RESUMO
Mutations in DNA mismatch repair (MMR) genes cause hereditary nonpolyposis colorectal cancer (HNPCC), and MMR defects are associated with a significant proportion of sporadic cancers. MMR maintains genome stability and suppresses tumor formation by preventing the accumulation of mutations and by mediating an apoptotic response to DNA damage. We describe the analysis of a dominant MSH6 missense mutation in yeast and mice that causes loss of DNA repair function while having no effect on the apoptotic response to DNA damaging agents. Our results demonstrate that MSH6 missense mutations can effectively separate the two functions, and that increased mutation rates associated with the loss of DNA repair are sufficient to drive tumorigenesis in MMR-defective tumors.
Assuntos
Reparo do DNA , Proteínas de Ligação a DNA/metabolismo , Mutação de Sentido Incorreto , Neoplasias/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Animais , Apoptose/fisiologia , Células Cultivadas , Dano ao DNA , Proteínas de Ligação a DNA/genética , Suscetibilidade a Doenças , Ensaios de Seleção de Medicamentos Antitumorais , Fibroblastos/citologia , Fibroblastos/metabolismo , Humanos , Camundongos , Repetições de Microssatélites , Neoplasias/metabolismo , Neoplasias/patologia , Fenótipo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Taxa de SobrevidaRESUMO
Exonuclease 1 (Exo1) is a 5'-3' exonuclease that interacts with MutS and MutL homologs and has been implicated in the excision step of DNA mismatch repair. To investigate the role of Exo1 in mammalian mismatch repair and assess its importance for tumorigenesis and meiosis, we generated an Exo1 mutant mouse line. Analysis of Exo1(-/-) cells for mismatch repair activity in vitro showed that Exo1 is required for the repair of base:base and single-base insertion/deletion mismatches in both 5' and 3' nick-directed repair. The repair defect in Exo1(-/-) cells also caused elevated microsatellite instability at a mononucleotide repeat marker and a significant increase in mutation rate at the Hprt locus. Exo1(-/-) animals displayed reduced survival and increased susceptibility to the development of lymphomas. In addition, Exo1(-/-) male and female mice were sterile because of a meiotic defect. Meiosis in Exo1(-/-) animals proceeded through prophase I; however, the chromosomes exhibited dynamic loss of chiasmata during metaphase I, resulting in meiotic failure and apoptosis. Our results show that mammalian Exo1 functions in mutation avoidance and is essential for male and female meiosis.
