title: hSMG-1 and ATM sequentially and independently regulate the G1 checkpoint during oxidative stress.
abstract: Genotoxic stress activates the phosphatidylinositol 3-kinase-like kinases (PIKKs) that phosphorylate proteins involved in cell cycle arrest, DNA repair and apoptosis. Previous work showed that the PIKK ataxia telangiectasia mutated (ATM) but not ATM and Rad3 related phosphorylates p53 (Ser15) during hyperoxia, a model of prolonged oxidative stress and DNA damage. Here, we show hSMG-1 is responsible for the rapid and early phosphorylation of p53 (Ser15) and that ATM helps maintain phosphorylation after 24 h. Despite reduced p53 phosphorylation and abundance in cells depleted of hSMG-1 or ATM, levels of the p53 target p21 were still elevated and the G(1) checkpoint remained intact. Conditional overexpression of p21 in p53-deficient cells revealed that hyperoxia also stimulates wortmannin-sensitive degradation of p21. siRNA depletion of hSMG-1 or ATM restored p21 stability and the G(1) checkpoint during hyperoxia. These findings establish hSMG-1 as a proximal regulator of DNA damage signaling and reveal that the G(1) checkpoint is tightly regulated during prolonged oxidative stress by both PIKK-dependent synthesis and proteolysis of p21.
authors.affiliation: Department of Environmental Medicine, The University of Rochester, Rochester, NY 14642, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Gehen
authors.forename: R J
authors.initials: RJ
authors.lastname: Staversky
authors.forename: R A
authors.initials: RA
authors.lastname: Bambara
authors.forename: P C
authors.initials: PC
authors.lastname: Keng
authors.forename: M A
authors.initials: MA
authors.lastname: O'Reilly
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004249:DNA Damage / Q000187:drug effects / Q000502:physiology; D004260:DNA Repair / Q000187:drug effects / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D018496:Hyperoxia / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D019869:Phosphatidylinositol 3-Kinases; D010726:Phosphodiesterase Inhibitors; D017346:Protein Serine-Threonine Kinases; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D000077191:Wortmannin; C495901:TP53 protein, human; C576324:ATM protein, human; C514704:SMG1 protein, human