Endothelial cells use α2β1 integrin as a laminin receptor

Abstract

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 surface-iodinated endothelial cells on human laminin-Sepharose yielded a heterodimeric complex, the subunits of which migrated with molecular sizes corresponding to 160/120 kD and 160/140 kD under non-reducing 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 α2β1 integrin because monoclonal and polyclonal antibodies directed against the α2 and β1 subunits immunoprecipitated the receptor. Cytofluorometric analysis and immunoprecipitation showed that the α2 subunit is an abundant integrin α subunit in the endothelial cells and that the α subunits associated with laminin binding in other types of cells are expressed in these cells only at low levels. The α2β1 integrin appears to be a major receptor for laminin in the endothelial cells, because an anti-α2 monoclonal antibody inhibited the attachment of the endothelial cells to human laminin. These results define a new role for the α2 subunit in laminin binding and suggest that the ligand specificity of the α2β1 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.