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p21 inhibits Thr161 phosphorylation of Cdc2 to enforce the G2 DNA damage checkpoint

V A Smits1, R Klompmaker, T Vallenius

  • 1Jordan Laboratory, Department of Hematology, University Medical Center Utrecht G03-647, P.O. Box 85500, 3508 GA Utrecht, The Netherlands.

The Journal of Biological Chemistry
|July 27, 2000
PubMed

Insights

The cyclin-dependent kinase inhibitor p21 is essential for sustained G2 arrest following DNA damage. P21 blocks Cdc2 activation by preventing phosphorylation at Thr161, revealing a second DNA damage checkpoint pathway.

Area of Science:

  • Cell cycle regulation
  • DNA damage response
  • Molecular biology

Background:

  • The DNA damage checkpoint is crucial for maintaining genomic stability.
  • Cyclin-dependent kinase inhibitor p21 plays a role in G2 arrest after DNA damage.
  • The precise mechanism of p21's contribution to G2 arrest is not fully understood.

Purpose of the Study:

  • To elucidate the mechanism by which p21 contributes to sustained G2 arrest.
  • To investigate how p21 influences Cdc2 activation in response to DNA damage.

Main Methods:

  • Western blotting to detect phosphorylation states of Cdc2.
  • Analysis of p21's interaction with Cdc2 and its effect on phosphorylation sites.

Main Results:

  • P21 inhibits the activating phosphorylation of Cdc2 at Thr161.
  • P21 does not affect the dephosphorylation of inhibitory sites Thr14 and Tyr15 on Cdc2.
  • This indicates p21 acts independently of the Chk1/Cdc25C pathway.

Conclusions:

  • Cells possess at least two independent pathways to inhibit Cdc2 activity upon DNA damage.
  • These pathways target both positive (Thr161) and negative (Thr14, Tyr15) regulatory phosphorylation events on Cdc2.
  • P21 is a key component in one of these independent pathways, ensuring robust cell cycle arrest.

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