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Oncogenic Ras-mediated cell growth arrest and apoptosis are associated with increased ubiquitin-dependent cyclin D1

J Shao1, H Sheng, R N DuBois

  • 1Department of Medicine, The Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.

The Journal of Biological Chemistry
|April 27, 2000
PubMed

Insights

Activated Ras triggers distinct cellular responses. In Rat-1 fibroblasts, Ras-induced cyclin D1 degradation leads to growth arrest and apoptosis, unlike in intestinal cells where it promotes proliferation.

Area of Science:

  • Cell Biology
  • Oncology
  • Molecular Biology

Background:

  • Cellular responses to activated Ras proteins, such as Ha-Ras, are context-dependent.
  • Normal cells typically undergo growth arrest, senescence, or apoptosis to prevent tumor formation.
  • Ras signaling pathways play critical roles in cell proliferation and survival.

Purpose of the Study:

  • To investigate the differential cellular responses to activated Ha-Ras(Val-12) in Rat-1 fibroblasts versus a rat intestinal epithelial cell line.
  • To elucidate the role of cyclin D1 regulation in Ras-mediated cellular outcomes.
  • To identify signaling pathways involved in Ras-induced cyclin D1 modulation.

Main Methods:

  • Induction of Ha-Ras(Val-12) in Rat-1 fibroblasts and a rat intestinal epithelial cell line.
  • Analysis of cell cycle progression (G1 arrest), apoptosis, and cell viability.
  • Measurement of cyclin D1 levels and assessment of its degradation via the ubiquitin-proteasome pathway.
  • Expression of a cyclin D1 mutant (T286A) resistant to degradation.
  • Inhibition of mitogen-activated protein kinase (MEK1/2) and analysis of Akt and glycogen-synthase-3beta kinase activity.

Main Results:

  • Ha-Ras(Val-12) induction in Rat-1 cells caused G1 growth arrest and apoptosis, associated with decreased cyclin D1 levels due to enhanced degradation.
  • In contrast, Ha-Ras(Val-12) in rat intestinal cells led to transformation, sustained proliferation, and increased cyclin D1 levels without apoptosis.
  • Expression of a degradation-resistant cyclin D1 mutant in Ras-expressing Rat-1 cells promoted a transformed phenotype and bypassed G1 arrest.
  • MEK1/2 pathway inhibition partially rescued Ras-mediated cyclin D1 reduction.
  • Ras activation led to Akt activation and GSK3beta inactivation, correlating with reduced cyclin D1 protein.

Conclusions:

  • Ras-mediated cyclin D1 degradation in Rat-1 fibroblasts is a key mechanism for inducing anti-tumorigenic responses like growth arrest and apoptosis.
  • The differential regulation of cyclin D1 stability contributes to the contrasting cellular outcomes (arrest vs. transformation) observed in different cell types upon Ras activation.
  • The Ras-mediated decrease in cyclin D1 in Rat-1 cells is partially dependent on MEK1/2 pathway activation but independent of GSK3beta pathway signaling.

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