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ATM and Chk2-dependent phosphorylation of MDMX contribute to p53 activation after DNA damage

Lihong Chen1, Daniele M Gilkes, Yu Pan

  • 1Molecular Oncology Program, H Lee Moffitt Comprehensive Cancer Center and Research Institute, Tampa, FL 33612, USA.

The EMBO Journal
|September 16, 2005
PubMed

Insights

DNA damage triggers ATM-dependent MDMX phosphorylation and degradation by MDM2, enhancing tumor suppressor p53 activation. This pathway is crucial for maintaining genomic stability and preventing cancer.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Signaling

Background:

  • The p53 tumor suppressor is critical for genomic stability and cancer prevention, activated by DNA damage.
  • ATM kinase signaling and MDM2/MDMX proteins are key regulators of p53 response.
  • Understanding MDMX regulation is vital for cancer therapy development.

Purpose of the Study:

  • To investigate the role of ATM and Chk2 kinases in MDMX regulation following DNA damage.
  • To elucidate the mechanism by which MDMX is degraded and how this impacts p53 activation.
  • To identify specific phosphorylation sites on MDMX involved in its regulation.

Main Methods:

  • Mass spectrometry for phosphosite identification.
  • RNA interference (RNAi) to reduce MDMX levels.
  • Phosphopeptide-specific antibodies for site validation.
  • Site-directed mutagenesis to assess phosphorylation site function.
  • Western blotting to detect protein levels and modifications.

Main Results:

  • DNA damage induces ATM-dependent phosphorylation and MDM2-mediated degradation of MDMX.
  • Specific phosphorylation sites (S342, S367, S403) on MDMX were identified and confirmed.
  • Mutation of these sites confers resistance to MDM2-mediated degradation.
  • Chk2 kinase is required for MDMX phosphorylation at S342/S367 and subsequent degradation.
  • Reduced MDMX levels enhance p53 activation in response to DNA damage.

Conclusions:

  • ATM and Chk2 kinases orchestrate MDMX phosphorylation, targeting it for MDM2-mediated degradation after DNA damage.
  • This MDMX degradation is a critical step for p53 stabilization and activation, promoting genomic integrity.
  • The findings reveal a novel regulatory axis contributing to the DNA damage response and offer potential therapeutic targets.

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