Cellular Distribution and Heterogeneity of Endothelial Cell Adhesion Receptors
On the outer surface of the plasma membrane of endothelial cells, glycoprotein complexes are exposed that serve an important role in controlling the anchorage of endothelial cells to their extracellular matrix. These adhesion molecules mediate the attachment of endothelial cells by binding certain ligands, such as fibronectin, von Willebrand factor or vitronectin, which in turn are associated with the extracellular matrix. (For reviews, see: Hynes, 1987; Ginsberg et al., 1988; Phillips et al., 1988) One of these adhesion receptors or “integrins” (Hynes, 1987) is the vitronectin receptor. The vitronectin receptor is a heterodimeric molecule, consisting of an alpha- and a beta-chain held together by non-covalent bonds, which may serve as a receptor for several extracellular ligands. The vitronectin receptor not only functions as a receptor for vitronectin; it may also bind fibrinogen and von Willebrand factor (Charo et al., 1987; Cheresh, 1987). Both structurally and functionally, the vitronectin receptor is very similar to the platelet glycoprotein (GP) IIb/IIIa complex, an abundant membrane receptor on platelets. Also, the platelet GP IIb/IIIa complex is composed of two non-covalently linked subunits, which are significantly homologous to the subunits of the vitronectin receptor and can bind the same adhesive proteins. Indeed, a major advance in our understanding of the structure and function of the vitronectin receptor was the discovery that this membrane receptor is both immunologically and structurally very similar to platelet GP IIb/IIIa. Deduced amino acid sequences from GP-cDNAs revealed that the vitronectin receptor and GP IIb/IIIa share common beta-subunits and partially homologous alpha chains.
KeywordsAdhesion Receptor Platelet Glycoprotein Leukocyte Adhesion Deficiency Vitronectin Receptor Normal Endothelial Cell
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