title: Ku affects the CHK1-dependent G(2) checkpoint after ionizing radiation.
abstract: There are two major pathways for repairing DNA double strand breaks in mammalian cells: nonhomologous end joining (NHEJ) and homologous recombination repair (HRR). The nonhomologous end joining repair is deficient in cells without Ku, whereas HRR is highly efficient in such cells compared with their wild-type counterparts. The mechanism remains unclear. We reported previously that Ku80(-/-) cells show a stronger ATM-dependent S-phase checkpoint response than Ku80(+/+) cells after ionizing radiation (IR; X-Y. Zhou et al., Oncogene, 21:6377-6381, 2002). We report in this study that Ku80(-/-) cells also show a much stronger G(2) accumulation than Ku80(+/+) cells after IR. The stronger G(2) checkpoint response in Ku80(-/-) cells is ATM independent but is accompanied with a higher activity of CHK1 kinase. Treatment with Chk1 antisense oligonucleotide abolishes the stronger G(2) checkpoint response and sensitizes Ku80(-/-) cells to IR. These data indicate that the stronger G(2) checkpoint response shown in Ku80(-/-) cells is CHK1 dependent and suggest that the CHK1-dependent checkpoint response contributes to the highly efficient HRR in such cells.
authors.affiliation: Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.forename: Gloria C
authors.initials: GC
authors.lastname: Li
authors.forename: George
authors.initials: G
authors.lastname: Iliakis
authors.forename: Ya
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D000071877:Checkpoint Kinase 1; D004265:DNA Helicases; D004260:DNA Repair / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D016195:G2 Phase / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014162:Transfection; D025521:Tumor Suppressor Proteins
chemical_list: D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen