title: Ku affects the ATM-dependent S phase checkpoint following ionizing radiation.
abstract: Following exposure to genotoxic stress, proliferating cells actively slow down DNA replication through an S phase checkpoint to provide time for repair. The ATM-dependent pathway plays an important role in the S phase checkpoint response following ionizing irradiation. We report that there is a stronger S phase checkpoint response in irradiated Ku80(-/-) cells as compared with their wild-type counterparts, which has no relationship to DNA-dependent protein kinase (DNA-PK) activity but correlates with a higher ATM activity and with more ATM bound to chromatin DNA in such cells. Wortmannin, a nonspecific inhibitor of ATM, not only reduces the higher activity of ATM kinase, but also abolishes the stronger S phase checkpoint response in Ku80(-/-) cells. Furthermore, a specific ATM antisense oligonucleotide abolishes the stronger S checkpoint response in Ku80(-/-) cells and renders these cells practically indistinguishable from Ku80(+/+) cells for this endpoint. These results in aggregate indicate that the stronger S checkpoint in irradiated Ku80(-/-) cells is due to the higher ATM kinase activity.
authors.affiliation: Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, PA 19107, USA.
authors.forename: Xiang-Yang
authors.initials: XY
authors.lastname: Zhou
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.forename: Hongyan
authors.initials: H
authors.lastname: Wang
authors.forename: David J
authors.initials: DJ
authors.lastname: Chen
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: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D034961:Antigens, Nuclear; D064007:Ataxia Telangiectasia Mutated Proteins; D016466:CHO Cells; D018797:Cell Cycle Proteins; D006224:Cricetinae; D004249:DNA Damage / Q000528:radiation effects; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017353:Gene Deletion; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D016196:S Phase / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D025521:Tumor Suppressor Proteins; D000077191:Wortmannin; D014965:X-Rays
chemical_list: D000730:Androstadienes; D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D000077191:Wortmannin