title: Plasminogen activator inhibitors regulate cell adhesion through a uPAR-dependent mechanism.
abstract: Binding of type-1 plasminogen activator inhibitor (PAI-1) to cell surface urokinase (uPA) promotes inactivation and internalization of adhesion receptors (e.g., urokinase receptor (uPAR), integrins) and leads to cell detachment from a variety of extracellular matrices. In this report, we begin to examine the mechanism of this process. We show that neither specific antibodies to uPA, nor active site inhibitors of uPA, can detach the cells. Thus, cell detachment is not simply the result of the binding of macromolecules to uPA and/or of the inactivation of uPA. We further demonstrate that another uPA inhibitor, protease nexin-1 (PN-1), also stimulates cell detachment in a uPA/uPAR-dependent manner. The binding of both inhibitors to uPA leads to the specific inactivation of the matrix-engaged integrins and the subsequent detachment of these integrins from the underlying extracellular matrix (ECM). This inhibitor-mediated inactivation of integrins requires direct interaction between uPAR and those integrins since cells attached to the ECM through integrins incapable of binding uPAR do not respond to the presence of either PAI-1 of PN-1. Although both inhibitors initiate the clearance of uPAR, only PAI-1 triggers the internalization of integrins. However, cell detachment by PAI-1 or PN-1 does not depend on the endocytosis of these integrins since cell detachment was also observed when clearance of these integrins was blocked. Thus, PAI-1 and PN-1 induce cell detachment through two slightly different mechanisms that affect integrin metabolism. These differences may be important for distinct cellular processes that require controlled changes in the subcellular localization of these receptors.
authors.affiliation: Albany Medical College, Center for Cell Biology & Cancer Research, 47 New Scotland Avenue, Albany, NY 12208, USA. czekayr@mail.amc.edu
authors.forename: Ralf-Peter
authors.initials: RP
authors.lastname: Czekay
authors.forename: David J
authors.initials: DJ
authors.lastname: Loskutoff
mesh_terms: D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D000911:Antibodies, Monoclonal; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D004705:Endocytosis; D005109:Extracellular Matrix / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D039422:Integrin alpha3 / Q000378:metabolism; D051379:Mice; D009154:Mutation; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism*; D058255:Protease Nexins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D058258:Serpin E2; D014162:Transfection; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*; D019096:Vitronectin / Q000378:metabolism
chemical_list: D016564:Amyloid beta-Protein Precursor; D000911:Antibodies, Monoclonal; D005353:Fibronectins; D039422:Integrin alpha3; D017395:Plasminogen Activator Inhibitor 1; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins; C545486:SERPINE2 protein, human; D058258:Serpin E2; D019096:Vitronectin; D014568:Urokinase-Type Plasminogen Activator