title: Mutation spectrum of MSH3-deficient HHUA/chr.2 cells reflects in vivo activity of the MSH3 gene product in mismatch repair.
abstract: The endometrial tumor cell line HHUA carries mutations in two mismatch repair (MMR) genes MSH3 and MSH6. We have established an MSH3-deficient HHUA/chr.2 cell line by introducing human chromosome 2, which carries wild-type MSH6 and MSH2 genes, to HHUA cells. Introduction of chromosome 2 to HHUA cells partially restored G:G MMR activity to the cell extract and reduced the frequency of mutation at the hypoxanthine-guanine phosphoribosyltransferase (hprt*) locus to about 3% that of the parental HHUA cells, which is five-fold the frequency in MMR-proficient cells, indicating that the residual mutator activity in HHUA/chr.2 is due to an MSH3-deficiency in these cells. The spectrum of mutations occurring at the HPRT locus of HHUA/chr.2 was determined with 71 spontaneous 6TG(r) clones. Base substitutions and +/-1 bp frameshifts were the major mutational events constituting, respectively, 54% and 42% of the total mutations, and more than 70% of them occurred at A:T sites. A possible explanation for the apparent bias of mutations to A:T sites in HHUA/chr.2 is haploinsufficiency of the MSH6 gene on the transferred chromosome 2. Comparison of the mutation spectra of HHUA/chr.2 with that of the MSH6-deficient HCT-15 cell line [S. Ohzeki, A. Tachibana, K. Tatsumi, T. Kato, Carcinogenesis 18 (1997) 1127-1133.] suggests that in vivo the MutSalpha (MSH2:MSH6) efficiently repairs both mismatch and unpaired extrahelical bases, whereas MutSbeta (MSH2:MSH3) efficiently repairs extrahelical bases and repairs mismatch bases to a limited extent.
authors.affiliation: Department of Radiation Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tauchi
authors.forename: K
authors.initials: K
authors.lastname: Komatsu
authors.forename: K
authors.initials: K
authors.lastname: Ishizaki
authors.forename: F
authors.initials: F
authors.lastname: Yatagai
authors.forename: T
authors.initials: T
authors.lastname: Kato
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D020137:Base Pair Mismatch / Q000235:genetics*; D001483:Base Sequence; D002889:Chromosomes, Human, Pair 2 / Q000235:genetics; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000235:genetics; D016368:Frameshift Mutation; D006801:Humans; D006822:Hybrid Cells; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D000074081:MutS Homolog 3 Protein; D016254:Mutagenesis, Insertional; D009154:Mutation; D017354:Point Mutation; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D007041:Hypoxanthine Phosphoribosyltransferase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D000074081:MutS Homolog 3 Protein; C094443:G-T mismatch-binding protein; C078444:MSH3 protein, human; C421109:multidrug resistance-associated protein 1