title: Activation of ataxia telangiectasia mutated by DNA strand break-inducing agents correlates closely with the number of DNA double strand breaks.
abstract: The protein kinase ataxia telangiectasia mutated (ATM) is activated when cells are exposed to ionizing radiation (IR). It has been assumed that ATM is specifically activated by the few induced DNA double strand breaks (DSBs), although little direct evidence for this assumption has been presented. DSBs constitute only a few percent of the IR-induced DNA damage, whereas the more frequent single strand DNA breaks (SSBs) and base damage account for over 98% of the overall DNA damage. It is therefore unclear whether DSBs are the only IR-induced DNA lesions that activate ATM. To test directly whether or not DSBs are responsible for ATM activation, we exposed cells to drugs and radiation that produce different numbers of DSBs and SSBs. We determined the resulting ATM activation by measuring the amount of phosphorylated Chk2 and the numbers of SSBs and DSBs in the same cells after short incubation periods. We found a strong correlation between the number of DSBs and ATM activation but no correlation with the number of SSBs. In fact, hydrogen peroxide, which, similar to IR, induces DNA damage through hydroxyl radicals but fails to induce DSBs, did not activate ATM. In contrast, we found that calicheamicin-induced strand breaks activated ATM more efficiently than IR and that ATM activation correlated with the relative DSB induction by these agents. Our data indicate that ATM is specifically activated by IR-induced DSBs, with little or no contribution from SSBs and other types of DNA damage. These findings have implications for how ATM might recognize DSBs in cells.
authors.affiliation: Department of Clinical Chemistry and Transfusion Medicine, Sahlgrenska University Hospital, Göteborg University, SE-413 45 Göteborg, Sweden.
authors.forename: Ismail Hassan
authors.initials: IH
authors.lastname: Ismail
authors.forename: Susanne
authors.initials: S
authors.lastname: Nyström
authors.forename: Jonas
authors.initials: J
authors.lastname: Nygren
authors.forename: Ola
authors.initials: O
authors.lastname: Hammarsten
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D064447:Checkpoint Kinase 2; D020552:Comet Assay; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D006657:Histones / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology; D017665:Hydroxyl Radical; D008214:Lymphocytes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D010766:Phosphorylation; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011839:Radiation, Ionizing; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D025521:Tumor Suppressor Proteins; D017665:Hydroxyl Radical; D004247:DNA; D006861:Hydrogen Peroxide; D011065:Poly(ADP-ribose) Polymerases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases