Tetraspanin CD9 Is Associated With Very Late–Acting Integrins in Human Vascular Smooth Muscle Cells and Modulates Collagen Matrix Reorganization

Abstract

Abstract-CD9, a member of the tetraspanin family, and very late-acting (VLA) integrins are known to associate and form functional units on the surface of several cell types. We studied the changes in expression of CD9 and ␤ 1 -integrins (CD29, VLA) in human vascular smooth muscle cells (VSMCs) under in vitro culture conditions mimicking proliferative vascular diseases. We also investigated possible interactions between CD9 and VLA integrins in VSMCs. We found that CD9 is highly expressed in VSMCs and is subject to modulation, depending on the proliferative/ contractile state of the cells. In the contractile phenotype, the levels of CD9, CD81, another tetraspanin, and CD29 are Ϸ50% of those found in the proliferative phenotype. Coimmunoprecipitation experiments showed physical association between CD9 and CD29. CD9 was mainly associated with ␣ 2 and ␣ 3 -integrins (CD49b and c) and also with ␣ 5 -integrin to a weaker extent. Functionally, the addition of anti-CD9 monoclonal antibodies (MoAbs) doubled the extent of collagen gel contraction mediated by VSMCs, a model for the reorganization of the extracellular collagen matrix occurring in the vessel wall. Anti-CD29 MoAbs inhibited gel contraction, but anti-CD9 MoAbs counteracted this inhibitory effect of anti-CD29 MoAbs. Transfection of human CD9 into Chinese hamster ovary cells more than doubled the extent of Chinese hamster ovary cell-mediated collagen gel contraction (130% stimulation), confirming a role for CD9 in extracellular matrix reorganization. Thus, CD9 seems to be involved in the modulation of VLA integrinmediated collagen matrix reorganization by VSMCs. These findings suggest that high CD9 expression is associated with a proliferative state of VSMCs. The role of CD9 could be to modulate the function of VLA integrins on the surface of VSMCs.

α2β1 integrin controls association of Rac with the membrane and triggers quiescence of endothelial cells

“…The association of various tetraspanins with integrins is documented, modulating post ligand-binding events such as adhesion strengthening or receptor recycling (Hemler, 2005;Liu et al, 2007). Although interaction of CD9 with 3 or 6 integrins has been observed in several cell types (Berditchevski, 2001), an association with 2 integrin was only reported in vascular smooth muscle cells (Scherberich et al, 1998). Our results in yeast suggest the direct interaction of these two molecules.…”

CD9 Is a Unique Marker for Marginal Zone B Cells, B1 Cells, and Plasma Cells in Mice

“…Although its exact function is unknown, previous studies implicated CD9 in cell adhesion, migration, or signal transduction (32)(33)(34). Biochemical studies have shown that CD9 is physically associated with various membrane proteins such as integrins (preferentially ␤ 1 integrin), MHC class II, CD19, CD5, or other tetraspanin members, depending on the cell types (32,(35)(36)(37)(38)(39). Collectively, these studies show that CD9 may modulate the function of associated molecules.…”

The association of the tetraspanin D6.1A with the α6β4 integrin supports cell motility and liver metastasis formation

“…They form protein complexes that are mostly composed of different tetraspanins and integrins, but can also contain members of other protein families Horvath et al, 1998;Indig et al, 1997;Lozahic et al, 2000;Mannion et al, 1996;Rubinstein et al, 1997;Scherberich et al, 1998;Serru et al, 1999;Sincock et al, 1999;Tiwari-Woodruff et al, 2001;Yauch et al, 1998). The strongest association between tetraspanins and integrins has been described for CD151 and the α3 and α6 integrins Yauch et al, 1998;Yauch et al, 2000).…”