title: Mutational specificity of mice defective in the MTH1 and/or the MSH2 genes.
abstract: Oxidative damage of nucleotides within DNA or precursor pools caused by oxygen radicals is thought to play an important role in spontaneous mutagenesis, as well as carcinogenesis and aging. In particular, 8-oxodGTP and 2-OHdATP are potent mutagenic substrate for DNA synthesis. Mammalian MTH1 catalyzes hydrolysis of these mutagenic substrates, suggesting that it functions to prevent mutagenesis caused by these oxidized nucleotides. We have established MTH1(-/-) mice lacking the 8-oxodGTPase activity, which were shown to be susceptible to lung, liver and stomach cancers. To examine in vivo mutation events due to the MTH1-deficiency, a reporter gene, rpsL of Escherichia coli, was introduced into MTH1(-/-) mice. Interestingly, the net frequency of rpsL(-) forward mutants showed no apparent increase in MTH1(-/-) mice as compared to MTH1(+/+) mice. However, we found differences between these two genotypes in the class- and site-distributions of the rpsL(-) mutations recovered from the mice. Unlike MutT-deficient E. coli showing 1000-fold higher frequency of A:T-->C:G transversion than the wild type cells, an increase in frequency of A:T-->C:G transversion was not evident in MTH1 nullizygous mice. Nevertheless, the frequency of single-base frameshifts at mononucleotide runs was 5.7-fold higher in spleens of MTH1(-/-) mice than in those of wild type mice. Since the elevated incidence of single-base frameshifts at mononucleotide runs is a hallmark of the defect in MSH2-dependent mismatch repair system, this weak site-specific mutator effect of MTH1(-/-) mice could be attributed to a partial sequestration of the mismatch repair function that may act to correct mispairs with the oxidized nucleotides. Consistent with this hypothesis, a significant increase in the frequency of G:C-->T:A transversions was observed with MTH1(-/-) MSH2(-/-) mice over MSH2(-/-) mice alone. These results suggest a possible involvement of multiple anti-mutagenic pathways, including the MTH1 protein and other repair system(s), in mutagenesis caused by the oxidized nucleotides.
authors.affiliation: Department of Medical Biophysics and Radiation Biology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Egashira
authors.forename: Kazumi
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yoshiyama
authors.forename: Hisaya
authors.initials: H
authors.lastname: Kawate
authors.forename: Motoya
authors.initials: M
authors.lastname: Katsuki
authors.forename: Mutsuo
authors.initials: M
authors.lastname: Sekiguchi
authors.forename: Keizo
authors.initials: K
authors.lastname: Sugimachi
authors.forename: Hisaji
authors.initials: H
authors.lastname: Maki
authors.forename: Teruhisa
authors.initials: T
authors.lastname: Tsuzuki
mesh_terms: D000818:Animals; D020137:Base Pair Mismatch; D001483:Base Sequence; D004249:DNA Damage; D004252:DNA Mutational Analysis; D017931:DNA Primers / Q000737:chemistry; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins; D003848:Deoxyguanine Nucleotides / Q000378:metabolism; D029968:Escherichia coli Proteins; D005260:Female; D005787:Gene Frequency; D018390:Gene Targeting; D005838:Genotype; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D051718:MutS Homolog 2 Protein; D016296:Mutagenesis / Q000187:drug effects; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D013154:Spleen / Q000378:metabolism
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D003848:Deoxyguanine Nucleotides; D029968:Escherichia coli Proteins; D011518:Proto-Oncogene Proteins; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; C000717190:RpsI protein, E coli; C034212:ribosomal protein S12; C078206:8-oxodeoxyguanosine triphosphate; D010744:Phosphoric Monoester Hydrolases; C497173:Msh2 protein, mouse; D051718:MutS Homolog 2 Protein; C078207:8-oxodGTPase; D045643:DNA Repair Enzymes