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p21(Cip1) protects against oxidative stress by suppressing ER-dependent activation of mitochondrial death pathways

Peter F Vitiello1, Yu-Chieh M Wu, Rhonda J Staversky

  • 1Department of Environmental Medicine, The University of Rochester, NY 14642, USA.

Free Radical Biology & Medicine
|October 25, 2008
PubMed

Insights

The cell cycle inhibitor p21 protects cells from DNA damage and oxidative stress. Cytoplasmic p21 delays the loss of antiapoptotic proteins by coordinating endoplasmic reticulum and mitochondrial pathways.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Stress Response

Background:

  • The cell cycle inhibitor p21 is known to protect against genotoxic stress by inhibiting DNA replication.
  • Recent findings indicate that cytoplasmic p21 also confers cytoprotection by delaying the degradation of antiapoptotic proteins like Mcl-1 and Bcl-X(L).
  • The precise mechanism regulating this cytoplasmic function remains unclear.

Purpose of the Study:

  • To investigate the role and mechanism of cytoplasmic p21 in cytoprotection under chronic oxidative stress.
  • To determine if p21 coordinates endoplasmic reticulum (ER) and mitochondrial stress pathways.

Main Methods:

  • Utilized hyperoxia as a model for chronic oxidative stress and DNA damage.
  • Detected p21 localization in both nucleus and cytoplasm.
  • Fractionated cellular components to identify subcellular localization of p21, including enrichment in mitochondria and ER fractions.
  • Assessed the impact of p21 on ER stress markers (BiP) and apoptotic protein levels (Mcl-1, Bcl-X(L)).

Main Results:

  • Cytoplasmic expression of p21 was sufficient for cytoprotection during hyperoxia.
  • p21 was found to be enriched in subcellular fractions containing mitochondria and ER.
  • p21 suppressed hyperoxia-induced downregulation of BiP and subsequent ER stress signaling.
  • p21 affected Mcl-1 levels but not Bcl-X(L) levels, with both proteins inhibiting hyperoxic cell death.

Conclusions:

  • p21 integrates the DNA damage response with ER stress signaling pathways.
  • This integration by p21 regulates mitochondrial death pathways during chronic genotoxic stress.
  • Cytoplasmic p21 plays a crucial role in cellular defense against combined DNA damage and ER stress.

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