1996 Volume 8 Issue 43 Pages 327-340
Vitronectin is a plasma protein which is also found in the extracellular matrix. The plasma form of vitronectin is synthesized by the liver and forms complexes with both thrombin-antithrombin and the C5b-7 complex of complement and may function as an opsonin mediating the clearance of thrombinserpin complexes from both the blood and the tissues. The functions of complexed forms of vitronectin and monomeric forms of vitronectin are distinct, in that they elicit different cellular responses perhaps by clustering unique sets of cell surface receptors. Vitronectin binds to several integrin receptors as well as to heparan sulfate proteoglycans. Under certain conditions vitronectin may be locally synthesized by tissues particularly by cells involved in migration. Vitronectin in the matrix can support cell adhesion and migration. Vitronectin expression is temporally and spatially regulated during development and is upregulated in several tumors. The αVβ3 and αVβ5 integrin receptors for vitronectin have been shown to function during angiogenesis and tumor invasion. In the extracellular matrix, vitronectin is the primary binding site for plasminogen activator inhibitor Type I and can regulate the activity and localization of urokinase-type plasminogen activator on the cell surface. The ability of vitronectin to regulate pericellular proteolysis suggests that in addition to providing a substrate for adhesion, vitronectin participates in the matrix remodeling which accompanies cell migration.
