RESUMO
Germline mutations in the mismatch repair (MMR) genes are associated with Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC) syndrome. Here, we characterise a variant of hMLH1 that confers a loss-of-function MMR phenotype. The mutation changes the highly conserved Gly67 residue to a glutamate (G67E) and is reminiscent of the hMLH1-p.Gly67Arg mutation, which is present in several Lynch syndrome cohorts. hMLH1-Gly67Arg has previously been shown to confer loss-of-function (Shimodaira et al, 1998), and two functional assays suggest that the hMLH1-Gly67Glu protein fails to sustain normal MMR functions. In the first assay, hMLH1-Gly67Glu abolishes the protein's ability to interfere with MMR in yeast. In the second assay, mutation of the analogous residue in yMLH1 (yMLH1-Gly64Glu) causes a loss-of-function mutator phenotype similar to yMLH1-Gly64Arg. Despite these molecular similarities, an unusual spectrum of tumours is associated with hMLH1-Gly67Glu, which is not typical of those associated with Lynch syndrome and differs from those found in families carrying the hMLH1-Gly67Arg allele. This suggests that hMLH1 may have different functions in certain tissues and/or that additional factors may modify the influence of hMLH1 mutations in causing Lynch syndrome.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Neoplasias Colorretais Hereditárias sem Polipose/genética , Reparo de Erro de Pareamento de DNA/genética , Mutação/genética , Proteínas Nucleares/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Neoplasias Colorretais Hereditárias sem Polipose/metabolismo , Neoplasias Colorretais Hereditárias sem Polipose/patologia , Família , Teste de Complementação Genética , Humanos , Immunoblotting , Masculino , Pessoa de Meia-Idade , Proteína 1 Homóloga a MutL , Proteínas Nucleares/metabolismo , Fenótipo , SaccharomycetalesRESUMO
Inherited mutations in the BRCA2 gene predispose women to breast and ovarian cancer. We created a mutation in the mouse Brca2 gene that terminates translation in exon 11 at 45% of the normal transcript length. Ninety % of Brca2(tm1Cam) homozygous mutant mice die prenatally or perinatally. The location of the Brca2(tm1Cam) mutation differs from those reported previously, and this phenotype suggests a correlation with genotype analogous to that previously reported in humans. Although heterozygote mice have remained free of tumors for 10 months, Brca2(tm1Cam) homozygous mutants that survived to adulthood died with thymic lymphomas between 12 and 14 weeks of age.
Assuntos
Linfoma/genética , Mutação , Proteínas de Neoplasias/genética , Timo/fisiologia , Fatores de Transcrição/genética , Alelos , Animais , Proteína BRCA2 , Éxons , Genótipo , Homozigoto , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Proteínas de Neoplasias/fisiologia , Fenótipo , Fatores de Transcrição/fisiologiaRESUMO
Cancer-causing mutations often arise from gross chromosomal rearrangements (GCRs) such as translocations, which involve genetic exchange between nonhomologous chromosomes. Here we show that murine Brca2 has an essential function in suppressing GCR formation after chromosome breakage. Cells that harbor truncated Brca2 spontaneously incur GCRs and genomic DNA breaks during division. They exhibit hypersensitivity to DNA damage by interstrand cross-linkers, which even at low doses trigger aberrant genetic exchange between nonhomologous chromosomes. Therefore, genetic instability in Brca2-deficient cells results from the mutagenic processing of spontaneous or induced DNA damage into gross chromosomal rearrangements, providing a mechanistic basis for cancer predisposition.
Assuntos
Aberrações Cromossômicas , Cromossomos/genética , Inativação Gênica , Proteínas de Neoplasias/genética , Fatores de Transcrição/genética , Translocação Genética , Animais , Anexina A5/metabolismo , Proteína BRCA2 , Células Cultivadas , Reagentes de Ligações Cruzadas/farmacologia , Dano ao DNA , Reparo do DNA/genética , Proteínas de Ligação a DNA/genética , Citometria de Fluxo , Predisposição Genética para Doença , Marcação In Situ das Extremidades Cortadas , Cariotipagem , Fígado/embriologia , Camundongos , Mitomicina/farmacologia , Mutagênese , Rad51 Recombinase , Recombinação GenéticaRESUMO
Abnormalities precipitated by a targeted truncation in the murine gene Brca2 define its involvement in DNA repair. In culture, cells harboring truncated Brca2 exhibit a proliferative impediment that worsens with successive passages. Arrest in the G1 and G2/M phases is accompanied by elevated p53 and p21 expression. Increased sensitivity to genotoxic agents, particularly ultraviolet light and methylmethanesulfonate, shows that Brca2 function is essential for the ability to survive DNA damage. But checkpoint activation and apoptotic mechanisms are largely unaffected, thereby implicating Brca2 in repair. This is substantiated by the spontaneous accumulation of chromosomal abnormalities, including breaks and aberrant chromatid exchanges. These findings define a function of Brca2 in DNA repair, whose loss precipitates replicative failure, mutagen sensitivity, and genetic instability reminiscent of Bloom syndrome and Fanconi anemia.