The interaction of plasminogen activator inhibitor 1 with plasminogen activators (tissue-type and urokinase-type) and fibrin: localization of interaction sites and physiologic relevance.
Plasminogen activator inhibitor 1 (PAI-1), an essential regulatory protein of the fibrinolytic system, harbors interaction sites for plasminogen activators (tissue-type [t-PA] and urokinase-type [u-PA]) and for fibrin. In this study, anti-PAI-1 monoclonal antibodies (MoAbs) were used to identify interaction sites of PAI-1 with these components. The binding sites of 18 different MoAbs were established and are located on five distinct "linear" areas of PAI-1. MoAbs, binding to two distinct areas of PAI-1, are able to prevent the inhibition of t-PA by PAI-1. In addition, two interaction sites for fibrin were identified on PAI-1. The area located between amino acids 110 and 145 of PAI-1 contains a binding site for both components and its significance is discussed in the context of the t-PA inhibition by fibrin-bound PAI-1. Subsequently, the MoAbs were used to assess the role of platelet-PAI-1 in clot-lysis. An in vitro clot-lysis system was used to demonstrate that clot-lysis resistance is dependent on the presence of activated platelets and that PAI-1 is a major determinant for lysis-resistance. We propose that, upon activation of platelets, PAI-1 is fixed within the clot by binding to fibrin and retains its full capacity to inhibit t-PA and u-PA.
Keijer
J
J
Department of Molecular Biology, Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam.
Linders
M
M
van Zonneveld
A J
AJ
Ehrlich
H J
HJ
de Boer
J P
JP
Pannekoek
H
H
D000911:Antibodies, Monoclonal; D001665:Binding Sites; D002872:Chromosome Deletion; D004792:Enzyme Precursors / Q000378:metabolism / Q000502:physiology; D000939:Epitopes / Q000032:analysis; D005337:Fibrin / Q000378:metabolism; D005342:Fibrinolysis; D006801:Humans; D010960:Plasminogen Activators / Q000378:metabolism* / Q000502:physiology; D015849:Plasminogen Inactivators / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000378:metabolism* / Q000502:physiology; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism* / Q000502:physiology
D000911:Antibodies, Monoclonal; D004792:Enzyme Precursors; D000939:Epitopes; D015849:Plasminogen Inactivators; D005337:Fibrin; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator