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Blockade of TGFbeta3 up-regulation of p27Kip1 and p21Cip1 by expression of RasN17 in epithelial cells

J Yue1, A Buard, K M Mulder

  • 1Department of Pharmacology, Pennsylvania State University College of Medicine, Hershey 17033, USA.

Oncogene
|July 22, 1998
PubMed

Insights

Ras activation is essential for TGFbeta3 to increase CKI levels, which then inhibit Cdk2 activity in intestinal epithelial cells. This study clarifies the role of Ras in TGFbeta3 signaling pathways.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Ras activation is crucial for transforming growth factor beta (TGFbeta)-mediated Erk1 activation.
  • Ras is partially required for TGFbeta's inhibition of Cdk2 activity, cyclin A expression, and DNA synthesis.

Purpose of the Study:

  • To investigate the kinetics and role of Ras in TGFbeta3-mediated effects on G1 cell cycle components.
  • To analyze these effects in TGFbeta-sensitive (4-1) and TGFbeta-resistant (4-6) intestinal epithelial cells (IECs).

Main Methods:

  • Stable, inducible expression of a dominant-negative Ras mutant (RasN17) to inactivate Ras.
  • Treatment with ZnCl2 in control cells.
  • Analysis of CKI (p27Kip1, p21Cip1) levels, protein synthesis, and association with Cdk2.

Main Results:

  • Ras inactivation abrogated TGFbeta3-induced up-regulation of CKIs.
  • TGFbeta3-induced up-regulation of p27Kip1 and p21Cip1 was maintained in control cells.
  • Ras inactivation blocked TGFbeta-mediated increases in p27Kip1 synthesis.
  • Up-regulation of p21Cip1 and p27Kip1 preceded Cdk2 activity inhibition by TGFbeta.

Conclusions:

  • p21Cip1 and p27Kip1 are upstream effectors of TGFbeta-mediated Cdk2 inhibition in IEC 4-1 cells.
  • Ras activation is obligatory for TGFbeta-mediated up-regulation of CKIs in untransformed epithelial cells.

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