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Negative regulation of SCFSkp2 ubiquitin ligase by TGF-beta signaling

Wei Wang1, Dana Ungermannova, Jianpin Jin

  • 1Department of Chemistry and Biochemistry, University of Colorado-Boulder, Boulder, CO 80309, USA.

Oncogene
|December 17, 2003
PubMed

Insights

Transforming growth factor-beta (TGF-beta) stabilizes the cell cycle inhibitor p27Kip1 by downregulating SCFSkp2 ubiquitin ligase activity. This mechanism contributes to TGF-beta-induced cell growth inhibition and tumor suppression.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Transforming growth factor-beta (TGF-beta) is a critical regulator of cell growth and a known tumor suppressor.
  • TGF-beta induces cell cycle arrest at the G1 to S phase transition.
  • TGF-beta inhibits cyclin-dependent kinase 2 (Cdk2)-cyclin E activity by enhancing the binding of p27Kip1 to Cdk2-cyclin E complexes.

Purpose of the Study:

  • To elucidate the molecular mechanisms by which TGF-beta stabilizes the cell cycle inhibitor p27Kip1.
  • To investigate the regulation of the SCFSkp2 ubiquitin ligase complex by TGF-beta.
  • To understand how TGF-beta controls p27Kip1 degradation during the G1 to S phase transition.

Main Methods:

  • Pulse-chase analysis to assess protein stability.
  • In vitro degradation assays using cell extracts from TGF-beta-treated cells.
  • Quantitative analysis of Cks1 mRNA levels.

Main Results:

  • TGF-beta treatment leads to the stabilization of p27Kip1 during the G1 to S phase transition.
  • TGF-beta treatment decreases the stability of Skp2, a key component of the SCFSkp2 complex, through ubiquitin-mediated proteolysis.
  • TGF-beta treatment reduces Cks1 mRNA levels, impacting SCFSkp2 ligase activity.
  • Deficiency in Cks1 results in p27Kip1 stabilization and Skp2 destabilization due to impaired ubiquitination of p27Kip1 and increased self-ubiquitination of Skp2.

Conclusions:

  • TGF-beta inhibits p27Kip1 degradation via both transcriptional and post-transcriptional regulation of the SCFSkp2 ubiquitin ligase.
  • Stabilization of p27Kip1 and subsequent cell growth inhibition by TGF-beta are mediated, in part, by limiting SCFSkp2 ligase activity.
  • These findings reveal a novel regulatory pathway for cell cycle control involving TGF-beta and the SCFSkp2 complex.

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