Mutations associated with base excision repair deficiency and methylation-induced genotoxic stress.
The long-term effect of exposure to DNA alkylating agents is entwined with the cell's genetic capacity for DNA repair and appropriate DNA damage responses. A unique combination of environmental exposure and deficiency in these responses can lead to genomic instability; this "gene-environment interaction" paradigm is a theme for research on chronic disease etiology. In the present study, we used mouse embryonic fibroblasts with a gene deletion in the base excision repair (BER) enzymes DNA beta-polymerase (beta-pol) and alkyladenine DNA glycosylase (AAG), along with exposure to methyl methanesulfonate (MMS) to study mutagenesis as a function of a particular gene-environment interaction. The beta-pol null cells, defective in BER, exhibit a modest increase in spontaneous mutagenesis compared with wild-type cells. MMS exposure increases mutant frequency in beta-pol null cells, but not in isogenic wild-type cells; UV light exposure or N-methyl-N'-nitro-N-nitrosoguanidine exposure increases mutant frequency similarly in both cell lines. The MMS-induced increase in mutant frequency in beta-pol null cells appears to be caused by DNA lesions that are AAG substrates, because overexpression of AAG in beta-pol null cells eliminates the effect. In contrast, beta-pol/AAG double null cells are slightly more mutable than the beta-pol null cells after MMS exposure. These results illustrate that BER plays a role in protecting mouse embryonic fibroblast cells against methylation-induced mutations and characterize the effect of a particular combination of BER gene defect and environmental exposure.
Sobol
Robert W
RW
Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Watson
David E
DE
Nakamura
Jun
J
Yakes
F Michael
FM
Hou
Esther
E
Horton
Julie K
JK
Ladapo
Joseph
J
Van Houten
Bennett
B
Swenberg
James A
JA
Tindall
Kenneth R
KR
Samson
Leona D
LD
Wilson
Samuel H
SH
D000477:Alkylating Agents / Q000494:pharmacology; D000818:Animals; D010582:Bacteriophage lambda / Q000235:genetics; D020029:Base Pairing; D001665:Binding Sites; D019757:Carbon-Oxygen Lyases / Q000378:metabolism; D002478:Cells, Cultured; D004249:DNA Damage; D045647:DNA Glycosylases; D019175:DNA Methylation; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D005814:Genes, Viral; D008698:Mesylates / Q000494:pharmacology; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D016296:Mutagenesis; D009153:Mutagens / Q000494:pharmacology; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014764:Viral Proteins
D000477:Alkylating Agents; D008698:Mesylates; D009153:Mutagens; D014157:Transcription Factors; D014764:Viral Proteins; C039000:cII protein, bacteriophage lambda; C045880:methanesulfonic acid; D008769:Methylnitronitrosoguanidine; D019951:DNA Polymerase beta; C021565:3-methyladenine-DNA glycosylase; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D019757:Carbon-Oxygen Lyases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase