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

Mol Cell. 2005 Sep 2;19(5):607-18. doi: 10.1016/j.molcel.2005.07.019.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bromodeoxyuridine
  • Camptothecin / toxicity
  • Cell Cycle Proteins / physiology
  • Cell Line
  • Cell Line, Tumor
  • Checkpoint Kinase 1
  • Cullin Proteins / physiology
  • DNA Damage / physiology*
  • Down-Regulation / drug effects
  • Genes, Reporter
  • Humans
  • Proteasome Endopeptidase Complex / physiology*
  • Protein Kinases / metabolism*
  • S Phase / drug effects
  • S Phase / physiology
  • Ubiquitin / physiology*


  • CUL4A protein, human
  • Cell Cycle Proteins
  • Cullin 1
  • Cullin Proteins
  • Ubiquitin
  • Protein Kinases
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • Proteasome Endopeptidase Complex
  • Bromodeoxyuridine
  • Camptothecin