title: Protumorigenic activity of plasminogen activator inhibitor-1 through an antiapoptotic function.
abstract: BACKGROUND
  Plasminogen activator inhibitor-1 (PAI-1) is a protease inhibitor but is paradoxically associated with poor outcomes in cancer patients. However, the mechanisms of its effects on tumor cells have not been explored.
  
  
  METHODS
  Endogenous PAI-1 in human tumor cell lines (HT-1080, A549, HCT-116, and MDA-MB-231) was suppressed by small interfering RNAs (siRNAs) and PAI-039, a small molecule inhibitor of PAI-1, and the effects on apoptosis were examined. Tumorigenicity of PAI-1 knockdown (KD) tumor cells was examined in immunodeficient PAI-1 wild-type and knockout (KO) mice (9-15 per group), and event-free survival was analyzed by the Kaplan-Meier method. The effect of PAI-1 suppression on HT-1080 xenotransplanted tumors was evaluated for cell proliferation, apoptosis, and angiogenesis. All statistical tests were two-sided.
  
  
  RESULTS
  Genetic and pharmacological inhibition of PAI-1 in the four tumor cell lines increased spontaneous apoptosis (mean fold increase relative to control: HT-1080, siRNA#1, mean = 4.0, 95% CI = 2.6 to 5.3, P < .001; siRNA#2, mean = 2.6, 95% CI = 2.4 to 2.9, P < .001, Student t test), which was blocked in the presence of recombinant PAI-1, a caspase-8 inhibitor, or Fas/FasL neutralizing antibodies and was partially attenuated by a plasmin inhibitor-aprotinin. PAI-1 KO mice implanted with PAI-1 KD HT-1080 cells had decreased tumorigenesis and prolonged survival compared with control mice (P = .002, log-rank test), and their tumors exhibited decreased cell proliferation and angiogenesis and increased apoptosis. Furthermore, five of 15 PAI-1 KO mice implanted with PAI-1 KD HT-1080 cells never developed tumors.
  
  
  CONCLUSIONS
  These data suggest that PAI-1 exerts a protective effect against tumor cell apoptosis by a mechanism that, in part, involves plasmin activation and inhibition of Fas/Fas-L-mediated apoptosis and may be a promising therapeutic target.
authors.affiliation: Division of Hematology-Oncology, Department of Pediatrics, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Fang
authors.forename: Veronica R
authors.initials: VR
authors.lastname: Placencio
authors.forename: Yves A
authors.initials: YA
authors.lastname: DeClerck
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D061945:Caspase Inhibitors / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018450:Disease Progression; D018572:Disease-Free Survival; D015536:Down-Regulation; D053222:Fas Ligand Protein / Q000276:immunology; D005260:Female; D005340:Fibrinogen / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007210:Indoleacetic Acids; D053208:Kaplan-Meier Estimate; D051379:Mice; D018345:Mice, Knockout; D009389:Neovascularization, Pathologic / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D010958:Plasminogen / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics* / Q000378:metabolism*; D034741:RNA, Small Interfering; D014183:Transplantation, Heterologous; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
chemical_list: D057134:Antibodies, Neutralizing; D061945:Caspase Inhibitors; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D007210:Indoleacetic Acids; D009842:Oligopeptides; D017395:Plasminogen Activator Inhibitor 1; D034741:RNA, Small Interfering; C403753:benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; C488103:tiplaxtinin; D005340:Fibrinogen; D010958:Plasminogen; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator