title: Binding of protease nexin-1 to the fibroblast surface alters its target proteinase specificity.
abstract: Protease nexin-1 is a protein proteinase inhibitor that is secreted by a variety of cultured cells and rapidly forms complexes with thrombin, urokinase, and plasmin; the complexes then bind back to the cells and are internalized and degraded. In fibroblast cultures, protease nexin-1 is localized to the extracellular matrix. Here we report that protease nexin-1, which is bound to the surface of fibroblasts, forms complexes with thrombin, but not urokinase or plasmin. Experiments were conducted to determine directly if protease nexin-1 binding to the fibroblast surface alters its proteinase specificity. To do this, cell surface protease nexin-1 was inhibited using anti-protease nexin-1 monoclonal antibodies that stoichiometrically block its ability to form complexes with target proteinases. Then, purified protease nexin-1 was added to these cells; the cell-bound molecule formed complexes with thrombin, but not urokinase or plasmin. Similar experiments showed that protease nexin-1 bound to preparations of fibroblast extracellular matrix also formed complexes with thrombin, but not urokinase or plasmin. Components of the extracellular matrix other than heparin-like glycosaminoglycans are required for this regulation since heparin did not block the formation of complexes between protease nexin-1 and urokinase or plasmin. These results suggest that protease nexin-1 is primarily a thrombin inhibitor in interstitial fluids where much of it would be bound to cell surfaces.
authors.affiliation: Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine 92717.
authors.forename: S L
authors.initials: SL
authors.lastname: Wagner
authors.forename: A L
authors.initials: AL
authors.lastname: Lau
authors.forename: D D
authors.initials: DD
authors.lastname: Cunningham
mesh_terms: D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000201:enzymology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism*; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D058258:Serpin E2; D012867:Skin / Q000201:enzymology; D013917:Thrombin / Q000378:metabolism
chemical_list: D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D011480:Protease Inhibitors; D058255:Protease Nexins; D011956:Receptors, Cell Surface; C545486:SERPINE2 protein, human; D058258:Serpin E2; D006493:Heparin; D010447:Peptide Hydrolases; D013917:Thrombin