Distinct functions of Nijmegen breakage syndrome in ataxia telangiectasia mutated-dependent responses to DNA damage.
Phosphorylation of NBS1, the product of the gene mutated in Nijmegen breakage syndrome (NBS), by ataxia telangiectasia mutated (ATM), the product of the gene mutated in ataxia telangiectasia, is required for activation of the S phase checkpoint in response to ionizing radiation (IR). However, NBS1 is also thought to play additional roles in the cellular response to DNA damage. To clarify these additional functions of NBS1, we generated NBS cell lines stably expressing various NBS1 mutants from retroviral vectors. The ATM-dependent activation of CHK2 by IR was defective in NBS cells but was restored by ectopic expression of wild-type NBS1. The defects in ATM-dependent activation of CHK2, S phase checkpoint control, IR-induced nuclear focus formation, and radiation sensitivity apparent in NBS cells were not corrected by expression of NBS1 mutants that lack an intact MRE11 binding domain, suggesting that formation of the NBS1-MRE11-RAD50 complex is required for the corresponding normal phenotypes. Expression of NBS1 proteins with mutated ATM-targeted phosphorylation sites (serines 278 or 343) did not restore S phase checkpoint control but did restore the ability of IR to activate CHK2 and to induce nuclear focus formation and normalized the radiation sensitivity of NBS cells. Expression of NBS1 containing mutations in the forkhead-associated or BRCA1 COOH terminus domains did not correct the defects in radiation sensitivity or nuclear focus formation but did restore S phase checkpoint control in NBS cells. Together, these data demonstrate that multiple functional domains of NBS1 are required for ATM-dependent activation of CHK2, nuclear focus formation, S phase checkpoint control, and cell survival after exposure to IR.
Lee
Joo Hyeon
JH
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.
Xu
Bo
B
Lee
Chang-Hun
CH
Ahn
Jun-Young
JY
Song
Min Sup
MS
Lee
Ho
H
Canman
Christine E
CE
Lee
Jong-Soo
JS
Kastan
Michael B
MB
Lim
Dae-Sik
DS
D017766:Acid Anhydride Hydrolases; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D064447:Checkpoint Kinase 2; D004249:DNA Damage / Q000528:radiation effects; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D000076228:MRE11 Homologue Protein; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011839:Radiation, Ionizing; D013577:Syndrome; D025521:Tumor Suppressor Proteins; D018631:ras Proteins / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; C084355:RRAD protein, human; D025521:Tumor Suppressor Proteins; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D018631:ras Proteins; D045643:DNA Repair Enzymes