title: An overactivated ATR/CHK1 pathway is responsible for the prolonged G2 accumulation in irradiated AT cells.
abstract: Induction of checkpoint responses in G1, S, and G2 phases of the cell cycle after exposure of cells to ionizing radiation (IR) is essential for maintaining genomic integrity. Ataxia telangiectasia mutated (ATM) plays a key role in initiating this response in all three phases of the cell cycle. However, cells lacking functional ATM exhibit a prolonged G2 arrest after IR, suggesting regulation by an ATM-independent checkpoint response. The mechanism for this ataxia telangiectasia (AT)-independent G2-checkpoint response remains unknown. We report here that the G2 checkpoint in irradiated human AT cells derives from an overactivation of the ATR/CHK1 pathway. Chk1 small interfering RNA abolishes the IR-induced prolonged G2 checkpoint and radiosensitizes AT cells to killing. These results link the activation of ATR/CHK1 with the prolonged G2 arrest in AT cells and show that activation of this G2 checkpoint contributes to the survival of AT 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: Jay
authors.initials: J
authors.lastname: Khadpe
authors.forename: Baocheng
authors.initials: B
authors.lastname: Hu
authors.forename: George
authors.initials: G
authors.lastname: Iliakis
authors.forename: Ya
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000502:physiology / Q000528:radiation effects; D000071877:Checkpoint Kinase 1; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects; D016195:G2 Phase / Q000502:physiology / Q000528:radiation effects*; D006801:Humans; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering; D011839:Radiation, Ionizing; D019311:Staurosporine / Q000031:analogs & derivatives
chemical_list: D000470:Alkaloids; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D002110:Caffeine; C054852:7-hydroxystaurosporine; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D019311:Staurosporine