title: Ku affects the ataxia and Rad 3-related/CHK1-dependent S phase checkpoint response after camptothecin treatment.
abstract: Camptothecin (CPT) that targets DNA topoisomerase I is one of the most promising broad-spectrum anticancer drugs in development today. The cytotoxicity of CPT is S phase (S)-specific because the collision of advancing replication forks with CPT-topoisomerase I-DNA complexes results in DNA damage. After DNA damage, proliferating cells could actively slow down the DNA replication through an S checkpoint to provide time for repair. We report now that there is an activated S checkpoint response in CPT-treated mammalian cells. This response is regulated by Ataxia and Rad3-related (ATR)/CHK1 pathway. Compared with their wild-type counterparts, CPT-treated Ku80-/- cells showed stronger inhibition of DNA replication. This stronger inhibition had no relationship with DNA-dependent protein kinase (DNA-PK) activity but correlated with the higher activities of ATR and the higher activities of CHK1 in such cells. Not only caffeine, the nonspecific inhibitor of ATR, or UCN-01, the nonspecific inhibitor of CHK1, but also the specific CHK1 antisense oligonucleotide abolished the stronger inhibition of DNA replication in CPT-treated Ku80-/- cells. These results in aggregate indicated that the stronger S checkpoint in CPT-treated Ku80-/- cells is regulated through the highly activated ATR/CHK1 pathway.
authors: Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors: Hongyan
authors: H
authors: Wang
authors: Xiang
authors: X
authors: Wang
authors: Xiang-Yang
authors: XY
authors: Zhou
authors: David J
authors: DJ
authors: Chen
authors: Gloria C
authors: GC
authors: Li
authors: George
authors: G
authors: Iliakis
authors: Ya
authors: Y
authors: Wang
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear; D064007:Ataxia Telangiectasia Mutated Proteins; D002166:Camptothecin / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D004247:DNA / Q000096:biosynthesis; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D015536:Down-Regulation; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D016196:S Phase / Q000187:drug effects* / Q000502:physiology
chemical_list: D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D047428:Protein Kinase Inhibitors; D004247:DNA; D011494:Protein Kinases; C576897:Atr protein, mouse; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; 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; D002166:Camptothecin