5-Methylcytosine in CpG Sites and the Reactivity of Nearest Neighboring Guanines Toward the Carcinogen Aflatoxin B1-8,9-Epoxide

Ross, Matthew K.; Mathison, Brian H.; Said, Boctor; Shank, Ronald C.

doi:10.1006/bbrc.1998.9895

Cited by 12 publications

(6 citation statements)

References 20 publications

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“…Our findings are in accord with previous reports by Mathison et al (30) and Sendowski and Rajewsky (29), who observed a reduction of N7-Me-G and O 6 -Me-dG adduct yields in synthetic oligomers with repeating sequence upon incorporation of Me C. We saw a similar protective effect of Me C against O 6 -pyridyloxobutylation (Figure 5), suggesting that this may be a general phenomenon for O 6 -guanine alkylation. Our results for codon 248 contradict the earlier study by Ross and collaborators (53), who reported that N7-Me-G yields are not affected by Me C. This discrepancy can be rationalized by the use of different methylating agents (dimethyl sulfate vs methyldiazohydroxide) and different detection methods (mass spectrometry of DNA hydrolysates vs gel electrophoresis of hot piperidine-cleaved DNA) (53). NNK diazohydroxides produce positively charged diazonium ions and/or carbocations that are likely to have different DNA sequence preferences than electrically neutral DMS.…”

Section: Discussioncontrasting

confidence: 98%

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

et al. 2003

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All CG dinucleotides along exons 5-8 of the p53 tumor suppressor gene contain endogenous 5-methylcytosine (MeC). These same sites (e.g., codons 157, 158, 245, 248, and 273) are mutational hot spots in smoking-induced lung cancer. Several groups used the UvrABC endonuclease incision assay to demonstrate that methylated CG dinucleotides of the p53 gene are the preferred binding sites for the diol epoxides of bay region polycyclic aromatic hydrocarbons (PAH). In contrast, effects of endogenous cytosine methylation on the distribution of DNA lesions induced by tobacco-specific nitrosamines, e.g., 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), have not been elucidated. In the work presented here, a stable isotope labeling HPLC-ESI-MS/MS approach was employed to analyze the reactivity of the N7 and O6 positions of guanines within hemimethylated and fully methylated CG dinucleotides toward NNK-derived methylating and pyridyloxobutylating species. 15N3-labeled guanine bases were placed within synthetic DNA sequences representing endogenously methylated p53 codons 154, 157, and 248, followed by treatment with acetylated precursors to NNK diazohydroxides. HPLC-ESI-MS/MS analysis was used to determine the relative yields of N7- and O6-guanine adducts at the 15N3-labeled position. In all cases, the presence of MeC inhibited the formation of N7-methylguanine, O6-methylguanine, and O6-pyridyloxobutylguanine at a neighboring G, with the greatest decrease observed in fully methylated dinucleotides and at guanines preceded by MeC. Furthermore, the O6-Me-dG/N7-Me-G molar ratios were decreased in the presence of the 5'-neighboring MeC, suggesting that the observed decline in O6-alkylguanine adduct yields is, at least partially, a result of an altered reactivity pattern in methylated CG dinucleotides. These results indicate that, unlike N2-guanine adducts of PAH diol epoxides, NNK-induced N7- and O6-alkylguanine adducts are not preferentially formed at the endogenously methylated CG sites within the p53 tumor suppressor gene.

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Section: Discussioncontrasting

confidence: 98%

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

et al. 2003

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“…The presence of a 5-methyl group on cytosine within Me CG sites induces a small change in DNA structure and dynamics, leading to altered DNA–protein interactions and chromatin remodeling – . It is also capable of increasing the reactivity of guanine bases in Me CG dinucleotides towards carcinogens ,– . We have previously shown that a neighboring Me C can have opposite effects on the reactivity of guanine bases towards two prominent tobacco carcinogens, a tobacco-specific nitrosamine (NNK) and a PAH, benzo[ a ]pyrene (B[ a ]P) , .…”

Section: Resultsmentioning

confidence: 99%

Sequence Distribution of Acetaldehyde-Derived N²-Ethyl-dG Adducts along Duplex DNA

Matter

Guza

Zhao

et al. 2007

Chem. Res. Toxicol.

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Acetaldehyde (AA) is the major metabolite of ethanol and may be responsible for an increased gastrointestinal cancer risk associated with alcohol beverage consumption. Furthermore, AA is one of the most abundant carcinogens in tobacco smoke and induces tumors of the respiratory tract in laboratory animals. AA binding to DNA induces Schiff base adducts at the exocyclic amino group of dG, N2-ethylidene-dG, which are reversible on the nucleoside level but can be stabilized by reduction to N2-ethyl-dG. Mutagenesis studies in the HPRT reporter gene and in the p53 tumor suppressor gene have revealed the ability of AA to induce G-->A transitions and A-->T transversions, as well as frameshift and splice mutations. AA-induced point mutations are most prominent at 5'-AGG-3' trinucleotides, possibly a result of sequence specific adduct formation, mispairing, and/or repair. However, DNA sequence preferences for the formation of acetaldehyde adducts have not been previously examined. In the present work, we employed a stable isotope labeling-HPLC-ESI+-MS/MS approach developed in our laboratory to analyze the distribution of acetaldehyde-derived N2-ethyl-dG adducts along double-stranded oligodeoxynucleotides representing two prominent lung cancer mutational "hotspots" and their surrounding DNA sequences. 1,7,NH 2-(15)N-2-(13)C-dG was placed at defined positions within DNA duplexes derived from the K-ras protooncogene and the p53 tumor suppressor gene, followed by AA treatment and NaBH 3CN reduction to convert N2-ethylidene-dG to N2-ethyl-dG. Capillary HPLC-ESI+-MS/MS was used to quantify N2-ethyl-dG adducts originating from the isotopically labeled and unlabeled guanine nucleobases and to map adduct formation along DNA duplexes. We found that the formation of N2-ethyl-dG adducts was only weakly affected by the local sequence context and was slightly increased in the presence of 5-methylcytosine within CG dinucleotides. These results are in contrast with sequence-selective formation of other tobacco carcinogen-DNA adducts along K-ras- and p53-derived duplexes and the preferential modification of endogenously methylated CG dinucleotides by benzo[a]pyrene diol epoxide and acrolein.

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“…Therefore, the observed hotspot in A-10 may reflect strong AFB 1 binding and weak repair at a methylated CGC sequence. To date, in vitro studies have provided contradictory evidence as to whether the presence of a 5-methylcytosine adjacent to a guanine enhances reactivity toward the AFB 1 -epoxide (33,34). It is also possible that an AFB 1 adduct, once formed in a methylated CpG site, is refractory to repair, because methylated sites are often bound by regulatory proteins (e.g., MBD4) (35).…”

Section: Discussionmentioning

confidence: 99%

Mutational spectra of aflatoxin B ₁ in vivo establish biomarkers of exposure for human hepatocellular carcinoma

Chawanthayatham

Valentine

Fedeles

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

110

113

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Aflatoxin B 1 (AFB 1 ) and/or hepatitis B and C viruses are risk factors for human hepatocellular carcinoma (HCC). Available evidence supports the interpretation that formation of AFB 1 -DNA adducts in hepatocytes seeds a population of mutations, mainly G:C→T:A, and viral processes synergize to accelerate tumorigenesis, perhaps via inflammation. Responding to a need for early-onset evidence predicting disease development, highly accurate duplex sequencing was used to monitor acquisition of high-resolution mutational spectra (HRMS) during the process of hepatocarcinogenesis. Four-day-old male mice were treated with AFB 1 using a regimen that induced HCC within 72 wk. For analysis, livers were separated into tumor and adjacent cellular fractions. HRMS of cells surrounding the tumors revealed predominantly G:C→T:A mutations characteristic of AFB 1 exposure. Importantly, 25% of all mutations were G→T in one trinucleotide context (CGC; the underlined G is the position of the mutation), which is also a hotspot mutation in human liver tumors whose incidence correlates with AFB 1 exposure. The technology proved sufficiently sensitive that the same distinctive spectrum was detected as early as 10 wk after dosing, well before evidence of neoplasia. Additionally, analysis of tumor tissue revealed a more complex pattern than observed in surrounding hepatocytes; tumor HRMS were a composite of the 10-wk spectrum and a more heterogeneous set of mutations that emerged during tumor outgrowth. We propose that the 10-wk HRMS reflects a short-term mutational response to AFB 1 , and, as such, is an early detection metric for AFB 1 -induced liver cancer in this mouse model that will be a useful tool to reconstruct the molecular etiology of human hepatocarcinogenesis. duplex sequencing | mycotoxins | cancer | mutagenesis | mouse model

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5-Methylcytosine in CpG Sites and the Reactivity of Nearest Neighboring Guanines Toward the Carcinogen Aflatoxin B1-8,9-Epoxide

Cited by 12 publications

References 20 publications

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Sequence Distribution of Acetaldehyde-Derived N²-Ethyl-dG Adducts along Duplex DNA

Mutational spectra of aflatoxin B ₁ in vivo establish biomarkers of exposure for human hepatocellular carcinoma

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5-Methylcytosine in CpG Sites and the Reactivity of Nearest Neighboring Guanines Toward the Carcinogen Aflatoxin B1-8,9-Epoxide

Cited by 12 publications

References 20 publications

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O6-Methylation and O6-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O6-Methylation and O6-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Sequence Distribution of Acetaldehyde-Derived N2-Ethyl-dG Adducts along Duplex DNA

Mutational spectra of aflatoxin B 1 in vivo establish biomarkers of exposure for human hepatocellular carcinoma

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Product

Resources

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Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Endogenous 5-Methylcytosine Protects Neighboring Guanines from N7 and O⁶-Methylation and O⁶-Pyridyloxobutylation by the Tobacco Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

Sequence Distribution of Acetaldehyde-Derived N²-Ethyl-dG Adducts along Duplex DNA

Mutational spectra of aflatoxin B ₁ in vivo establish biomarkers of exposure for human hepatocellular carcinoma