Binding of plasminogen activator inhibitor type-1 to extracellular matrix of Hep G2 cells. Evidence that the binding protein is vitronectin.
Catabolism of plasminogen activators by Hep G2 cells is mediated by a specific receptor which recognizes complexes of these serine proteases with their physiological inhibitor, plasminogen activator inhibitor type-1 (PAI-1). This catabolic process is initiated by interaction of exogenous plasminogen activators with bioactive PAI-1, which is secreted and localizes in an active form to the extracellular matrix (ECM) of Hep G2 cells. We now report that vitronectin (VN) mediates the specific binding of PAI-1 to the ECM of these cells. Purified bovine or human VN competes for specific binding of PAI-1 to Hep G2 ECM, and ligand blotting reveals specific binding of PAI-1 to ECM-associated VN. Hep G2 cells secrete both VN and PAI-1, and pulse-chase studies strongly suggest that these proteins associate only following secretion. Although Hep G2 cell-derived VN does not significantly bind to ECM in vitro, 30-40% of endogenous PAI-1 binds to the ECM, even in the presence of human serum, suggesting that ECM-associated VN is entirely derived from bovine serum. PAI-1 was localized by indirect immunofluorescence to ECM beneath cells and at cell margins, whereas VN exhibited a uniform distribution throughout the growth substratum. VN associated with the ECM may confer retention and bioactivity to PAI-1, potentially facilitating both pericellular regulation of plasmin generation and the rapid hepatic clearance of plasminogen activators.
Owensby
D A
DA
Department of Medicine, St. Louis Children's Hospital, Washington University School of Medicine, St. Louis, Missouri 63110.
Morton
P A
PA
Wun
T C
TC
Schwartz
A L
AL
D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008113:Liver Neoplasms / Q000378:metabolism; D015849:Plasminogen Inactivators / Q000378:metabolism*; D013696:Temperature; D014407:Tumor Cells, Cultured; D019096:Vitronectin
D006023:Glycoproteins; D015849:Plasminogen Inactivators; D019096:Vitronectin