title: The absence of Mth1 inactivation and DNA polymerase kappa overexpression in rat mammary carcinomas with frequent A:T to C:G transversions.
abstract: Single nucleotide instability (SNI), an increase in spontaneous point mutation rates (MRs) without involvement of microsatellite instability, is present in rat mammary carcinoma cell lines and human breast cancer cell lines. A:T to C:G transversions, which are generally rare, were frequently observed in two rat mammary carcinoma cell lines and in their primary carcinomas, and were considered to be related to the molecular mechanism of SNI. In this study, two known molecular mechanisms that cause increases of A:T to C:G transversions, inactivation of the MutT mammalian homologue (Mth1) gene and overexpression of the DNA polymerase k (Pol k) gene, were analyzed in two rat mammary carcinoma cell lines and 11 rat primary carcinomas. PCR-SSCP analysis revealed no mutations in the entire Mth1 coding region. Quantitative real-time RT-PCR analysis showed that Mth1 mRNA expression was slightly, but significantly, increased in the primary carcinomas (P = 0.001 using GAPDH for normalization, and P = 0.002 using histone H4, t-test), contrary to our expectation, and was decreased to 1 / 2 in the cell lines. The expression of Pol k, which is known to be error-prone with frequent A:T to C:G transversions, was rather decreased in the cell lines and primary carcinomas. Inactivation of Mth1 and overexpression of Pol k were unlikely to have caused SNI in the two rat mammary carcinoma cell lines with a high frequency of A:T to C:G transversions, and searching for other unknown molecular mechanisms is important.
authors.affiliation: Carcinogenesis Division, National Cancer Center Research Institute, Chuo-ku, Tokyo 104-0045.
authors.forename: Eriko
authors.initials: E
authors.lastname: Okochi
authors.forename: Shizue
authors.initials: S
authors.lastname: Ichimura
authors.forename: Takashi
authors.initials: T
authors.lastname: Sugimura
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Ushijima
mesh_terms: D000818:Animals; D016587:Antimutagenic Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D045643:DNA Repair Enzymes; D018076:DNA, Complementary / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000096:biosynthesis*; D005091:Exons; D006801:Humans; D015674:Mammary Neoplasms, Animal / Q000235:genetics* / Q000378:metabolism*; D018895:Microsatellite Repeats; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D018807:Polymorphism, Single-Stranded Conformational; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D000099270:Y-Family DNA Polymerases
chemical_list: D016587:Antimutagenic Agents; D045643:DNA Repair Enzymes; D018076:DNA, Complementary; D004259:DNA-Directed DNA Polymerase; D010744:Phosphoric Monoester Hydrolases; D012333:RNA, Messenger; C404302:POLK protein, human; D000099270:Y-Family DNA Polymerases; C498614:Polk protein, rat; C078207:8-oxodGTPase