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ERK1/2 and p38 cooperate to delay progression through G1 by promoting cyclin D1 protein turnover

Ruth M Densham1, Daniel E Todd, Kathy Balmanno

  • 1Laboratory of Molecular Signalling, The Babraham Institute, Babraham Research Campus, Cambridge, CB22 3AT, England, UK.

Cellular Signalling
|July 31, 2008
PubMed

Insights

The DeltaMEKK3:ER kinase activates cell cycle arrest pathways. It causes rapid cyclin D1 destruction and slower p21(CIP1) expression, halting cell cycle progression.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The conditional kinase DeltaMEKK3:ER activates JNK, p38, and ERK1/2 pathways without inducing cellular stress.
  • These pathways are crucial for regulating apoptosis and cell cycle progression.
  • Previous studies showed DeltaMEKK3:ER activation leads to a p21(CIP1)-dependent G1 cell cycle arrest.

Purpose of the Study:

  • To investigate the mechanism behind the transient cell cycle re-entry delay observed in p21(CIP1)-deficient cells upon DeltaMEKK3:ER activation.
  • To elucidate the role of cyclin D1 in DeltaMEKK3:ER-induced cell cycle regulation.
  • To determine the signaling pathways involved in DeltaMEKK3:ER-mediated cyclin D1 phosphorylation and degradation.

Main Methods:

  • Utilized a conditional DeltaMEKK3:ER kinase system in cell culture.
  • Assessed cell cycle progression using flow cytometry.
  • Investigated protein levels and degradation pathways (proteasome-dependent turnover).
  • Examined protein-protein interactions (ERK1/2 and cyclin D1 association).
  • Analyzed the role of specific phosphorylation sites (T286) and mutations (cyclin D1T286A).

Main Results:

  • DeltaMEKK3:ER activation causes a delay in cell cycle re-entry in cells lacking p21(CIP1) due to reduced cyclin D1 levels.
  • Cyclin D1 undergoes proteasome-dependent degradation, requiring phosphorylation at Threonine 286 (T286).
  • Expression of a non-phosphorylatable cyclin D1 mutant (cyclin D1T286A) rescued the G1/S progression delay.
  • DeltaMEKK3:ER-induced T286 phosphorylation is independent of GSK3beta but requires activation of both ERK1/2 and p38 pathways.
  • Coincident activation of ERK1/2 and p38 pathways is necessary for cyclin D1 phosphorylation.

Conclusions:

  • DeltaMEKK3:ER induces a sustained G1 cell cycle arrest through a dual mechanism.
  • This mechanism involves rapid degradation of cyclin D1 and sustained expression of p21(CIP1).
  • This bipartite response mirrors pathways observed in response to ionizing radiation and p53-independent cell cycle arrest in yeast.

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