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Phosphorylation of Ser-20 mediates stabilization of human p53 in response to DNA damage

N H Chehab1, A Malikzay, E S Stavridi

  • 1Department of Molecular Genetics, The Wistar Institute, Philadelphia, PA 19104, USA.

Proceedings of the National Academy of Sciences of the United States of America
|November 26, 1999
PubMed

Insights

DNA damage triggers p53 stabilization by weakening its interaction with Mdm2. This process is mediated by phosphorylation of p53 on Ser-20, not Ser-15, via an unknown kinase activated by ATM and ATR.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Biochemistry

Background:

  • p53 protein stabilization after DNA damage is crucial for cellular response.
  • Mdm2 protein targets p53 for proteasomal degradation, inhibiting its function.
  • ATM and ATR kinases phosphorylate p53 on Ser-15 upon DNA damage, but this modification is linked to apoptosis, not stabilization.

Purpose of the Study:

  • To determine which p53 posttranslational modifications are responsible for disrupting the p53-Mdm2 complex after DNA damage.
  • To investigate the role of Ser-20 phosphorylation in p53 stabilization and its interaction with Mdm2.

Main Methods:

  • Analysis of p53 stabilization in response to ionizing radiation (IR) and UV light using p53 proteins with Ser substitutions.
  • In vitro assays to assess the interaction between p53 and Mdm2.
  • Detection of p53 phosphorylation on Ser-20 after DNA damage.

Main Results:

  • Substitution of Ser-20 abrogated p53 stabilization following IR and UV exposure.
  • IR and UV light induced phosphorylation of p53 on Ser-20, weakening the p53-Mdm2 interaction in vitro.
  • ATM and ATR kinases do not directly phosphorylate p53 on Ser-20.

Conclusions:

  • p53 stabilization after DNA damage is critically dependent on Ser-20 phosphorylation.
  • An unidentified kinase, activated by ATM/ATR, likely phosphorylates p53 on Ser-20, leading to dissociation from Mdm2 and subsequent stabilization.

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