Biochemical Basis of Genotoxicity of Heterocyclic Arylamine Food Mutagens

Abstract

Heterocyclic arylamines are highly mutagenic and cause tumors in animal models. The mutagenicity is attributed to the C 8 -and N 2 -G adducts, the latter of which accumulates due to slower repair. The C 8 -and N 2 -G adducts derived from 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ) were placed at the G 1 and G 3 sites of the NarI sequence, in which the G 3 site is an established hot spot for frameshift mutation with the model arylamine derivative 2-acetylaminofluorene but G 1 is not. Human DNA polymerase (pol) extended primers beyond template G-IQ adducts better than did pol and much better than pol or ␦. In 1-base incorporation studies, pol inserted C and A, pol inserted T, and pol inserted G. Steady-state kinetic parameters were measured for these dNTPs opposite the C 8 -and N 2 -IQ adducts at both sites, being most favorable for pol . Mass spectrometry of pol extension products revealed a single major product in each of four cases; with the G 1 and G 3 C 8 -IQ adducts, incorporation was largely error-free. With the G 3 N 2 -IQ adduct, a ؊2 deletion occurred at the site of the adduct. With the G 1 N 2 -IQ adduct, the product was error-free at the site opposite the base and then stalled. Thus, the pol products yielded frameshifts with the N 2 but not the C 8 IQ adducts. We show a role for pol and the complexity of different chemical adducts of IQ, DNA position, and DNA polymerases.

Replication Bypass of N2-Deoxyguanosine Interstrand Cross-Links by Human DNA Polymerases η and ι

“…31 It also efficiently extends from the matched primer termini opposite such lesions. In contrast, this polymerase shows a very ineffective bypass and a high propensity for misincorporation when it replicates past bulky benzo[ a ]pyrene diol epoxide, 32 CH 2 -9-anthracenyl, CH 2 -6-benzo[ a ]pyrenyl, 31 or 2-amino-3-methyimidazo[4,5- f ]quinoline 33 N 2 -dG adducts. Certain N 2 -dG lesions, such as the ring-closed analog of acrolein- N 2 -dG, 29 completely block pol η-catalyzed DNA synthesis in vitro , both at the insertion and extension step.…”

Mass spectrometry for the assessment of the occurrence and biological consequences of DNA adducts

“…4-aminobiphenyl, 4-ABP), 50 nitroaromatic compounds ( e.g. 2-nitrofluorene), 51 and heterocyclic aromatic amines found in cooked fish and meats, such as 2-amino-3-methylimidazo[4,5- f ]quinoline (IQ), 52 2-amino-1-methyl-6-phenylimidazo[4,5- b ]pyridine (PhIP), 53 and 2-amino-3,8-dimethylimidazo-[4,5- f ]quinoxaline (MeIQx). 54 Although the sites of substitution on nucleobases vary substantially, it appears that the C8 atom and the exocyclic amino nitrogen of the purine bases, particularly of guanine, are the major targets for arylamination.…”

Base-displaced intercalation of the 2-amino-3-methylimidazo[4,5-f]quinolone N2-dG adduct in the NarI DNA recognition sequence

“…The G 3 position is a hot spot for two-base frameshift deletions in bacterial mutagenesis assays, while the G 1 position is not (68–71). In addition, human DNA polymerase (hpol) η produces two-base deletions when replicating past the N 2 -dG-IQ adduct at position G 3 , in vitro (72). Thus, this sequence provides a platform for investigating sequence-specific conformational perturbation of DNA structure by IQ adducts, in relationship to their biological processing (68–71,73,74).…”