title: The C-terminus of tissue factor pathway inhibitor-α inhibits factor V activation by protecting the Arg1545cleavage site.
abstract: Essentials The C-terminus of tissue factor pathway inhibitor (TFPIα) binds to the B-domain of factor V (FV). The functional consequences of this interaction were investigated in plasma and model systems. The TFPIα C-terminus inhibited thrombin generation in plasma, but not in the presence of FVa. The TFPIα C-terminus inhibited FV activation by preventing cleavage at Arg1545.
  
  
  
  Background Factor V (FV) is a carrier and a cofactor of the anticoagulant protein tissue factor pathway inhibitor-α (TFPIα), whose basic C-terminus binds to an acidic region in the B-domain of FV. Proteolysis of FV at Arg709, Arg1018and Arg1545by activated FX (FXa) or thrombin removes the B-domain, and converts FV into a procoagulant cofactor (activated FV [FVa]) of FXa in the prothrombinase complex. However, retention of the acidic region in partially activated FV makes prothrombinase activity susceptible to inhibition by TFPIα. Objective/Methods To investigate the effect of the TFPIα C-terminal peptide (TFPIα C-term) on thrombin generation in plasma and on FV activation in model systems. Results TFPIα C-term inhibited tissue factor-initiated and FXa-initiated thrombin generation in a dose-dependent manner. Failure to inhibit thrombin generation in FV-depleted plasma reconstituted with FVa indicated that the peptide effect was mediated by the acidic region of FV, and was localized at the level of FV activation and/or prothrombinase. In model systems, TFPIα C-term inhibited both FV activation and prothrombinase activity. Western blot analysis showed that the peptide impaired cleavage at Arg1545by both thrombin and FXa. The inhibition was stronger for FV-short, which binds TFPIα with higher affinity. Similar results were obtained with full-length TFPIα. Conclusions Cleavage of FV at Arg1545, which abolishes the anticoagulant properties of FV and commits FV to the procoagulant pathway, is inhibited by binding of the TFPIα C-terminus to the FV acidic region. Possible targets of this new anticoagulant function of TFPIα are low-abundance FV(a) species retaining the acidic region.
authors: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, the Netherlands.
authors: P
authors: P
authors: van Doorn
authors: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, the Netherlands.
authors: J
authors: J
authors: Rosing
authors: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, the Netherlands.
authors: S J
authors: SJ
authors: Wielders
authors: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, the Netherlands.
authors: T M
authors: TM
authors: Hackeng
authors: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, the Netherlands.
authors: E
authors: E
authors: Castoldi
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000737:chemistry; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D005165:Factor V / Q000737:chemistry*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008074:Lipoproteins / Q000737:chemistry*; D008297:Male; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D000072417:Protein Domains; D013917:Thrombin / Q000737:chemistry
chemical_list: D000925:Anticoagulants; D008074:Lipoproteins; D010455:Peptides; C051928:lipoprotein-associated coagulation inhibitor; D005165:Factor V; D001120:Arginine; D013917:Thrombin
keywords: factor V; factor Xa; prothrombinase complex; thrombin; tissue factor pathway inhibitor