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Point mutation at the Nbs1 Threonine 278 site does not affect mouse development, but compromises the Chk2 and Smc1

Tangliang Li1, Zhao-Qi Wang

  • 1Leibniz Institute for Age Research - Fritz Lipmann Institute, Jena, Germany.

Mechanisms of Ageing and Development
|June 14, 2011
PubMed

Insights

Nijmegen breakage syndrome protein 1 (NBS1) phosphorylation at Threonine 278 is not essential for mouse development or DNA repair. However, this site influences DNA damage response signaling at higher radiation doses.

Area of Science:

  • Molecular Biology
  • Genetics
  • Cell Biology

Background:

  • NBS1 protein is crucial for sensing DNA double-strand breaks (DSBs) and initiating the DNA damage response (DDR) by activating ATM kinase.
  • ATM phosphorylates NBS1 at Serine 278 and Serine 343, aiding the activation of downstream targets.
  • Investigating the physiological role of NBS1 phosphorylation is essential for understanding DDR mechanisms.

Purpose of the Study:

  • To investigate the in vivo function of NBS1 phosphorylation at Threonine 278 (equivalent to human Serine 278).
  • To assess the impact of mutating this phosphorylation site on mouse development, genomic stability, and DNA damage response signaling.

Main Methods:

  • Generation of Nbs1(T278A) knock-in mice to mutate the Threonine 278 phosphorylation site.
  • Analysis of mouse development, proliferation, and genomic stability.
  • Irradiation of primary Nbs1(T278A) mouse embryonic fibroblasts (MEFs) with varying doses of ionizing radiation (IR).
  • Assessment of Chk2 and Smc1 phosphorylation, and HU-induced ATR-Chk1 activation.

Main Results:

  • Nbs1(T278A) knock-in mice exhibit normal development without gross defects, unaffected proliferation, or genomic instability.
  • MEFs from these mice show no significant defects in Chk2 phosphorylation at low IR doses (1Gy).
  • Delayed phosphorylation of Chk2 and Smc1 is observed at intermediate (4.5Gy) and high (10Gy) IR doses, respectively.
  • The T278A mutation does not affect HU-induced ATR-Chk1 activation, unlike the Serine 343 mutation.

Conclusions:

  • NBS1 phosphorylation at Threonine 278 is dispensable for mouse development and overall genomic stability.
  • This phosphorylation site plays a dose-dependent, differential role in facilitating the DNA damage response of specific downstream effectors in vivo.
  • The findings highlight the nuanced contribution of NBS1 phosphorylation sites to the complex DNA damage response network.

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