Endothelial Cells Use tx 2 / 3 t Integrin as a Laminin Receptor

Human umbilical vein endothelial cells attach and spread on laminin-coated substrates. Affinity chromatography was used to identify the attachment receptor. Fractionation of extracts from surfaceiodinated endothelial cells on human lamininSepharose yielded a heterodimeric complex, the subunits of which migrated with molecular sizes corresponding to 160/120 kD and 160/140 kD under nonreducing and reducing conditions, respectively. The purified receptor bound to laminin and slightly less to fibronectin and type IV collagen in a radioreceptor assay. This endothelial cell laminin receptor was classified as an t~zB, integrin because monoclonal and polyclonal antibodies directed against the ct2 and/3, subunits immunoprecipitated the receptor. Cytofluorometric analysis arid immunoprecipitation showed that the ix2 subunit is an abundant integrin ~t subunit in the endothelial cells and that the ot subunits associated with laminin binding in other types of cells are expressed in these cells only at low levels. The ,v~, integrin appears to be a major receptor for laminin in the endothelial cells, because an anti-ix2 monoclonal antibody inhibited the attachment of the endothelial cells to human laminin. These results define a new role for the o~2 subunit in laminin binding and suggest that the ligand specificity of the tx2/3t integrin, which is known as a collagen receptor in other types of cells, can be modulated by cell type-specific factors to include laminin binding. HESIVE properties of endothelial cells play an important role in the maintenance of the vessel wall integrity and in diseases such as thrombosis and arteriosclerosis (Gimbrone, 1986). On the luminal side these cells form a nonthrombogenic surface, whereas on the basal side they rest on a basement membrane to which they adhere. The endothelial basement membrane contains laminin, type IV collagen, type V collagen, and protcoglycans (Madri et al., 1980; Palotie et al., 1983; Fujiwara et al., 1984; Siebold et al., 1988; for review see T'tmpl, 1989). Many of these basement membrane components mediate endothelial cell adherence. Laminin, in particular is thought to be important in this regard (Form et al., 1986; Madri and Williams, 1983; Herbst et al., 1988). Various types of cells have been shown to have laminin receptors that arc members of the integrin family. Integrins are heterodimeric proteins that consist of an c~ and a subunit; each intcgrin is, therefore, defined by its subunits (Pytela et al., 1986; Buck and Horwitz, 1987; Hynes, 1987; Ruoslahti and Picrschbacher, 1987; Hemler et al., 1987; Takada et al., 1987). Intcgrins o~3B~ (Wayner and Carter, 1987; Takada et al., 1988; Gehlsen et al., 1988; Gehlsen et al., 1989) and ad3~ (Sonnenberg et al., 1988), as well as an integrin similar to o~,13t (Tomaselli et al., 1988; Ignatius and Reichardt, 1988) have each been implicated as laminin receptors. Endothelial cells are known to express the ~B,, O[3/~1, and ot~, integrins (Albelda et al., 1989; Conforti et al., 1989; Giltay et al., 1989). The as/~l integrin is a fibronectin receptor (Argraves et al., 1987); ot3~1 is known as a laminin, fibronectin, and collagen receptor (Wayner et al., 1988); while t~2B, has previously been identified as a collagen receptor in platelets and in other cells (Wayner and Carter, 1987; Kunicki et al., 1988; Staatz et al., 1989). In addition, endothelial cells also express the vitronectin receptor (o~v/33) (Suzuki et al., 1987; Cheresh, 1987). Endothelial cells attach to laminin through an integrin-mediated mechanism; that is suggested by the inhibition of endothelial cell attachment to laminin by an antibody directed against the/~ integrin subunit (Cheng, Y. E, C. Damsky, and R. H. Kramer, unpublished observations). However, endothelial cells have also been suggested to interact with laminin through a 69-kD protein (Yarmariello-Brown et al., 1988) that is not an integrin. To characterize the endothelial cell receptor for laminin, we have used affinity chromatography procedures similar to those applied to other types of cells (Pytela et al., 1985a,b; Gehlsen et al., 1988), as well as antibody probes. Our results show that the endothelial cells bind laminln through an integrin composed of or2 and/~. Since the a2B, integrin in other types of cells binds only to collagens, this finding reveals cell type-specific functional heterogeneity of the ot2/3, integrin. © The Rockefeller University Press, 0021-9525/89/11/2455/8 $2.00 The Journal of Cell Biology, Volume 109, November 1989 2455-2462 2455 on F ebuary 1, 2013 jcb.rress. org D ow nladed fom Published November 1, 1989