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Transforming growth factor-beta requires its target plasminogen activator inhibitor-1 for cytostatic activity

Roderik M Kortlever1, Jeroen H Nijwening, René Bernards

  • 1Division of Molecular Carcinogenesis, Center for Cancer Genomics and Center for Biomedical Genetics, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.

The Journal of Biological Chemistry
|July 11, 2008
PubMed

Insights

Transforming growth factor beta (TGFbeta) uses plasminogen activator inhibitor-1 (PAI-1) to stop cell growth. Suppressing PAI-1 allows cells to resist TGFbeta

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Oncogenesis

Background:

  • Transforming growth factor beta (TGFbeta) exhibits potent antiproliferative effects in normal cells.
  • TGFbeta's role in later-stage oncogenesis is complex, involving tumor progression.
  • The specific TGFbeta target genes mediating its cytostatic activity remain incompletely understood.

Purpose of the Study:

  • To investigate the role of plasminogen activator inhibitor-1 (PAI-1) in mediating TGFbeta's cytostatic effects.
  • To elucidate the molecular mechanisms by which PAI-1 influences TGFbeta-induced growth arrest.
  • To determine if PAI-1 acts independently of canonical TGFbeta signaling pathways.

Main Methods:

  • RNA interference (RNAi) was used to suppress PAI-1 expression in human keratinocytes (HaCaTs) and mouse embryo fibroblasts (MEFs).
  • PAI-1 knockout MEFs were utilized to assess TGFbeta response in the absence of PAI-1.
  • Ectopic expression of PAI-1 was performed in HaCaT cells to evaluate its growth-arresting potential.
  • SMAD phosphorylation and the induction of known TGFbeta target genes were analyzed to assess canonical signaling.
  • Protein kinase B (Akt) activation was monitored following PAI-1 knockdown.

Main Results:

  • Suppression of PAI-1 via RNAi conferred resistance to TGFbeta-induced cytostasis in HaCaTs and MEFs.
  • PAI-1 knockout MEFs demonstrated resistance to TGFbeta-mediated growth arrest.
  • Ectopic PAI-1 expression in HaCaTs induced a significant growth arrest.
  • PAI-1 knockdown did not disrupt canonical TGFbeta signaling, evidenced by SMAD phosphorylation and target gene induction.
  • Knockdown of PAI-1 led to sustained activation of protein kinase B (Akt).
  • Constitutive Akt activity was found to enable evasion of TGFbeta's growth-inhibitory effects.

Conclusions:

  • TGFbeta induction of PAI-1 is critical for mediating TGFbeta's antiproliferative action.
  • PAI-1 functions in a pathway that is essential for TGFbeta-induced proliferation arrest.
  • Sustained protein kinase B (Akt) activation, downstream of PAI-1, contributes to resistance against TGFbeta growth inhibition.

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