Protumorigenic activity of plasminogen activator inhibitor-1 through an antiapoptotic function

J Natl Cancer Inst. 2012 Oct 3;104(19):1470-84. doi: 10.1093/jnci/djs377. Epub 2012 Sep 13.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Neutralizing / pharmacology
  • Apoptosis* / drug effects
  • Blotting, Western
  • Caspase Inhibitors / pharmacology
  • Cell Line, Tumor
  • Cell Proliferation* / drug effects
  • Disease Progression
  • Disease-Free Survival
  • Down-Regulation
  • Fas Ligand Protein / immunology
  • Female
  • Fibrinogen / metabolism
  • Fibrinolysin / metabolism
  • Flow Cytometry
  • Gene Knockdown Techniques
  • Humans
  • Immunohistochemistry
  • In Situ Nick-End Labeling
  • Indoleacetic Acids
  • Kaplan-Meier Estimate
  • Mice
  • Mice, Knockout
  • Neovascularization, Pathologic* / metabolism
  • Oligopeptides / pharmacology
  • Plasminogen / metabolism
  • Plasminogen Activator Inhibitor 1 / genetics*
  • Plasminogen Activator Inhibitor 1 / metabolism*
  • RNA, Small Interfering
  • Transplantation, Heterologous
  • Urokinase-Type Plasminogen Activator / metabolism

Substances

  • Antibodies, Neutralizing
  • Caspase Inhibitors
  • Fas Ligand Protein
  • Fasl protein, mouse
  • Indoleacetic Acids
  • Oligopeptides
  • Plasminogen Activator Inhibitor 1
  • RNA, Small Interfering
  • benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone
  • tiplaxtinin
  • Fibrinogen
  • Plasminogen
  • Fibrinolysin
  • Urokinase-Type Plasminogen Activator