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Phosphorylation of Hdmx mediates its Hdm2- and ATM-dependent degradation in response to DNA damage

Yaron Pereg1, Dganit Shkedy, Petra de Graaf

  • 1The David and Inez Myers Laboratory for Genetic Research, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.

Proceedings of the National Academy of Sciences of the United States of America
|March 25, 2005
PubMed

Insights

Ataxia-telangiectasia, mutated (ATM) kinase targets Hdmx for degradation following DNA double-strand breaks (DSBs). This ATM-dependent Hdmx phosphorylation and degradation enhances the DNA damage response by stabilizing p53.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Genetics

Background:

  • Genomic stability is maintained by the DNA damage response (DDR), crucial for preventing mutations.
  • The protein kinase ataxia-telangiectasia, mutated (ATM) is a key initiator of the DDR upon detecting DNA double-strand breaks (DSBs).
  • ATM regulates p53 stability and function through post-translational modifications of p53 and its regulators, Mdm2 and Mdmx.

Purpose of the Study:

  • To investigate the role of ATM in the regulation of Hdmx during the DNA damage response.
  • To identify specific phosphorylation sites on Hdmx targeted by ATM in response to DSBs.
  • To elucidate the mechanism by which ATM-mediated Hdmx modification influences p53 activation.

Main Methods:

  • Cellular assays to induce DNA double-strand breaks.
  • Western blotting to detect protein levels and phosphorylation.
  • Site-directed mutagenesis to analyze the function of Hdmx phosphorylation sites.
  • Ubiquitination assays to assess Hdm2 activity.

Main Results:

  • ATM kinase activity is essential for the efficient degradation of human Hdmx following DSB induction.
  • At least three distinct sites on Hdmx are phosphorylated in response to DSBs, with S403 identified as a direct ATM target.
  • Phosphorylation of these sites is critical for Hdm2-mediated ubiquitination and subsequent degradation of Hdmx.

Conclusions:

  • ATM employs a sophisticated mechanism to fine-tune p53 activation during the DDR.
  • ATM directly phosphorylates Hdmx at specific sites, promoting its degradation.
  • This process ensures optimal stabilization and activation of p53, reinforcing genomic stability.

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