Rapid PIKK-dependent release of Chk1 from chromatin promotes the DNA-damage checkpoint response

Curr Biol. 2006 Jan 24;16(2):150-9. doi: 10.1016/j.cub.2005.11.066. Epub 2005 Dec 15.


Background: Checkpoint signaling pathways are of crucial importance for the maintenance of genomic integrity. Within these pathways, the effector kinase Chk1 plays a central role in mediating cell-cycle arrest in response to DNA damage, and it does so by phosphorylating key cell-cycle regulators.

Results: By investigating the subcellular distribution of Chk1 by cell fractionation, we observed that around 20% of it localizes to chromatin during all phases of the cell cycle. Furthermore, we found that in response to DNA damage, Chk1 rapidly dissociates from the chromatin. Significantly, we observed a tight correlation between DNA-damage-induced Chk1 phosphorylation and chromatin dissociation, suggesting that phosphorylated Chk1 does not stably associate with chromatin. Consistent with these events being triggered by active checkpoint signaling, inhibition of the DNA-damage-activated kinases ATR and ATM, or siRNA-mediated downregulation of the DNA-damage mediator proteins Claspin and TopBP1, impaired DNA-damage-induced dissociation of Chk1 from chromatin. Finally, we established that Chk1 phosphorylation occurs at localized sites of DNA damage and that constitutive immobilization of Chk1 on chromatin results in a defective DNA-damage-induced checkpoint arrest.

Conclusions: Chromatin association and dissociation appears to be important for proper Chk1 regulation. We propose that in response to DNA damage, PIKK-dependent checkpoint signaling leads to phosphorylation of chromatin-bound Chk1, resulting in its rapid release from chromatin and facilitating the transmission of DNA-damage signals to downstream targets, thereby promoting efficient cell-cycle arrest.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / physiology*
  • Cell Line
  • Checkpoint Kinase 1
  • Chromatin / enzymology*
  • DNA Damage*
  • DNA-Binding Proteins / physiology*
  • Humans
  • Models, Biological
  • Phosphorylation
  • Protein Kinases / metabolism
  • Protein Kinases / physiology*
  • Protein Processing, Post-Translational
  • Protein-Serine-Threonine Kinases / physiology*
  • Signal Transduction* / radiation effects
  • Tumor Suppressor Proteins / physiology*
  • Ultraviolet Rays


  • Cell Cycle Proteins
  • Chromatin
  • DNA-Binding Proteins
  • Tumor Suppressor Proteins
  • Protein Kinases
  • ATM protein, human
  • ATR protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • Protein-Serine-Threonine Kinases