title: MSH2-deficient human cells exhibit a defect in the accurate termination of homology-directed repair of DNA double-strand breaks.
abstract: Mutations in the mismatch repair (MMR) genes hMSH2 and hMLH1 have been associated with hereditary nonpolyposis colorectal cancer. Tumor cell lines that are deficient in MMR exhibit a high mutation rate, a defect in the response to certain types of DNA damage and in transcription-coupled repair, as well as an increase in the rate of gene amplification. We show here that hMSH2-deficient tumor cell lines lost most of their ability to accurately repair plasmid DNA double-strand breaks (DSBs) by homologous recombination, compared with MMR-proficient or hMLH1-deficient tumor cell lines. In all of these cell lines, DSB repair occurred almost exclusively by nonreciprocal homologous recombination: gene conversion (GC). However, there were two types of GC products: precise and rearranged. The rearranged products contained deletions or insertions of sequences and represented GC intermediates trapped at various stages and shunted to nonhomologous end joining. In MMR-proficient or MLH1-deficient cells, >50% of GC products were of the precise type, whereas in two MSH2-deficient backgrounds, this proportion decreased to 8%, whereas that of rearranged GC products increased by 2-fold. These results seem to predict a novel way by which MSH2-deficiency could promote mutation: deletion or insertion mutations associated with DSB repair, which may also contribute to cancer predisposition.
authors.affiliation: Department of Biochemistry, Université de Montréal, Succ. Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors.forename: Josée-France
authors.initials: JF
authors.lastname: Villemure
authors.forename: Christine
authors.initials: C
authors.lastname: Abaji
authors.forename: Isabelle
authors.initials: I
authors.lastname: Cousineau
authors.forename: Abdellah
authors.initials: A
authors.lastname: Belmaaza
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology; D020137:Base Pair Mismatch / Q000235:genetics*; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology; D004260:DNA Repair / Q000235:genetics*; D004261:DNA Replication; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins; D005785:Gene Conversion; D020022:Genetic Predisposition to Disease; D006801:Humans; D051718:MutS Homolog 2 Protein; D016296:Mutagenesis; D016254:Mutagenesis, Insertional; D010957:Plasmids / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D011995:Recombination, Genetic; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein