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Chronic hypoxia compromises repair of DNA double-strand breaks to drive genetic instability

Ramya Kumareswaran1, Olga Ludkovski, Alice Meng

  • 1Ontario Cancer Institute, Princess Margaret Hospital (University Health Network), Toronto, Ontario, Canada.

Journal of Cell Science
|January 24, 2012
PubMed

Insights

Hypoxia impairs DNA double-strand break (DNA-DSB) repair in human fibroblasts, leading to increased residual DNA damage and chromosomal instability. This suggests aberrant repair under hypoxia contributes to genetic instability in tumors.

Area of Science:

  • Cellular Biology
  • Radiation Oncology
  • Genetics

Background:

  • Hypoxic conditions are prevalent in solid tumors and linked to genetic instability and poor prognosis.
  • The precise mechanisms connecting DNA repair, genetic instability, and hypoxia remain incompletely understood.

Purpose of the Study:

  • To investigate the impact of sustained oxic, hypoxic, and anoxic conditions on DNA double-strand break (DNA-DSB) sensing and repair in irradiated human fibroblasts.
  • To determine if altered DNA repair under hypoxia contributes to genetic instability.

Main Methods:

  • Human fibroblasts synchronized in G0-G1 phase were exposed to varying oxygen levels (anoxia, hypoxia, oxia) before irradiation (0-10 Gy).
  • DNA double-strand break (DNA-DSB) repair markers (γ-H2AX, ATM(Ser1981), 53BP1 foci) were quantified using immunofluorescence and western blotting.
  • Neutral comet assays and analysis of chromosomal aberrations were performed to assess DNA damage and genomic instability.
  • Clonogenic survival assays evaluated cell viability under different oxygen conditions.

Main Results:

  • Persistently elevated levels of residual DNA double-strand breaks (DNA-DSBs), indicated by γ-H2AX, ATM(Ser1981), and 53BP1 foci, were observed in hypoxic cells 24 hours post-irradiation.
  • Neutral comet assays confirmed increased residual DNA-DSBs in hypoxic cells.
  • Chronic hypoxia resulted in reduced clonogenic survival and a higher frequency of chromosomal aberrations.
  • These findings indicate impaired repair of G1-associated DNA-DSBs under hypoxic conditions.

Conclusions:

  • Continued hypoxia impairs the repair of DNA double-strand breaks (DNA-DSBs) in the G1 phase of the cell cycle.
  • This deficient DNA repair under hypoxia leads to increased residual DNA damage and subsequent chromosomal instability.
  • Aberrant DNA-DSB repair in hypoxia is a significant contributor to hypoxia-mediated genetic instability in cancer cells.

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