Apoptosis induced by ectopic expression of cyclin D1 but not cyclin E

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Preparation of Cell-lines for Conditional Knockdown of Gene Expression and Measurement of the Knockdown Effects on E4orf4-Induced Cell Death
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Preparation of Cell-lines for Conditional Knockdown of Gene Expression and Measurement of the Knockdown Effects on E4orf4-Induced Cell Death

Published on: October 21, 2012

Y Sofer-Levi1, D Resnitzky

  • 1Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.

Oncogene
|December 5, 1996
PubMed

Insights

Deregulation of the pRb/E2F pathway can cause cell death. Specifically, cyclin D1 expression in starved cells induces apoptosis, possibly by phosphorylating pRb, highlighting a new role for G1 cell cycle regulators.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • The pRb/E2F pathway is crucial for cell cycle control at the G1/S transition and its deregulation is linked to cancer.
  • While typically associated with cell transformation, aberrant pRb/E2F pathway signaling can also induce apoptosis.
  • The role of G1 cyclin-dependent kinases (Cdks) in this apoptotic process remains less understood.

Purpose of the Study:

  • To investigate whether deregulation of G1 Cdks can drive apoptotic cell death.
  • To explore the specific roles of cyclin D1 and cyclin E in apoptosis induction.
  • To elucidate the mechanism by which G1 Cdk deregulation might lead to apoptosis, focusing on pRb phosphorylation.

Main Methods:

  • Utilized inducible rat fibroblast cell lines expressing cyclin E, cyclin D1, or both via a tetracycline-responsive promoter.
  • Maintained cells under serum starvation conditions to study G1/S transition and apoptosis.
  • Analyzed the phosphorylation status of the retinoblastoma protein (pRb) using Western blotting or similar techniques.

Main Results:

  • Ectopic expression of both cyclin D1 and cyclin E in serum-starved fibroblasts led to deregulated S-phase entry and subsequent apoptosis.
  • Expression of cyclin D1 alone was sufficient to induce apoptosis under serum starvation, whereas cyclin E alone was not.
  • Both cyclin D1 and co-expression of cyclins D1/E increased hyper-phosphorylated pRb levels, suggesting pRb inactivation, while cyclin E alone did not.

Conclusions:

  • Cyclin D1 expression, independent of cyclin E, can trigger apoptosis in serum-starved cells.
  • The induction of apoptosis by cyclin D1 may be mediated through the phosphorylation and inactivation of the retinoblastoma protein (pRb).
  • These findings suggest that G1 Cdk deregulation, particularly involving cyclin D1, plays a significant role in inducing programmed cell death.

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