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ATM phosphorylates p95/nbs1 in an S-phase checkpoint pathway

D S Lim1, S T Kim, B Xu

  • 1Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.

Nature
|April 15, 2000
PubMed

Insights

Ataxia-telangiectasia (AT) and Nijmegen breakage syndrome (NBS) share radiation sensitivity. ATM kinase activation in NBS cells and ATM-dependent p95/nbs1 phosphorylation link these proteins in a common DNA damage response pathway.

Area of Science:

  • Genetics
  • Molecular Biology
  • Cell Biology

Background:

  • Ataxia-telangiectasia (AT) and Nijmegen breakage syndrome (NBS) are rare diseases with shared symptoms like chromosomal instability and radiation sensitivity.
  • Mutations in ATM (AT) and p95/nbs1 (NBS) genes underlie these conditions, affecting DNA damage response pathways.

Purpose of the Study:

  • To investigate the functional relationship between ATM and p95/nbs1 due to observed similarities between AT and NBS.
  • To elucidate the role of ATM-dependent phosphorylation of p95/nbs1 in cellular responses to ionizing radiation.

Main Methods:

  • Assessing ATM kinase activation and ATM-dependent responses in NBS cells following ionizing radiation.
  • Evaluating the in vitro and in vivo phosphorylation of p95/nbs1 at serine 343.
  • Utilizing a mutated p95/nbs1 construct (non-phosphorylatable) to examine S-phase checkpoint function.

Main Results:

  • Ionizing radiation activated ATM kinase and induced ATM-dependent responses in NBS cells, suggesting p95/nbs1 is not essential for ATM signaling post-irradiation.
  • p95/nbs1 undergoes ATM-dependent phosphorylation at serine 343 after ionizing radiation.
  • A mutated p95/nbs1 construct lacking the ATM phosphorylation site disrupted the S-phase checkpoint in normal cells and failed to rescue the defect in NBS cells.

Conclusions:

  • ATM and p95/nbs1 are functionally linked within a common signaling pathway.
  • ATM-dependent phosphorylation of p95/nbs1 is crucial for the S-phase checkpoint response to ionizing radiation, explaining the phenotypic overlap between AT and NBS.

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