MS-1, a high-molecular-mass protein expressed by non-continuous and angiogenic endothelial cells and by alternatively activated macrophages (Mφ2), and the hepatic sinusoidal endothelial hyaluronan clearance receptor are similar with respect to tissue distribution and biochemical characteristics. In the present study we purified these proteins by immuno- and hyaluronan-affinity chromatography respectively, sequenced tryptic peptides and generated full-length cDNA sequences in both mouse and human. The novel genes, i.e. stabilin-1 and stabilin-2, code for homologous transmembrane proteins featuring seven fasciclin-like adhesion domains, 18–20 epidermal-growth-factor domains, one X-link domain and three to six B-(X7)-B hyaluronan-binding motifs. Northern-blotting experiments revealed the presence of both stabilins in organs with predominant endothelial sinuses such as liver, spleen and lymph node: stabilin-1 mRNA was also detected in organs with predominant Mφ2 cells, such as placenta, and in interleukin-4/glucocorticoid-stimulated Mφ2 cells in vitro. A polyclonal antibody made against human recombinant stabilin-1 confirmed the expression of stabilin-1 protein in splenic sinus endothelial cells in vivo and in Mφ2 in vitro. On the basis of high similarity at the protein level and the unique domain composition, which differs from that of all other known fasciclin-like proteins and hyaluronan receptors, stabilin-1 and stabilin-2 define a novel family of fasciclin-like hyaluronan receptor homologues that might play a role in cell—cell and cell—matrix interactions in vascular function and inflammatory processes.
Abbreviations used: ECM, extracellular matrix; EGF, epidermal growth factor; EST, expressed sequence tag; FD, fasciclin domain; HA, hyaluronan; HUAEC-p, primary human umbilical artery endothelial cells; hstabilin, recombinant human stabilin; HUVEC-p, primary human umbilical vein endothelial cells; IFN, interferon; IL, interleukin; mAb, monoclonal antibody; MALDI-TOF MS, matrix-assisted laser-desorption—ionization time-of-flight MS; mstabilin, recombinant mouse stabilin; MTN™ (ClonTech), multiple-tissue Northern; Mφ, macrophage(s); Mφ2, alternatively activated macrophages; PSD, post-source decay; RHAMM, receptor of HA-mediated motility; RACE, rapid amplification of cDNA ends; TSG-6, tumour-necrosis-factor-stimulated gene-6.
The final human stabilin-1 (hstabilin-1) cDNA sequence (7870 bp), the final mstabilin-1 cDNA sequence (7935bp), the final hstabilin-2 cDNA sequence (8266bp) and the final mouse stabilin-2 (mstabilin-2) cDNA sequence (8147bp) have been deposited with the DDBJ, EMBL, GenBank® and GSDB Nucleotide Sequence Databases under the accession numbers AJ275213, AF290914, AJ295695 and AF364951 respectively.