title: ATR dependent activation of Chk2.
abstract: 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.
authors.affiliation: Department of Radiation Oncology, University of California Irvine, California, USA.
authors.forename: Xiao Qi
authors.initials: XQ
authors.lastname: Wang
authors.forename: J Leslie
authors.initials: JL
authors.lastname: Redpath
authors.forename: Sheung Tat
authors.initials: ST
authors.lastname: Fan
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Stanbridge
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000378:metabolism* / Q000528:radiation effects; D002460:Cell Line; D064447:Checkpoint Kinase 2; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000528:radiation effects; D004789:Enzyme Activation; D005347:Fibroblasts; D006801:Humans; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000378:metabolism* / Q000528:radiation effects; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000528:radiation effects
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D002110:Caffeine; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases