Conformational Insights Into Aminobiphenyl-Modified DNA: Implications for Mutation and Repair

Abstract

Cancer is a major public health problem worldwide. An estimated 1.6 million new cases of cancer will be diagnosed in the United States in 2017. Most cancers are assumed to develop from the initiation of chemically induced DNA damages. Chemical carcinogens are genotoxic and they undergo enzymatic activation into reactive electrophilic species to form covalent bonds with the electron-rich DNA that form adducts. Aromatic amines are one of the most examined chemical carcinogens, and once activated, these amines attack the C-8 position of guanine to form C8-dG adducts (ABP [N-(2′-deoxyguanosin-8-yl)-2-aminobiphenyl], AF [N-(2′-deoxyguanosin-8-yl)-2-aminofluorene], and AAF [N-(2′-deoxyguanosin-8-yl)-2 acetylaminofluorene]); these formations result in DNA lesions. These bulky DNA lesions at the replication fork can induce a conformational heterogeneity, which complicates mutational outcomes. These outcomes are due to a single DNA adduct that can adopt multiple conformations at the replication fork, and a polymerase may process each conformation in different ways. Studies have shown differences in the mutational consequences of arylamine adducts in different DNA sequences. AF, AAF, and ABP all adopt anti B-DNA , syn stacked (S), and wedge (W) DNA conformational heterogeneity depending on sequence contexts. A replication polymerase is likely to stall or completely stop DNA synthesis when it encounters a bulky DNA lesion; this outcome allows recruitment of various bypass polymerases. This move will determine whether the synthesis is to be error free or error prone. Understanding the processes involving replication polymerases in arylamine-induced translesion synthesis is important; these processes are implicated in mutation and repair. Our working hypothesis is that the sequence-dependent arylamine-conformational heterogeneity is an important consideration for its mutational and repair outcomes. In Manuscript I (to be submitted to Journal of Chemical Research in Toxicology), we explored the arylamine-conformational heterogeneity. We previously reported a 3′-next flanking sequence effect [G*CT vs. G*CA; G*, FABP, N-(2′-deoxyguanosin-8-yl)-4′-fluoro-4-aminobiphenyl; FAF, N-(2′-deoxyguanosin-8-yl)-7-fluoro-2-aminofluorene] on arylamine-DNA lesions in relation to DNA replication and repair. In the present study, we present an unusual sequence effect on a 16-mer fully paired DNA duplex 5′-CTTCTG1G2TCCTCATTC-3′, in which the same lesion modification at G1 and G2 revealed a dramatic difference in S (base-displaced stacked)/B (major groove binding B-type) conformational heterogeneity. We obtained conformational (19F-NMR/CD), calorimetric (DSC and ITC), and binding (SPR) data for a set of four 16-mer modified templates (FABP vs. FAF and TG1*G2T vs. TG1G2*T) during primer elongation. Dynamic 19F-NMR results indicate that FABP modification at G1 and G2 resulted in 67%:33% of B:S and 100% B