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Regulation of MDM2 E3 ligase activity by phosphorylation after DNA damage

Qian Cheng1, Brittany Cross, Baozong Li

  • 1Molecular Oncology Department, Moffitt Cancer Center, Tampa, Florida 33612, USA.

Molecular and Cellular Biology
|October 12, 2011
PubMed

Insights

MDM2

Area of Science:

  • Molecular Biology
  • Cellular Regulation
  • Cancer Research

Background:

  • MDM2 (mouse double minute 2 homolog) is a key E3 ubiquitin ligase regulating the tumor suppressor p53.
  • Both the acidic domain and RING domain of MDM2 are essential for p53 ubiquitination.
  • Previous work indicated ATM phosphorylation inhibits MDM2 RING domain oligomerization, stabilizing p53 post-DNA damage.

Purpose of the Study:

  • To investigate how ATM phosphorylation allosterically regulates MDM2's acidic and RING domains.
  • To elucidate the role of MDM2 RING domain oligomerization in p53 ubiquitination.
  • To understand how C-terminal ATM phosphorylation impacts MDM2's interaction with p53.

Main Methods:

  • Chemical cross-linking to assess MDM2 RING domain oligomerization in vivo.
  • Analysis of upstream sequence regulation on RING domain dimerization.
  • Investigating the effect of ATM-mediated phosphorylation on MDM2 function.
  • Assessing the impact of forced MDM2 oligomerization on p53 ubiquitination.
  • Evaluating MDM2 acidic domain binding to p53 core domain and p53 misfolding.

Main Results:

  • MDM2's RING domain forms dimers and higher-order oligomers in vivo.
  • RING domain dimerization is negatively regulated by an upstream sequence.
  • ATM phosphorylation of this upstream sequence further inhibits RING dimerization.
  • Forced MDM2 oligomerization partially reverses phosphorylation's inhibitory effects and enhances p53 ubiquitination.
  • ATM phosphorylation at C-terminal sites suppresses MDM2's acidic domain binding to p53 and p53 misfolding.

Conclusions:

  • MDM2's acidic and RING domains are allosterically linked to ATM phosphorylation sites.
  • A single C-terminal ATM modification regulates multiple MDM2 functions crucial for p53 ubiquitination.
  • This allosteric regulation provides a mechanism for coordinating p53 ubiquitination after DNA damage.

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