins have two separate membrane-recruitment domains (PX and PH) coupled to a PLD domain 
PX-PXB SNX20 (SLIC-1), SNX21 SNX20 and SNX21 are highly homologous and share a conserved helical domain (PXB) of ~140 residues downstream of the PX domain. The PXB domain may be composed of up to three TPR helical repeats 
PX-only SNX3, SNX10, SNX11, SNX12, SNX22, SNX24, SNX29, HS1BP3 These proteins have been annotated as having no identified domains outside of the PX domain [3,37]. In all cases, the proteins possess short extra sequences without predicted secondary structure. The C-terminal tail of HS1BP3 is a proline-rich region 
Kinesin-PX SNX23 (KIF16B) SNX23 is a member of the kinesin family of microtubule motors. It includes an N-terminal kinesin motor domain, a putative forkhead association (FHA) domain and a central coiled-coil dimerization domain 
PX-MIT SNX15 SNX15 includes a C-terminal MIT domain 
PX-LRR-IRAS IRAS (nischarin) IRAS is a large protein ~1504 residues in length. Apart from the N-terminal PX domain, IRAS has a predicted leucine-rich repeat region from approximately residues 220 to 397, and secondary structure predictions indicate that the C-terminal region from approximately residue 570 onwards is composed of one or more structural domains with mixed α/β topologies. 
PX-SNX16 SNX16 SNX16 possesses significant predicted helical structure from between approximately residues 220 and 310 downstream of the PX domain 
SNX29-PX SNX29 SNX29 possesses significant predicted helical structure between approximately residues 80 and 250 upstream of the PX domain 
PX-SNX34 SNX34 (C6ORF145) SNX34 has not been annotated previously and was identified in the present study via bioinformatics searches. It potentially contains a small C-terminal β-sheet domain between approximately residues 160 and 230 

Classification and domain organization of human PX proteins

Figure 2
Classification and domain organization of human PX proteins

Structural classification of PX proteins was based on known domains, and novel conserved domains were identified by secondary-structure prediction and sequence comparison. Note that the diagrams are not to scale. Domains with broken outlines indicate a domain that is only found in some members of the subfamily (PDZ domain in SNX27; MIT domain in RPK118; RGS domain missing in SNX19; TM domains missing in SNX25), or found in variable numbers (SH3 domains of PX-SH3 proteins).

Figure 2
Classification and domain organization of human PX proteins

Structural classification of PX proteins was based on known domains, and novel conserved domains were identified by secondary-structure prediction and sequence comparison. Note that the diagrams are not to scale. Domains with broken outlines indicate a domain that is only found in some members of the subfamily (PDZ domain in SNX27; MIT domain in RPK118; RGS domain missing in SNX19; TM domains missing in SNX25), or found in variable numbers (SH3 domains of PX-SH3 proteins).

We have also produced a curated list of proteins that are found to associate with PX domain proteins and, where possible, have defined interacting domains, further highlighting the functional relationships between members of the same subfamilies (Supplementary Table S2). In constructing this Table, we restricted interactions to those that appeared to be direct as shown by immunoprecipitations or other assays, including yeast two-hybrid, pull-downs with purified proteins or co-crystal structures. Importantly, these analyses also reveal that ligands for PX proteins can be assigned to several major functional groups: transmembrane cargo molecules, regulators of intracellular membrane trafficking, cellular signalling and cytoskeletal reorganization/attachment.

PX-BAR and SH3-PX-BAR subfamilies

The subfamily of PX proteins possessing a C-terminal BAR domain are perhaps the best characterized of all PX subfamilies. An excellent review by van Weering et al. [39] highlights their importance in endocytic and endosomal membrane sorting processes. Sorting of proteins by PX-BAR molecules is dependent on the membrane remodelling and sensing properties of the BAR domain, which drives the formation of membrane tubules and preferentially associates with curved membrane domains [44,45]. Examples include the formation of endosomal transport tubules by SNX1 [46] and membrane deformation during clathrin-coated vesicle formation by SNX9 [18,47]. Therefore the overarching question about the PX-BAR proteins is this: why are there so many? Does each protein control the sorting of cargo molecules within specific membrane domains, are they regulated by different signals or do they function in different intracellular compartments? Attempts to answer these questions have borne significant fruit in the last few years; however, dissecting the individual roles of PX-BAR proteins is severely complicated by the requirement that they form homo- or hetero-dimers (a feature of the BAR domain) and higher-order oligomeric complexes during membrane tubulation.

It is plain that in some cases different PX-BAR proteins can have overlapping functions. For example, one of the best-characterized roles of the PX-BAR proteins is to co-operate with the retromer protein complex in endosome-to-TGN (trans-Golgi network) recycling of a variety of transmembrane cargo proteins. Retromer is a heterotrimeric assembly composed of the proteins VPS35 (vacuolar protein sorting-associated protein 35), VPS29 and VPS26 thought to participate in cargo loading into membrane tubules coated by PX-BAR proteins, including SNX1, SNX2 SNX5 and SNX6 [40,48,49]. The highly homologous SNX1 and SNX2 have been shown to participate somewhat interchangeably in retrograde endosomal protein trafficking of both the bacterial toxin StxB (Shiga-like toxin β subunit), where siRNA (small interfering RNA) knockdown of both proteins results in a greater defect in protein trafficking than that of either one alone [50], and the CI-MPR (cation-independent mannose-6-phosphate receptor) whereby knockdown of both proteins together is required to observe a defect in retromer membrane tethering and CI-MPR endosome-to-Golgi retrieval [51]. Each protein has been shown to both self-associate and form heterodimers with each other, suggesting that they have very similar biochemical properties [5156]. These data are somewhat clouded, however, by separate reports that SNX2 does not participate in either trafficking process [46,57,58], whereas other evidence suggests that SNX1 and SNX2 can also have independent functions, as shown by their differential roles in down-regulation of activated EGFR (EGF receptor) or PAR1 (protease-activated receptor 1) [52,59]. Perhaps the most compelling evidence for functional overlap is that deletion of both SNX1 and SNX2 in mice results in a lethal phenotype, strongly implying that the two proteins can functionally compensate for each other to a certain extent [60].

Other examples of PX-BAR proteins with overlapping functions include the highly similar SNX5 and SNX6 proteins, as well as the endocytic SH3 domain-containing proteins SNX9, SNX18 and SNX33. In the former case, both SNX5 and SNX6 were found to play similar roles in the endosome-to-Golgi retrieval of the CI-MPR, and both form heteromeric complexes with the retromer-associated SNX protein SNX1 [24,56,61]. Interestingly, SNX5 has been shown to have a significantly different membrane recruitment response to EGFR-mediated signalling, with SNX5 showing both endosomal and plasma membrane localization in stimulated cells, perhaps regulated by an affinity for PtdIns(4,5)P2, whereas SNX1 remains endosomally bound [22,62]. This is strong evidence that PX-BAR proteins may have differing functions depending on whether they are partnered with one particular PX-BAR protein or another.

SNX9 plays a well-established role in clathrin-mediated endocytosis, in part controlling the membrane remodelling of the narrow neck region of the forming vesicle, and acting as a molecular scaffold for assembly and recruitment of essential vesicle components, such as dynamin, AP2 (adaptor protein complex 2), clathrin and components of the actin cytoskeleton (reviewed in [47]). Studies of SNX18 and SNX33 indicate that they have overlapping, but also distinct, intracellular localizations with SNX9 [6365]. However, all bind to dynamin and the effector WASP, and SNX9 and SNX33 have a similar ability to affect endocytosis of APP (amyloid precursor protein) [66]. The data are conflicting as to whether these proteins can form heteromeric assemblies with each other [6365], but these initial studies suggest that the three proteins probably have both overlapping and distinct roles in dynamin-dependent endocytosis and protein trafficking. The functional interplay between the different members of the PX-BAR subfamilies is therefore highly complex, and the task now will be to dissect both the common and unique properties of each PX-BAR protein and protein assembly. Ongoing goals will be to determine the repertoires of functional PX-BAR dimeric complexes, examine which of these possess inherent membrane associating and tubulating properties, and how these complexes correlate to the in vivo assemblies based on criteria such as overlapping tissue distribution and cellular colocalization.

Studies of the SNX9 PX and BAR domains provide important details on how dimeric SH3-PX-BAR complexes are assembled and how their structures contribute to membrane attachment and remodelling (Figure 1B) [18,67]. An interesting finding was the presence of a so-called ‘yoke’ domain, which is critical for holding the PX domain in a fixed orientation with respect to the BAR domain. Although it is assumed that related PX-BAR proteins will adopt overall similar tertiary assemblies, the recent structure of the SNX5 PX domain may have important implications for the assembly of SNX5 into functional complexes [22]. SNX5 possesses a novel helix–turn–helix insertion following the polyproline loop that forms an extended structure protruding from the PX domain. When the SNX5 PX domain is aligned with SNX9, the helical insertion protrudes in such a way that it will penetrate significantly into the predicted plane of the membrane (Figure 1B). This suggests that either the PX domain is oriented differently in SNX5 compared with SNX9, or that SNX5 may have different membrane-modulating properties compared with related SH3-PX-BAR proteins. High-resolution studies of homo- and hetero-dimeric PX-BAR complexes will be required for a firm understanding of their assembly and membrane interaction.

To generate or sense tubular membrane structures, BAR domain proteins must organize into polymeric arrays, involving lateral interactions between membrane-associated dimers. Multiscale structural characterization, such as performed in landmark studies of F-BAR proteins (where F is the FCH domain) [68], will hopefully provide a more detailed understanding of the membrane association and higher-order oligomerization properties of PX-BAR proteins. An important question, as outlined previously [37,39], is how different SNX proteins may control formation or sorting into alternative membrane transport tubules in vivo. For example, how exclusive are PX-BAR membrane tubules? Can mixtures of different PX-BAR proteins exist on the same tubules, and how do cargo receptors and accessory proteins (for example the retromer complex) integrate into these membrane domains? All of this information will ultimately help us to understand how different homo- and hetero-dimeric combinations of PX-BAR proteins control protein sorting within the endocytic system.

Other questions of immediate interest include determining the function of the uncharacterized PX-BAR proteins. For example, does SNX32 participate in endosomal retrograde transport similarly to the homologous proteins SNX5 and SNX6? Given the highly dynamic nature of PX-BAR- and SH3-PX-BAR-derived membrane structures, another question of prime interest will be to determine how these proteins associate with other regulatory molecules and with cargo receptors themselves (Supplementary Table S2). For example SNX1 was originally identified by its ability to associate with EGFR and other signalling receptors [41,54], and with the protein Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) [69]. Subsequent studies have also suggested direct interactions between SNX1 and GPCRs (G-protein-coupled receptors) [59,70]. Perhaps the best-characterized interaction of SNX1 is with the retromer complex [5153,71], but even in this case the mechanism of association is very poorly understood. One of the most exciting discoveries has been the identification of interactions between endosomal PX-BAR proteins and components of the cytoskeleton [39,56,72]. These findings demonstrate the importance of dynein-mediated microtubule translocation for PX-BAR trafficking processes and have opened an important area of investigation for these molecules.

PX-FERM subfamily

The PX-FERM molecules serve as a prime example of the important endosomal scaffolding and trafficking functions of many PX proteins. Recent work from our laboratory has shown that three proteins, SNX17, SNX31 and SNX27, constitute a conserved subfamily containing a C-terminal FERM domain [11]. In addition SNX27 possesses an N-terminal PDZ (postsynaptic density 95/discs large/zonula occludens) domain. FERM domains are approximately 300 amino acids in length and are found in numerous signalling and scaffolding proteins, where they serve a role in membrane tethering and/or binding to the cytosolic domains of transmembrane proteins [73]. The FERM domain is composed of three subdomains or modules named F1, F2 and F3. The F1 subdomain possesses a ubiquitin-like fold and the C-terminal F3 subdomain possesses a similar structure to the PH and PTB domains. The F1 and F3 modules are oriented with relation to each other by the central F2 subdomain composed of four α-helices. The sequence homology of the PX-associated FERM domains with the canonical FERM domain is low, and the central F2 subdomain is significantly smaller than normal [11]. The PX domains are essential for endosomal localization via PtdIns3P binding [11,7480], and the FERM domains of these proteins regulate endosomal cargo interactions and, possibly, scaffolding of signalling complexes [11] (Figure 3).

A network of molecular interactions regulated by the PX-FERM proteins in endosomal membrane transport and signalling

Figure 3
A network of molecular interactions regulated by the PX-FERM proteins in endosomal membrane transport and signalling

The PX domain binds to PtdIns3P with high specificity, and the similarity of the F3 module of the FERM domain suggests that it will be responsible for binding cargo receptors via NPxY sequences. The proteins can bind Ras-GTP, and this is proposed to be via the F1 module similar to structurally related Ras-association domains. SNX17 has been reported to use its polyproline sequence within the PX domain to interact with a variety of SH3 domain proteins, including Src-related kinases and PLCγ1. SNX27 possesses an additional N-terminal PDZ domain that binds cytosolic and transmembrane proteins via C-terminal type I PDZbms, ExE[S/T]x[F/V]. β2-AR, β2 adrenergic receptor; CNKRS2, connector enhancer of kinase suppressor of Ras2; FEEL1, fasciclin, EGF-like, laminin-type EGF-like and link domain-containing scavenger receptor 1 (also called stabilin-1); Grb2, growth-factor-receptor-bound protein 2; MAP1A, microtubule-associated protein 1A; Nck1, non-catalytic region of tyrosine kinase adaptor protein 1; PTCH1, protein patched homologue 1; PTPN2, protein tyrosine phosphatase non-receptor type 2; RhoGDI, Rho GDP-dissociation inhibitor; VLDLR, very-low-density lipoprotein receptor; vl-GPCR, very large GPCR.

Figure 3
A network of molecular interactions regulated by the PX-FERM proteins in endosomal membrane transport and signalling

The PX domain binds to PtdIns3P with high specificity, and the similarity of the F3 module of the FERM domain suggests that it will be responsible for binding cargo receptors via NPxY sequences. The proteins can bind Ras-GTP, and this is proposed to be via the F1 module similar to structurally related Ras-association domains. SNX17 has been reported to use its polyproline sequence within the PX domain to interact with a variety of SH3 domain proteins, including Src-related kinases and PLCγ1. SNX27 possesses an additional N-terminal PDZ domain that binds cytosolic and transmembrane proteins via C-terminal type I PDZbms, ExE[S/T]x[F/V]. β2-AR, β2 adrenergic receptor; CNKRS2, connector enhancer of kinase suppressor of Ras2; FEEL1, fasciclin, EGF-like, laminin-type EGF-like and link domain-containing scavenger receptor 1 (also called stabilin-1); Grb2, growth-factor-receptor-bound protein 2; MAP1A, microtubule-associated protein 1A; Nck1, non-catalytic region of tyrosine kinase adaptor protein 1; PTCH1, protein patched homologue 1; PTPN2, protein tyrosine phosphatase non-receptor type 2; RhoGDI, Rho GDP-dissociation inhibitor; VLDLR, very-low-density lipoprotein receptor; vl-GPCR, very large GPCR.

SNX17 and SNX31 are the most closely related within this subfamily. There are currently no published data on the function of SNX31, but several groups have determined that SNX17 is endosome-associated and controls intracellular trafficking of a number of transmembrane cargo proteins. Proteins whose cellular localization is regulated by SNX17 include LRP1 [LDLR (low-density lipoprotein receptor)-related protein 1] [76,8183], LDLR [83,84], P-selectin [75,85,86] and APP [87]. Overexpression of SNX17 enhances LDLR endocytosis [83], whereas expression of a truncated SNX17 molecule causes LDLR to be mislocalized [84]. It was subsequently found that SNX17 regulates the recycling of LDLR from endosomes to the cell surface in non-polarized cells [76] and from basolateral sorting endosomes to the basolateral plasma membrane in polarized MDCK (Madin–Darby canine kidney) cells [82]. The role of SNX17 in trafficking of LDLR and related lipoprotein receptors suggests a potentially central function in lipid metabolism, and it will be important to determine whether this is indeed the case. SNX17 was also found to promote cellular uptake of the endothelial receptor P-selectin and, additionally, it colocalizes with P-selectin on endosomal organelles where it is able to inhibit its transport to late endosomes/lysosomes for degradation [75]. Finally, SNX17 is expressed in neurons, associates with APP on endosomes and inhibits its proteolytic processing to the toxic amyloid Aβ peptide [87]. The role of PX proteins in inflammation and AD (Alzheimer's disease) is discussed further below.

In addition to transmembrane cargo proteins, SNX17 has been found to associate with the cytosolic protein Krit1 (Krev-interaction trapped 1), which is able to enhance recruitment of SNX17 to endosomes [74]. SNX17 binds receptors and effectors via short peptide motifs with the consensus Asn-Pro-Xaa-Tyr (NPxY) via its C-terminal FERM domain. In addition to these NPxY-motif interactions, a proteomics study has also identified SNX17 as a ligand for various SH3 domain-containing proteins, including a number of Src-related tyrosine kinases and PLCγ1 [88]. In these cases, the interaction involves the SH3 domain binding directly to the SNX17 PX domain polyproline loop.

The determination that SNX27 shares structural similarity with SNX17 and SNX31 led to the demonstration that it also possesses NPxY-motif binding affinity, although it has yet to be confirmed that SNX27 is able to direct endosomal sorting of NPxY cargo proteins [11]. SNX27 was annotated as possessing a C-terminal RA (Ras-association) or B41 domain [3,37,43]. However, it is now clear that it possesses a similar FERM C-terminal domain to SNX17 and SNX31. This confusion is due to the fact that both RA and B41 domains share a ubiquitin-like fold, as does the F1 module of FERM proteins. Nonetheless, as mentioned above, the F1 module of FERM domains shares structural similarity with the RA domain, and this prompted an investigation of the Ras-binding properties of the PX-FERM proteins [11]. These preliminary experiments show that PX-FERM proteins are able to bind the activated H-Ras GTPase, and suggest a potential link between endosomal Ras-mediated signalling and membrane trafficking that requires further investigation [89]. A hint that the PX-FERM proteins can indeed affect Ras-mediated signalling comes from recent studies showing that SNX27 knockdown by siRNA results in enhanced ERK (extracellular-signal-regulated kinase) phosphorylation [79]. However, the actual Ras isoform(s) targeted by the PX-FERM proteins in vivo remains unknown.

SNX27 is unique amongst the PX-FERM proteins in that it also contains a PDZ domain upstream of the PX domain. Like SNX17, SNX27 is highly expressed in brain tissue, and was in fact first identified as a molecule up-regulated upon stimulation of dopamine receptors with methamphetamines [9092]. The PDZ domain of SNX27 has been implicated in binding to a number of proteins via a C-terminal type I PDZbm (PDZ-binding motif) (E[S/T]x[V/F]), and structural studies of the SNX27 PDZ domain show that the preferred motif is enhanced by the presence of an upstream glutamic acid side chain (ExE[S/T]xV/F]) [90]. The first identified binding partner for SNX27 was 5-HT4R (5-hydroxytryptamine type 4 receptor), a GPCR involved in feeding and respiratory control [77]. SNX27 was found to be essential for transport of 5-HT4R to EEA1-positive early endosomes. DGKζ (diacylglycerolkinase ζ) was identified as a SNX27 binding partner by proteomics and can regulate SNX27 association with early and recycling endosomes [80]. Other proteins found to associate with the SNX27 PDZ domain are CASP (cytohesin-associated scaffolding protein), a cellular adaptor protein found in cells of haemopoietic origin [93,94], Kir3, G-protein-gated inwardly rectifying potassium channels that control a slow inhibitory postsynaptic response in neurons [78,90,95], and most recently the NR2C [NMDA (N-methyl-D-aspartate) receptor 2C] ligand-gated ion channel [96]. SNX27 and Kir3 channels show colocalization in endosomes, and overexpression of SNX27 results in reduced Kir3.3 expression at the cell surface, suggesting that it either promotes Kir3.3 endocytosis or inhibits its recycling. Finally, a recent paper by Lauffer et al. [97] demonstrated that SNX27 can bind to β2AR (β2-adrenergic receptor) via its C-terminal PDZbm and regulate its endosomal recycling to the cell surface, perhaps analogously to the recycling role demonstrated for SNX17.

The exact function of the PX-FERM molecules in protein trafficking remains unclear and their mechanisms of action are unknown. Do they form a protein coat regulating membrane transport, do they act as adaptors for other membrane scaffolding molecules or do they play a facilitating role by concentrating transport cargoes into membrane domains destined for recycling to the cell surface? The first clue to the function of these proteins emerged with the identification of SNX27 as a binding partner for the WASH [WASP and SCAR (suppressor of cAMP receptor) homologue] complex [98]. The WASH complex is an endosome-associated assembly that induces actin polymerization in an Arp2/3 complex (actin-related protein 2/3 complex)-dependent manner, and has an important function in endosomal trafficking and membrane dynamics (reviewed in [99]). Interestingly, WASH is believed to co-ordinate endosomal sorting in association with the retromer complex [100,101]. Knockdown of retromer perturbs cell-surface recycling of the β1- and β2-adrenergic receptors similarly to SNX27, and SNX27 was found to be associated with retromer after cross-linking [98]. The authors propose that SNX27 can act as a cargo-specific adaptor for endosomal sorting of PDZbm-containing receptors within retromer-coated membrane tubules, and also propose a role for retromer and SNX27 in rapid cell-surface recycling via a Rab4-dependent pathway, which contrasts significantly with the canonical role of retromer in endosome–TGN retrograde transport. This specific process is unique to SNX27 as it only operates on PDZbm-containing proteins, so it remains to be seen whether PX-FERM molecules also co-ordinate endosomal trafficking of NPxY cargo, such as APP and LDLR family members, with WASH and retromer.

PXA-RGS-PX-PXC subfamily

Four proteins, SNX13, SNX14, SNX19 and SNX25, display a unique architecture consisting of a central PX domain flanked by several conserved domains (Figure 4A). The first domain identified was the RGS (regulator of G-protein signalling) domain, found in a number of molecules that attenuate GPCR and related G-protein signalling. This domain is seen only in SNX13, SNX14 and SNX25. Two other domains (each approximately 150 amino acids) have previously been annotated as the PXA domain (PX-associated domain A) lying N-terminal to the RGS and canonical PX domains, and the C-terminal PX-associated domain lying downstream of the PX domain [3,37]. For clarity, we refer to the N- and C-terminal domains as the PXA and PXC (PX-associated domain C) domains respectively, to denote that they are as yet uncharacterized PX-associated domains. Finally, each member of the family possesses two putative N-terminal transmembrane helices resulting in a predicted topology of a short cytoplasmic leader, two closely spaced transmembrane domains, and a long C-terminal structure containing the three (SNX19; PXA-PX-PXC) or four (SNX13, SNX14 and SNX25; PXA-RGS-PX-PXC) modular domains (Figure 4B). Currently, SNX25 is predominantly annotated as lacking transmembrane sequences, but our analyses of the rat, mouse and human genomes identified a conserved N-terminal coding sequence that is clearly transcribed and encodes two potential transmembrane helices.

Architecture and interactions of PXA-RGS-PX-PXC proteins

Figure 4
Architecture and interactions of PXA-RGS-PX-PXC proteins

(A) Schematic diagrams of the human PXA-RGS-PX-PXC proteins SNX13, SNX14, SNX19 and SNX25. Transmembrane (TM), N-terminal PXA, RGS, PX and C-terminal PXC domains are indicated with shaded boxes. Proteins and domains are drawn to scale. (B) Model for SNX13 function in GPCR signalling [103]. SNX13 is predicted to possess two transmembrane domains. After activation of a GPCR by ligand binding, GDP is displaced and exchanged for GTP in the Gαs subunit of the trimeric G-protein, releasing the Gβ and Gγ subunits and resulting in signal transduction. The RGS domain of SNX13 binds to Gαs and SNX13 acts as a GAP to stimulate GTPase activity. The G-protein complex can then reform and signal transduction is ablated. Because SNX13 has a PtdIns3P-binding PX domain and is localized to endosomes, it probably functions in signal attenuation in this intracellular compartment and also interacts with Hrs, a component of the ubiquitin-mediated protein sorting and degradation pathway in late endosomes.

Figure 4
Architecture and interactions of PXA-RGS-PX-PXC proteins

(A) Schematic diagrams of the human PXA-RGS-PX-PXC proteins SNX13, SNX14, SNX19 and SNX25. Transmembrane (TM), N-terminal PXA, RGS, PX and C-terminal PXC domains are indicated with shaded boxes. Proteins and domains are drawn to scale. (B) Model for SNX13 function in GPCR signalling [103]. SNX13 is predicted to possess two transmembrane domains. After activation of a GPCR by ligand binding, GDP is displaced and exchanged for GTP in the Gαs subunit of the trimeric G-protein, releasing the Gβ and Gγ subunits and resulting in signal transduction. The RGS domain of SNX13 binds to Gαs and SNX13 acts as a GAP to stimulate GTPase activity. The G-protein complex can then reform and signal transduction is ablated. Because SNX13 has a PtdIns3P-binding PX domain and is localized to endosomes, it probably functions in signal attenuation in this intracellular compartment and also interacts with Hrs, a component of the ubiquitin-mediated protein sorting and degradation pathway in late endosomes.

There are only a small number of reports that address the function of the PXA-RGS-PX-PXC proteins. These describe the role of SNX13 (also called RGS-PX1) as a GAP and regulator of the trimeric G-protein subunit Gαs via its RGS domain [102104], and of SNX25 as a modulator of TGF-β signalling [105]. The former studies confirmed SNX13 as an important member of the family of RGS proteins, a family with diverse roles in modulating GPCR-mediated signalling [106,107]. Initial work identified SNX13 after database searches for the putative GAP for Gαs, which at the time had not been identified. SNX13 was subsequently cloned and shown to both bind to and promote GTPase activity of Gαs with high specificity and attenuate Gαs-mediated signalling [103]. Endosomes are increasingly being recognized as critical sites of signal regulation [1,2,108], and the affinity of SNX13 for PtdIns3P and localization to endosomes suggests a potential role in GPCR signal attenuation in this compartment. SNX13 was subsequently shown to form a heteromeric complex with both Gαs and Hrs on endosomes and co-operate in the lysosomal targeting of the EGFR, suggesting a role both in signalling and trafficking [102]. A model for SNX13 function in endosomal signal attenuation is presented in Figure 4(B). SNX13-null mice show embryonic lethality, and yolk-sac endoderm cells of these embryos display highly disrupted endosome morphology, demonstrating that it plays a role in endosomal function that is critical for normal development and that other PXA-RGS-PX-PXC proteins are unable to compensate for its loss [104]. SNX25 was identified through bioinformatics searches for novel PX domain proteins and is proposed to modulate TGF-β signalling via endosomal sorting of TGF-β receptors for lysosomal degradation [105]. Another study has implicated SNX19 in chondrogenic regeneration in cartilage, although the mechanism for this function is not proposed [109]. A final interesting finding is that the Drosophila protein snazarus (sorting nexin lazarus), for which SNX25 is the closest homologue, plays a role in regulating longevity, as snazarus mutants display significantly increased lifespans [110].

PX-only and PX proteins with putative novel domains

The subfamily of proteins that have been annotated as PX-only proteins is a relatively poorly characterized group of molecules [3,37]. As the name suggests, bioinformatics analyses do not detect any conserved domains outside the defining PX domain. Structurally, however, these proteins are of various lengths and typically contain long extended sequences with no predicted secondary structure. In several cases, such sequences have been found to be critical for function [111,112]. Of the PX-only proteins, SNX3 is perhaps the best characterized. Like the majority of PX proteins, SNX3 binds to PtdIns3P via its PX domain and this interaction drives its association with the limiting membrane of early endosomes [113] and MVBs (multivesicular bodies) [114]. Overexpression of SNX3 was found to alter endosome morphology [113], and the protein is essential for the formation of the intralumenal vesicles of MVBs [114]. Ubiquitylation is a critical feature of protein sorting into MVBs, and SNX3 itself has been found to be ubiquitylated, with its stability being regulated by the de-ubiquitylating enzyme Usp10 [115]. SNX3 has also been linked to neurite outgrowth, and its expression is induced by lithium treatment [116]. The yeast homologue Grd19p/Snx3p appears to co-operate with the retromer coat complex in endosome-to-Golgi retrieval [117119], and elegant studies have recently shown that it also co-operates with retromer in endosome-to-Golgi recycling of the Wnt receptor Wntless in Caenorhabditis elegans, Drosophila melanogaster and mammalian cells, indicating an evolutionarily conserved function in retromer-mediated membrane trafficking [120].

HS1BP3 (HS1-binding protein 3) is a unique PX domain protein identified by proteomic screening as a binder of the HS1 protein, which in turn is a substrate of the Lck tyrosine kinase involved in T-cell differentiation [121]. HS1BP3 has an extended C-terminal region rich in proline residues that is bound by the HS1 SH3 domain. Expression of a truncated HS1BP3 construct resulted in reduced IL-2 (interleukin-2) production, suggesting a role in T-cell-receptor-mediated signalling, and genetic studies also indicate that a variant (A265G) is associated with familial essential tremor [122124]. The only other PX-only protein that has been characterized to any extent is SNX10, which induces the formation of giant vacuoles when overexpressed [111]. This vacuolization is sensitive to disruption of the Golgi, suggesting that SNX10 may in some way enhance the fusion of Golgi-derived vesicles with endosomes.

In addition to the PX-only proteins, several PX molecules possess regions of predicted secondary structure that almost certainly form folded domains of unknown function. SNX20 and SNX21 are a prime example. These proteins are highly homologous and share a conserved domain of ~140 residues containing six α-helices downstream of the PX domain on the basis of secondary-structure predictions (Supplementary Figure S2 at http://www.BiochemJ.org/bj/441/bj4410039add.htm). We propose that this be named the PXB domain (PX-associated domain B), continuing the nomenclature adopted for the PXA-RGS-PX-PXC proteins. Results from the TPRpred server suggest that this region may contain up to three TPRs (tetratricopeptide repeats), α–α-hairpin structures that form helical solenoids [125]. SNX16 possesses a predicted helical structure between residues ~220 and 310 C-terminal to the PX domain. SNX29 has significant predicted helical structure between residues ~80 and 250 upstream of the PX domain. Therefore technically, SNX16, SNX29, SNX20 and SNX21 proteins should not be classified as ‘PX-only’ molecules. During bioinformatic searches we also identified the novel open reading frame C6ORF145, which we have designated SNX34. SNX34 is 231 residues in length and secondary-structure predictions indicate the presence of a small domain composed of β-strands at the C-terminus (residues 160–225).

SNX16 associates with endosomes via PtdIns3P binding to its PX domain, and the helical C-terminal domain appears to be important for self-association, possibly by forming a coiled-coil [126,127]. This domain regulates SNX16 distribution between early and late endosomes and is important for processing of cargo molecules, such as EGFR, into the late compartments. Interestingly, SNX16 was recently found to be a PtdIns3P effector that is able to inhibit the export of viral RNA into the cytoplasm from late endosomes, although the mechanism of function is unknown [128]. A recent study of D. melanogaster SNX16 identified an interaction with the WASP-activating F-BAR molecule Nwk on recycling endosomes, and highlighted a role for this interaction in down-regulating BMP (bone morphogenetic protein) and Wg (Wingless) synaptic growth signalling pathways in nerve terminals [129].

One final PX protein of interest with novel structural domains is IRAS (imidazoline receptor antisera-selected), also called nischarin in mice. IRAS/nischarin is a large protein of 1504 amino acids. Apart from the N-terminal PX domain, IRAS/nischarin also has a predicted leucine-rich repeat region (residues ~220–397). Leucine-rich repeats display a characteristic three-dimensional structure composed of repeating β-strands and α-helices, and often participate in protein–protein interactions [130]. In addition, secondary-structure predictions indicate that the C-terminal region of IRAS/nischarin (from residue ~570 onwards) is composed of one or more structural domains with mixed α/β topologies. IRAS/nischarin was originally cloned as a putative imidazoline receptor, although it is probably not a bona fide receptor [131], and is localized to endosomes in HEK (human embryonic kidney)-293 cells via its PX domain [132]. It was subsequently found to bind to IRSs (insulin receptor substrates) and enhanced IRS-dependent insulin stimulation of ERK [133]. A number of other papers have centred on the ability of IRAS/nischarin to bind to α5 integrins [132,134138]. IRAS/nischarin binds to a short peptide in the cytoplasmic tail of α5 integrin via a C-terminal region (residues ~710–810) [132]. It also regulates Rac-induced cell migration and Rac/PAK (p21-activated kinase) signalling [134,135,137,138], although these data must be viewed with some degree of caution as all of these studies employed a mouse version of IRAS/nischarin that lacks the N-terminal PX domain [132,135], apparently due to a truncation in the original IRAS/nischarin clone. The current mouse IRAS/nischarin entry in the NCBI database (accession number NM_022656) has the PX domain and is homologous with the full-length human gene. It is possible, therefore, that the previous studies of IRAS/nischarin function in Rac signalling employed a dominant-negative version of the protein.

Other unique PX proteins

SNX15, which includes a C-terminal MIT domain (microtubule-interacting and trafficking molecule domain), was first identified via database searches for SNX1 homologues, and despite the lack of a C-terminal BAR domain for dimerization was found to associate with SNX1, SNX2 and SNX4 [139]. It was also found to associate with the receptor for PDGF (platelet-derived growth factor), and interestingly all of these identified interactions were dependent on the PX domain itself. SNX15 is localized to endosomes and overexpression of the protein has numerous phenotypic consequences, including disrupted endosomal morphology, reduced processing of several growth factor receptors and inhibited trafficking of several proteins such as furin, TGN38 and transferrin [139,140]. Although its exact function is not clear, it appears that SNX15 plays an important role in endosomal transport processes. MIT domains are found in a number of endosomal proteins, including Vps4 {an ATPase that controls the disassembly of the ESCRT (endosomal sorting complex required for transport) complex [141]}, spastin and another PX protein, the serine/threonine-pseudokinase RPK118 [142]. The structure of the MIT domain reveals a small three-helix bundle, and its function appears to be to act as a protein–protein interaction module, specifically binding small MIT-interaction motifs [143,144]. The exact role of the SNX15 MIT domain, however, is unknown.

KIF16B (kinesin-family protein 16B, also known as SNX23) is a member of the kinesin superfamily of proteins [145]. It contains kinesin motor, FHA (forkhead association) and coiled-coil dimerization domains. KIFs are microtubule-binding motors with numerous roles in the transport of organelles, protein complexes and RNA [146,147]. KIF16B is a plus-end-directed microtubule motor that associates with PtdIns3P-containing endosomes via its C-terminal PX domain and regulates the localization of endosomal organelles in the cell as well as receptor recycling within the endosomal system [145,148].

EVOLUTIONARY INSIGHTS FROM THE YEAST PX PROTEOME

The conservation of PX proteins in yeast and other simple eukaryotes demonstrates a deep evolutionary heritage in eukaryotes, in line with their critical function in membrane trafficking, organization and cell signalling. Several interesting observations are made when the human PX proteome is compared with that of yeast. First, it is clear that higher eukaryotes have evolved an arsenal of PX domain proteins more diverse than those of their single-celled cousins. Secondly, it is seen that not all subfamilies of PX proteins are found in all eukaryotes. There are 15 known PX domain proteins in yeast, divided into several subfamilies that generally reflect those found in humans (Supplementary Table S3 at http://www.BiochemJ.org/bj/441/bj4410039add.htm). The most populous subfamily consists of the PX-BAR molecules (seven in yeast compared with nine in humans). Homologues are also seen for the PX-PH-PLD (Pld1p), PXA-RGS-PX-PXC (Mdm1p) and PX-only subfamilies (Snx3p and Ypt35p). However, in yeast each of these families has only one or two members. Yeast does have a PX domain-containing GAP, Bem3p; however, this molecule has a different architecture to the PX-SH3-GAP proteins found in humans, replacing the central SH3 domain with a membrane-binding PH domain.

Many PX subfamilies found in humans are not identified in yeast, including the PX-FERM, PX-S/T-kinase (serine/threonine kinase) and SH3-PX-BAR proteins; conversely, yeast has three PX proteins not identified in humans. The SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) protein Vam7p has, in addition to the canonical PX domain, C-terminal t-SNARE (target SNARE) motifs for forming SNARE complexes with Vam3p and Vti1p during vacuolar membrane fusion. The SH3-PX-CAD (caspase-activated DNase) protein Bem1p has two SH3 domains N-terminal to the PX domain and a C-terminal CAD/PB1 domain, which belongs to the ubiquitin-fold superfamily. The poorly characterized Ypr097Wp is a large protein and appears to contain a highly divergent PX domain on the basis of sequence and secondary-structure predictions (see [9]). Outside the PX domain, it is predicted to be primarily α-helical in structure, although no other known domains can be identified. Overall, it appears that eukaryotic organisms have employed both overlapping and distinct PX protein families throughout evolution.

PX PROTEINS AND DISEASE

There are now many reported links between PX proteins and various disease processes (Table 2). Currently, there is only one known case where a specific PX protein mutation is known to be the causative agent of a disorder: mutation of the p47phox subunit of the NADPH oxidase in CGD (chronic granulomatous disease) [149151]. Patients with CGD have a primary failure in neutrophil function and do not mount the normal NADPH oxidase-mediated respiratory burst required for phagocytosis. In particular, it is known that the R42Q mutation is implicated in CGD and that this mutation disrupts the phosphoinositide-binding site and membrane coupling of the protein [152]. Another PX protein, SNX3, was found to be disrupted in a patient with MMEP (microcephaly, microphthalmia, ectrodactyly and prognathism) [153]; however, subsequent studies were unable to detect coding mutations in SNX3 in MMEP patients [154], so it remains to be determined whether SNX3 is directly involved in this family of diseases. Other PX molecules have been implicated in disease on the basis of differential transcription or protein expression. PXK (PX domain-containing serine/threonine-kinase) has been linked to SLE (systemic lupus erythematosus) by genome-wide association studies [155]. SNX19 was found to be up-regulated in cartilage cells during progression of osteoarthritis, and studies in a model chondrogenic cell line implicated it as a protective factor against cartilage degradation [109]. SNX2 was also isolated in a screen for genes with potential involvement in epilepsy, but it remains to be confirmed that SNX2 is important for the disease [156].

Table 2
PX proteins implicated in disease
Family PX protein Disease References 
PX-BAR SNX1 STx uptake [50,57,58,221
  Salmonella uptake [212
  Down-regulated in ovarian cancer [224
  Gefitinib-sensitive non-small lung cancer [225
  Down-regulated in colon cancer [166,167
  Aβ production (AD) [186
 SNX2 STx uptake [50
  Salmonella uptake [213
  Epilepsy [156
 SNX4 −  
 SNX5 Uptake of Ebola virus via macropinocytosis [223
 SNX6 Aβ production (AD) [190
 SNX7 −  
 SNX8 STx uptake [222
 SNX30 −  
 SNX32 −  
SH3-PX-BAR SNX9 EPEC (enteropathic Escherichia coli) infection [226,227
  Aβ production (AD) [66
 SNX18 −  
 SNX33 Prion disease mediated by PrPc (normal cellular prion protein) [66,228
  Aβ production (AD) [66
PX-SH3 SH3PXD2A (SH3MD1, FISH, Tks5) Aβ production (AD) [199,200
  Tumour metastasis [163,164
 SH3PXD2B (Tks4) −  
 SNX28 (NOXO1, p41NOX, SH3PXD5) −  
 p40phox (NCF4, SH3PXD4) −  
 p47phox (NCF1, SH3PXD1A) Chronic granulomatous disease [149151
PX-SH3-GAP SNX26 (TC-GAP) −  
 PX-RICS (GC-GAP, p250GAP, p200GAP, Grit) −  
PX-FERM SNX17 Aβ production (AD) [87
 SNX27 −  
 SNX31 −  
PXA-RGS-PX-PXC SNX13 (RGSPX1) −  
 SNX14 −  
 SNX19 Candidate gene involved in Jacobsen syndrome [229
  May be a chondrogenic factor in osteoarthritis [109
  Genetic risk factor in myocardial infarction [230
  Transcriptionally up-regulated in thyroid oncocytic tumours [231
  Potential oncogene in myeloid leukaemia [232
 SNX25 Homozygous deletion of 3′ exons found in B-cell non-Hodgkin's lymphoma cell lines [233
PX-S/T kinase PXK (MONaKA) Systemic lupus erythematosus [155
 RPS6KC1 (RPK118, humS6PKh1) −  
 SGK3 (CISK, SGKL) Akt-independent cancer cell survival [168
  Up-regulated and promotes cell survival in oestrogen-receptor-positive breast cancer [169
PI3K-PX PIK3C2A (PI3K-C2α) −  
 PIK3C2B (PI3K-C2β) Prostate cancer risk [165
  Up-regulated in some glioblastoma brain tumours [234,235
 PIK3C2G (PI3K-C2γ) −  
PX-PH-PLD PLD1 Aβ production (AD) [202206
  Up-regulated in endometrial cancer cells [236
  Invasion by metastatic breast cancer cells [237240
  Colon cancer [241
 PLD2 Aβ production (AD) [207
  Invasion by metastatic breast cancer cells [240,242
  Metastatic mammary adenocarcinoma [162
  Lymphoma cell proliferation [243
  Colon cancer [244,245
PX-PXB SNX20 −  
 SNX21 −  
PX-only SNX3 Salmonella uptake [213
  An effector of lithium treatment for bipolar disorder, and a regulator of neurite outgrowth [112,116
  Gene disrupted in MMEP [153,154
 SNX10 −  
 SNX11 −  
 SNX12 −  
 SNX22 −  
 SNX24 Oestrogen-regulated expression in breast cancer cell lines [246
 HS1BP3 Familial essential tremor [122124
Kinesin-PX KIF16B (SNX23) −  
PX-MIT SNX15 Metastatic mammary adenocarcinoma [162
  Salmonella uptake [213
PX-LRR-IRAS IRAS (nischarin) −  
PX-SNX16 SNX16 VSV infection [128
  Differential expression used as a biomarker in bladder cancer [247
  Undergoes alternative splicing in certain melanoma cell lines [248
SNX29-PX SNX29 −  
PX-SNX34 SNX34 (C6ORF145) −  
Family PX protein Disease References 
PX-BAR SNX1 STx uptake [50,57,58,221
  Salmonella uptake [212
  Down-regulated in ovarian cancer [224
  Gefitinib-sensitive non-small lung cancer [225
  Down-regulated in colon cancer [166,167
  Aβ production (AD) [186
 SNX2 STx uptake [50
  Salmonella uptake [213
  Epilepsy [156
 SNX4 −  
 SNX5 Uptake of Ebola virus via macropinocytosis [223
 SNX6 Aβ production (AD) [190
 SNX7 −  
 SNX8 STx uptake [222
 SNX30 −  
 SNX32 −  
SH3-PX-BAR SNX9 EPEC (enteropathic Escherichia coli) infection [226,227
  Aβ production (AD) [66
 SNX18 −  
 SNX33 Prion disease mediated by PrPc (normal cellular prion protein) [66,228
  Aβ production (AD) [66
PX-SH3 SH3PXD2A (SH3MD1, FISH, Tks5) Aβ production (AD) [199,200
  Tumour metastasis [163,164
 SH3PXD2B (Tks4) −  
 SNX28 (NOXO1, p41NOX, SH3PXD5) −  
 p40phox (NCF4, SH3PXD4) −  
 p47phox (NCF1, SH3PXD1A) Chronic granulomatous disease [149151
PX-SH3-GAP SNX26 (TC-GAP) −  
 PX-RICS (GC-GAP, p250GAP, p200GAP, Grit) −  
PX-FERM SNX17 Aβ production (AD) [87
 SNX27 −  
 SNX31 −  
PXA-RGS-PX-PXC SNX13 (RGSPX1) −  
 SNX14 −  
 SNX19 Candidate gene involved in Jacobsen syndrome [229
  May be a chondrogenic factor in osteoarthritis [109
  Genetic risk factor in myocardial infarction [230
  Transcriptionally up-regulated in thyroid oncocytic tumours [231
  Potential oncogene in myeloid leukaemia [232
 SNX25 Homozygous deletion of 3′ exons found in B-cell non-Hodgkin's lymphoma cell lines [233
PX-S/T kinase PXK (MONaKA) Systemic lupus erythematosus [155
 RPS6KC1 (RPK118, humS6PKh1) −  
 SGK3 (CISK, SGKL) Akt-independent cancer cell survival [168
  Up-regulated and promotes cell survival in oestrogen-receptor-positive breast cancer [169
PI3K-PX PIK3C2A (PI3K-C2α) −  
 PIK3C2B (PI3K-C2β) Prostate cancer risk [165
  Up-regulated in some glioblastoma brain tumours [234,235
 PIK3C2G (PI3K-C2γ) −  
PX-PH-PLD PLD1 Aβ production (AD) [202206
  Up-regulated in endometrial cancer cells [236
  Invasion by metastatic breast cancer cells [237240
  Colon cancer [241
 PLD2 Aβ production (AD) [207
  Invasion by metastatic breast cancer cells [240,242
  Metastatic mammary adenocarcinoma [162
  Lymphoma cell proliferation [243
  Colon cancer [244,245
PX-PXB SNX20 −  
 SNX21 −  
PX-only SNX3 Salmonella uptake [213
  An effector of lithium treatment for bipolar disorder, and a regulator of neurite outgrowth [112,116
  Gene disrupted in MMEP [153,154
 SNX10 −  
 SNX11 −  
 SNX12 −  
 SNX22 −  
 SNX24 Oestrogen-regulated expression in breast cancer cell lines [246
 HS1BP3 Familial essential tremor [122124
Kinesin-PX KIF16B (SNX23) −  
PX-MIT SNX15 Metastatic mammary adenocarcinoma [162
  Salmonella uptake [213
PX-LRR-IRAS IRAS (nischarin) −  
PX-SNX16 SNX16 VSV infection [128
  Differential expression used as a biomarker in bladder cancer [247
  Undergoes alternative splicing in certain melanoma cell lines [248
SNX29-PX SNX29 −  
PX-SNX34 SNX34 (C6ORF145) −  

Several reviews highlight the critical role of dysregulation of phosphoinositide homoeostasis in many different disorders [157160]. Enzymes that regulate phosphoinositide generation and breakdown (kinases and phosphatases) are found to be mutated in a number of diseases. Of particular relevance to the PX proteins are disorders relating to enzymes regulating PtdIns3P synthesis at the early endosome, PtdIns(3,5)P2 generation from PtdIns3P at late endosomes and their respective levels during endosomal maturation (reviewed in [160]). These include disorders such as the family of Charcot–Marie–Tooth neuropathies caused by mutations in the 5-phosphatases (Sac3/Fig4 and myotubularins) regulating conversion of PtdIns(3,5)P2 into PtdIns3P, and corneal fleck dystrophy caused by mutations in the PIKfyve kinase that converts PtdIns3P into PtdIns(3,5)P2. Further evidence for the importance of PtdIns3P levels comes from studies highlighting the role of PIKfyve in Salmonella uptake into macropinosomes and progression of the pathogen through the endosomal system [161]. Although the underlying mechanisms that lead to these different pathologies are still not clear, the PX domain proteins are extremely strong candidates for molecules whose function will be perturbed by defects in PtdIns3P metabolism.

PX proteins in cancer

Many PX proteins have been linked to cancers on the basis of differential expression and other criteria (Table 2). Both the unique PX protein SNX15 and the PX-PH-PLD family member PLD2 are up-regulated in metastatic mammary tumour cells [162]. SH3PXD2A (SH3 and PX domain protein 2A) is essential for the formation of podosomes, actin-rich structures required for invasion of many types of cancers. It has been shown that SH3PXD2A is required for podosome formation and invasion of several cancer cell lines in a PX domain-dependent manner [163], and that inhibiting its expression correlates with reduced tumour growth in mouse transplantation models [164]. It is hypothesized that SH3PXD2A may act to regulate the recruitment of essential factors, such as N-WASP, to podosomes via its SH3 domains. Single-nucleotide polymorphisms in the gene encoding PI3K (phosphoinositide 3-kinase)-C2β (PI3KC2β) have been associated with increased risk of prostate cancer, suggested to be due to either enhanced cell migration or increased insulin signalling [165]. There is strong evidence for a role for SNX1 as a tumour suppressor. SNX1 expression assessed by both immunohistochemistry and microarray data indicates that SNX1 is reduced in colon carcinoma cells, and, furthermore, inhibition of SNX1 expression by shRNA (small hairpin RNA) leads to increased cell proliferation and decreased apoptosis [166]. The authors provide evidence that SNX1 depletion leads to increased EGFR phosphorylation and subsequent ERK signalling from endosomes, and that this may be important for tumour progression. Further support for a role for SNX1 depletion in colorectal tumour progression comes from a study showing that a microRNA up-regulated in colon carcinomas, miR-95, specifically targets SNX1 [167]. This model fits with the original identification of the SNX1 protein as a molecule that can enhance the degradation of the EGFR [41], but it does not fit with subsequent knockdown data indicating that depletion of SNX1 by siRNA has little effect on EGFR degradation [46] and therefore will need further investigation before it can be confirmed.

Two other families of PX proteins have been implicated in cancer due to their function as cell signalling modulators: the serine/threonine kinase SGK3 (serum- and glucocorticoid-induced protein kinase 3) and the phospholipases PLD1 and PLD2. Vasudevan et al. [168] established that oncogenic mutations in the PI3K subunit PIK3CA can result in cancers that are either dependent or independent of up-regulation in Akt signalling. In Akt-independent cancer cells, the key factor promoting cell survival is increased activation of SGK3 by the concerted signalling of PI3K and PDK1 (phosphoinositide-dependent kinase 1). Furthermore, studies have found that SGK3 is up-regulated in ER (oestrogen receptor)-positive breast tumours, is required for oestrogen-mediated cell survival and can protect cells against apoptosis induced by chemotherapeutics [169]. Few substrates for SGK3 have been identified; however, SGK3 can attenuate the endosomal activity of ubiquitin ligases and thus impair lysosomal degradation of signalling molecules, such as the chemokine receptor CXCR4 involved in breast cancer [170]. Enhanced signalling due to inhibited receptor degradation is one possible mechanism by which SGK3 could promote cell survival. Perhaps the best-characterized PX proteins in terms of oncogenic potential are PLD1 and PLD2. There is not scope in the present paper to review all of the evidence for the role of PLD isoforms in cancer, so instead we refer to several previous reviews [171173]. Very briefly, it appears that their importance in cancer is due to their role in the synthesis of PA (phosphatidic acid) from PC (phosphatidylcholine) and the effect of PA on downstream signalling, anti-apoptotic and membrane-remodelling processes. Importantly, PLD isoforms are now validated targets for the development of small-molecule inhibitors as chemotherapeutics [173175].

PX proteins in inflammation

An interesting example of how endosomal trafficking of receptors by PX proteins can affect disease-related processes is how the PX proteins SNX17 and SNX20 play complementary roles in haemopoietic cells during the inflammatory response. The importance of platelets in inflammation lies in their ability to co-operate with endothelial cells to co-ordinate the adherence and extravasation of leucocytes during the inflammatory response [176]. The release of chemokines and cytokines by macrophages within injured tissue initiates a sequence of events whereby leucocytes are attached to the endothelium, first by low-affinity interaction of adhesion molecules called selectins on endothelial and platelet cells with glycoproteins on the leucocytes (‘leucocyte rolling’), and secondly by high-affinity attachment via cell-surface integrins that are able to resist the fluid shear forces within the blood vessel. Similar mechanisms are also known to contribute to coagulation and haematogenous tumour metastasis [177]. The reciprocal arrangement of adhesion molecules on leucocytes, platelets and endothelial cells is carefully controlled by regulating their subcellular localization. PX domain proteins have been linked to the trafficking and cell-surface presentation of two key molecules in this process: P-selectin on endothelial and platelet cells by SNX17 [75,85,86], and PSGL-1 on leucocytes by SNX20 [35] (Supplementary Figure S3 at http://www.BiochemJ.org/bj/441/bj4410039add.htm). P-selectin is stored within specific intracellular compartments from which it is released to the cell surface upon stimulation: α-granules in platelets and Weibel-Palade bodies in endothelial cells. It also undergoes endocytosis, after which it is either recycled through the endocytic system or degraded within lysosomes [177,178]. SNX17 was identified as a P-selectin-interacting protein [75,85], and we have also observed binding of SNX27, suggesting that this may be a common function of the PX-FERM subfamily (R. Ghai and B.M. Collins, unpublished work). Overexpression of SNX17 was found to enhance the internalization of P-selectin from the cell surface, and to retard the degradation of P-selectin in lysosomes by restricting its transport into late endosomes/multivesicular bodies and causing an accumulation in SNX17-positive endosomes [75,86]. Within the opposing leucocyte cells, SNX20 was identified as a binder of the cytoplasmic tail of PSGL-1 [35]. Overexpression of SNX20 caused a significant redistribution of PSGL-1 from the cell surface into endosomes; however, mice deficient in SNX20 appeared to be normal and healthy and their neutrophils displayed no significant defects in PSGL-1-mediated cell adhesion or signalling, possibly due to compensation by the highly homologous SNX21. Further studies will be required to determine if this is true and whether the SNX20/SNX21 proteins control trafficking of other transmembrane cargoes.

PX proteins in Alzheimer's disease

AD is caused, at least in part, by the accumulation of the toxic amyloid peptide Aβ [179]. Aβ is derived from the sequential cleavage of the APP by transmembrane enzymes called secretases, first by β-secretase to release a soluble ectodomain fragment, and subsequently by γ-secretase within the transmembrane domain to form the 40–42-residue Aβ peptide. This degradation is thought to occur primarily within intracellular organelles, whereas a non-amyloidogenic pathway involving initial cleavage by the α-secretase is thought to occur primarily at the cell surface [180]. For detailed reviews of APP trafficking and processing see [181185]. The production of Aβ is therefore dependent on a delicate balance between the trafficking of APP, the trafficking of secretase enzymes and the degree to which the molecules encounter each other within the organelles of the neuronal cell. It is increasingly apparent that many PX proteins and their partners such as the retromer complex play important roles in APP and secretase trafficking, regulating the subsequent accumulation of toxic Aβ peptide (Figure 5). This can occur in a number of ways, as described below.

Cartoon outlining potential roles of PX proteins in the trafficking and processing of APP to neurotoxic Aβ implicated in AD

Figure 5
Cartoon outlining potential roles of PX proteins in the trafficking and processing of APP to neurotoxic Aβ implicated in AD

For reviews of APP trafficking and processing, see [181185]. See the text for a detailed discussion.

Figure 5
Cartoon outlining potential roles of PX proteins in the trafficking and processing of APP to neurotoxic Aβ implicated in AD

For reviews of APP trafficking and processing, see [181185]. See the text for a detailed discussion.

(i) Trafficking of β-secretase and SorLA, which is a co-receptor involved in the retrograde trafficking of APP from endosomes to the TGN, is co-ordinated by the retromer retrograde trafficking complex [186189]. Removal of APP from the endosomal system is expected to result in less Aβ production, due to avoidance of β- and γ-secretases, which function predominantly within these organelles. SNX1, SNX2, SNX5 and SNX6 are key regulators of retromer-mediated trafficking, although a direct role for these PX-BAR proteins in APP trafficking and degradation is yet to be demonstrated.

(ii) A recent study has shown an important role for SNX6 in regulating BACE1 (β-secretase 1; also called β-site APP-cleaving enzyme 1) trafficking and APP degradation [190]. It was found that SNX6 forms a complex with β-secretase, and that SNX6 suppression leads to modulation of β-secretase retrograde trafficking, increased levels of β-secretase and subsequent increased production of Aβ peptide. In contrast with the normal function of the retromer complex and SNX1, this study suggests that SNX6 inhibits the retrograde traffic of BACE1 from endosomes to the Golgi. It is proposed that SNX6 may either antagonize SNX1 function in BACE1 transport or form retromer complexes with differential cargo selectivity. Indirect support for this latter hypothesis is supplied by data showing that alternative retromer-associated PX-BAR proteins can mediate trafficking of different cargo proteins [58].

(iii) SNX17 is highly expressed in neurons [83,87] and is implicated directly in the recycling of APP from endosomes to the cell surface, as it binds to the APP NPxY sorting motif and inhibition by siRNA results in an increased level of APP breakdown and Aβ peptide production within the endosomal compartment [11,87]. In addition, one of the most intriguing aspects of SNX17-receptor trafficking is the relationship between many of the identified SNX17 cargos. Many studies over the last few years have highlighted the complexity of APP processing, and in particular have shown a critical role for ApoE (apolipoprotein E) and its receptors from the LDLR family in APP processing and Aβ clearance in AD (reviewed in [181183]). SNX17 regulates the endosome-to-cell surface recycling of many receptors of the LDLR family, including LRP1, which facilitates the transport of the APP protein through an interaction mediated by FE65 [8185], and others implicated directly in both the clearance and generation of Aβ plaques via their role as receptors for the Aβ chaperone ApoE [181183]. Therefore SNX17 appears to be functioning at a nexus of trafficking pathways critical for APP processing, not only controlling APP directly, but also affecting other receptors with important roles in the process of Aβ peptide production and clearance. It is possible that trafficking of APP and LDLR family proteins may be influenced by the other PX-FERM molecules SNX27 and SNX31, but this remains to be confirmed.

(iv) SNX33 and SNX9 have been shown to affect the uptake of APP from the cell surface, although the mechanism is poorly understood [66]. Increased expression of SNX33 or SNX9 was shown to significantly increase the level of soluble APP released into the extracellular space by α-secretase (sAPPα). A similar effect was seen for dominant-negative constructs of the dynamin GTPase required for scission of endocytic vesicles. SNX33 was shown to bind dynamin via its SH3 domain and its expression was able to inhibit the endocytosis of APP. Therefore the SH3-PX-BAR proteins in this system are able to affect the balance of α- and β-secretase cleavage and the level of Aβ production. The authors suggest that SNX33 and SNX9 may be working to inhibit dynamin during endocytosis. Given the role of SNX9 in promoting clathrin-dependent and -independent endocytosis, this may at first appear counterintuitive [17,21,47,191,192]. However, other studies have also shown that either overexpression or knockdown of SNX9 can effectively perturb clathrin-mediated endocytosis, indicating that altered SNX9 protein levels may impair the homoeostasis of protein-interaction networks required for endocytic vesicle formation [191193]. One possible explanation is that overexpression of SNX33 or SNX9 results in competition for APP-specific adaptors such as Dab2 [87,194] for binding to the AP2 complex, clathrin and dynamin during endocytic vesicle formation, and therefore acts to slow the dynamics of APP endocytosis. More work will be required to dissect the mechanisms by which SH3-PX-BAR proteins affect APP uptake.

(v) SH3PXD2A was shown to play a role in mediating Aβ-induced neurotoxicity through its interaction with members of the ADAM (a disintegrin and metalloproteinase) family of enzymes (for reviews of ADAMs, see [195,196]). SH3PXD2A can bind to (at least) ADAM12, ADAM15 and ADAM19 through association of its fifth SH3 domain with polyproline sequences in the cytosplasmic tails of the transmembrane proteases [197,198]. Exposure of neurons to cytotoxic Aβ peptide results in tyrosine phosphorylation of SH3PXD2A and relocalization of the protein, and SH3PXD2A is then able to stimulate the metalloproteinase activity of ADAM12 [199]. Treating cells with toxic Aβ peptide results in increased ADAM12 proteolytic activity, whereas expression of protease-deficient ADAM12 or an ADAM12-binding mutant of SH3PXD2A blocks Aβ-induced cell death. In addition, SNPs (single nucleotide polymorphisms) in ADAM12 and SH3PXD2A may confer susceptibility to late-onset AD [200]. Although the mechanism is very poorly understood, the hypothesis is that neuronal cell death induced by toxic Aβ peptides is at least partly mediated by ADAM12 and SH3PXD2A. These proteins therefore may be potential targets for therapeutic applications.

(vi) Another family of PX proteins implicated as negative regulators of Aβ production in AD are the PX-PH-PLD proteins [201]. PLD1 is significantly up-regulated in brains of AD patients, in particular within mitochondrial fractions, and is able to interact with the cytoplasmic tail of APP via its PH domain [202,203]. There is now strong evidence that PLD1 can influence the trafficking of both APP and the PS1 (presenilin 1) subunit of γ-secretase (and, through PS1, presumably other γ-secretase subunits), in particular promoting the formation of TGN-derived transport vesicles destined for the cell surface [204206]. It is thought that PLD1 enhances egress of APP from the TGN and internal endosomes where Aβ production predominantly occurs, thereby reducing the level of toxic Aβ production. In addition to a role in APP trafficking, PLD1 was also found to inhibit Aβ production directly, by interfering with the assembly of γ-secretase via association with PS1 [204]. Adding to the complexity of PLD function in AD, other studies indicate that PLD activity is increased in neurons exposed to Aβ, that PLD2 is critical for mediating Aβ neuronal toxicity and that PLD2 ablation in amyloidogenic transgenic mouse models improves memory deficits and synaptic function, suggesting that PLD activity may be a valid target for therapeutic action [207].

It is becoming increasingly apparent that intracellular trafficking is central to the process of APP homoeostasis and Aβ manufacture [180,208]. Taken together, the evidence is overwhelming that PX proteins regulate various APP and secretase trafficking pathways and modulate production and toxicity of the Aβ peptide, so determining the precise roles of the PX proteins and the molecular mechanisms that underpin their function in Aβ regulation represents an important area of investigation.

PX proteins in pathogen invasion

Another disease process that has gained recent attention is that of pathogen invasion via corruption of the endocytic system (reviewed in [209]). The invasion of Salmonella enterica via coercion of normal cellular macropinocytic processes [161,210,211] has been found to be critically dependent on the action of PX proteins. Bujny et al. [212] found that SNX1 undergoes rapid translocation to sites of bacterial entry and SCVs (Salmonella-containing vacuoles), resulting in the formation of extensive long-range membrane tubules that are thought to mediate membrane contraction during SCV maturation. Critically, suppression of SNX1 was found to halt the progression of SCVs into the cell. Recently, Braun et al. [213], demonstrated that the PX-only protein SNX3 is also important for the process. Similarly to SNX1, SNX3 is recruited to SCVs and to the SCV membrane tubules, and its depletion leads to impaired SCV maturation. However it was found that SNX3 recruitment occurs after SNX1, and in fact SNX3 depends on SNX1 (and SNX2) for localization to these tubules. From a mechanistic standpoint, this correlates well with the known role of SNX1 and SNX2 as proteins regulating membrane tubulation. The generation of an SCV is dependent on bacterially secreted enzymes that promote the generation of PtdIns3P on its limiting membrane during the early stages of formation. Given the central role of PtdIns3P in early stages of Salmonella invasion, it is very likely that other PX proteins will also be important for the process. Indeed, SNX15 was recently found to be recruited to early SCVs (but not to tubules) [213], and given the role of PX-BAR proteins other than SNX1 in macropinocytosis [24,214], these are also likely to be involved in pathogen invasion. SNX1, SNX6, SNX9 and SNX33 have all been identified as being involved in the internalization of apoptotic cells via phagocytosis and the subsequent transport into a degradative organelle [215217]. However, their role in phagocytosis of pathogens remains uncharacterized. Other PX family members have central roles in host defence against pathogens, with p47phox, p40phox and NOXO1 (NADPH oxidase organizer 1) associated with the NADPH oxidase complex, which is responsible for the formation of superoxide anions [218,219]. Following phagocytosis of pathogens, the NADPH oxidase complex is activated, resulting in an oxidative burst that can kill the pathogen directly, or indirectly by activating other components of the innate immune system.

In addition to a role in bacterial invasion, endocytosis and trafficking through the endosomal system is also critical for the uptake of bacterial toxins and the processing and assembly of viruses [209]. STx (Shiga toxin) is secreted by Shigella dysenteriae and is endocytosed by target cells by clathrin-mediated uptake, bypasses the degradative pathways and is eventually translocated into the cytosol from the endoplasmic reticulum [220]. SNX1 has been found to be important for the efficient passage of STx [50,57,58,221]. SNX2 has also been implicated [50], although other studies suggest that SNX2 does not play an important role in the process [57,58]. In contrast, depletion of another PX-BAR protein SNX8 increases the rate of endosome–Golgi transport of STx, suggesting an antagonistic role in STx passage through the endosomal compartment [222]. Finally, SNX5 has been implicated in the uptake via macropinocytosis of Ebola virus [223], and the protein SNX16 has been found to be important for infection by VSV (vesicular stomatitis virus) [128]. For infection, VSV and other enveloped viruses must be endocytosed and transported to late endosomes where the acidic pH of the lumen triggers fusion of the viral envelope with the endosomal membrane and release of the nucleocapsid into the cytosol for viral replication. SNX16 was found to localize to these late endosomes and its overexpression significantly inhibited the export of the nucleocapsid. It remains to be determined, however, how SNX16 acts to regulate this process.

CONCLUDING REMARKS

In the last few years there has been major progress in understanding the functions of PX proteins. Of course, the diversity of these proteins makes it impossible to present a single unified picture of how they work. It is clear, however, that the coupling of the membrane-localizing PX domain with different functional modules is a mechanism by which eukaryotic cells have constructed tools to control a multitude of protein binding, membrane remodelling, signalling, motor and enzymatic functions localized to specific regions of the secretory and endocytic system.

Many questions remain regarding the functional, structural and pathological roles of the PX proteins. From a cellular perspective, it will be important to develop quantitative tools for analysing the localization, interactions and, most importantly, the spatiotemporal regulation of PX proteins by different cellular signals. Structurally, although we now have a firm grasp of how the PX domain associates with PtdIns3P, there is a severe paucity of information regarding how the PX domain regulates protein–protein interactions. There is also a significant lack of knowledge regarding the structures of many of the PX-associated protein domains and the overall tertiary structures of the full-length molecules. Most importantly, it will be essential to combine these cellular and structural insights with broader systems approaches to develop an understanding of how the vast networks of interactions controlled by the PX proteins regulate cellular fate. Finally, it is imperative to determine how PX proteins contribute to different disease processes, such as pathogen invasion and amyloid production, both in order to determine whether they might be suitable therapeutic targets and also to gain insights into how such interventions might be achieved.

Abbreviations

     
  • AD

    Alzheimer's disease

  •  
  • ADAM

    a disintegrin and metalloproteinase

  •  
  • AP2

    adaptor protein complex 2

  •  
  • ApoE

    apolipoprotein E

  •  
  • APP

    amyloid precursor protein

  •  
  • BACE

    β-secretase

  •  
  • BAR

    Bin/amphiphysin/Rvs

  •  
  • CASP

    cytohesin-associated scaffolding protein

  •  
  • CGD

    chronic granulomatous disease

  •  
  • CI-MPR

    cation-independent mannose-6-phosphate receptor

  •  
  • DGK

    diacylglycerolkinase

  •  
  • EGF

    epidermal growth factor

  •  
  • EGFR

    epidermal growth factor receptor

  •  
  • ERK

    extracellular-signal-regulated kinase

  •  
  • FERM

    band4.1/ezrin/radixin/moesin

  •  
  • FHA

    forkhead association

  •  
  • FISH

    five SH3 domains

  •  
  • FYVE

    Fab1p/YOTB/Vac1p/EEA1

  •  
  • GAP

    GTPase-activating protein

  •  
  • GC-GAP

    GAB/cdc42 GAP

  •  
  • GPCR

    G-protein-coupled receptor

  •  
  • Hrs

    hepatocyte growth factor-regulated tyrosine kinase substrate

  •  
  • HS1BP3

    HS1-binding protein 3

  •  
  • 5-HT4R

    5-hydroxytryptamine type 4 receptor

  •  
  • IRAS

    imidazoline receptor antisera selected

  •  
  • IRS

    insulin receptor substrate

  •  
  • KIF

    kinesin-family protein

  •  
  • Krit1

    Krev-interaction trapped 1

  •  
  • LDLR

    low-density lipoprotein receptor

  •  
  • LRP1

    LDLR-related protein 1

  •  
  • LRR

    leucine-rich repeat

  •  
  • MIT domain

    microtubule-interacting and trafficking molecule domain

  •  
  • MMEP

    microcephaly, micropthalmia, ectrodactyly and prognathism

  •  
  • MVB

    multivesicular body

  •  
  • NCF

    neutrophil cytosolic factor

  •  
  • NMDA

    N-methyl-D-aspartate

  •  
  • NOXO1

    NADPH oxidase organizer 1

  •  
  • NR

    NMDA receptor

  •  
  • PA

    phosphatidic acid

  •  
  • PDZ

    postsynaptic density 95/discs large/zonula occludens

  •  
  • PDZbm

    PDZ-binding motif

  •  
  • PH

    pleckstrin homology

  •  
  • PI3K

    phosphoinositide 3-kinase

  •  
  • PLCγ1

    phospholipase Cγ1

  •  
  • PLD

    phospholipase D

  •  
  • PS1

    presenilin 1

  •  
  • PSGL

    P-selectin glycoprotein ligand

  •  
  • PTB

    phosphotyrosine binding

  •  
  • PX

    phox-homology

  •  
  • PXA domain

    PX-associated domain A

  •  
  • PXC

    PX-associated domain C

  •  
  • RA

    Ras-association

  •  
  • RGS

    regulator of G-protein signalling

  •  
  • RPS6K

    ribosomal protein S6 kinase

  •  
  • SCV

    Salmonella-containing vacuole

  •  
  • SGK

    serum- and glucocorticoid-induced protein kinase

  •  
  • SH

    Src homology

  •  
  • SH3PXD2A

    SH3 and PX domain protein 2A

  •  
  • siRNA

    small interfering RNA

  •  
  • SLIC-1

    selectin ligand interactor cytoplasmic-1

  •  
  • SNARE

    soluble N-ethylmaleimide-sensitive factor-attachment protein receptor

  •  
  • snazarus

    sorting nexin lazarus

  •  
  • SNX

    sorting nexin

  •  
  • S/T kinase

    serine/threonine kinase

  •  
  • STx

    Shiga toxin

  •  
  • TC-GAP

    TC10/cdc42 GAP

  •  
  • TGF-β

    transforming growth factor β

  •  
  • TGN

    trans-Golgi network

  •  
  • TPR

    tetratricopeptide repeat

  •  
  • VPS

    vacuolar protein sorting-associated protein

  •  
  • VSV

    vesicular stomatitis virus

  •  
  • WASP

    Wiskott–Aldrich syndrome protein

  •  
  • WASH

    WASP and SCAR (suppressor of cAMP receptor) homologue

  •  
  • N-WASP

    neuronal WASP

FUNDING

Research in the laboratories of B.M.C. and R.D.T. is supported by funds from the Australian Research Council (ARC) and the National Health and Medical Research Council (NHMRC). B.M.C. is an ARC Future Fellow [grant number FT100100027]. R.D.T. is an NHMRC Senior Research Fellow [grant number 511042].

References

References
1
Scita
G.
Di Fiore
P. P.
The endocytic matrix
Nature
2010
, vol. 
463
 (pg. 
464
-
473
)
2
Sorkin
A.
von Zastrow
M.
Endocytosis and signalling: intertwining molecular networks
Nat. Rev. Mol. Cell Biol.
2009
, vol. 
10
 (pg. 
609
-
622
)
3
Seet
L. F.
Hong
W.
The Phox (PX) domain proteins and membrane traffic
Biochim. Biophys. Acta
2006
, vol. 
1761
 (pg. 
878
-
896
)
4
Karathanassis
D.
Stahelin
R. V.
Bravo
J.
Perisic
O.
Pacold
C. M.
Cho
W.
Williams
R. L.
Binding of the PX domain of p47phox to phosphatidylinositol 3,4-bisphosphate and phosphatidic acid is masked by an intramolecular interaction
EMBO J.
2002
, vol. 
21
 (pg. 
5057
-
5068
)
5
Stahelin
R. V.
Ananthanarayanan
B.
Blatner
N. R.
Singh
S.
Bruzik
K. S.
Murray
D.
Cho
W.
Mechanism of membrane binding of the phospholipase D1 PX domain
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
54918
-
54926
)
6
Stahelin
R. V.
Burian
A.
Bruzik
K. S.
Murray
D.
Cho
W.
Membrane binding mechanisms of the PX domains of NADPH oxidase p40phox and p47phox
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
14469
-
14479
)
7
Stahelin
R. V.
Karathanassis
D.
Bruzik
K. S.
Waterfield
M. D.
Bravo
J.
Williams
R. L.
Cho
W.
Structural and membrane binding analysis of the Phox homology domain of phosphoinositide 3-kinase-C2α
J. Biol. Chem.
2006
, vol. 
282
 (pg. 
39396
-
39406
)
8
Stahelin
R. V.
Karathanassis
D.
Murray
D.
Williams
R. L.
Cho
W.
Structural and membrane binding analysis of the Phox homology domain of Bem1p: basis of phosphatidylinositol 4-phosphate specificity
J. Biol. Chem.
2007
, vol. 
282
 (pg. 
25737
-
25747
)
9
Yu
J. W.
Lemmon
M. A.
All phox homology (PX) domains from Saccharomyces cerevisiae specifically recognize phosphatidylinositol 3-phosphate
J. Biol. Chem.
2001
, vol. 
276
 (pg. 
44179
-
44184
)
10
Falasca
M.
Maffucci
T.
Rethinking phosphatidylinositol 3-monophosphate
Biochim. Biophys. Acta
2009
, vol. 
1793
 (pg. 
1795
-
1803
)
11
Ghai
R.
Mobli
M.
Norwood
S. J.
Bugarcic
A.
Teasdale
R. D.
King
G. F.
Collins
B. M.
Phox homology band 4.1/ezrin/radixin/moesin-like proteins function as molecular scaffolds that interact with cargo receptors and Ras GTPases
Proc. Natl. Acad. Sci. U.S.A.
2011
, vol. 
108
 (pg. 
7763
-
7768
)
12
Song
J.
Zhao
K. Q.
Newman
C. L.
Vinarov
D. A.
Markley
J. L.
Solution structure of human sorting nexin 22
Protein Sci.
2007
, vol. 
16
 (pg. 
807
-
814
)
13
Carlton
J. G.
Cullen
P. J.
Coincidence detection in phosphoinositide signaling
Trends Cell Biol.
2005
, vol. 
15
 (pg. 
540
-
547
)
14
Lemmon
M. A.
Membrane recognition by phospholipid-binding domains
Nat. Rev. Mol. Cell Biol.
2008
, vol. 
9
 (pg. 
99
-
111
)
15
Narayan
K.
Lemmon
M. A.
Determining selectivity of phosphoinositidebinding domains
Methods
2006
, vol. 
39
 (pg. 
122
-
133
)
16
Badour
K.
McGavin
M. K.
Zhang
J.
Freeman
S.
Vieira
C.
Filipp
D.
Julius
M.
Mills
G. B.
Siminovitch
K. A.
Interaction of the Wiskott–Aldrich syndrome protein with sorting nexin 9 is required for CD28 endocytosis and cosignaling in T cells
Proc. Natl. Acad. Sci. U.S.A.
2007
, vol. 
104
 (pg. 
1593
-
1598
)
17
Lundmark
R.
Carlsson
S. R.
Sorting nexin 9 participates in clathrinmediated endocytosis through interactions with the core components
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
46772
-
46781
)
18
Pylypenko
O.
Lundmark
R.
Rasmuson
E.
Carlsson
S. R.
Rak
A.
The PX-BAR membrane-remodeling unit of sorting nexin 9
EMBO J.
2007
, vol. 
26
 (pg. 
4788
-
4800
)
19
Shin
N.
Ahn
N.
Chang-Ileto
B.
Park
J.
Takei
K.
Ahn
S. G.
Kim
S. A.
Di Paolo
G.
Chang
S.
SNX9 regulates tubular invagination of the plasma membrane through interaction with actin cytoskeleton and dynamin 2
J. Cell Sci.
2008
, vol. 
121
 (pg. 
1252
-
1263
)
20
Yarar
D.
Surka
M. C.
Leonard
M. C.
Schmid
S. L.
SNX9 activities are regulated by multiple phosphoinositides through both PX and BAR domains
Traffic
2008
, vol. 
9
 (pg. 
133
-
146
)
21
Yarar
D.
Waterman-Storer
C. M.
Schmid
S. L.
SNX9 couples actin assembly to phosphoinositide signals and is required for membrane remodeling during endocytosis
Dev. Cell
2007
, vol. 
13
 (pg. 
43
-
56
)
22
Koharudin
L. M.
Furey
W.
Liu
H.
Liu
Y. J.
Gronenborn
A. M.
The phox domain of sorting nexin 5 lacks phosphatidylinositol 3-phosphate (PtdIns(3)P) specificity and preferentially binds to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2)
J. Biol. Chem.
2009
, vol. 
284
 (pg. 
23697
-
23707
)
23
Liu
H.
Liu
Z. Q.
Chen
C. X.
Magill
S.
Jiang
Y.
Liu
Y. J.
Inhibitory regulation of EGF receptor degradation by sorting nexin 5
Biochem. Biophys. Res. Commun.
2006
, vol. 
342
 (pg. 
537
-
546
)
24
Kerr
M. C.
Lindsay
M. R.
Luetterforst
R.
Hamilton
N.
Simpson
F.
Parton
R. G.
Gleeson
P. A.
Teasdale
R. D.
Visualisation of macropinosome maturation by the recruitment of sorting nexins
J. Cell Sci.
2006
, vol. 
119
 (pg. 
3967
-
3980
)
25
Hiroaki
H.
Ago
T.
Ito
T.
Sumimoto
H.
Kohda
D.
Solution structure of the PX domain, a target of the SH3 domain
Nat. Struct. Biol.
2001
, vol. 
8
 (pg. 
526
-
530
)
26
Sumimoto
H.
Kage
Y.
Nunoi
H.
Sasaki
H.
Nose
T.
Fukumaki
Y.
Ohno
M.
Minakami
S.
Takeshige
K.
Role of Src homology 3 domains in assembly and activation of the phagocyte NADPH oxidase
Proc. Natl. Acad. Sci. U.S.A.
1994
, vol. 
91
 (pg. 
5345
-
5349
)
27
Jang
I. H.
Lee
S.
Park
J. B.
Kim
J. H.
Lee
C. S.
Hur
E. M.
Kim
I. S.
Kim
K. T.
Yagisawa
H.
Suh
P. G.
Ryu
S. H.
The direct interaction of phospholipase C-γ1 with phospholipase D2 is important for epidermal growth factor signaling
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
18184
-
18190
)
28
Prehoda
K. E.
Lim
W. A.
The double life of PX domains
Nat. Struct. Biol.
2001
, vol. 
8
 (pg. 
570
-
572
)
29
Lee
C. S.
Kim
I. S.
Park
J. B.
Lee
M. N.
Lee
H. Y.
Suh
P. G.
Ryu
S. H.
The phox homology domain of phospholipase D activates dynamin GTPase activity and accelerates EGFR endocytosis
Nat. Cell Biol.
2006
, vol. 
8
 (pg. 
477
-
484
)
30
Lee
H. Y.
Park
J. B.
Jang
I. H.
Chae
Y. C.
Kim
J. H.
Kim
I. S.
Suh
P. G.
Ryu
S. H.
Munc-18–1 inhibits phospholipase D activity by direct interaction in an epidermal growth factor-reversible manner
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
16339
-
16348
)
31
Parks
W. T.
Frank
D. B.
Huff
C.
Renfrew Haft
C.
Martin
J.
Meng
X.
de Caestecker
M. P.
McNally
J. G.
Reddi
A.
Taylor
S. I.
, et al. 
Sorting nexin 6, a novel SNX, interacts with the transforming growth factor-β family of receptor serine-threonine kinases
J. Biol. Chem.
2001
, vol. 
276
 (pg. 
19332
-
19339
)
32
Abdul-Ghani
M.
Hartman
K. L.
Ngsee
J. K.
Abstrakt interacts with and regulates the expression of sorting nexin-2
J. Cell. Physiol.
2005
, vol. 
204
 (pg. 
210
-
218
)
33
Skanland
S. S.
Walchli
S.
Brech
A.
Sandvig
K.
SNX4 in complex with clathrin and dynein: implications for endosome movement
PLoS ONE
2009
, vol. 
4
 pg. 
e5935
 
34
Ishibashi
Y.
Maita
H.
Yano
M.
Koike
N.
Tamai
K.
Ariga
H.
Iguchi-Ariga
S. M.
Pim-1 translocates sorting nexin 6/TRAF4-associated factor 2 from cytoplasm to nucleus
FEBS Lett.
2001
, vol. 
506
 (pg. 
33
-
38
)
35
Schaff
U. Y.
Shih
H. H.
Lorenz
M.
Sako
D.
Kriz
R.
Milarski
K.
Bates
B.
Tchernychev
B.
Shaw
G. D.
Simon
S. I.
SLIC-1/sorting nexin 20: a novel sorting nexin that directs subcellular distribution of PSGL-1
Eur. J. Immunol.
2008
, vol. 
38
 (pg. 
550
-
564
)
36
DiNitto
J. P.
Lambright
D. G.
Membrane and juxtamembrane targeting by PH and PTB domains
Biochim. Biophys. Acta
2006
, vol. 
1761
 (pg. 
850
-
867
)
37
Cullen
P. J.
Endosomal sorting and signalling: an emerging role for sorting nexins
Nat. Rev. Mol. Cell Biol.
2008
, vol. 
9
 (pg. 
574
-
582
)
38
Carlton
J.
Bujny
M.
Rutherford
A.
Cullen
P.
Sorting nexins – unifying trends and new perspectives
Traffic
2005
, vol. 
6
 (pg. 
75
-
82
)
39
van Weering
J. R.
Verkade
P.
Cullen
P. J.
SNX-BAR proteins in phosphoinositide-mediated, tubular-based endosomal sorting
Semin. Cell Dev. Biol.
2010
, vol. 
21
 (pg. 
371
-
380
)
40
Attar
N.
Cullen
P. J.
The retromer complex
Adv. Enzyme Regul.
2010
, vol. 
50
 (pg. 
216
-
236
)
41
Kurten
R. C.
Cadena
D. L.
Gill
G. N.
Enhanced degradation of EGF receptors by a sorting nexin, SNX1
Science
1996
, vol. 
272
 (pg. 
1008
-
1010
)
42
Teasdale
R. D.
Loci
D.
Houghton
F.
Karlsson
L.
Gleeson
P. A.
A large family of endosome-localized proteins related to sorting nexin 1
Biochem. J.
2001
, vol. 
358
 (pg. 
7
-
16
)
43
Worby
C. A.
Dixon
J. E.
Sorting out the cellular functions of sorting nexins
Nat. Rev. Mol. Cell Biol.
2002
, vol. 
3
 (pg. 
919
-
931
)
44
Bhatia
V. K.
Madsen
K. L.
Bolinger
P. Y.
Kunding
A.
Hedegard
P.
Gether
U.
Stamou
D.
Amphipathic motifs in BAR domains are essential for membrane curvature sensing
EMBO J.
2009
, vol. 
28
 (pg. 
3303
-
3314
)
45
Gallop
J. L.
McMahon
H. T.
BAR domains and membrane curvature: bringing your curves to the BAR
Biochem. Soc. Symp.
2005
, vol. 
72
 (pg. 
223
-
231
)
46
Carlton
J.
Bujny
M.
Peter
B. J.
Oorschot
V. M.
Rutherford
A.
Mellor
H.
Klumperman
J.
McMahon
H. T.
Cullen
P. J.
Sorting nexin-1 mediates tubular endosome-to-TGN transport through coincidence sensing of high-curvature membranes and 3-phosphoinositides
Curr. Biol.
2004
, vol. 
14
 (pg. 
1791
-
1800
)
47
Lundmark
R.
Carlsson
S. R.
SNX9 – a prelude to vesicle release
J Cell Sci.
2009
, vol. 
122
 (pg. 
5
-
11
)
48
Bonifacino
J. S.
Hurley
J. H.
Retromer
Curr. Opin. Cell Biol.
2008
, vol. 
20
 (pg. 
427
-
436
)
49
Collins
B. M.
The structure and function of the retromer protein complex
Traffic.
2008
, vol. 
9
 (pg. 
1811
-
1822
)
50
Utskarpen
A.
Slagsvold
H. H.
Dyve
A. B.
Skanland
S. S.
Sandvig
K.
SNX1 and SNX2 mediate retrograde transport of Shiga toxin
Biochem. Biophys. Res. Commun.
2007
, vol. 
358
 (pg. 
566
-
570
)
51
Rojas
R.
Kametaka
S.
Haft
C. R.
Bonifacino
J. S.
Interchangeable but essential functions of SNX1 and SNX2 in the association of retromer with endosomes and the trafficking of mannose 6-phosphate receptors
Mol. Cell. Biol.
2007
, vol. 
27
 (pg. 
1112
-
1124
)
52
Gullapalli
A.
Garrett
T. A.
Paing
M. M.
Griffin
C. T.
Yang
Y.
Trejo
J.
A role for sorting nexin 2 in epidermal growth factor receptor down-regulation: evidence for distinct functions of sorting nexin 1 and 2 in protein trafficking
Mol. Biol. Cell
2004
, vol. 
15
 (pg. 
2143
-
2155
)
53
Haft
C. R.
de la Luz Sierra
M.
Bafford
R.
Lesniak
M. A.
Barr
V. A.
Taylor
S. I.
Human orthologs of yeast vacuolar protein sorting proteins Vps26, 29, and 35: assembly into multimeric complexes
Mol. Biol. Cell.
2000
, vol. 
11
 (pg. 
4105
-
4116
)
54
Haft
C. R.
de la Luz Sierra
M.
Barr
V. A.
Haft
D. H.
Taylor
S. I.
Identification of a family of sorting nexin molecules and characterization of their association with receptors
Mol. Cell. Biol
1998
, vol. 
18
 (pg. 
7278
-
7287
)
55
Wang
Y.
Zhou
Y.
Szabo
K.
Haft
C. R.
Trejo
J.
Down-regulation of protease-activated receptor-1 is regulated by sorting nexin 1
Mol. Biol. Cell
2002
, vol. 
13
 (pg. 
1965
-
1976
)
56
Wassmer
T.
Attar
N.
Harterink
M.
van Weering
J. R.
Traer
C. J.
Oakley
J.
Goud
B.
Stephens
D. J.
Verkade
P.
Korswagen
H. C.
Cullen
P. J.
The retromer coat complex coordinates endosomal sorting and dynein-mediated transport, with carrier recognition by the trans-Golgi network
Dev. Cell
2009
, vol. 
17
 (pg. 
110
-
122
)
57
Bujny
M. V.
Popoff
V.
Johannes
L.
Cullen
P. J.
The retromer component sorting nexin-1 is required for efficient retrograde transport of Shiga toxin from early endosome to the trans Golgi network
J. Cell Sci.
2007
, vol. 
120
 (pg. 
2010
-
2021
)
58
Lieu
Z. Z.
Gleeson
P. A.
Identification of different itineraries and retromer components for endosome-to-Golgi transport of TGN38 and Shiga toxin
Eur. J. Cell Biol.
2010
, vol. 
89
 (pg. 
379
-
393
)
59
Gullapalli
A.
Wolfe
B. L.
Griffin
C. T.
Magnuson
T.
Trejo
J.
An essential role for SNX1 in lysosomal sorting of protease-activated receptor-1: evidence for retromer-, Hrs-, and Tsg101-independent functions of sorting nexins
Mol. Biol. Cell
2006
, vol. 
17
 (pg. 
1228
-
1238
)
60
Schwarz
D. G.
Griffin
C. T.
Schneider
E. A.
Yee
D.
Magnuson
T.
Genetic analysis of sorting nexins 1 and 2 reveals a redundant and essential function in mice
Mol. Biol. Cell
2002
, vol. 
13
 (pg. 
3588
-
3600
)
61
Wassmer
T.
Attar
N.
Bujny
M. V.
Oakley
J.
Traer
C. J.
Cullen
P. J.
A loss-of-function screen reveals SNX5 and SNX6 as potential components of the mammalian retromer
J. Cell Sci
2007
, vol. 
120
 (pg. 
45
-
54
)
62
Merino-Trigo
A.
Kerr
M. C.
Houghton
F.
Lindberg
A.
Mitchell
C.
Teasdale
R. D.
Gleeson
P. A.
Sorting nexin 5 is localized to a subdomain of the early endosomes and is recruited to the plasma membrane following EGF stimulation
J. Cell Sci.
2004
, vol. 
117
 (pg. 
6413
-
6424
)
63
Haberg
K.
Lundmark
R.
Carlsson
S. R.
SNX18 is an SNX9 paralog that acts as a membrane tubulator in AP-1-positive endosomal trafficking
J. Cell Sci.
2008
, vol. 
121
 (pg. 
1495
-
1505
)
64
Zhang
J.
Zhang
X.
Guo
Y.
Xu
L.
Pei
D.
Sorting nexin 33 induces mammalian cell micronucleated phenotype and actin polymerization by interacting with Wiskott–Aldrich syndrome protein
J. Biol. Chem.
2009
, vol. 
284
 (pg. 
21659
-
21669
)
65
Park
S.
Kim
Y.
Lee
S.
Park
P.
Park
Z.
Sun
W.
Kim
H.
Chang
S.
SNX18 shares a redundant role with SNX9 and modulates endoctyic trafficking at the plasma membrane
J. Cell Sci.
2010
, vol. 
123
 (pg. 
1742
-
1750
)
66
Schobel
S.
Neumann
S.
Hertweck
M.
Dislich
B.
Kuhn
P. H.
Kremmer
E.
Seed
B.
Baumeister
R.
Haass
C.
Lichtenthaler
S. F.
A novel sorting nexin modulates endocytic trafficking and α-secretase cleavage of the amyloid precursor protein
J. Biol. Chem.
2008
, vol. 
283
 (pg. 
14257
-
14268
)
67
Wang
Q.
Kaan
H. Y.
Hooda
R. N.
Goh
S. L.
Sondermann
H.
Structure and plasticity of Endophilin and Sorting Nexin 9
Structure
2008
, vol. 
16
 (pg. 
1574
-
1587
)
68
Frost
A.
Perera
R.
Roux
A.
Spasov
K.
Destaing
O.
Egelman
E. H.
De Camilli
P.
Unger
V. M.
Structural basis of membrane invagination by F-BAR domains
Cell
2008
, vol. 
132
 (pg. 
807
-
817
)
69
Chin
L. S.
Raynor
M. C.
Wei
X.
Chen
H. Q.
Li
L.
Hrs interacts with sorting nexin 1 and regulates degradation of epidermal growth factor receptor
J. Biol. Chem.
2001
, vol. 
276
 (pg. 
7069
-
7078
)
70
Heydorn
A.
Sondergaard
B. P.
Ersboll
B.
Holst
B.
Nielsen
F. C.
Haft
C. R.
Whistler
J.
Schwartz
T. W.
A library of 7TM receptor C-terminal tails. Interactions with the proposed post-endocytic sorting proteins ERM-binding phosphoprotein 50 (EBP50), N-ethylmaleimide-sensitive factor (NSF), sorting nexin 1 (SNX1), and G protein-coupled receptor-associated sorting protein (GASP)
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
54291
-
54303
)
71
Swarbrick
J. D.
Shaw
D. J.
Chhabra
S.
Ghai
R.
Valkov
E.
Norwood
S. J.
Seaman
M. N.
Collins
B. M.
VPS29 is not an active metallo-phosphatase but is a rigid scaffold required for retromer interaction with accessory proteins
PLoS ONE
2011
, vol. 
6
 pg. 
e20420
 
72
Traer
C. J.
Rutherford
A. C.
Palmer
K. J.
Wassmer
T.
Oakley
J.
Attar
N.
Carlton
J. G.
Kremerskothen
J.
Stephens
D. J.
Cullen
P. J.
SNX4 coordinates endosomal sorting of TfnR with dynein-mediated transport into the endocytic recycling compartment
Nat. Cell Biol.
2007
, vol. 
9
 (pg. 
1370
-
1380
)
73
Chishti
A. H.
Kim
A. C.
Marfatia
S. M.
Lutchman
M.
Hanspal
M.
Jindal
H.
Liu
S. C.
Low
P. S.
Rouleau
G. A.
Mohandas
N.
, et al. 
The FERM domain: a unique module involved in the linkage of cytoplasmic proteins to the membrane
Trends Biochem. Sci.
1998
, vol. 
23
 (pg. 
281
-
282
)
74
Czubayko
M.
Knauth
P.
Schluter
T.
Florian
V.
Bohnensack
R.
Sorting nexin 17, a non-self-assembling and a PtdIns(3)P high class affinity protein, interacts with the cerebral cavernous malformation related protein KRIT1
Biochem. Biophys. Res. Commun.
2006
, vol. 
345
 (pg. 
1264
-
1272
)
75
Knauth
P.
Schluter
T.
Czubayko
M.
Kirsch
C.
Florian
V.
Schreckenberger
S.
Hahn
H.
Bohnensack
R.
Functions of sorting nexin 17 domains and recognition motif for P-selectin trafficking
J. Mol. Biol.
2005
, vol. 
347
 (pg. 
813
-
825
)
76
van Kerkhof
P.
Lee
J.
McCormick
L.
Tetrault
E.
Lu
W.
Schoenfish
M.
Oorschot
V.
Strous
G. J.
Klumperman
J.
Bu
G.
Sorting nexin 17 facilitates LRP recycling in the early endosome
EMBO J.
2005
, vol. 
24
 (pg. 
2851
-
2861
)
77
Joubert
L.
Hanson
B.
Barthet
G.
Sebben
M.
Claeysen
S.
Hong
W.
Marin
P.
Dumuis
A.
Bockaert
J.
New sorting nexin (SNX27) and NHERF specifically interact with the 5-HT4a receptor splice variant: roles in receptor targeting
J. Cell Sci.
2004
, vol. 
117
 (pg. 
5367
-
5379
)
78
Lunn
M. L.
Nassirpour
R.
Arrabit
C.
Tan
J.
McLeod
I.
Arias
C. M.
Sawchenko
P. E.
Yates
J.R.
III
Slesinger
P. A.
A unique sorting nexin regulates trafficking of potassium channels via a PDZ domain interaction
Nat. Neurosci.
2007
, vol. 
10
 (pg. 
1249
-
1259
)
79
Rincon
E.
de Guinoa
J. S.
Gharbi
S. I.
Sorzano
C. O.
Carrasco
Y. R.
Merida
I.
Translocation dynamics of sorting nexin 27 in activated T cells
J. Cell Sci.
2011
, vol. 
124
 (pg. 
776
-
788
)
80
Rincon
E.
Santos
T.
Avila-Flores
A.
Albar
J. P.
Lalioti
V.
Lei
C.
Hong
W.
Merida
I.
Proteomics identification of sorting nexin 27 as a diacylglycerol kinase ζ-associated protein: new diacylglycerol kinase roles in endocytic recycling
Mol. Cell. Proteomics
2007
, vol. 
6
 (pg. 
1073
-
1087
)
81
Betts
G. N.
van der Geer
P.
Komives
E. A.
Structural and functional consequences of tyrosine phosphorylation in the LRP1 cytoplasmic domain
J. Biol. Chem.
2008
, vol. 
283
 (pg. 
15656
-
15664
)
82
Donoso
M.
Cancino
J.
Lee
J.
van Kerkhof
P.
Retamal
C.
Bu
G.
Gonzalez
A.
Caceres
A.
Marzolo
M. P.
Polarized traffic of LRP1 involves AP1B and SNX17 operating on Y-dependent sorting motifs in different pathways
Mol. Biol. Cell
2009
, vol. 
20
 (pg. 
481
-
497
)
83
Stockinger
W.
Sailler
B.
Strasser
V.
Recheis
B.
Fasching
D.
Kahr
L.
Schneider
W. J.
Nimpf
J.
The PX-domain protein SNX17 interacts with members of the LDL receptor family and modulates endocytosis of the LDL receptor
EMBO J.
2002
, vol. 
21
 (pg. 
4259
-
4267
)
84
Burden
J. J.
Sun
X. M.
Garcia
A. B.
Soutar
A. K.
Sorting motifs in the intracellular domain of the low density lipoprotein receptor interact with a novel domain of sorting nexin-17
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
16237
-
16245
)
85
Florian
V.
Schluter
T.
Bohnensack
R.
A new member of the sorting nexin family interacts with the C-terminus of P-selectin
Biochem. Biophys. Res. Commun.
2001
, vol. 
281
 (pg. 
1045
-
1050
)
86
Williams
R.
Schluter
T.
Roberts
M. S.
Knauth
P.
Bohnensack
R.
Cutler
D. F.
Sorting nexin 17 accelerates internalization yet retards degradation of P-selectin
Mol. Biol. Cell
2004
, vol. 
15
 (pg. 
3095
-
3105
)
87
Lee
J.
Retamal
C.
Cuitino
L.
Caruano-Yzermans
A.
Shin
J. E.
van Kerkhof
P.
Marzolo
M. P.
Bu
G.
Adaptor protein sorting nexin 17 regulates amyloid precursor protein trafficking and processing in the early endosomes
J. Biol. Chem.
2008
, vol. 
283
 (pg. 
11501
-
11508
)
88
Wu
C.
Ma
M. H.
Brown
K. R.
Geisler
M.
Li
L.
Tzeng
E.
Jia
C. Y.
Jurisica
I.
Li
S. S.
Systematic identification of SH3 domain-mediated human protein–protein interactions by peptide array target screening
Proteomics
2007
, vol. 
7
 (pg. 
1775
-
1785
)
89
Ghai
R.
Collins
B. M.
PX-FERM proteins: a link between endosomal trafficking and signaling?
Small GTPases
2011
, vol. 
2
 (pg. 
1
-
5
)
90
Balana
B.
Maslennikov
I.
Kwiatkowski
W.
Stern
K. M.
Bahima
L.
Choe
S.
Slesinger
P. A.
Mechanism underlying selective regulation of G protein-gated inwardly rectifying potassium channels by the psychostimulant-sensitive sorting nexin 27
Proc. Natl. Acad. Sci. U.S.A.
2011
, vol. 
108
 (pg. 
5831
-
5836
)
91
Fujiyama
K.
Kajii
Y.
Hiraoka
S.
Nishikawa
T.
Differential regulation by stimulants of neocortical expression of mrt1, arc, and homer1a mRNA in the rats treated with repeated methamphetamine
Synapse
2003
, vol. 
49
 (pg. 
143
-
149
)
92
Kajii
Y.
Muraoka
S.
Hiraoka
S.
Fujiyama
K.
Umino
A.
Nishikawa
T.
A developmentally regulated and psychostimulant-inducible novel rat gene mrt1 encoding PDZ-PX proteins isolated in the neocortex
Mol. Psychiatry
2003
, vol. 
8
 (pg. 
434
-
444
)
93
MacNeil
A. J.
Mansour
M.
Pohajdak
B.
Sorting nexin 27 interacts with the Cytohesin associated scaffolding protein (CASP) in lymphocytes
Biochem. Biophys. Res. Commun.
2007
, vol. 
359
 (pg. 
848
-
853
)
94
MacNeil
A. J.
Pohajdak
B.
Getting a GRASP on CASP: properties and role of the cytohesin-associated scaffolding protein in immunity
Immunol. Cell Biol.
2009
, vol. 
87
 (pg. 
72
-
80
)
95
Nassirpour
R.
Slesinger
P. A.
Subunit-specific regulation of Kir3 channels by sorting nexin 27
Channels
2007
, vol. 
1
 (pg. 
331
-
333
)
96
Cai
L.
Loo
L. S.
Atlashkin
V.
Hanson
B. J.
Hong
W.
Deficiency of sorting nexin 27 (SNX27) leads to growth retardation and elevated levels of N-methylD-aspartate receptor 2C (NR2C)
Mol. Cell. Biol.
2011
, vol. 
31
 (pg. 
1734
-
1747
)
97
Lauffer
B. E.
Melero
C.
Temkin
P.
Lei
C.
Hong
W.
Kortemme
T.
von Zastrow
M.
SNX27 mediates PDZ-directed sorting from endosomes to the plasma membrane
J. Cell Biol.
2010
, vol. 
190
 (pg. 
565
-
574
)
98
Temkin
P.
Lauffer
B.
Jager
S.
Cimermancic
P.
Krogan
N. J.
von Zastrow
M.
SNX27 mediates retromer tubule entry and endosome-to-plasma membrane trafficking of signalling receptors
Nat. Cell Biol.
2011
, vol. 
13
 (pg. 
715
-
721
)
99
Rottner
K.
Hanisch
J.
Campellone
K. G.
WASH, WHAMM and JMY: regulation of Arp2/3 complex and beyond
Trends Cell Biol.
2010
, vol. 
20
 (pg. 
650
-
661
)
100
Gomez
T. S.
Billadeau
D. D.
A FAM21-containing WASH complex regulates retromer-dependent sorting
Dev. Cell
2009
, vol. 
17
 (pg. 
699
-
711
)
101
Harbour
M. E.
Breusegem
S. Y.
Antrobus
R.
Freeman
C.
Reid
E.
Seaman
M. N.
The cargo-selective retromer complex is a recruiting hub for protein complexes that regulate endosomal tubule dynamics
J. Cell Sci.
2010
, vol. 
123
 (pg. 
3703
-
3717
)
102
Zheng
B.
Lavoie
C.
Tang
T. D.
Ma
P.
Meerloo
T.
Beas
A.
Farquhar
M. G.
Regulation of epidermal growth factor receptor degradation by heterotrimeric Gαs protein
Mol. Biol. Cell
2004
, vol. 
15
 (pg. 
5538
-
5550
)
103
Zheng
B.
Ma
Y. C.
Ostrom
R. S.
Lavoie
C.
Gill
G. N.
Insel
P. A.
Huang
X. Y.
Farquhar
M. G.
RGS-PX1, a GAP for Gαs and sorting nexin in vesicular trafficking
Science
2001
, vol. 
294
 (pg. 
1939
-
1942
)
104
Zheng
B.
Tang
T.
Tang
N.
Kudlicka
K.
Ohtsubo
K.
Ma
P.
Marth
J. D.
Farquhar
M. G.
Lehtonen
E.
Essential role of RGS-PX1/sorting nexin 13 in mouse development and regulation of endocytosis dynamics
Proc. Natl. Acad. Sci. U.S.A.
2006
, vol. 
103
 (pg. 
16776
-
16781
)
105
Hao
X.
Wang
Y.
Ren
F.
Zhu
S.
Ren
Y.
Jia
B.
Li
Y. P.
Shi
Y.
Chang
Z.
SNX25 regulates TGF-β signaling by enhancing the receptor degradation
Cell. Signal.
2011
, vol. 
23
 (pg. 
935
-
946
)
106
Jean-Baptiste
G.
Yang
Z.
Greenwood
M. T.
Regulatory mechanisms involved in modulating RGS function
Cell. Mol. Life Sci.
2006
, vol. 
63
 (pg. 
1969
-
1985
)
107
Willars
G. B.
Mammalian RGS proteins: multifunctional regulators of cellular signalling
Semin. Cell Dev. Biol.
2006
, vol. 
17
 (pg. 
363
-
376
)
108
Sadowski
L.
Pilecka
I.
Miaczynska
M.
Signaling from endosomes: location makes a difference
Exp. Cell Res.
2009
, vol. 
315
 (pg. 
1601
-
1609
)
109
Kan
A.
Ikeda
T.
Saito
T.
Yano
F.
Fukai
A.
Hojo
H.
Ogasawara
T.
Ogata
N.
Nakamura
K.
Chung
U. I.
Kawaguchi
H.
Screening of chondrogenic factors with a real-time fluorescence-monitoring cell line ATDC5-C2ER: identification of sorting nexin 19 as a novel factor
Arthritis Rheum.
2009
, vol. 
60
 (pg. 
3314
-
3323
)
110
Suh
J. M.
Stenesen
D.
Peters
J. M.
Inoue
A.
Cade
A.
Graff
J. M.
An RGS-containing sorting nexin controls Drosophila lifespan
PLoS ONE
2008
, vol. 
3
 pg. 
e2152
 
111
Qin
B.
He
M.
Chen
X.
Pei
D.
Sorting nexin 10 induces giant vacuoles in mammalian cells
J. Biol. Chem.
2006
, vol. 
281
 (pg. 
36891
-
36896
)
112
Mor
A.
Wynne
J. P.
Ahearn
I. M.
Dustin
M. L.
Du
G.
Philips
M. R.
Phospholipase D1 regulates lymphocyte adhesion via upregulation of Rap1 at the plasma membrane
Mol. Cell. Biol.
2009
, vol. 
29
 (pg. 
3297
-
3306
)
113
Xu
Y.
Hortsman
H.
Seet
L.
Wong
S. H.
Hong
W.
SNX3 regulates endosomal function through its PX-domain-mediated interaction with PtdIns(3)P
Nat. Cell Biol.
2001
, vol. 
3
 (pg. 
658
-
666
)
114
Pons
V.
Luyet
P. P.
Morel
E.
Abrami
L.
van der Goot
F. G.
Parton
R. G.
Gruenberg
J.
Hrs and SNX3 functions in sorting and membrane invagination within multivesicular bodies
PLoS Biol.
2008
, vol. 
6
 pg. 
e214
 
115
Boulkroun
S.
Ruffieux-Daidie
D.
Vitagliano
J. J.
Poirot
O.
Charles
R. P.
Lagnaz
D.
Firsov
D.
Kellenberger
S.
Staub
O.
Vasopressin-inducible ubiquitin-specific protease 10 increases ENaC cell surface expression by deubiquitylating and stabilizing sorting nexin 3
Am. J. Physiol. Renal Physiol.
2008
, vol. 
295
 (pg. 
F889
-
F900
)
116
Mizutani
R.
Yamauchi
J.
Kusakawa
S.
Nakamura
K.
Sanbe
A.
Torii
T.
Miyamoto
Y.
Tanoue
A.
Sorting nexin 3, a protein upregulated by lithium, contains a novel phosphatidylinositol-binding sequence and mediates neurite outgrowth in N1E-115 cells
Cell. Signal.
2009
, vol. 
21
 (pg. 
1586
-
1594
)
117
Strochlic
T. I.
Schmiedekamp
B. C.
Lee
J.
Katzmann
D. J.
Burd
C. G.
Opposing activities of the Snx3-retromer complex and ESCRT proteins mediate regulated cargo sorting at a common endosome
Mol. Biol. Cell
2008
, vol. 
19
 (pg. 
4694
-
4706
)
118
Strochlic
T. I.
Setty
T. G.
Sitaram
A.
Burd
C. G.
Grd19/Snx3p functions as a cargo-specific adapter for retromer-dependent endocytic recycling
J. Cell Biol.
2007
, vol. 
177
 (pg. 
115
-
125
)
119
Voos
W.
Stevens
T. H.
Retrieval of resident late-Golgi membrane proteins from the prevacuolar compartment of Saccharomyces cerevisiae is dependent on the function of Grd19p
J. Cell Biol.
1998
, vol. 
140
 (pg. 
577
-
590
)
120
Harterink
M.
Port
F.
Lorenowicz
M. J.
McGough
I. J.
Silhankova
M.
Betist
M. C.
van Weering
J. R.
van Heesbeen
R. G.
Middelkoop
T. C.
Basler
K.
, et al. 
A SNX3-dependent retromer pathway mediates retrograde transport of the Wnt sorting receptor Wntless and is required for Wnt secretion
Nat. Cell Biol.
2011
, vol. 
13
 (pg. 
914
-
923
)
121
Takemoto
Y.
Furuta
M.
Sato
M.
Kubo
M.
Hashimoto
Y.
Isolation and characterization of a novel HS1 SH3 domain binding protein, HS1BP3
Int. Immunol.
1999
, vol. 
11
 (pg. 
1957
-
1964
)
122
Higgins
J. J.
Lombardi
R. Q.
Pucilowska
J.
Jankovic
J.
Golbe
L. I.
Verhagen
L.
HS1-BP3 gene variant is common in familial essential tremor
Mov. Disord.
2006
, vol. 
21
 (pg. 
306
-
309
)
123
Higgins
J. J.
Lombardi
R. Q.
Pucilowska
J.
Jankovic
J.
Tan
E. K.
Rooney
J. P.
A variant in the HS1-BP3 gene is associated with familial essential tremor
Neurology
2005
, vol. 
64
 (pg. 
417
-
421
)
124
Shatunov
A.
Jankovic
J.
Elble
R.
Sambuughin
N.
Singleton
A.
Hallett
M.
Goldfarb
L.
A variant in the HS1-BP3 gene is associated with familial essential tremor
Neurology
2005
, vol. 
65
 pg. 
1995
 
125
Karpenahalli
M. R.
Lupas
A. N.
Soding
J.
TPRpred: a tool for prediction of TPR-, PPR- and SEL1-like repeats from protein sequences
BMC Bioinformatics
2007
, vol. 
8
 pg. 
2
 
126
Choi
J. H.
Hong
W. P.
Kim
M. J.
Kim
J. H.
Ryu
S. H.
Suh
P. G.
Sorting nexin 16 regulates EGF receptor trafficking by phosphatidylinositol-3-phosphate interaction with the Phox domain
J. Cell Sci.
2004
, vol. 
117
 (pg. 
4209
-
4218
)
127
Hanson
B. J.
Hong
W.
Evidence for a role of SNX16 in regulating traffic between the early and later endosomal compartments
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
34617
-
34630
)
128
Le Blanc
I.
Luyet
P. P.
Pons
V.
Ferguson
C.
Emans
N.
Petiot
A.
Mayran
N.
Demaurex
N.
Faure
J.
Sadoul
R.
, et al. 
Endosome-to-cytosol transport of viral nucleocapsids
Nat. Cell Biol.
2005
, vol. 
7
 (pg. 
653
-
664
)
129
Rodal
A. A.
Blunk
A. D.
Akbergenova
Y.
Jorquera
R. A.
Buhl
L. K.
Littleton
J. T.
A presynaptic endosomal trafficking pathway controls synaptic growth signaling
J. Cell. Biol.
2011
, vol. 
193
 (pg. 
201
-
217
)
130
Buchanan
S. G.
Gay
N. J.
Structural and functional diversity in the leucine-rich repeat family of proteins
Prog. Biophys. Mol. Biol.
1996
, vol. 
65
 (pg. 
1
-
44
)
131
Piletz
J. E.
Ivanov
T. R.
Sharp
J. D.
Ernsberger
P.
Chang
C. H.
Pickard
R. T.
Gold
G.
Roth
B.
Zhu
H.
Jones
J. C.
, et al. 
Imidazoline receptor antisera-selected (IRAS) cDNA: cloning and characterization
DNA Cell Biol.
2000
, vol. 
19
 (pg. 
319
-
329
)
132
Lim
K. P.
Hong
W.
Human Nischarin/imidazoline receptor antisera-selected protein is targeted to the endosomes by a combined action of a PX domain and a coiled-coil region
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
54770
-
54782
)
133
Sano
H.
Liu
S. C.
Lane
W. S.
Piletz
J. E.
Lienhard
G. E.
Insulin receptor substrate 4 associates with the protein IRAS
J. Biol. Chem.
2002
, vol. 
277
 (pg. 
19439
-
19447
)
134
Alahari
S. K.
Nischarin inhibits Rac induced migration and invasion of epithelial cells by affecting signaling cascades involving PAK
Exp. Cell Res.
2003
, vol. 
288
 (pg. 
415
-
424
)
135
Alahari
S. K.
Lee
J. W.
Juliano
R. L.
Nischarin, a novel protein that interacts with the integrin α5 subunit and inhibits cell migration
J. Cell Biol.
2000
, vol. 
151
 (pg. 
1141
-
1154
)
136
Alahari
S. K.
Nasrallah
H.
A membrane proximal region of the integrin α5 subunit is important for its interaction with nischarin
Biochem. J.
2004
, vol. 
377
 (pg. 
449
-
457
)
137
Alahari
S. K.
Reddig
P. J.
Juliano
R. L.
The integrin-binding protein Nischarin regulates cell migration by inhibiting PAK
EMBO J.
2004
, vol. 
23
 (pg. 
2777
-
2788
)
138
Reddig
P. J.
Xu
D.
Juliano
R. L.
Regulation of p21-activated kinaseindependent Rac1 signal transduction by nischarin
J. Biol. Chem.
2005
, vol. 
280
 (pg. 
30994
-
31002
)
139
Phillips
S. A.
Barr
V. A.
Haft
D. H.
Taylor
S. I.
Haft
C. R.
Identification and characterization of SNX15, a novel sorting nexin involved in protein trafficking
J. Biol. Chem.
2001
, vol. 
276
 (pg. 
5074
-
5084
)
140
Barr
V. A.
Phillips
S. A.
Taylor
S. I.
Haft
C. R.
Overexpression of a novel sorting nexin, SNX15, affects endosome morphology and protein trafficking
Traffic
2000
, vol. 
1
 (pg. 
904
-
916
)
141
Henne
W. M.
Buchkovich
N. J.
Emr
S. D.
The ESCRT pathway
Dev. Cell
2011
, vol. 
21
 (pg. 
77
-
91
)
142
Ciccarelli
F. D.
Proukakis
C.
Patel
H.
Cross
H.
Azam
S.
Patton
M. A.
Bork
P.
Crosby
A. H.
The identification of a conserved domain in both spartin and spastin, mutated in hereditary spastic paraplegia
Genomics
2003
, vol. 
81
 (pg. 
437
-
441
)
143
Hurley
J. H.
Yang
D.
MIT domainia
Dev. Cell
2008
, vol. 
14
 (pg. 
6
-
8
)
144
Scott
A.
Gaspar
J.
Stuchell-Brereton
M. D.
Alam
S. L.
Skalicky
J. J.
Sundquist
W. I.
Structure and ESCRT-III protein interactions of the MIT domain of human VPS4A
Proc. Natl. Acad. Sci. U.S.A.
2005
, vol. 
102
 (pg. 
13813
-
13818
)
145
Hoepfner
S.
Severin
F.
Cabezas
A.
Habermann
B.
Runge
A.
Gillooly
D.
Stenmark
H.
Zerial
M.
Modulation of receptor recycling and degradation by the endosomal kinesin KIF16B
Cell
2005
, vol. 
121
 (pg. 
437
-
450
)
146
Miki
H.
Okada
Y.
Hirokawa
N.
Analysis of the kinesin superfamily: insights into structure and function
Trends Cell Biol.
2005
, vol. 
15
 (pg. 
467
-
476
)
147
Hirokawa
N.
Noda
Y.
Tanaka
Y.
Niwa
S.
Kinesin superfamily motor proteins and intracellular transport
Nat. Rev. Mol. Cell Biol.
2009
, vol. 
10
 (pg. 
682
-
696
)
148
Blatner
N. R.
Wilson
M. I.
Lei
C.
Hong
W.
Murray
D.
Williams
R. L.
Cho
W.
The structural basis of novel endosome anchoring activity of KIF16B kinesin
EMBO J.
2007
, vol. 
26
 (pg. 
3709
-
3719
)
149
Casimir
C. M.
Bu-Ghanim
H. N.
Rodaway
A. R.
Bentley
D. L.
Rowe
P.
Segal
A. W.
Autosomal recessive chronic granulomatous disease caused by deletion at a dinucleotide repeat
Proc. Natl. Acad. Sci. U.S.A.
1991
, vol. 
88
 (pg. 
2753
-
2757
)
150
Goldblatt
D.
Thrasher
A. J.
Chronic granulomatous disease
Clin. Exp. Immunol.
2000
, vol. 
122
 (pg. 
1
-
9
)
151
Noack
D.
Rae
J.
Cross
A. R.
Ellis
B. A.
Newburger
P. E.
Curnutte
J. T.
Heyworth
P. G.
Autosomal recessive chronic granulomatous disease caused by defects in NCF-1, the gene encoding the phagocyte p47-phox: mutations not arising in the NCF-1 pseudogenes
Blood
2001
, vol. 
97
 (pg. 
305
-
311
)
152
Kanai
F.
Liu
H.
Field
S. J.
Akbary
H.
Matsuo
T.
Brown
G. E.
Cantley
L. C.
Yaffe
M. B.
The PX domains of p47phox and p40phox bind to lipid products of PI(3)K
Nat. Cell Biol.
2001
, vol. 
3
 (pg. 
675
-
678
)
153
Vervoort
V. S.
Viljoen
D.
Smart
R.
Suthers
G.
DuPont
B. R.
Abbott
A.
Schwartz
C. E.
Sorting nexin 3 (SNX3) is disrupted in a patient with a translocation t(6;13)(q21;q12) and microcephaly, microphthalmia, ectrodactyly, prognathism (MMEP) phenotype
J. Med. Genet.
2002
, vol. 
39
 (pg. 
893
-
899
)
154
Kumar
R. A.
Everman
D. B.
Morgan
C. T.
Slavotinek
A.
Schwartz
C. E.
Simpson
E. M.
Absence of mutations in NR2E1 and SNX3 in five patients with MMEP (microcephaly, microphthalmia, ectrodactyly, and prognathism) and related phenotypes
BMC Med. Genet.
2007
, vol. 
8
 pg. 
48
 
155
Harley
J. B.
Alarcon-Riquelme
M. E.
Criswell
L. A.
Jacob
C. O.
Kimberly
R. P.
Moser
K. L.
Tsao
B. P.
Vyse
T. J.
Langefeld
C. D.
Nath
S. K.
, et al. 
Genome-wide association scan in women with systemic lupus erythematosus identifies susceptibility variants in ITGAM, PXK, KIAA1542 and other loci
Nat. Genet.
2008
, vol. 
40
 (pg. 
204
-
210
)
156
Stefaniuk
M.
Lukasiuk
K.
Cloning of expressed sequence tags (ESTs) representing putative epileptogenesis-related genes and the localization of their expression in the normal brain
Neurosci. Lett.
2010
, vol. 
482
 (pg. 
230
-
234
)
157
Vicinanza
M.
D'Angelo
G.
Di Campli
A.
De Matteis
M. A.
Function and dysfunction of the PI system in membrane trafficking
EMBO J.
2008
, vol. 
27
 (pg. 
2457
-
2470
)
158
Vicinanza
M.
D'Angelo
G.
Di Campli
A.
De Matteis
M. A.
Phosphoinositides as regulators of membrane trafficking in health and disease
Cell. Mol. Life Sci.
2008
, vol. 
65
 (pg. 
2833
-
2841
)
159
Vanhaesebroeck
B.
Guillermet-Guibert
J.
Graupera
M.
Bilanges
B.
The emerging mechanisms of isoform-specific PI3K signalling
Nat. Rev. Mol. Cell Biol.
2010
, vol. 
11
 (pg. 
329
-
341
)
160
Nicot
A. S.
Laporte
J.
Endosomal phosphoinositides and human diseases
Traffic
2008
, vol. 
9
 (pg. 
1240
-
1249
)
161
Kerr
M. C.
Wang
J. T.
Castro
N. A.
Hamilton
N. A.
Town
L.
Brown
D. L.
Meunier
F. A.
Brown
N. F.
Stow
J. L.
Teasdale
R. D.
Inhibition of the PtdIns(5) kinase PIKfyve disrupts intracellular replication of Salmonella
EMBO J.
2010
, vol. 
29
 (pg. 
1331
-
1347
)
162
Krol
M.
Polanska
J.
Pawlowski
K. M.
Turowski
P.
Skierski
J.
Majewska
A.
Ugorski
M.
Morty
R. E.
Motyl
T.
Transcriptomic signature of cell lines isolated from canine mammary adenocarcinoma metastases to lungs
J. Appl. Genet.
2010
, vol. 
51
 (pg. 
37
-
50
)
163
Seals
D. F.
Azucena
E.F.
Jr
Pass
I.
Tesfay
L.
Gordon
R.
Woodrow
M.
Resau
J. H.
Courtneidge
S. A.
The adaptor protein Tks5/Fish is required for podosome formation and function, and for the protease-driven invasion of cancer cells
Cancer Cell
2005
, vol. 
7
 (pg. 
155
-
165
)
164
Blouw
B.
Seals
D. F.
Pass
I.
Diaz
B.
Courtneidge
S. A.
A role for the podosome/invadopodia scaffold protein Tks5 in tumor growth in vivo
Eur. J. Cell Biol.
2008
, vol. 
87
 (pg. 
555
-
567
)
165
Koutros
S.
Schumacher
F. R.
Hayes
R. B.
Ma
J.
Huang
W. Y.
Albanes
D.
Canzian
F.
Chanock
S. J.
Crawford
E. D.
Diver
W. R.
, et al. 
Pooled analysis of phosphatidylinositol 3-kinase pathway variants and risk of prostate cancer
Cancer Res.
2010
, vol. 
70
 (pg. 
2389
-
2396
)
166
Nguyen
L. N.
Holdren
M. S.
Nguyen
A. P.
Furuya
M. H.
Bianchini
M.
Levy
E.
Mordoh
J.
Liu
A.
Guncay
G. D.
Campbell
J. S.
Parks
W. T.
Sorting nexin 1 down-regulation promotes colon tumorigenesis
Clin. Cancer Res.
2006
, vol. 
12
 (pg. 
6952
-
6959
)
167
Huang
Z.
Huang
S.
Wang
Q.
Liang
L.
Ni
S.
Wang
L.
Sheng
W.
He
X.
Du
X.
MicroRNA-95 promotes cell proliferation and targets sorting nexin 1 in human colorectal carcinoma
Cancer Res.
2011
, vol. 
71
 (pg. 
2582
-
2589
)
168
Vasudevan
K. M.
Barbie
D. A.
Davies
M. A.
Rabinovsky
R.
McNear
C. J.
Kim
J. J.
Hennessy
B. T.
Tseng
H.
Pochanard
P.
Kim
S. Y.
, et al. 
AKT-independent signaling downstream of oncogenic PIK3CA mutations in human cancer
Cancer Cell
2009
, vol. 
16
 (pg. 
21
-
32
)
169
Wang
Y.
Zhou
D.
Phung
S.
Masri
S.
Smith
D.
Chen
S.
SGK3 is an estrogen-inducible kinase promoting estrogen-mediated survival of breast cancer cells
Mol. Endocrinol.
2011
, vol. 
25
 (pg. 
72
-
82
)
170
Slagsvold
T.
Marchese
A.
Brech
A.
Stenmark
H.
CISK attenuates degradation of the chemokine receptor CXCR4 via the ubiquitin ligase AIP4
EMBO J.
2006
, vol. 
25
 (pg. 
3738
-
3749
)
171
Foster
D. A.
Xu
L.
Phospholipase D in cell proliferation and cancer
Mol. Cancer Res.
2003
, vol. 
1
 (pg. 
789
-
800
)
172
Peng
X.
Frohman
M. A.
Mammalian phospholipase D physiological and pathological roles
Acta Physiol.
2011
 
doi: 10.1111/j.1748-1716.2011.02298.x
173
Su
W.
Chen
Q.
Frohman
M. A.
Targeting phospholipase D with small-molecule inhibitors as a potential therapeutic approach for cancer metastasis
Future Oncol.
2009
, vol. 
5
 (pg. 
1477
-
1486
)
174
Lavieri
R. R.
Scott
S. A.
Selvy
P. E.
Kim
K.
Jadhav
S.
Morrison
R. D.
Daniels
J. S.
Brown
H. A.
Lindsley
C. W.
Design, synthesis, and biological evaluation of halogenated N-(2-(4-oxo-1-phenyl-1,3,8-triazaspiro[4.5]decan-8-yl)ethyl)benzamides: discovery of an isoform-selective small molecule phospholipase D2 inhibitor
J. Med. Chem.
2010
, vol. 
53
 (pg. 
6706
-
6719
)
175
Scott
S. A.
Selvy
P. E.
Buck
J. R.
Cho
H. P.
Criswell
T. L.
Thomas
A. L.
Armstrong
M. D.
Arteaga
C. L.
Lindsley
C. W.
Brown
H. A.
Design of isoform-selective phospholipase D inhibitors that modulate cancer cell invasiveness
Nat. Chem. Biol.
2009
, vol. 
5
 (pg. 
108
-
117
)
176
Tabuchi
A.
Kuebler
W. M.
Endothelium-platelet interactions in inflammatory lung disease
Vascul. Pharmacol.
2008
, vol. 
49
 (pg. 
141
-
150
)
177
Ludwig
R. J.
Schon
M. P.
Boehncke
W. H.
P-selectin: a common therapeutic target for cardiovascular disorders, inflammation and tumour metastasis
Expert Opin. Ther. Targets
2007
, vol. 
11
 (pg. 
1103
-
1117
)
178
Chen
M.
Geng
J. G.
P-selectin mediates adhesion of leukocytes, platelets, and cancer cells in inflammation, thrombosis, and cancer growth and metastasis
Arch. Immunol. Ther. Exp.
2006
, vol. 
54
 (pg. 
75
-
84
)
179
Querfurth
H. W.
LaFerla
F. M.
Alzheimer's disease
N. Engl. J. Med.
2010
, vol. 
362
 (pg. 
329
-
344
)
180
Sannerud
R.
Annaert
W.
Trafficking, a key player in regulated intramembrane proteolysis
Semin. Cell Dev. Biol.
2009
, vol. 
20
 (pg. 
183
-
190
)
181
Andersen
O. M.
Willnow
T. E.
Lipoprotein receptors in Alzheimer's disease
Trends Neurosci.
2006
, vol. 
29
 (pg. 
687
-
694
)
182
Bu
G.
Apolipoprotein E and its receptors in Alzheimer's disease: pathways, pathogenesis and therapy
Nat. Rev. Neurosci.
2009
, vol. 
10
 (pg. 
333
-
344
)
183
Bu
G.
Cam
J.
Zerbinatti
C.
LRP in amyloid-β production and metabolism
Ann. N. Y. Acad. Sci.
2006
, vol. 
1086
 (pg. 
35
-
53
)
184
Thinakaran
G.
Koo
E. H.
Amyloid precursor protein trafficking, processing, and function
J. Biol. Chem.
2008
, vol. 
283
 (pg. 
29615
-
29619
)
185
Wolfe
M. S.
Guenette
S. Y.
APP at a glance
J. Cell Sci.
2007
, vol. 
120
 (pg. 
3157
-
3161
)
186
Nielsen
M. S.
Gustafsen
C.
Madsen
P.
Nyengaard
J. R.
Hermey
G.
Bakke
O.
Mari
M.
Schu
P.
Pohlmann
R.
Dennes
A.
Petersen
C. M.
Sorting by the cytoplasmic domain of the amyloid precursor protein binding receptor SorLA
Mol. Cell. Biol.
2007
, vol. 
27
 (pg. 
6842
-
6851
)
187
Rogaeva
E.
Meng
Y.
Lee
J. H.
Gu
Y.
Kawarai
T.
Zou
F.
Katayama
T.
Baldwin
C. T.
Cheng
R.
Hasegawa
H.
, et al. 
The neuronal sortilin-related receptor SORL1 is genetically associated with Alzheimer disease
Nat. Genet.
2007
, vol. 
39
 (pg. 
168
-
177
)
188
He
X.
Li
F.
Chang
W. P.
Tang
J.
GGA proteins mediate the recycling pathway of memapsin 2 (BACE)
J. Biol. Chem.
2005
, vol. 
280
 (pg. 
11696
-
11703
)
189
Muhammad
A.
Flores
I.
Zhang
H.
Yu
R.
Staniszewski
A.
Planel
E.
Herman
M.
Ho
L.
Kreber
R.
Honig
L. S.
, et al. 
Retromer deficiency observed in Alzheimer's disease causes hippocampal dysfunction, neurodegeneration, and Aβ accumulation
Proc. Natl. Acad. Sci. U.S.A.
2008
, vol. 
105
 (pg. 
7327
-
7332
)
190
Okada
H.
Zhang
W.
Peterhoff
C.
Hwang
J. C.
Nixon
R. A.
Ryu
S. H.
Kim
T. W.
Proteomic identification of sorting nexin 6 as a negative regulator of BACE1mediated APP processing
FASEB J.
2010
, vol. 
24
 (pg. 
2783
-
2794
)
191
Shin
N.
Lee
S.
Ahn
N.
Kim
S. A.
Ahn
S. G.
YongPark
Z.
Chang
S.
Sorting nexin 9 interacts with dynamin 1 and N-WASP and coordinates synaptic vesicle endocytosis
J. Biol. Chem.
2007
, vol. 
282
 (pg. 
28939
-
28950
)
192
Soulet
F.
Yarar
D.
Leonard
M.
Schmid
S. L.
SNX9 regulates dynamin assembly and is required for efficient clathrin-mediated endocytosis
Mol. Biol. Cell
2005
, vol. 
16
 (pg. 
2058
-
2067
)
193
Lundmark
R.
Carlsson
S. R.
The β-appendages of the four adaptor-protein (AP) complexes: structure and binding properties, and identification of sorting nexin 9 as an accessory protein to AP-2
Biochem J.
2002
, vol. 
362
 (pg. 
597
-
607
)
194
Yun
M.
Keshvara
L.
Park
C. G.
Zhang
Y. M.
Dickerson
J. B.
Zheng
J.
Rock
C. O.
Curran
T.
Park
H. W.
Crystal structures of the Dab homology domains of mouse disabled 1 and 2
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
36572
-
36581
)
195
Duffy
M. J.
McKiernan
E.
O'Donovan
N.
McGowan
P. M.
The role of ADAMs in disease pathophysiology
Clin. Chim. Acta
2009
, vol. 
403
 (pg. 
31
-
36
)
196
Kveiborg
M.
Albrechtsen
R.
Couchman
J. R.
Wewer
U. M.
Cellular roles of ADAM12 in health and disease
Int. J. Biochem. Cell. Biol.
2008
, vol. 
40
 (pg. 
1685
-
1702
)
197
Abram
C. L.
Seals
D. F.
Pass
I.
Salinsky
D.
Maurer
L.
Roth
T. M.
Courtneidge
S. A.
The adaptor protein fish associates with members of the ADAMs family and localizes to podosomes of Src-transformed cells
J. Biol. Chem.
2003
, vol. 
278
 (pg. 
16844
-
16851
)
198
Zhong
J. L.
Poghosyan
Z.
Pennington
C. J.
Scott
X.
Handsley
M. M.
Warn
A.
Gavrilovic
J.
Honert
K.
Kruger
A.
Span
P. N.
, et al. 
Distinct functions of natural ADAM-15 cytoplasmic domain variants in human mammary carcinoma
Mol. Cancer Res.
2008
, vol. 
6
 (pg. 
383
-
394
)
199
Malinin
N. L.
Wright
S.
Seubert
P.
Schenk
D.
Griswold-Prenner
I.
Amyloid-β neurotoxicity is mediated by FISH adapter protein and ADAM12 metalloprotease activity
Proc. Natl. Acad. Sci. U.S.A.
2005
, vol. 
102
 (pg. 
3058
-
3063
)
200
Harold
D.
Jehu
L.
Turic
D.
Hollingworth
P.
Moore
P.
Summerhayes
P.
Moskvina
V.
Foy
C.
Archer
N.
Hamilton
B. A.
, et al. 
Interaction between the ADAM12 and SH3MD1 genes may confer susceptibility to late-onset Alzheimer's disease
Am. J. Med. Genet. B Neuropsychiatr. Genet.
2007
, vol. 
144B
 (pg. 
448
-
452
)
201
Oliveira
T. G.
Di Paolo
G.
Phospholipase D in brain function and Alzheimer's disease
Biochim. Biophys. Acta
2010
, vol. 
1801
 (pg. 
799
-
805
)
202
Jin
J. K.
Ahn
B. H.
Na
Y. J.
Kim
J. I.
Kim
Y. S.
Choi
E. K.
Ko
Y. G.
Chung
K. C.
Kozlowski
P. B.
Min do
S.
Phospholipase D1 is associated with amyloid precursor protein in Alzheimer's disease
Neurobiol. Aging
2007
, vol. 
28
 (pg. 
1015
-
1027
)
203
Jin
J. K.
Kim
N. H.
Lee
Y. J.
Kim
Y. S.
Choi
E. K.
Kozlowski
P. B.
Park
M. H.
Kim
H. S.
Min do
S.
Phospholipase D1 is up-regulated in the mitochondrial fraction from the brains of Alzheimer's disease patients
Neurosci. Lett.
2006
, vol. 
407
 (pg. 
263
-
267
)
204
Cai
D.
Netzer
W. J.
Zhong
M.
Lin
Y.
Du
G.
Frohman
M.
Foster
D. A.
Sisodia
S. S.
Xu
H.
Gorelick
F. S.
Greengard
P.
Presenilin-1 uses phospholipase D1 as a negative regulator of β-amyloid formation
Proc. Natl. Acad. Sci. U.S.A.
2006
, vol. 
103
 (pg. 
1941
-
1946
)
205
Cai
D.
Zhong
M.
Wang
R.
Netzer
W. J.
Shields
D.
Zheng
H.
Sisodia
S. S.
Foster
D. A.
Gorelick
F. S.
Xu
H.
Greengard
P.
Phospholipase D1 corrects impaired βAPP trafficking and neurite outgrowth in familial Alzheimer's disease-linked presenilin-1 mutant neurons
Proc. Natl. Acad. Sci. U.S.A.
2006
, vol. 
103
 (pg. 
1936
-
1940
)
206
Liu
Y.
Zhang
Y. W.
Wang
X.
Zhang
H.
You
X.
Liao
F. F.
Xu
H.
Intracellular trafficking of presenilin 1 is regulated by β-amyloid precursor protein and phospholipase D1
J. Biol. Chem.
2009
, vol. 
284
 (pg. 
12145
-
12152
)
207
Oliveira
T. G.
Chan
R. B.
Tian
H.
Laredo
M.
Shui
G.
Staniszewski
A.
Zhang
H.
Wang
L.
Kim
T. W.
Duff
K. E.
, et al. 
Phospholipase D2 ablation ameliorates Alzheimer's disease-linked synaptic dysfunction and cognitive deficits
J. Neurosci.
2010
, vol. 
30
 (pg. 
16419
-
16428
)
208
Owen
D. J.
Collins
B. M.
Vesicle transport: a new player in APP trafficking
Curr. Biol.
2010
, vol. 
20
 (pg. 
R413
-
R415
)
209
Gruenberg
J.
van der Goot
F. G.
Mechanisms of pathogen entry through the endosomal compartments
Nat. Rev. Mol. Cell Biol.
2006
, vol. 
7
 (pg. 
495
-
504
)
210
Kerr
M. C.
Teasdale
R. D.
Defining macropinocytosis
Traffic
2009
, vol. 
10
 (pg. 
364
-
371
)
211
Schroeder
N.
Mota
L. J.
Meresse
S.
Salmonella-induced tubular networks
Trends Microbiol.
2011
, vol. 
19
 (pg. 
268
-
277
)
212
Bujny
M. V.
Ewels
P. A.
Humphrey
S.
Attar
N.
Jepson
M. A.
Cullen
P. J.
Sorting nexin-1 defines an early phase of Salmonella-containing vacuole-remodeling during Salmonella infection
J. Cell Sci.
2008
, vol. 
121
 (pg. 
2027
-
2036
)
213
Braun
V.
Wong
A.
Landekic
M.
Hong
W. J.
Grinstein
S.
Brumell
J. H.
Sorting nexin 3 (SNX3) is a component of a tubular endosomal network induced by Salmonella and involved in maturation of the Salmonella-containing vacuole
Cell. Microbiol.
2010
, vol. 
12
 (pg. 
1352
-
1367
)
214
Wang
J. T.
Kerr
M. C.
Karunaratne
S.
Jeanes
A.
Yap
A. S.
Teasdale
R. D.
The SNX-PX-BAR family in macropinocytosis: the regulation of macropinosome formation by SNX-PX-BAR proteins
PLoS ONE
2010
, vol. 
5
 pg. 
e13763
 
215
Almendinger
J.
Doukoumetzidis
K.
Kinchen
J. M.
Kaech
A.
Ravichandran
K. S.
Hengartner
M. O.
A conserved role for SNX9-family members in the regulation of phagosome maturation during engulfment of apoptotic cells
PLoS ONE
2011
, vol. 
6
 pg. 
e18325
 
216
Chen
D.
Xiao
H.
Zhang
K.
Wang
B.
Gao
Z.
Jian
Y.
Qi
X.
Sun
J.
Miao
L.
Yang
C.
Retromer is required for apoptotic cell clearance by phagocytic receptor recycling
Science
2010
, vol. 
327
 (pg. 
1261
-
1264
)
217
Lu
N.
Shen
Q.
Mahoney
T. R.
Liu
X.
Zhou
Z.
Three sorting nexins drive the degradation of apoptotic cells in response to PtdIns(3)P signaling
Mol. Biol. Cell
2011
, vol. 
22
 (pg. 
354
-
374
)
218
Cheng
G.
Lambeth
J. D.
NOXO1, regulation of lipid binding, localization, and activation of Nox1 by the Phox homology (PX) domain
J. Biol. Chem.
2004
, vol. 
279
 (pg. 
4737
-
4742
)
219
Park
J. B.
Phagocytosis induces superoxide formation and apoptosis in macrophages
Exp. Mol. Med.
2003
, vol. 
35
 (pg. 
325
-
335
)
220
Sandvig
K.
Grimmer
S.
Lauvrak
S. U.
Torgersen
M. L.
Skretting
G.
van Deurs
B.
Iversen
T. G.
Pathways followed by ricin and Shiga toxin into cells
Histochem. Cell Biol.
2002
, vol. 
117
 (pg. 
131
-
141
)
221
Popoff
V.
Mardones
G. A.
Bai
S. K.
Chambon
V.
Tenza
D.
Burgos
P. V.
Shi
A.
Benaroch
P.
Urbe
S.
Lamaze
C.
, et al. 
Analysis of articulation between clathrin and retromer in retrograde sorting on early endosomes
Traffic
2009
, vol. 
10
 (pg. 
1868
-
1880
)
222
Dyve
A. B.
Bergan
J.
Utskarpen
A.
Sandvig
K.
Sorting nexin 8 regulates endosome-to-Golgi transport
Biochem. Biophys. Res. Commun.
2009
, vol. 
390
 (pg. 
109
-
114
)
223
Nanbo
A.
Imai
M.
Watanabe
S.
Noda
T.
Takahashi
K.
Neumann
G.
Halfmann
P.
Kawaoka
Y.
Ebolavirus is internalized into host cells via macropinocytosis in a viral glycoprotein-dependent manner
PLoS Pathog.
2010
, vol. 
6
 pg. 
e1001121
 
224
Ju
W.
Yoo
B. C.
Kim
I. J.
Kim
J. W.
Kim
S. C.
Lee
H. P.
Identification of genes with differential expression in chemoresistant epithelial ovarian cancer using high-density oligonucleotide microarrays
Oncol. Res.
2009
, vol. 
18
 (pg. 
47
-
56
)
225
Nishimura
Y.
Yoshioka
K.
Bereczky
B.
Itoh
K.
Evidence for efficient phosphorylation of EGFR and rapid endocytosis of phosphorylated EGFR via the early/late endocytic pathway in a gefitinib-sensitive non-small cell lung cancer cell line
Mol. Cancer.
2008
, vol. 
7
 pg. 
42
 
226
Alto
N. M.
Weflen
A. W.
Rardin
M. J.
Yarar
D.
Lazar
C. S.
Tonikian
R.
Koller
A.
Taylor
S. S.
Boone
C.
Sidhu
S. S.
, et al. 
The type III effector EspF coordinates membrane trafficking by the spatiotemporal activation of two eukaryotic signaling pathways
J. Cell Biol.
2007
, vol. 
178
 (pg. 
1265
-
1278
)
227
Marches
O.
Batchelor
M.
Shaw
R. K.
Patel
A.
Cummings
N.
Nagai
T.
Sasakawa
C.
Carlsson
S. R.
Lundmark
R.
Cougoule
C.
, et al. 
EspF of enteropathogenic Escherichia coli binds sorting nexin 9
J. Bacteriol.
2006
, vol. 
188
 (pg. 
3110
-
3115
)
228
Heiseke
A.
Schobel
S.
Lichtenthaler
S. F.
Vorberg
I.
Groschup
M. H.
Kretzschmar
H.
Schatzl
H. M.
Nunziante
M.
The novel sorting nexin SNX33 interferes with cellular PrP formation by modulation of PrP shedding
Traffic
2008
, vol. 
9
 (pg. 
1116
-
1129
)
229
Ji
T.
Wu
Y.
Wang
H.
Wang
J.
Jiang
Y.
Diagnosis and fine mapping of a deletion in distal 11q in two Chinese patients with developmental delay
J. Hum. Genet.
2010
, vol. 
55
 (pg. 
486
-
489
)
230
Bare
L. A.
Morrison
A. C.
Rowland
C. M.
Shiffman
D.
Luke
M. M.
Iakoubova
O. A.
Kane
J. P.
Malloy
M. J.
Ellis
S. G.
Pankow
J. S.
, et al. 
Five common gene variants identify elevated genetic risk for coronary heart disease
Genet. Med.
2007
, vol. 
9
 (pg. 
682
-
689
)
231
Jacques
C.
Baris
O.
Prunier-Mirebeau
D.
Savagner
F.
Rodien
P.
Rohmer
V.
Franc
B.
Guyetant
S.
Malthiery
Y.
Reynier
P.
Two-step differential expression analysis reveals a new set of genes involved in thyroid oncocytic tumors
J. Clin. Endocrinol. Metab.
2005
, vol. 
90
 (pg. 
2314
-
2320
)
232
Tyybakinoja
A.
Saarinen-Pihkala
U.
Elonen
E.
Knuutila
S.
Amplified, lost, and fused genes in 11q23–25 amplicon in acute myeloid leukemia, an array-CGH study
Genes Chromosomes Cancer
2006
, vol. 
45
 (pg. 
257
-
264
)
233
Mestre-Escorihuela
C.
Rubio-Moscardo
F.
Richter
J. A.
Siebert
R.
Climent
J.
Fresquet
V.
Beltran
E.
Agirre
X.
Marugan
I.
Marin
M.
, et al. 
Homozygous deletions localize novel tumor suppressor genes in B-cell lymphomas
Blood
2007
, vol. 
109
 (pg. 
271
-
280
)
234
Knobbe
C. B.
Reifenberger
G.
Genetic alterations and aberrant expression of genes related to the phosphatidyl-inositol-3′-kinase/protein kinase B (Akt) signal transduction pathway in glioblastomas
Brain Pathol.
2003
, vol. 
13
 (pg. 
507
-
518
)
235
Traer
C. J.
Foster
F. M.
Abraham
S. M.
Fry
M. J.
Are class II phosphoinositide 3-kinases potential targets for anticancer therapies?
Bull. Cancer
2006
, vol. 
93
 (pg. 
E53
-
E58
)
236
Shen
Q.
Stanton
M. L.
Feng
W.
Rodriguez
M. E.
Ramondetta
L.
Chen
L.
Brown
R. E.
Duan
X.
Morphoproteomic analysis reveals an overexpressed and constitutively activated phospholipase D1–mTORC2 pathway in endometrial carcinoma
Int. J. Clin. Exp. Pathol.
2010
, vol. 
4
 (pg. 
13
-
21
)
237
Kang
D. W.
Park
M. H.
Lee
Y. J.
Kim
H. S.
Lindsley
C. W.
Alex Brown
H.
Min do
S.
Autoregulation of phospholipase D activity is coupled to selective induction of phospholipase D1 expression to promote invasion of breast cancer cells
Int. J. Cancer
2011
, vol. 
128
 (pg. 
805
-
816
)
238
Kang
D. W.
Min do
S.
Platelet derived growth factor increases phospholipase D1 but not phospholipase D2 expression via NFκB signaling pathway and enhances invasion of breast cancer cells
Cancer Lett.
2010
, vol. 
294
 (pg. 
125
-
133
)
239
Kang
D. W.
Lee
J. Y.
Oh
D. H.
Park
S. Y.
Woo
T. M.
Kim
M. K.
Park
M. H.
Jang
Y. H.
Min do
S.
Triptolide-induced suppression of phospholipase D expression inhibits proliferation of MDA-MB-231 breast cancer cells
Exp. Mol. Med.
2009
, vol. 
41
 (pg. 
678
-
685
)
240
Zhong
M.
Shen
Y.
Zheng
Y.
Joseph
T.
Jackson
D.
Foster
D. A.
Phospholipase D prevents apoptosis in v-Src-transformed rat fibroblasts and MDA-MB-231 breast cancer cells
Biochem. Biophys. Res. Commun.
2003
, vol. 
302
 (pg. 
615
-
619
)
241
Kang
D. W.
Park
M. H.
Lee
Y. J.
Kim
H. S.
Kwon
T. K.
Park
W. S.
Min do
S.
Phorbol ester up-regulates phospholipase D1 but not phospholipase D2 expression through a PKC/Ras/ERK/NFκB-dependent pathway and enhances matrix metalloproteinase-9 secretion in colon cancer cells
J. Biol. Chem.
2008
, vol. 
283
 (pg. 
4094
-
4104
)
242
Henkels
K. M.
Farkaly
T.
Mahankali
M.
Segall
J. E.
Gomez-Cambronero
J.
Cell invasion of highly metastatic MTLn3 cancer cells is dependent on phospholipase D2 (PLD2) and Janus kinase 3 (JAK3)
J. Mol. Biol.
2011
, vol. 
408
 (pg. 
850
-
862
)
243
Knoepp
S. M.
Chahal
M. S.
Xie
Y.
Zhang
Z.
Brauner
D. J.
Hallman
M. A.
Robinson
S. A.
Han
S.
Imai
M.
Tomlinson
S.
Meier
K. E.
Effects of active and inactive phospholipase D2 on signal transduction, adhesion, migration, invasion, and metastasis in EL4 lymphoma cells
Mol. Pharmacol.
2008
, vol. 
74
 (pg. 
574
-
584
)
244
Saito
M.
Iwadate
M.
Higashimoto
M.
Ono
K.
Takebayashi
Y.
Takenoshita
S.
Expression of phospholipase D2 in human colorectal carcinoma
Oncol. Rep.
2007
, vol. 
18
 (pg. 
1329
-
1334
)
245
Oshimoto
H.
Okamura
S.
Yoshida
M.
Mori
M.
Increased activity and expression of phospholipase D2 in human colorectal cancer
Oncol. Res.
2003
, vol. 
14
 (pg. 
31
-
37
)
246
Wright
P. K.
May
F. E.
Darby
S.
Saif
R.
Lennard
T. W.
Westley
B. R.
Estrogen regulates vesicle trafficking gene expression in EFF-3, EFM-19 and MCF-7 breast cancer cells
Int. J. Clin. Exp. Pathol.
2009
, vol. 
2
 (pg. 
463
-
475
)
247
Osman
I.
Bajorin
D. F.
Sun
T. T.
Zhong
H.
Douglas
D.
Scattergood
J.
Zheng
R.
Han
M.
Marshall
K. W.
Liew
C. C.
Novel blood biomarkers of human urinary bladder cancer
Clin. Cancer Res.
2006
, vol. 
12
 (pg. 
3374
-
3380
)
248
Watahiki
A.
Waki
K.
Hayatsu
N.
Shiraki
T.
Kondo
S.
Nakamura
M.
Sasaki
D.
Arakawa
T.
Kawai
J.
Harbers
M.
, et al. 
Libraries enriched for alternatively spliced exons reveal splicing patterns in melanocytes and melanomas
Nat. Methods
2004
, vol. 
1
 (pg. 
233
-
239
)