ATR dependent activation of Chk2

J Cell Physiol. 2006 Sep;208(3):613-9. doi: 10.1002/jcp.20700.


ATM and ATR are essential regulators of DNA damage checkpoints in mammalian cells through their respective effectors, Chk2 and Chk1. Cross regulation of the ATM-Chk2 and ATR-Chk1 pathways is very limited, although ATM and ATR show overlapping function in a partnership and time-dependent manner. In this study, we report that Chk2 is a substrate of ATR in response to ionizing and ultraviolet radiation. ATR activation induced by ionizing radiation (IR) is weak in ATM+/+ cells. However, when ATM is inhibited by caffeine, ATR activation is markedly enhanced. Total Chk2 and Chk2 Thr68 are also hyperphosphorylated in the presence of caffeine. Both ATM+/+ and ATM-/- cells display normal ATR activation in response to UV radiation-induced DNA damage, which is caffeine sensitive. In two lines of ATM-deficient, as well as in an ATM siRNA silencing cell line, ATR is activated when the cells are exposed to IR and is able to phosphorylate Chk2 in vitro. These observations suggest that ATR is one of the kinases that is likely involved in phosphorylation of Chk2 in response to IR when ATM is deficient.

Publication types

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

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Caffeine / pharmacology
  • Cell Cycle Proteins / metabolism*
  • Cell Cycle Proteins / radiation effects
  • Cell Line
  • Checkpoint Kinase 2
  • DNA-Binding Proteins / deficiency
  • DNA-Binding Proteins / radiation effects
  • Enzyme Activation
  • Fibroblasts
  • Humans
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / deficiency
  • Protein-Serine-Threonine Kinases / metabolism*
  • Protein-Serine-Threonine Kinases / radiation effects
  • Tumor Suppressor Proteins / deficiency
  • Tumor Suppressor Proteins / radiation effects


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Tumor Suppressor Proteins
  • Caffeine
  • Checkpoint Kinase 2
  • ATM protein, human
  • ATR protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • CHEK2 protein, human
  • Protein-Serine-Threonine Kinases