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Genotoxic stress targets human Chk1 for degradation by the ubiquitin-proteasome pathway.

The Chk1 kinase is a major effector of S phase checkpoint signaling during the cellular response to genotoxic stress. Here, we report that replicative stress induces the polyubiquitination and degradation of Chk1 in human cells. This response is triggered by phosphorylation of Chk1 at Ser-345, a known target site for the upstream activating kinase ATR. The ubiquitination of Chk1 is mediated by E3 ligase complexes containing Cul1 or Cul4A. Treatment of cells with the anticancer agent camptothecin (CPT) triggers Chk1 destruction, which blocks recovery from drug-induced S phase arrest and leads to cell death. These findings indicate that ATR-dependent phosphorylation of Chk1 delivers a signal that both activates Chk1 and marks this protein for proteolytic degradation. Proteolysis of activated Chk1 may promote checkpoint termination under normal conditions, and may play an important role in the cytotoxic effects of CPT and related anticancer drugs.

Pubmed ID: 16137618


  • Zhang YW
  • Otterness DM
  • Chiang GG
  • Xie W
  • Liu YC
  • Mercurio F
  • Abraham RT


Molecular cell

Publication Data

September 2, 2005

Associated Grants

  • Agency: NCI NIH HHS, Id: CA97950
  • Agency: NCI NIH HHS, Id: F32 CA099354

Mesh Terms

  • Bromodeoxyuridine
  • Camptothecin
  • Cell Cycle Proteins
  • Cell Line
  • Cell Line, Tumor
  • Cullin Proteins
  • DNA Damage
  • Down-Regulation
  • Genes, Reporter
  • Humans
  • Proteasome Endopeptidase Complex
  • Protein Kinases
  • S Phase
  • Ubiquitin