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p53 accumulates but is functionally impaired when DNA synthesis is blocked

V Gottifredi1, S Shieh, Y Taya

  • 1Department of Biological Sciences, Columbia University, New York, NY 10027, USA.

Proceedings of the National Academy of Sciences of the United States of America
|February 7, 2001
PubMed

Insights

DNA replication blocks stabilize p53 but impair its transcriptional activity, unlike gamma irradiation. This suggests stalled forks activate kinases that inhibit p53

Area of Science:

  • Cellular response to DNA damage
  • Tumor suppressor gene regulation
  • Cell cycle control

Background:

  • p53 protein is crucial for cell cycle arrest following DNA damage.
  • Gamma irradiation (IR) induces G1/G2 arrest dependent on p53.
  • Blocked DNA replication typically causes p53-independent S-phase arrest.

Purpose of the Study:

  • To investigate p53 protein response to DNA replication blocks.
  • To compare p53 activity after gamma IR versus replication stress.
  • To elucidate the mechanisms regulating p53 transcriptional function.

Main Methods:

  • Cellular treatment with hydroxyurea (HU) or aphidicolin to block DNA synthesis.
  • Gamma irradiation (IR) to induce DNA damage.
  • Analysis of p53 phosphorylation, nuclear localization, and transcriptional target induction.
  • Assessment of ATM kinase activity and p53 stabilization.

Main Results:

  • Blocked DNA synthesis, like IR, increases phosphorylated nuclear p53 levels.
  • p53 transcriptional targets are weakly induced by replication blocks compared to IR.
  • Pretreatment with HU/aphidicolin inhibits p53 response to IR, indicating impaired transcription factor activity.
  • HU-induced p53 stabilization is ATM-independent and does not affect IR-induced ATM activation.
  • Stalled replication forks activate kinases that stabilize p53 but inhibit its transcriptional function downstream of ATM.

Conclusions:

  • Blocked DNA replication activates p53 stabilization pathways independently of ATM.
  • Replication stress impairs p53's transcriptional activity, suggesting a novel regulatory mechanism.
  • This regulation impacts the cell's overall response to DNA damage and replication stress.

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