title: NBS1 is regulated by two kind of mechanisms: ATM-dependent complex formation with MRE11 and RAD50, and cell cycle-dependent degradation of protein.
abstract: Nijmegen breakage syndrome (NBS), a condition similar to Ataxia-Telangiectasia (A-T), is a radiation-hypersensitive genetic disorder showing chromosomal instability, radio-resistant DNA synthesis, immunodeficiency, and predisposition to malignances. The product of the responsible gene, NBS1, forms a complex with MRE11 and RAD50 (MRN complex). The MRN complex is necessary for the DNA damage-induced activation of ATM. However, the regulation of MRN complex formation is still unclear. Here, we investigated the regulatory mechanisms of MRN complex formation. We used an immunoprecipitation assay to determine whether levels of the MRN complex were increased by radiation-induced DNA damage and found that the levels of these proteins and their mRNAs did not increase. ATM-dependent phosphorylation of NBS1 contributed to the DNA damage-induced MRN complex formation. However, pre-treatment of cells with an ATM-specific inhibitor did not affect homologous recombination (HR) and non-homologous end-joining (NHEJ) repair. G0 phase cells, decreasing NBS1 and HR activity but not NHEJ, gained HR-related chromatin association of RAD51 by overexpression of NBS1, suggesting that the amount of NBS1 may be important for repressing accidental activation of HR. These evidences suggest that NBS1 is regulated by two kind of mechanisms: complex formation dependent on ATM, and protein degradation mediated by an unknown MG132-resistant pathway. Such regulation of NBS1 may contribute to cellular responses to double-strand breaks.
authors.affiliation: Laboratory of Stress Response Biology, Graduate School of Science, Kyoto University, Kitashirakawa-oiwakecho, Sakyo-ku, Kyoto 606-8501, Japan.|Department of Genome Repair Dynamics, Radiation Biology Center, Kyoto University, Yoshidakonoecho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Department of Genome Repair Dynamics, Radiation Biology Center, Kyoto University, Yoshidakonoecho, Sakyo-ku, Kyoto 606-8501, Japan.|Department of Interdisciplinary Environment, Graduate School of Human and Environmental Sciences, Kyoto University, Yoshidanihonmatsucho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Kasumi
authors.initials: K
authors.lastname: Kawamura
authors.affiliation: Department of Genetics and Cell Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Yanagihara
authors.affiliation: Department of Genome Repair Dynamics, Radiation Biology Center, Kyoto University, Yoshidakonoecho, Sakyo-ku, Kyoto 606-8501, Japan.|Department of Interdisciplinary Environment, Graduate School of Human and Environmental Sciences, Kyoto University, Yoshidanihonmatsucho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Kobayashi
authors.affiliation: Laboratory of Stress Response Biology, Graduate School of Science, Kyoto University, Kitashirakawa-oiwakecho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Qiu-Mei
authors.initials: QM
authors.lastname: Zhang-Akiyama
mesh_terms: D017766:Acid Anhydride Hydrolases; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D000076228:MRE11 Homologue Protein / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D016192:Resting Phase, Cell Cycle / Q000187:drug effects
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D007976:Leupeptins; C112156:NBN protein, human; D009687:Nuclear Proteins; D064007:Ataxia Telangiectasia Mutated Proteins; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: ATM; DNA damage; NBS1; cell cycle checkpoint; homologous recombination