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Purification of Ubiquitinated p53 Proteins from Mammalian Cells
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Purification of Ubiquitinated p53 Proteins from Mammalian Cells

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ATM activates p53 by regulating MDM2 oligomerization and E3 processivity

Qian Cheng1, Lihong Chen, Zhenyu Li

  • 1Department of Molecular Oncology, Moffitt Cancer Center, Tampa, FL, USA.

The EMBO Journal
|October 10, 2009
PubMed

Insights

ATM kinase phosphorylates MDM2, a key E3 ligase, to stabilize p53 after DNA damage. This phosphorylation prevents MDM2 self-assembly, halting p53 degradation and enabling DNA repair responses.

Area of Science:

  • Molecular Biology
  • Cellular Signaling
  • DNA Damage Response

Background:

  • Ionizing irradiation rapidly activates p53, a crucial tumor suppressor, through the ATM kinase.
  • The precise signaling pathway and target responsible for p53 stabilization post-DNA damage remain unclear.

Purpose of the Study:

  • To identify the direct signaling target of ATM kinase in the p53 stabilization pathway.
  • To elucidate the mechanism by which ATM regulates p53 stability.

Main Methods:

  • Investigated the interaction between ATM kinase and MDM2.
  • Utilized phosphorylation site mutagenesis (alanine substitution) to block MDM2 phosphorylation.
  • Assessed p53 and MDM2 ubiquitination and degradation levels via Western blotting and proteasomal assays.

Main Results:

  • ATM kinase directly phosphorylates the ubiquitin E3 ligase MDM2 at multiple sites near its RING domain.
  • Phosphorylation by ATM inhibits MDM2 RING domain oligomerization, which is essential for p53 polyubiquitination and degradation.
  • Blocking MDM2 phosphorylation leads to continuous p53 degradation, even after DNA damage.

Conclusions:

  • ATM controls p53 stability by regulating MDM2 RING domain oligomerization and E3 ligase activity.
  • MDM2 RING domain oligomerization is a critical step in p53 ubiquitination and degradation.
  • Modulating E3 ligase oligomerization represents a potential therapeutic strategy for cancer treatment.

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