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HSP72 depletion suppresses gammaH2AX activation by genotoxic stresses via p53/p21 signaling

V L Gabai1, M Y Sherman, J A Yaglom

  • 1Department of Biochemistry, Boston University School of Medicine, Boston, MA, USA. gabai@bu.edu

Oncogene
|January 12, 2010
PubMed

Insights

Heat shock protein Hsp72 downregulation impairs DNA repair pathways in human tumor cells, increasing sensitivity to genotoxic stress and radiation. This occurs via the p53/p21 pathway, leading to senescence.

Area of Science:

  • Cellular Biology
  • Molecular Oncology
  • DNA Damage Response

Background:

  • Heat shock protein 72 (Hsp72) plays a role in cellular stress response.
  • Previous studies linked Hsp72 knockout to chromosomal instability and radiation sensitivity in mouse cells.
  • The precise function of Hsp72 in the DNA damage response (DDR) of human tumor cells remains unclear.

Purpose of the Study:

  • To investigate the role of Hsp72 in the DNA damage response pathway in human tumor cells.
  • To determine the effect of Hsp72 downregulation on DNA repair mechanisms and cellular sensitivity to genotoxic agents.
  • To elucidate the involvement of the p53/p21 signaling pathway in Hsp72-mediated DDR.

Main Methods:

  • Downregulation of Hsp72 in human tumor cells using knockdown techniques.
  • Assessment of DNA damage response markers, including phosphorylated histone H2AX (gammaH2AX) accumulation and dephosphorylation rates.
  • Analysis of gammaH2AX and MDC1 foci formation following radiation exposure.
  • Evaluation of cell sensitivity to gamma-radiation and doxorubicin.
  • Investigation of the p53/p21 signaling pathway activation.

Main Results:

  • Hsp72 downregulation suppressed a key DNA damage response pathway, evidenced by reduced gammaH2AX accumulation.
  • This suppression was due to decreased H2AX expression and increased gammaH2AX dephosphorylation.
  • Impaired formation of gammaH2AX and MDC1 foci led to enhanced DNA damage and increased sensitivity to radiation and doxorubicin.
  • The observed effects were dependent on the activation of the p53/p21 signaling pathway.
  • A positive feedback loop was established where Hsp72 depletion activated p53/p21 signaling, which further impaired the gammaH2AX pathway, enhancing DNA damage and p53/p21 activation.

Conclusions:

  • Hsp72 downregulation disrupts the gammaH2AX pathway of the DNA damage response in human tumor cells.
  • This disruption enhances DNA damage and sensitizes cells to genotoxic insults like radiation and doxorubicin.
  • The p53/p21 signaling pathway plays a critical role in mediating these effects, leading to senescence and increased sensitivity.
  • Hsp72 is a crucial regulator of DNA repair and cellular response to genotoxic stress.

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