Plasminogen activator inhibitor-1 binds to fibrin and inhibits tissue-type plasminogen activator-mediated fibrin dissolution.
Plasminogen activator inhibitor-1 (PAI-1) accumulates within thrombi and forming whole blood clots. To explore this phenomenon at the molecular level, PAI-1 binding to fibrin was examined. The experiments were performed by adding 125I-PAI-1, which retains its complete tissue-type plasminogen (t-PA) inhibitory activity, to fibrin matrices formed in 2-cm2 tissue culture wells. Guanidine HCl-activated PAI-1 binding was reversible and was inhibited in the presence of excess, unlabeled PAI-1. Activated 125I-PAI-1 recognized 2 sites on fibrin: a very small number of high affinity sites (Kd less than 1 nM) and principally a large number of low affinity sites with an approximate Kd of 3.8 microM. Latent PAI-1 bound to fibrin at a site indistinguishable from the lower affinity site recognized by activated PAI-1. Fibrin, pretreated with activated PAI-1, was protected from t-PA-mediated plasmin degradation in a PAI-1 dose-responsive manner (IC50 = 12.3 nM). Clot protection correlated with partial occupancy of the low affinity PAI-1 binding site on fibrin and was due to the formation of sodium dodecyl sulfate-stable, PAI-1.t-PA complexes. Latent PAI-1 (27 nM) did not protect the fibrin from dissolution. The localization of PAI-1 to a thrombus by virtue of its fibrin binding potential could result in significant protection of the thrombus from the degradative effects of the fibrinolytic system.
Reilly
C F
CF
Department of Pharmacology, Merck Research Laboratories, West Point, Pennsylvania 19486.
Hutzelmann
J E
JE
D001667:Binding, Competitive; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000302:isolation & purification / Q000378:metabolism*; D005342:Fibrinolysis / Q000187:drug effects*; D005354:Fibrosarcoma; D006801:Humans; D007700:Kinetics; D008027:Light; D008970:Molecular Weight; D015849:Plasminogen Inactivators / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology*; D011485:Protein Binding; D012542:Scattering, Radiation; D010959:Tissue Plasminogen Activator / Q000037:antagonists & inhibitors*
D015849:Plasminogen Inactivators; D003907:Dexamethasone; D005337:Fibrin; D005340:Fibrinogen; D010959:Tissue Plasminogen Activator