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PPP1CA contributes to the senescence program induced by oncogenic Ras

Maria E Castro1, Irene Ferrer, Alberto Cascón

  • 1Experimental Therapeutics Programme, Spanish National Cancer Research Center (CNIO), 28029 Madrid, Spain.

Carcinogenesis
|January 22, 2008
PubMed

Insights

Oncogenic Ras and p53 induce senescence. Protein phosphatase 1-alpha (PPP1CA) loss bypasses this arrest by affecting ceramide levels and pRb dephosphorylation, suggesting a role in tumor suppression.

Area of Science:

  • Cellular senescence
  • Tumor suppressor pathways
  • Oncogene-induced signaling

Background:

  • Conditional murine p53 (p53val135) and oncogenic Ras induce a senescent-like growth arrest.
  • Identifying key regulators of Ras/p53-induced senescence is crucial for understanding tumor suppression.

Purpose of the Study:

  • To identify novel regulators involved in Ras/p53-induced senescence.
  • To elucidate the role of Protein Phosphatase 1-alpha catalytic subunit (PPP1CA) in this process.

Main Methods:

  • Retroviral-based genetic screening to identify genes involved in senescence bypass.
  • Short hairpin RNA (shRNA) mediated knockdown of PPP1CA.
  • Analysis of p53-dependent p21 induction and pRb dephosphorylation.
  • Ceramide level measurements and functional assays.
  • Analysis of PPP1CA gene status in human carcinomas.

Main Results:

  • Loss of PPP1CA function bypasses Ras/p53-induced growth arrest and senescence.
  • PPP1CA knockdown impairs p53-dependent p21 induction and pRb dephosphorylation.
  • Oncogenic Ras increases intracellular ceramide and PPP1CA protein levels.
  • Ceramide addition induces senescence, which is blocked by PPP1CA downregulation.
  • PPP1CA allele loss is observed in kidney and colorectal carcinomas; altered splice variants impact tumor growth.

Conclusions:

  • Oncogenic stress via Ras leads to ceramide accumulation, enhancing PPP1CA activity.
  • Increased PPP1CA activity promotes pRb dephosphorylation and initiates p53-induced arrest, contributing to tumor suppression.
  • PPP1CA is a critical mediator in the Ras/p53 senescence pathway and a potential tumor suppressor in carcinomas.

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