title: NBS1 regulates a novel apoptotic pathway through Bax activation.
abstract: DNA damage induced apoptosis, along with precise DNA damage repair, is a critical cellular function, and both of these functions are necessary for cancer prevention. The NBS1 protein is known to be a key regulator of DNA damage repair. It acts by forming a complex with Rad50/Mre11 and by activating ATM. We show here that NBS1 regulates a novel p53 independent apoptotic pathway in response to DNA damage. DNA damage induced apoptosis was significantly reduced in NBS1 deficient cells regardless of their p53 status. Experiments using a series of cell lines expressing mutant NBS1 proteins revealed that NBS1 is able to regulate the activation of Bax and Caspase-3 without the FHA, Mre11-binding, or the ATM-interacting domains, whereas the phosphorylation sites of NBS1 were essential for Bax activation. Expression of apoptosis-related transcription factors such as E2F1 and their downstream pro-apoptotic factors were not related to this apoptosis induction. Interestingly, NBS1 regulates a novel Bax activation pathway by disrupting the Ku70-Bax complex which is required for activation of the mitochondrial apoptotic pathway. This dissociation of the Ku70-Bax complex can be mediated by acetylation of Ku70, and NBS1 can function in this process through a protein-protein interaction with Ku70. Thus, NBS1 is a key protein involved in the prevention of carcinogenesis, not only through the precise repair of damaged DNA by homologous recombination (HR) but also by its role in the elimination of inappropriately repaired cells.
authors.affiliation: Department of Environmental Sciences, Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Iijima
authors.forename: Chizuko
authors.initials: C
authors.lastname: Muranaka
authors.forename: Junya
authors.initials: J
authors.lastname: Kobayashi
authors.forename: Shuichi
authors.initials: S
authors.lastname: Sakamoto
authors.forename: Kenshi
authors.initials: K
authors.lastname: Komatsu
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsuura
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kubota
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tauchi
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D002645:Chickens; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D000072200:Ku Autoantigen; D050505:Mutant Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000172:deficiency / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D034961:Antigens, Nuclear; D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050505:Mutant Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; D047428:Protein Kinase Inhibitors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen