title: Type 1 plasminogen activator inhibitor binds to fibrin via vitronectin.
abstract: Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), circulates as a complex with the abundant plasma glycoprotein, vitronectin. This interaction stabilizes the inhibitor in its active conformation In this report, the effects of vitronectin on the interactions of PAI-1 with fibrin clots were studied. Confocal microscopic imaging of platelet-poor plasma clots reveals that essentially all fibrin-associated PAI-1 colocalizes with fibrin-bound vitronectin. Moreover, formation of platelet-poor plasma clots in the presence of polyclonal antibodies specific for vitronectin attenuated the inhibitory effects of PAI-1 on t-PA-mediated fibrinolysis. Addition of vitronectin during clot formation markedly potentiates PAI-1-mediated inhibition of lysis of (125)I-labeled fibrin clots by t-PA. This effect is dependent on direct binding interactions of vitronectin with fibrin. There is no significant effect of fibrin-associated vitronectin on fibrinolysis in the absence of PAI-1. The binding of PAI-1 to fibrin clots formed in the absence of vitronectin was characterized by a low affinity (K(d) approximately 3.5 micrometer) and rapid loss of PAI-1 inhibitory activity over time. In contrast, a high affinity and stabilization of PAI-1 activity characterized the cooperative binding of PAI-1 to fibrin formed in the presence of vitronectin. These findings indicate that plasma PAI-1.vitronectin complexes can be localized to the surface of fibrin clots; by this localization, they may modulate fibrinolysis and clot reorganization.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University and the Hamilton Civic Hospitals Research Centre, Hamilton, Ontario L8V 1C3, Canada. podort@fhs.csu.mcmaster.ca
authors.forename: T J
authors.initials: TJ
authors.lastname: Podor
authors.forename: C B
authors.initials: CB
authors.lastname: Peterson
authors.forename: D A
authors.initials: DA
authors.lastname: Lawrence
authors.forename: S
authors.initials: S
authors.lastname: Stefansson
authors.forename: S G
authors.initials: SG
authors.lastname: Shaughnessy
authors.forename: D M
authors.initials: DM
authors.lastname: Foulon
authors.forename: M
authors.initials: M
authors.lastname: Butcher
authors.forename: J I
authors.initials: JI
authors.lastname: Weitz
mesh_terms: D001777:Blood Coagulation / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D010949:Plasma / Q000187:drug effects / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D011485:Protein Binding; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000378:metabolism; D019096:Vitronectin / Q000378:metabolism* / Q000502:physiology*
chemical_list: D017395:Plasminogen Activator Inhibitor 1; D019096:Vitronectin; D005337:Fibrin; D005340:Fibrinogen; D010959:Tissue Plasminogen Activator