title: Characterization of the binding of human tissue-type plasminogen activator to platelets.
abstract: Cell surface binding sites for the constituent proteins of the fibrinolytic system may play a role in the localization and regulation of fibrinolysis. In the present study, specific binding of recombinant human tissue-type plasminogen activator (rt-PA) to human blood platelets was identified and characterized. 125I-labeled rt-PA was found to bind specifically, saturably, and reversibly to the surface of gel-filtered platelets, reaching equilibrium within 5 min at 22 degrees C. Scatchard analysis revealed a single class of binding sites. Unstimulated platelets bound 120,000 +/- 24,000 (mean +/- S.D.) molecules/platelet with an apparent Kd of 340 +/- 25 nM, whereas thrombin-stimulated platelets bound 290,000 +/- 32,000 molecules/platelet with an apparent Kd of 800 +/- 60 nM. Binding of 0.1 microM 125I-rt-PA was greater than 90% reversible by a 50-fold excess of unlabeled rt-PA. Binding was not inhibited by fibrinogen or single chain urokinase-type plasminogen activator, but plasminogen partially competed for binding of 125I-rt-PA to platelets (up to 40% displacement). These findings indicate that the platelet surface possesses a large number of specific, low affinity binding sites for t-PA and provide further evidence for the role of platelets in localization and regulation of fibrinolysis.
authors.affiliation: Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
authors.forename: D E
authors.initials: DE
authors.lastname: Vaughan
authors.forename: M E
authors.initials: ME
authors.lastname: Mendelsohn
authors.forename: P J
authors.initials: PJ
authors.lastname: Declerck
authors.forename: E
authors.initials: E
authors.lastname: Van Houtte
authors.forename: D
authors.initials: D
authors.lastname: Collen
authors.forename: J
authors.initials: J
authors.lastname: Loscalzo
mesh_terms: D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005337:Fibrin / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010974:Platelet Aggregation; D011956:Receptors, Cell Surface / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins / Q000097:blood; D013917:Thrombin / Q000502:physiology; D010959:Tissue Plasminogen Activator / Q000097:blood*
chemical_list: C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins; D005337:Fibrin; D005340:Fibrinogen; D013917:Thrombin; D010959:Tissue Plasminogen Activator