Tetraspanins are ubiquitous membrane proteins that induce local membrane curvature and hence co-ordinate cell-to-cell contacts. This review highlights their role in inflammation, which requires control of the nano-architecture of attachment sites between endothelial cells and leukocytes. The active role of endothelial cells in preparing for transmigration of leukocytes and determining the severity of an inflammation is often underscored. A clear hint to endothelial pre-activation is their ability to protrude clustered adhesion proteins upward prior to leukocyte contact. The elevation of molecular adhesive platforms toward the blood stream is crucially dependent on tetraspanins. In addition, leukocytes require tetraspanins for their activation. The example of the B-cell receptor is referenced in some detail here, since it provides deeper insights into the receptor–coreceptor interplay. To lift the role of tetraspanins from an abstract model of inflammation toward a player of clinical significance, two pathologies are analyzed for the known contributions of tetraspanins. The recent publication of the first crystal structure of a full-length tetraspanin revealed a cholesterol-binding site, which provides a strong link to the pathophysiological condition of atherosclerosis. Dysregulation of the inflammatory cascade in autoimmune diseases by endothelial cells is exemplified by the involvement of tetraspanins in multiple sclerosis.

Introduction

Cell surface architecture is implicated in virtually all cell-to-cell interactions. The cellular inflammatory response is an example of cell interaction, where circulating leukocytes are recruited to the site of inflammation by resident endothelial cells.

The endothelium is a gatekeeper to the underlying tissues, controlling all flux of nutrients, signaling molecules and leukocytes. Immunological studies often focused on white blood cells, while the perception of the endothelium as a passive filter is just slowly replaced by the viewpoint of endothelia as active immunomodulators.

Endothelial cells prepare actively for a facilitated transmigration before any leukocyte contact [1,2]. Distinct morphological changes are attributed to this activation process, including formation and contraction of actin stress fibers, nanoscale membrane protrusions [37] or even transendothelial tunnel formation [8,9].

These pre-contact changes suggest the endothelium to be an active part of the immune system. In the context of infection and inflammation, tetraspanins (TSPs) play an important role [10], potentially by co-ordinating molecular adhesion clusters on the surface [7].

Here, we depict the role of TSPs in leukocyte–endothelial interaction with a focus on functional nano-architecture of endothelial surfaces.

The inflammatory cascade

Blood-patrolling leukocytes adhere and migrate through the vessel wall after tethering and rolling steers them to an inflammation site. A prerequisite for the transmigration step is an arrest (firm adhesion phase), achieved by binding of the leukocytic integrin LFA-1 to the endothelial integrin ICAM-1. This phase is still reversible, i.e. can return into a rolling phase, but the decision-making factors are not clarified yet.

Neither is it clear how a firm adhesion phase turns into an actual diapedesis step. The route of transmigration is nowadays widely accepted to be either the paracellular or the transcellular pathway (directly through a single endothelial cell) [1116], highlighting the importance of tunnel formation, which can already be provoked by bacterial toxins alone [9].

Since tunnel formation and reclosure would energetically challenge the cell through cytoskeletal remodeling, preformed so-called exit sites in the endothelium would save energy and time demand for the immune response. A functional study on lateral migration of freshly isolated leukocytes on primary human endothelium came to the conclusion that exit channels might explain the reversible arrest and rolling. Extravasation will be successful if leukocyte attachment happens close to pre-deletion sites; otherwise, adhesion will be reversed until the next try [1]. A search for morphological signs to indicate endothelial exit regions unraveled nanoscalar elevation of the molecular adhesion clusters (ICAM-1 clusters). This pre-contact formation of adhesive protrusions was crucially dependent on TSP CD9 [7].

TSPs and cellular morphology

TSPs are a family of transmembrane (TM) proteins found in many multicellular organisms from plants to mammals [17]. They contain four TM helices, which arrange themselves in a conical shape [18].

The superfamily of TSPs may be classified in four different groups, namely CD, CD63, Uroplakin and the RDS family [19,20]. The CD family contains nearly all the vertebrae TSPs, which are the main subject in this review (e.g. CD9, CD81, CD82 and CD151).

A flexible extracellular loop (EC2) is responsible for association to various membrane proteins as detailed below [5,21,22]. A link to the cytoskeleton is provided by binding of the C-terminal tail to the Ezrin–Radixin–Moesin proteins [23]. Moreover, TSPs CD9 and CD81 can modulate signaling pathways by interaction with G-protein-coupled receptors [24].

By these interactions, TSPs influence cellular morphology. During diapedesis, the close intertwining of leukocytes and endothelial cells requires dynamic modification of plasma membranes and the cytoskeleton. Both in leukocytes and in endothelial cells, TSPs induced cellular protrusions even before mutual contact. This has been exemplified by high-resolution methods like electron microscopy or atomic force microscopy (AFM) [25].

The TSP-induced subcellular structures, all associated with modulated membrane curvature, comprise nanotubes, microvilli, basal membrane tubes, podocytes, membrane blebbs and ridges [26]. The process of membrane bending can even exceed the villous state to finally shed microvesicles into the environment [25,27,28].

Endothelial inflammatory phenotype

When endothelial cells are activated by TNF-α, TSP-enriched molecular domains are observed containing adhesion molecules (like ICAM-1, ICAM-2, PECAM-1 and VCAM-1) [4,5]. Analyzing diffusion kinetics by advanced fluorescence techniques (FRET–FLIM, FRAP), ICAM-1 turned out to affiliate to CD9, while VCAM-1 prefers CD81. The increased diffusion constants of TSPs over other CAMs make them perfect candidates for an initial interaction orchestrator. For example, CD9 also regulates the activity of ADAM17, which is a sheddase (protease) for various inflammatory membrane proteins like ICAM-1 and the TNF-α receptor [29,30].

AFM allows to quantify the protrusion formation after endothelial activation. These protrusions were termed microvilli with respect of the general concept of microvilli, even though their dimensions appear to be mostly smaller than, for example, those of intestinal microvilli (height 160 nm vs. 1–3 µm). Knockdown of TSP CD9 displays the connection of the molecular clusters and the formation of TSP-enriched microvilli [7]. These microvilli are essential in the inflammatory cascade as they present not only adhesion molecules but also membrane-bound chemokines like Ccl-19 or IL-8 [31,32] and therefore facilitate leukocyte adhesion (Figure 1).

Another example of TSP impact on plasma membrane are protrusions called nanopodia, which are longer and thinner than filopodia [33]. In this example, a TSP-like membrane protein ‘Transmembrane-4-L-six-family-1’ (TM4SF1) having low sequence homology with TSPs but sharing TSP topology [34] is selectively expressed by endothelial cells in vitro and in vivo. TM4SF1 is necessary for the formation of unusually long (up to a 50 µm), thin (∼100–300 nm wide), F-actin-poor EC cell projections [33].

Inflammatory phenotype of leukocytes

In leukocytes, TSPs have at least two fundamental functional aspects. On the one hand, TSPs modulate the membrane dynamics, as for instance when inducing receptor clustering and microvilli formation. On the other hand, TSPs have an important role regarding the immune synapse. Here, the exchange of TSP-rich extracellular vesicles was reported [35].

Accordingly, overexpression of CD81 induces the formation of microvilli in peripheral blood mononuclear cells and pre-B cells, whereas a knockout (KO) reduced their number per cell [25].

Different TSPs can exert opposite effects: while CD81 induces convex curvature, CD82 inhibits the formation of microvilli. Not only is the number of microvilli a result of CD81/CD82 balance, but also their curvature at the very tip [25].

The triggering of internal signaling cascades by TSPs was demonstrated by externally induced clustering of CD9 with antibodies, which resulted in degranulation of eosinophils [36].

Heterogeneous association and clustering was investigated in detail in B cells. As visualized by dSTORM microscopy, endogenous IgM- and IgD-B cell receptors exist in ‘preformed nanoscale clusters’ with the B-cell co-receptor CD19. Disruption of the actin cytoskeleton did not reduce the clustering, but changed the diffusion of the clusters of IgM and IgD. The B-cell co-receptor CD19 diffuses independently of the disruption of the actin cytoskeleton by Latrunculin A. But in B cells of a TSP CD81 KO model, the diffusion was increased three-fold. This behavior of the co-receptor is interestingly independent of the diffusion of the B-cell receptor itself [37], showing that, for efficient B-cell activation, CD81 is required to organize the interplay of CD19 and the B-cell receptor.

Membrane curvature

To communicate with the exterior from a membrane-enclosed compartment by either releasing vesicles with signal molecules or physically palpating the environment, this membrane has to be bent. A major solution of the nature to actively control the shape of the membrane is the introduction of membrane proteins (like BAR, Caveolin, Cathrin, etc.) or specific lipids which minimize the energy toward a more or less curved membrane ([38,39]; for reviews, see refs [40,41]). A part of the mini-review is the special role of TSPs influencing membrane curvature.

Role of TSPs

The term ‘TSP web’ describes the generation of a sub-membrane domain of several TSPs bound to each other by hydrophobic interactions (ganglioside and cholesterol) ([17,42,43]; for review, see ref. [44]). Besides the hydrophobic interaction, a variable extracellular δ-domain was found by gSTED to organize CD81 clusters, stabilizing these clusters by dimerization [45,46].

Some experiments using super-resolution microscopy (STED) revisited the nature of a TSP web and observed only homophilic local clustering between TSPs and heterophilic near proximity clustering between TSPs and their non-TSP-binding partner. These mono-TSP clusters were found to partially overlap with mono-TSP clusters of a different TSP. This leaves the term ‘TSP web’ to be defined more precisely [47].

Apart from biophysically and biochemically defined integration of TSPs within the membrane, another explanation of membrane curvature initiation through TSPs would be an indirect option via actin signaling by modifying the TSP-dependent G-protein-coupled receptors ([23,24]; for review, see ref. [26]). However, it could not be unequivocally proved that actin nucleation is upstream of membrane bending.

Given the recent structural insight, an intuitive geometrical model emerges of how membrane bending is induced. The four transmembrane helices are arranged pairwise to form a cone (TM1/TM2 and TM3/TM4), with the tip reaching into the cytoplasm. With this structure given, the convex curvature induced by CD81 could be a simple geometrical consequence of close spatial association of TSPs. Since the sequence structure is evolutionarily conserved, it could also explain the membrane modulations of other TSPs like CD9 [18]. In contrast, the TSP CD82 decreases curvature and the number of protrusions of cells and is known to inhibit actin dynamics by reducing molecular activity of, for example, Rho [48]. The interplay of these competing mechanisms has to be further elucidated.

Direct TSP–lipid interactions

In 2016, Zimmerman et al. reported the first crystal structure of CD81. They discovered a cholesterol-binding pocket between the transmembrane columns. This pocket has two possible configurations, each correlating to a closed or open state of the EC2 domain, with the latter exhibiting higher affinity to TM-binding partners like, for instance, CD19. In the closed state, the EC2 domain is bound by a salt bridge over the two transmembrane columns and cholesterol is bound (Figure 2A) [18].

Tremendous explanatory power resides in the cholesterol-binding pocket, because this finding provides a mechanistic link between TSP structure and the vast knowledge about cholesterol function in endothelial (patho-)physiology like atherosclerosis.

Atherosclerosis

Endothelial inflammation induced by cholesterol

Atherosclerosis is a multifactorial disease of the arteries leading to a thickening of their wall by formation of atheromas. These atheromas initially narrow the lumen of the vessel by accumulating fatty, cholesterol-rich LDL (low-density lipoprotein) particles followed by a chronic inflammation with macrophages. The LDL cholesterol is the main source of cellular cholesterol and distributed after lysosomal processing [49]. The role of cholesterol in endothelium is intensely affiliated to the nanoscale invaginations of the plasma membrane termed caveolae. These membrane domains (50–100 nm) are enriched in cholesterol and harbor a transmembrane protein, which is named after the phenotype: caveolin. Caveolae act as cell signaling scaffolds, they can fission into vesicles or even form transcellular tunnels and are implicated in virtually all cellular functions [50,51]. Cholesterol acts rather pro-inflammatory: adhesion and transendothelial migration of leukocytes are increased. Cholesterol promotes LPS-induced adhesion of THP-1 cells (leukocytes) mediated through the translocation of ICAM-1 from caveolar domains to the plasma membrane [52].

In line with this, a removal of cholesterol using methyl-beta-cyclodextrin (MβCD) diminishes transendothelial migration rates [53]. In this study, a clustering of E-selectin in lipid rafts was the proposed mechanism, but in view of recent data, also a reduced formation of ICAM-1-decorated protrusions might explain the findings [7]. One hypothetical mechanism could be a release of CD9 from CD81, as CD81 retracts its large extracellular loop while it binds cholesterol (Figure 2B) [18].

A physical interaction of TSPs with cholesterol was already demonstrated more than a decade ago. The activation signaling of proteins by tyrosine phosphorylations in lymphoid B cells was decreased by MβCD and induced by MβCD with cholesterol [42]. Recently, MβCD was found to reduce the effect of invasive dissemination mediated by a TSP-like protein TM4SF-5 in hepatocellular carcinoma cells. This was presumably caused by removal of the TM4SF-5 molecular cluster with EGFR from the cellular membrane. The detailed interaction of cholesterol and TSP, e.g. in early endothelial inflammation like atherosclerosis, seems therefore to influence directly the structure and the signaling cascade of TSPs.

In accordance with the findings of Charrin (2003), a role for TSPs in early atherosclerotic plaques has also been shown [54]. Monocyte invasion is correlated to up-regulation of TSP CD81 on both mRNA and protein levels in human vascular tissue. The effect was correlated to increasing the available clusters of ICAM-1 at the cellular surface without a change in the expression level of ICAM-1. These observations are in line with Barreiro's finding of association of endothelial CD9, CD151 with ICAM-1, VCAM-1 and also CD81 in the docking structures as in the endothelial adhesive platforms [4,5]. This clearly supports a mechanistic model, where TSPs induce membrane protrusions at receptor clustering sites, thereby facilitating interaction with other cells.

The exact interplay between the inflammation-relevant TSPs, CD9, CD81, CD151, VCAM-1 and ICAM-1, and the modulating function of cholesterol, however, is still waiting for full elucidation [54].

Autoimmune diseases

TSPs in multiple sclerosis

Looking at the clinical picture, multiple sclerosis (MS) may illuminate the role of TSPs in immune diseases. The main focus in this context is on oligodendrocytes, which are known to regulate T- and B-cell activity [5558]. The so far proposed mechanistic models involve clustering of MHC molecules (for reviews, see refs [59,60]).

In this context, it is of note that endothelial cells are key to the development of MS as shown in a murine model of experimental autoimmune encephalomyelitis (EAE) (see MOG-induced EAE [61]), which revealed increased severity scores in the case of potassium channel TREK-1 deficiency. These KO mice lack any leukocyte phenotype, but exhibit increased ICAM-1, VCAM-1 and PECAM-1 levels at the brain endothelium [2]. Histological preparations of lesions from MS patients show up-regulated CD9 levels in blood vessels. To complete the evidence, an antibody against CD9, targeting either leukocytes or the endothelium, has been shown to lead to improved barrier function [62]. Preventive usage of CD81 antibodies reduced monocyte immigration and symptoms in EAE [63]. Supporting the relevance of TSP for the maintenance of the blood–brain barrier, even extracellular vesicles of brain endothelial cells contain CD9 and CD81 [64].

Theoretically, involvement of TSPs in autoimmune diseases might also arise from TPSs being the target of autoantibodies. But an investigation concerning CD9, CD81 and CD82 remained inconclusive, stating only a weak immunological reaction [65]. Hence, the overwhelming data on protrusion formation in endothelial cells and in leukocytes are the more likely explanation for TSP involvement in autoimmune disorders [6,7,31,32,66].

Conclusion

Cell-to-cell interactions are controlled by ligand–receptor binding. Not only expression levels but also their local distribution and steric accessibility are needed for proper cell communication. The biological solution to this geometrical problem is to either present interaction proteins at the tip of membrane protrusions like microvilli or to store them in caveolae. In endothelial cells and leukocytes, mainly the TSPs CD81, CD9 and CD82 control the local membrane curvature. Via this organization of surface nano-architecture, TSPs pave the way for an efficient immune response. The clinical relevance of TSPs is demonstrated by their involvement in atherosclerosis or autoimmune diseases like MS.Figure 1,Figure 2 

Sketch of endothelial activation in inflammatory conditions before leukocyte contact.

Figure 1.
Sketch of endothelial activation in inflammatory conditions before leukocyte contact.

The displayed proteins are exemplary for the proposed model of functional morphology. Upon activation, the adhesive receptors (like ICAM-1) cluster with the TSP (like CD9). Elevating these adhesion platforms increases the binding probability for leukocytes.

Figure 1.
Sketch of endothelial activation in inflammatory conditions before leukocyte contact.

The displayed proteins are exemplary for the proposed model of functional morphology. Upon activation, the adhesive receptors (like ICAM-1) cluster with the TSP (like CD9). Elevating these adhesion platforms increases the binding probability for leukocytes.

Molecular structure of TSPs integrates cholesterol effects on membranes.

Figure 2.
Molecular structure of TSPs integrates cholesterol effects on membranes.

(A) Structure of CD81 with a cholesterol-binding pocket. Reprinted from Zimmerman et al. [18], Copyright (2016) with permission from Elsevier. (B) Proposed pathomechanism involving cholesterol-dependent endothelial activation by relocalization of TSPs (CD9) from the cell membrane to the ‘positively’ curved microvilli or the ‘negatively’ curved invaginations like caveolae, inducing, e.g. ICAM-1 clustering.

Figure 2.
Molecular structure of TSPs integrates cholesterol effects on membranes.

(A) Structure of CD81 with a cholesterol-binding pocket. Reprinted from Zimmerman et al. [18], Copyright (2016) with permission from Elsevier. (B) Proposed pathomechanism involving cholesterol-dependent endothelial activation by relocalization of TSPs (CD9) from the cell membrane to the ‘positively’ curved microvilli or the ‘negatively’ curved invaginations like caveolae, inducing, e.g. ICAM-1 clustering.

Abbreviations

     
  • AFM

    atomic force microscopy

  •  
  • EAE

    experimental autoimmune encephalomyelitis

  •  
  • EC

    endothelial cell

  •  
  • EGFR

    epidermal growth factor receptor

  •  
  • FRAP

    fluorescence recovery after photobleaching

  •  
  • FRET-FLIM

    Förster resonance energy transfer-fluorescence lifetime imaging microscopy

  •  
  • ICAM-1

    intercellular adhesion molecule 1

  •  
  • KO

    knockout

  •  
  • LDL

    low-density lipoprotein

  •  
  • LFA-1

    lymphocyte function-associated antigen 1

  •  
  • MHC

    major histocompatibility complex

  •  
  • MS

    multiple sclerosis

  •  
  • MβCD

    methyl-beta-cyclodextrin

  •  
  • PECAM-1

    platelet endothelial cell adhesion molecule 1

  •  
  • STED

    stimulated emission depletion

  •  
  • STORM

    stochastic optical reconstruction microscopy

  •  
  • TM

    transmembrane

  •  
  • TM4SF1

    transmembrane-4-L-six-family-1

  •  
  • TSPs

    tetraspanins

  •  
  • VCAM-1

    vascular cell adhesion molecule 1

Funding

Funding for this work was granted by the Deutsche Forschungsgemeinschaft (DFG) [Grant No. SFB937] “Collective behavior of soft and biological matter” in the subproject A8 and the Volkswagen foundation, initiative Life, project “Living Foams” to Marco Tarantola.

Competing Interests

The Authors declare that there are no competing interests associated with the manuscript.

References

References
1
Stock
,
C.
and
Riethmuller
,
C.
(
2011
)
Endothelial activation drives lateral migration and diapedesis of leukocytes
.
Cell. Immunol.
271
,
180
183
doi:
2
Bittner
,
S.
,
Ruck
,
T.
,
Schuhmann
,
M.K.
,
Herrmann
,
A.M.
,
Maati
,
H.M.
,
Bobak
,
N.
et al. 
(
2013
)
Endothelial TWIK-related potassium channel-1 (TREK1) regulates immune-cell trafficking into the CNS
.
Nat. Med.
19
,
1161
1165
doi:
3
Wójciak-Stothard
,
B.
,
Entwistle
,
A.
,
Garg
,
R.
and
Ridley
,
A.J.
(
1998
)
Regulation of TNF-α-induced reorganization of the actin cytoskeleton and cell-cell junctions by Rho, Rac, and Cdc42 in human endothelial cells
.
J. Cell Physiol.
176
,
150
165
<150::AID-JCP17>3.0.CO;2-B
4
Barreiro
,
O.
,
Yáñez-Mó
,
M.
,
Sala-Valdés
,
M.
,
Gutiérrez-Lopéz
,
M.D.
,
Ovalle
,
S.
,
Higginbottom
,
A.
et al. 
(
2005
)
Endothelial tetraspanin microdomains regulate leukocyte firm adhesion during extravasation
.
Blood
105
,
2852
2861
doi:
5
Barreiro
,
O.
,
Zamai
,
M.
,
Yáñez-Mó
,
M.
,
Tejera
,
E.
,
López-Romero
,
P.
,
Monk
,
P.N.
et al. 
(
2008
)
Endothelial adhesion receptors are recruited to adherent leukocytes by inclusion in preformed tetraspanin nanoplatforms
.
J. Cell Biol.
183
,
527
542
doi:
6
van Buul
,
J.D.
,
van Rijssel
,
J.
,
van Alphen
,
F.P.J.
,
Hoogenboezem
,
M.
,
Tol
,
S.
,
Hoeben
,
K.A.
et al. 
(
2010
)
Inside-out regulation of ICAM-1 dynamics in TNF-α-activated endothelium
.
PLoS ONE
5
,
e11336
doi:
7
Franz
,
J.
,
Brinkmann
,
B.F.
,
König
,
M.
,
Hüve
,
J.
,
Stock
,
C.
,
Ebnet
,
K.
et al. 
(
2016
)
Nanoscale imaging reveals a tetraspanin-CD9 coordinated elevation of endothelial ICAM-1 clusters
.
PLoS ONE
11
,
e0146598
doi:
8
Maddugoda
,
M.P.
,
Stefani
,
C.
,
Gonzalez-Rodriguez
,
D.
,
Saarikangas
,
J.
,
Torrino
,
S.
,
Janel
,
S.
et al. 
(
2011
)
cAMP signaling by anthrax edema toxin induces transendothelial cell tunnels, which are resealed by MIM via Arp2/3-driven actin polymerization
.
Cell Host Microbe
10
,
464
474
doi:
9
Lemichez
,
E.
,
Gonzalez-Rodriguez
,
D.
,
Bassereau
,
P.
and
Brochard-Wyart
,
F.
(
2013
)
Transcellular tunnel dynamics: control of cellular dewetting by actomyosin contractility and I-BAR proteins
.
Biol. Cell
105
,
109
117
doi:
10
Monk
,
P.N.
and
Partridge
,
L.J.
(
2012
)
Tetraspanins: gateways for infection
.
Infect. Disord. Drug Targets
12
,
4
17
doi:
11
Carman
,
C.V.
and
Springer
,
T.A.
(
2004
)
A transmigratory cup in leukocyte diapedesis both through individual vascular endothelial cells and between them
.
J. Cell Biol.
167
,
377
388
doi:
12
Engelhardt
,
B.
and
Wolburg
,
H.
(
2004
)
Mini-review: transendothelial migration of leukocytes: through the front door or around the side of the house?
Eur. J. Immunol.
34
,
2955
2963
doi:
13
Yang
,
L.
,
Froio
,
R.M.
,
Sciuto
,
T.E.
,
Dvorak
,
A.M.
,
Alon
,
R.
and
Luscinskas
,
F.W.
(
2005
)
ICAM-1 regulates neutrophil adhesion and transcellular migration of TNF-α-activated vascular endothelium under flow
.
Blood
106
,
584
592
doi:
14
Riethmuller
,
C.
,
Nasdala
,
I.
and
Vestweber
,
D.
(
2008
)
Nano-surgery at the leukocyte-endothelial docking site
.
Pflugers Arch.
456
,
71
81
doi:
15
Wittchen
,
E.S.
(
2009
)
Endothelial signaling in paracellular and transcellular leukocyte transmigration
.
Front. Biosci.
14
,
2522
2545
doi:
16
Reglero-Real
,
N.
,
Marcos-Ramiro
,
B.
and
Millán
,
J.
(
2012
)
Endothelial membrane reorganization during leukocyte extravasation
.
Cell. Mol. Life Sci.
69
,
3079
3099
doi:
17
Charrin
,
S.
,
Jouannet
,
S.
,
Boucheix
,
C.
and
Rubinstein
,
E.
(
2014
)
Tetraspanins at a glance
.
J. Cell Sci.
127
,
3641
3648
doi:
18
Zimmerman
,
B.
,
Kelly
,
B.
,
McMillan
,
B.J.
,
Seegar
,
T.C.
,
Dror
,
R.O.
,
Kruse
,
A.C.
et al. 
(
2016
)
Crystal structure of a full-Length human tetraspanin reveals a cholesterol-binding pocket
.
Cell
167
,
1041
1051.e11
doi:
19
Fradkin
,
L.G.
,
Kamphorst
,
J.T.
,
DiAntonio
,
A.
,
Goodman
,
C.S.
and
Noordermeer
,
J.N.
(
2002
)
Genomewide analysis of the Drosophila tetraspanins reveals a subset with similar function in the formation of the embryonic synapse
.
Proc. Natl Acad. Sci. U.S.A.
99
,
13663
13668
doi:
20
Garcia-Espana
,
A.
,
Chung
,
P.-J.
,
Sarkar
,
I.N.
,
Stiner
,
E.
,
Sun
,
T.-T.
and
Desalle
,
R.
(
2008
)
Appearance of new tetraspanin genes during vertebrate evolution
.
Genomics
91
,
326
334
doi:
21
Stipp
,
C.S.
,
Kolesnikova
,
T.V.
and
Hemler
,
M.E.
(
2003
)
Functional domains in tetraspanin proteins
.
Trends Biochem. Sci.
28
,
106
112
doi:
22
Yáñez-Mó
,
M.
,
Barreiro
,
O.
,
Gordon-Alonso
,
M.
,
Sala-Valdés
,
M.
and
Sánchez-Madrid
,
F.
(
2009
)
Tetraspanin-enriched microdomains: a functional unit in cell plasma membranes
.
Trends Cell Biol.
19
,
434
446
doi:
23
Sala-Valdés
,
M.
,
Ursa
,
A.
,
Charrin
,
S.
,
Rubinstein
,
E.
,
Hemler
,
M.E.
,
Sánchez-Madrid
,
F.
et al. 
(
2006
)
EWI-2 and EWI-F link the tetraspanin web to the actin cytoskeleton through their direct association with ezrin-radixin-moesin proteins
.
J. Biol. Chem.
281
,
19665
19675
doi:
24
Little
,
K.D.
,
Hemler
,
M.E.
and
Stipp
,
C.S.
(
2004
)
Dynamic regulation of a GPCR-tetraspanin-G protein complex on intact cells: central role of CD81 in facilitating GPR56-Gαq/11 association
.
Mol. Biol. Cell
15
,
2375
2387
doi:
25
Bari
,
R.
,
Guo
,
Q.
,
Xia
,
B.
,
Zhang
,
Y.H.
,
Giesert
,
E.E.
,
Levy
,
S.
et al. 
(
2011
)
Tetraspanins regulate the protrusive activities of cell membrane
.
Biochem. Biophys. Res. Commun.
415
,
619
626
doi:
26
Zhang
,
X.A.
and
Huang
,
C.
(
2012
)
Tetraspanins and cell membrane tubular structures
.
Cell. Mol. Life Sci.
69
,
2843
2852
doi:
27
Aharon
,
A.
,
Tamari
,
T.
and
Brenner
,
B.
(
2008
)
Monocyte-derived microparticles and exosomes induce procoagulant and apoptotic effects on endothelial cells
.
Thromb. Haemost.
100
,
878
885
PMID:
[PubMed]
28
Yáñez-Mó
,
M.
,
Siljander
,
P.R.-M.
,
Andreu
,
Z.
,
Zavec
,
A.B.
,
Borrás
,
F.E.
,
Buzas
,
E.I.
et al. 
(
2015
)
Biological properties of extracellular vesicles and their physiological functions
.
J. Extracell. Vesicles
4
,
27066
doi:
29
Gutiérrez-López
,
M.D.
,
Gilsanz
,
A.
,
Yáñez-Mó
,
M.
,
Ovalle
,
S.
,
Lafuente
,
E.M.
,
Domínguez
,
C.
et al. 
(
2011
)
The sheddase activity of ADAM17/TACE is regulated by the tetraspanin CD9
.
Cell. Mol. Life Sci.
68
,
3275
3292
doi:
30
Lisi
,
S.
,
D'Amore
,
M.
and
Sisto
,
M.
(
2014
)
ADAM17 at the interface between inflammation and autoimmunity
.
Immunol. Lett.
162
,
159
169
doi:
31
Middleton
,
J.
,
Neil
,
S.
,
Wintle
,
J.
,
Clark-Lewis
,
I.
,
Moore
,
H.
,
Lam
,
C.
et al. 
(
1997
)
Transcytosis and surface presentation of IL-8 by venular endothelial cells
.
Cell
91
,
385
395
doi:
32
Baekkevold
,
E.S.
,
Yamanaka
,
T.
,
Palframan
,
R.T.
,
Carlsen
,
H.S.
,
Reinholt
,
F.P.
,
von Andrian
,
U.H.
et al. 
(
2001
)
The Ccr7 ligand ELC (Ccl19) is transcytosed in high endothelial venules and mediates T cell recruitment
.
In. J. Exp. Med.
193
,
1105
1112
doi:
33
Zukauskas
,
A.
,
Merley
,
A.
,
Li
,
D.
,
Ang
,
L.-H.
,
Sciuto
,
T.E.
,
Salman
,
S.
et al. 
(
2011
)
TM4SF1: a tetraspanin-like protein necessary for nanopodia formation and endothelial cell migration
.
Angiogenesis
14
,
345
354
doi:
34
Wright
,
M.D.
,
Ni
,
J.
and
Rudy
,
G.B.
(
2000
)
The L6 membrane proteins—a new four-transmembrane superfamily
.
Protein Sci.
9
,
1594
1600
doi:
35
Gutiérrez-Vázquez
,
C.
,
Villarroya-Beltri
,
C.
,
Mittelbrunn
,
M.
and
Sánchez-Madrid
,
F.
(
2013
)
Transfer of extracellular vesicles during immune cell-cell interactions
.
Immunol. Rev.
251
,
125
142
doi:
36
Kim
,
J.T.
,
Gleich
,
G.J.
and
Kita
,
H.
(
1997
)
Roles of CD9 molecules in survival and activation of human eosinophils
.
J. Immunol.
159
,
926
933
PMID:
[PubMed]
37
Mattila
,
P.K.
,
Feest
,
C.
,
Depoil
,
D.
,
Treanor
,
B.
,
Montaner
,
B.
,
Otipoby
,
K.L.
et al. 
(
2013
)
The actin and tetraspanin networks organize receptor nanoclusters to regulate B cell receptor-mediated signaling
.
Immunity
38
,
461
474
doi:
38
Veltman
,
D.M.
,
Auciello
,
G.
,
Spence
,
H.J.
,
Machesky
,
L.M.
,
Rappoport
,
J.Z.
and
Insall
,
R.H.
(
2011
)
Functional analysis of Dictyostelium IBARa reveals a conserved role of the I-BAR domain in endocytosis
.
Biochem. J.
436
,
45
52
doi:
39
Linkner
,
J.
,
Witte
,
G.
,
Zhao
,
H.
,
Junemann
,
A.
,
Nordholz
,
B.
,
Runge-Wollmann
,
P.
et al. 
(
2014
)
The inverse BAR domain protein IBARa drives membrane remodeling to control osmoregulation, phagocytosis and cytokinesis
.
J. Cell Sci.
127
,
1279
1292
doi:
40
McMahon
,
H.T.
and
Boucrot
,
E.
(
2015
)
Membrane curvature at a glance
.
J. Cell Sci.
128
,
1065
1070
doi:
41
Jarsch
,
I.K.
,
Daste
,
F.
and
Gallop
,
J.L.
(
2016
)
Membrane curvature in cell biology: an integration of molecular mechanisms
.
J. Cell Biol.
214
,
375
387
doi:
42
Charrin
,
S.
,
Manié
,
S.
,
Thiele
,
C.
,
Billard
,
M.
,
Gerlier
,
D.
,
Boucheix
,
C.
et al. 
(
2003
)
A physical and functional link between cholesterol and tetraspanins
.
Eur. J. Immunol.
33
,
2479
2489
doi:
43
Odintsova
,
E.
,
Butters
,
T.D.
,
Monti
,
E.
,
Sprong
,
H.
,
van Meer
,
G.
and
Berditchevski
,
F.
(
2006
)
Gangliosides play an important role in the organization of CD82-enriched microdomains
.
Biochem. J.
400
,
315
325
doi:
44
Rubinstein
,
E.
(
2011
)
The complexity of tetraspanins
.
Biochem. Soc. Trans.
39
,
501
505
doi:
45
Homsi
,
Y.
,
Schloetel
,
J.-G.
,
Scheffer
,
K.D.
,
Schmidt
,
T.H.
,
Destainville
,
N.
,
Florin
,
L.
et al. 
(
2014
)
The extracellular δ-domain is essential for the formation of CD81 tetraspanin webs
.
Biophys. J.
107
,
100
113
doi:
46
Homsi
,
Y.
and
Lang
,
T.
(
2017
)
The specificity of homomeric clustering of CD81 is mediated by its δ-loop
.
FEBS Open Bio.
7
,
274
283
doi:
47
Zuidscherwoude
,
M.
,
Göttfert
,
F.
,
Dunlock
,
V.M.E.
,
Figdor
,
C.G.
,
van den Bogaart
,
G.
and
van Spriel
,
A.B.
(
2015
)
The tetraspanin web revisited by super-resolution microscopy
.
Sci. Rep.
5
,
12201
doi:
48
Liu
,
W.M.
,
Zhang
,
F.
,
Moshiach
,
S.
,
Zhou
,
B.
,
Huang
,
C.
,
Srinivasan
,
K.
et al. 
(
2012
)
Tetraspanin CD82 inhibits protrusion and retraction in cell movement by attenuating the plasma membrane-dependent actin organization
.
PLoS ONE
7
,
e51797
doi:
49
Maxfield
,
F.R.
and
Tabas
,
I.
(
2005
)
Role of cholesterol and lipid organization in disease
.
Nature
438
,
612
621
doi:
50
Chidlow
, Jr,
J.H.
and
Sessa
,
W.C.
(
2010
)
Caveolae, caveolins, and cavins: complex control of cellular signalling and inflammation
.
Cardiovasc. Res.
86
,
219
225
doi:
51
Lajoie
,
P.
and
Nabi
,
I.R.
(
2010
)
Lipid rafts, caveolae, and their endocytosis
.
Int. Rev. Cell Mol. Biol.
282
,
135
163
doi:
52
Fu
,
C.
,
He
,
J.
,
Li
,
C.
,
Shyy
,
J.Y.-J.
and
Zhu
,
Y.
(
2010
)
Cholesterol increases adhesion of monocytes to endothelium by moving adhesion molecules out of caveolae
.
Biochim. Biophys. Acta, Mol. Cell Biol. Lipids
1801
,
702
710
doi:
53
Setiadi
,
H.
and
McEver
,
R.P.
(
2008
)
Clustering endothelial E-selectin in clathrin-coated pits and lipid rafts enhances leukocyte adhesion under flow
.
Blood
111
,
1989
1998
doi:
54
Rohlena
,
J.
,
Volger
,
O.L.
,
van Buul
,
J.D.
,
Hekking
,
L.H.P.
,
van Gils
,
J.M.
,
Bonta
,
P.I.
et al. 
(
2009
)
Endothelial CD81 is a marker of early human atherosclerotic plaques and facilitates monocyte adhesion
.
Cardiovasc. Res.
81
,
187
196
doi:
55
Sullivan
,
C.D.
and
Geisert
, Jr,
E.E.
(
1998
)
Expression of rat target of the antiproliferative antibody (TAPA) in the developing brain
.
J. Comp. Neurol.
396
,
366
380
doi:
56
Berry
,
M.V.
and
Dennis
,
M.R.
(
2000
)
Phase singularities in isotropic random waves
.
Proc. R. Soc. Lond. A
456
,
2059
2079
doi:
57
Mela
,
A.
and
Goldman
,
J.E.
(
2009
)
The tetraspanin KAI1/CD82 is expressed by late-lineage oligodendrocyte precursors and may function to restrict precursor migration and promote oligodendrocyte differentiation and myelination
.
J. Neurosci.
29
,
11172
11181
doi:
58
Mela
,
A.
and
Goldman
,
J.E.
(
2013
)
CD82 blocks cMet activation and overcomes hepatocyte growth factor effects on oligodendrocyte precursor differentiation
.
J. Neurosci.
33
,
7952
7960
doi:
59
Jones
,
E.L.
,
Demaria
,
M.C.
and
Wright
,
M.D.
(
2011
)
Tetraspanins in cellular immunity
.
Biochem. Soc. Trans.
39
,
506
511
doi:
60
Zeis
,
T.
,
Enz
,
L.
and
Schaeren-Wiemers
,
N.
(
2016
)
The immunomodulatory oligodendrocyte
.
Brain Res.
1641
,
139
148
doi:
61
Bittner
,
S.
,
Afzali
,
A.M.
,
Wiendl
,
H.
and
Meuth
,
S.G.
(
2014
)
Myelin oligodendrocyte glycoprotein (MOG35-55) induced experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice
.
J. Vis. Exp.
doi:
62
Schenk
,
G.J.
,
Dijkstra
,
S.
,
van het Hof
,
A.J.
,
van der Pol
,
S.M.A.
,
Drexhage
,
J.A.
,
van der Valk
,
P.
et al. 
(
2013
)
Roles for HB-EGF and CD9 in multiple sclerosis
.
Glia
61
,
1890
1905
doi:
63
Dijkstra
,
S.
,
Kooij
,
G.
,
Verbeek
,
R.
,
van der Pol
,
S.M.A.
,
Amor
,
S.
,
Geisert
, Jr,
E.E.
et al. 
(
2008
)
Targeting the tetraspanin CD81 blocks monocyte transmigration and ameliorates EAE
.
Neurobiol. Dis.
31
,
413
421
doi:
64
Haqqani
,
A.S.
,
Delaney
,
C.E.
,
Tremblay
,
T.-L.
,
Sodja
,
C.
,
Sandhu
,
J.K.
and
Stanimirovic
,
D.B.
(
2013
)
Method for isolation and molecular characterization of extracellular microvesicles released from brain endothelial cells
.
Fluids Barriers CNS
10
,
4
doi:
65
Miyaji
,
K.
,
Paul
,
F.
,
Shahrizaila
,
N.
,
Umapathi
,
T.
and
Yuki
,
N.
(
2016
)
Autoantibodies to tetraspanins (CD9, CD81 and CD82) in demyelinating diseases
.
J. Neuroimmunol.
291
,
78
81
doi:
66
Barreiro
,
O.
,
Vicente-Manzanares
,
M.
,
Urzainqui
,
A.
,
Yáñez-Mó
,
M.
and
Sánchez-Madrid
,
F.
(
2004
)
Interactive protrusive structures during leukocyte adhesion and transendothelial migration
.
Front. Biosci.
9
,
1849
1863
doi: