Base Excision Repair of N⁶-Deoxyadenosine Adducts of 1,3-Butadiene

Abstract

The important industrial and environmental carcinogen, 1,3-butadiene (BD), forms a range of adenine adducts in DNA, including N6-(2-hydroxy-3-buten-1-yl)-2′-deoxyadenosine (N6-HB-dA), 1,N6-(2-hydroxy-3-hydroxymethylpropan-1,3-diyl)-2′-deoxyadenosine (1,N6-HMHP-dA), and N6,N6-(2,3-dihydroxybutan-1,4-diyl)-2′-deoxyadenosine (N6,N6-DHB-dA). If not removed prior to DNA replication, these lesions can contribute to A → T and A → G mutations commonly observed following exposure to BD and its metabolites. In the present study, base excision repair of BD-induced 2′-deoxyadenosine (BD-dA) lesions was investigated. Synthetic DNA duplexes containing site- and stereospecific S-N6-HB-dA, R,S-1,N6-HMHP-dA, and R,R-N6,N6-DHB-dA adducts were prepared by a post-oligomerization strategy. Incision assays with nuclear extracts from human fibrosarcoma (HT1080) cells have revealed that BD-dA adducts were recognized and cleaved by a BER mechanism, with relative excision efficiency in the order: S-N6-HB-dA > R,R-N6,N6-DHB-dA > R,S-1,N6-HMHP-dA. Strand cleavage at the adduct site was decreased in the presence of BER inhibitor methoxyamine and by competitor duplexes containing known BER substrates. Similar strand cleavage assays conducted using several eukaryotic DNA glycosylases/lyases [AAG, Mutyh, hNEIL1, and hOGG1] have failed to observe correct incision products at the BD-dA lesion sites, suggesting that a different BER enzyme may be involved in the removal of BD-dA adducts in human cells.

Analysis and Identification of 2′-Deoxyadenosine-Derived Adducts in Lung and Liver DNA of F-344 Rats Treated with the Tobacco-Specific Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and Enantiomers of its Metabolite 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol

“…Since other N 1 -dIno adducts form Hoogstein base pairs and flip outside the DNA helix, it is possible that our POBand PHB-N 1 -dIno adducts are prime targets for base excision repair or other DNA repair mechanisms. 31,44,45 In our preliminary studies of the reaction of NNKOAc with calf thymus DNA, we observed an HPLC peak which decreased relatively rapidly with time, as peaks corresponding to N 6 -POB-dAdo and N 1 -POB-dIno increased (data not shown). We presume that this peak was N 1 -POB-dA.…”

“…Since other N 1 -dIno adducts form Hoogstein base pairs and flip outside the DNA helix, it is possible that our POB- and PHB- N 1 -dIno adducts are prime targets for base excision repair or other DNA repair mechanisms. 31,44,45 …”

“…Even after rigorous application of this method, the dIno adducts remained undetected, perhaps due to their efficient repair in vivo . Since other N 1 -dIno adducts form Hoogstein base pairs and flip outside the DNA helix, it is possible that our POB- and PHB- N 1 -dIno adducts are prime targets for base excision repair or other DNA repair mechanisms. ,, …”

1,3-Butadiene-Induced Adenine DNA Adducts Are Genotoxic but Only Weakly Mutagenic When Replicated in Escherichia coli of Various Repair and Replication Backgrounds

“…In our recent study, we have shown that BD-dA adducts are rapidly repaired by nuclear extracts from human cells, but the identity of the glycosylase involved is yet to be established. 52 However, the rapid repair hypothesis may be insufficient to explain why three of the BD-dA lesions were genotoxic but not mutagenic.…”

Interindividual Differences in DNA Adduct Formation and Detoxification of 1,3-Butadiene-Derived Epoxide in Human HapMap Cell Lines

“…EB forms covalent adducts with DNA including N 6 -(2-hydroxy-3-buten-1-yl)-2′-deoxyadenosine, 1-(1-hydroxy-3-buten-2-yl)-adenine, 1-(2-hydroxy-3-buten-1-yl)-adenine, 3-(1-hydroxy-3-buten-2-yl)-adenine, 3-(2-hydroxy-3-buten-1-yl)-adenine, 7-(2-hydroxy-3-buten-1-yl)-adenine (EB-GI), and 7-(1-hydroxy-3-buten-2-yl)­guanine (EB-GII). − These adducts can cause DNA polymerase stalling and misreading during DNA replication, leading to toxicity and mutations. , If present in a tumor suppressor gene or a proto-oncogene, such mutations can lead to unrestricted cell growth and the development of cancer. , …”