LIMITED PLASMIN PROTEOLYSIS OF VITRONECTIN - CHARACTERIZATION OF THE ADHESION PROTEIN AS MORPHO-REGULATORY AND ANGIOSTATIN-BINDING FACTOR

The adhesion protein vitronectin is associated with extracellular matr ices and serves as cofactor for plasminogen-activator inhibitor-1. Lim ited proteolysis by plasmin converts vitronectin into defined fragment s which are detectable al sites of inflammation and angiogenesis. The loss and gain of binding functions of vitronectin fragments for macrom olecular ligands was characterized in the present study. The initially generated 61-63-kDa vitronectin-(1-348)-fragment serves as typical bi nding component for plasminogen and binding function was lost upon car boxypeptidase B treatment indicating the importance of a C-terminal ly sine. Complementary binding sites reside in isolated plasminogen kingl es 1-3(designated angiostatin) as deduced from direct binding and liga nd blotting experiments. A synthetic vitronectin-(331-348)-peptide fro m the C-terminus of the 61-63-kDa fragment could mimic plasminogen and angiostatin binding. Also, the immobilized peptide bound tissue plasm inogen-activator and mediated plasmin formation, comparable to fibrino gen-derived peptides. The 61-63-kDa vitronectin fragment was indisting uishable in its adhesive properties to intact vitronectin and bound ac tive but not latent plasminogen-activator inhibitor-1. Late plasminoly sis of vitronectin resulted in the processing of the N-terminal region of the protein with the generation of 42 kDa/35-kDa fragments that ha d GlyS9 as new N-terminus and that were ineffective in promoting cell adhesion. Thus, at sites of cell-matrix interactions which become prot eolytically modified by plasmin during inflammatory and angiogenic pro cesses, vitronectin serves as plasminogen/angiostatin-binding factor. Due to this differential change in functions particularly at sites of deposition in the vascular system or at wound sites vitronectin is con sidered to be an important morpho-regulatory factor.