title: The mismatch repair system is required for S-phase checkpoint activation.
abstract: Defective S-phase checkpoint activation results in an inability to downregulate DNA replication following genotoxic insult such as exposure to ionizing radiation. This 'radioresistant DNA synthesis' (RDS) is a phenotypic hallmark of ataxia-telangiectasia, a cancer-prone disorder caused by mutations in ATM. The mismatch repair system principally corrects nucleotide mismatches that arise during replication. Here we show that the mismatch repair system is required for activation of the S-phase checkpoint in response to ionizing radiation. Cells deficient in mismatch repair proteins showed RDS, and restoration of mismatch repair function restored normal S-phase checkpoint function. Catalytic activation of ATM and ATM-mediated phosphorylation of the protein NBS1 (also called nibrin) occurred independently of mismatch repair. However, ATM-dependent phosphorylation and activation of the checkpoint kinase CHK2 and subsequent degradation of its downstream target, CDC25A, was abrogated in cells lacking mismatch repair. In vitro and in vivo approaches both show that MSH2 binds to CHK2 and that MLH1 associates with ATM. These findings indicate that the mismatch repair complex formed at the sites of DNA damage facilitates the phosphorylation of CHK2 by ATM, and that defects in this mechanism form the molecular basis for the RDS observed in cells deficient in mismatch repair.
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: Kevin D
authors.initials: KD
authors.lastname: Brown
authors.forename: Abhilasha
authors.initials: A
authors.lastname: Rathi
authors.forename: Ravindra
authors.initials: R
authors.lastname: Kamath
authors.forename: Dillon I
authors.initials: DI
authors.lastname: Beardsley
authors.forename: Qimin
authors.initials: Q
authors.lastname: Zhan
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Mannino
authors.forename: R
authors.initials: R
authors.lastname: Baskaran
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D064007:Ataxia Telangiectasia Mutated Proteins; D020137:Base Pair Mismatch / Q000235:genetics*; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D064447:Checkpoint Kinase 2; D004260:DNA Repair / Q000528:radiation effects; D004261:DNA Replication / Q000528:radiation effects; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D017353:Gene Deletion; D006801:Humans; D008954:Models, Biological; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011836:Radiation Tolerance / Q000235:genetics*; D011839:Radiation, Ionizing; D016196:S Phase / Q000528:radiation effects; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins; D020687:cdc25 Phosphatases / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; C112156:NBN protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein