title: Plasminogen activator inhibitor-1 inhibits factor VIIa bound to tissue factor.
abstract: OBJECTIVE
  A growing body of experimental evidence supports broad inhibitory and regulatory activity of plasminogen activator inhibitor 1 (PAI-1). The present study was designed to investigate whether PAI-1 inhibits factor (F) VIIa complexed with tissue factor (TF), a well-known procoagulant risk factor.
  
  
  RESULTS
  The ability of PAI-1 to inhibit FVIIa-TF activity was evaluated in both clotting and factor X (FX) activation assays. PAI-1 and its complex with vitronectin inhibit: (i) clotting activity of FVIIa-TF (PAI-1(IC50) , 817 and 125 nm, respectively); (ii) FVIIa-TF-mediated FX activation (PAI-1(IC50) , 260 and 50 nm, respectively); and (iii) FVIIa bound to TF expressed on the surface of stimulated endothelial cells (PAI-1(IC50) , 260 and 120 nm, respectively). The association rate constant (k(a)) for PAI-1 inhibition of FVIIa-TF was determined using a chromogenic assay. K(a) for PAI-1 inhibition of FVIIa bound to relipidated TF is 3.3-fold higher than that for FVIIa bound to soluble TF (k(a) = 0.09 ± 0.01 and 0.027 ± 0.03 μm(-1) min(-1), respectively). Vitronectin increases k(a) for both soluble and relipidated TF by 3.5- and 30-fold, respectively (to 0.094 ± 0.020 and 2.7 ± 0.2 μm(-1) min(-1)). However, only a 3.5- to 5.0-fold increase in the acylated FVIIa was observed on SDS PAGE in the presence of vitronectin for both relipidated and soluble TF, indicating fast formation of PAI-1/vitronectin/FVIIa/relipidated TF non-covalent complex.
  
  
  CONCLUSIONS
  Our results demonstrate potential anticoagulant activity of PAI-1 in the presence of vitronectin, which could contribute to regulation of hemostasis under pathological conditions such as severe sepsis, acute lung injury and pleural injury, where PAI-1 and TF are overexpressed.
authors.affiliation: Center for Biomedical Research and The Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, TX 75708, USA.
authors.forename: P
authors.initials: P
authors.lastname: Sen
authors.forename: A A
authors.initials: AA
authors.lastname: Komissarov
authors.forename: G
authors.initials: G
authors.lastname: Florova
authors.forename: S
authors.initials: S
authors.lastname: Idell
authors.forename: U R
authors.initials: UR
authors.lastname: Pendurthi
authors.forename: L
authors.initials: L
authors.lastname: Vijaya Mohan Rao
mesh_terms: D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D015942:Factor VIIa / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006487:Hemostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D013925:Thromboplastin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019096:Vitronectin / Q000378:metabolism / Q000494:pharmacology
chemical_list: D046912:Multiprotein Complexes; D017395:Plasminogen Activator Inhibitor 1; D011994:Recombinant Proteins; C051321:SERPINE1 protein, human; D019096:Vitronectin; D013925:Thromboplastin; C103587:recombinant FVIIa; D015942:Factor VIIa