Levels of H-ras codon 61 CAA to AAA mutation: response to 4-ABP-treatment and Pms2-deficiency.
DNA mismatch repair (MMR) deficiencies result in increased frequencies of spontaneous mutation and tumor formation. In the present study, we tested the hypothesis that a chemically-induced mutational response would be greater in a mouse with an MMR-deficiency than in the MMR-proficient mouse models commonly used to assay for chemical carcinogenicity. To accomplish this, the induction of H-ras codon 61 CAA-->AAA mutation was examined in Pms2 knockout mice (Pms2-/-, C57BL/6 background) and sibling wild-type mice (Pms2+/+). Groups of five or six neonatal male mice were treated with 0.3 micromol 4-aminobiphenyl (4-ABP) or the vehicle control, dimethylsulfoxide. Eight months after treatment, liver DNAs were isolated and analysed for levels of H-ras codon 61 CAA-->AAA mutation using allele-specific competitive blocker-PCR. In Pms2-proficient and Pms2-deficient mice, 4-ABP treatment caused an increase in mutant fraction (MF) from 1.65x10(-5) to 2.91x10(-5) and from 3.40x10(-5) to 4.70x10(-5), respectively. Pooling data from 4-ABP-treated and control mice, the approximately 2-fold increase in MF observed in Pms2-deficient as compared with Pms2-proficient mice was statistically significant (P=0.0207) and consistent with what has been reported previously in terms of induction of G:C-->T:A mutation in a Pms2-deficient background. Pooling data from both genotypes, the increase in H-ras MF in 4-ABP-treated mice, as compared with control mice, did not reach the 95% confidence level of statistical significance (P=0.0606). The 4-ABP treatment caused a 1.76-fold and 1.38-fold increase in average H-ras MF in Pms2-proficient and Pms2-deficient mice, respectively. Furthermore, the levels of induced mutation in Pms2-proficient and Pms2-deficient mice were nearly identical (1.26x10(-5) and 1.30x10(-5), respectively). We conclude that Pms2-deficiency does not result in an amplification of the H-ras codon 61 CAA-->AAA mutational response induced by 4-ABP.
Parsons
Barbara L
BL
Division of Genetic and Reproductive Toxicology, Division of Biometry and Risk Assessment and Division of Biochemical Toxicology, National Center for Toxicological Research, USFDA, Jefferson, AR 72079, USA. bparsons@nctr.fda.gov
Delongchamp
Robert R
RR
Beland
Frederick A
FA
Heflich
Robert H
RH
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000502:physiology*; D000611:Aminobiphenyl Compounds / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D002273:Carcinogens / Q000494:pharmacology*; D003062:Codon / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D008099:Liver / Q000187:drug effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000070976:Mismatch Repair Endonuclease PMS2; D017354:Point Mutation
D000611:Aminobiphenyl Compounds; D002273:Carcinogens; D003062:Codon; D004268:DNA-Binding Proteins; C006757:4-biphenylamine; D004247:DNA; D000251:Adenosine Triphosphatases; C499533:Pms2 protein, mouse; D000070976:Mismatch Repair Endonuclease PMS2; D045643:DNA Repair Enzymes