title: ATM is activated in response to N-methyl-N'-nitro-N-nitrosoguanidine-induced DNA alkylation.
abstract: p53 plays an important role in response to ionizing radiation by regulating cell cycle progression and triggering apoptosis. These activities are controlled, in part, by the phosphorylation of p53 by the protein kinase ATM. Recent evidence indicates that the monofunctional DNA alkylating agent N-methyl-N'-nitro-N- nitrosoguanidine (MNNG) also triggers up-regulation and phosphorylation of p53; however, the mechanism(s) responsible for this are unknown. We observed that in MNNG-treated normal human fibroblasts, up-regulation and phosphorylation of p53 was sensitive to the ATM kinase inhibitor wortmannin. ATM-deficient fibroblasts exhibited a delay in p53 up-regulation indicating a role for ATM in triggering the MNNG-induced response. Likewise, a mismatch repair (MMR)-deficient colorectal tumor line failed to show rapid up-regulation of p53. However, unlike ATM-deficient cells, these MMR-deficient cells displayed rapid phosphorylation of the p53 residue serine 15 after MNNG. In vitro kinase assays indicate that ATM is rapidly activated in both normal and MMR-deficient cells in response to MNNG. Using a number of morphological and biochemical approaches, we failed to observe MNNG-induced apoptosis in normal human fibroblasts, suggesting that apoptosis-induced DNA strand breaks are not required for the activation of ATM in response to MNNG. Comet assays indicated that strand breaks accumulated, and p53 up-regulation/phosphorylation occurred quite rapidly (within 30 min) after MNNG treatment, suggesting that DNA strand breaks that arise during the repair process activate ATM. These findings indicate that ATM activation is not limited to the ionizing radiation-induced response and potentially plays an important role in response to DNA alkylation.
authors.affiliation: Department of Biochemistry and Molecular Biology and the Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
authors.forename: Aaron W
authors.initials: AW
authors.lastname: Adamson
authors.forename: Wan-Ju
authors.initials: WJ
authors.lastname: Kim
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Shangary
authors.forename: R
authors.initials: R
authors.lastname: Baskaran
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Brown
mesh_terms: D000478:Alkylation; D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011839:Radiation, Ionizing; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D015854:Up-Regulation; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D008769:Methylnitronitrosoguanidine; D004247:DNA; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin