n-(deoxyguanosin-8-yl)-1-aminopyrene and 1-nitropyrene

1-Nitropyrene (1-NP), the predominant nitropolycyclic hydrocarbon found in diesel exhaust, is a mutagen and tumorigen. Nitroreduction is a major pathway by which 1-NP is metabolized. Reductively activated 1-NP forms a major DNA adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene (dGAP), both in vitro and in vivo. In Salmonella typhimurium 1-NP induces a CpG deletion in a CGCGCGCG sequence. In Escherichia coli, however, mostly -1 and +1 frame-shifts are observed, which occur predominantly in 5'-CG, 5'-GC, and 5'-GG sequences. In order to determine the mechanism of mutagenesis by dGAP in a CpG repetitive sequence, we constructed a single-stranded M13 genome containing the adduct at the underscored deoxyguanosine of an inserted CGCGCG sequence. In E. coli strains with normal repair capability the adduct induced approximately 2% CpG deletions, which was 20-fold that of the control. With SOS, the frequency of frame-shift mutations increased to 2.6%, even though the frequency of CpG deletion accompanied 50% reduction. The enhancement in mutagenesis was due to a +1 frame-shift that occurred at a high frequency. In strains with a defect in methyl-directed mismatch repair, 50-70% increase in mutation frequency was observed. When these strains were SOS induced, frame-shift mutagenesis increased by approximately 100%. When transfections were carried out in dnaQ strains that are impaired in 3'-->5'exonuclease activity of DNA polymerase III, frame-shift mutagenesis increased 5-7-fold. dGAP-induced frame-shifts in the (CG)3 sequence, therefore, varied from 2% to 17% depending on the state of repair of the host cells. We conclude that dGAP induces both -2 and +1 frame-shifts in a CpG repetitive sequence and that these two mutagenic events are competing pathways. The CpG deletion does not require SOS functions, whereas the +1 frame-shifts are SOS-dependent. On the basis of the data in repair-deficient strains, it appears that both types of frame-shifts occurred as a result of misalignment, which are corrected primarily by the proofreading exonuclease of the DNA polymerase. Misaligned structures that escape the exonuclease are repaired by the methyl-directed mismatch repair, albeit with limited efficiency.

Topics: Bacteriophage M13; Base Sequence; Deoxyguanosine; DNA Adducts; DNA Repair; DNA, Bacterial; Escherichia coli; Frameshift Mutation; Models, Genetic; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutagens; Pyrenes; RNA, Bacterial; Salmonella typhimurium; SOS Response, Genetics

A 25mer oligonucleotide containing a single N-(deoxyguanosin-8-yl-)-1-aminopyrene (dGAP), the major DNA adduct formed by reductively activated 1-nitropyrene, was synthesized. The adduct was located at nucleotide 21 from the 3' end. DNA synthesis on this template by human DNA polymerases alpha and beta, HIV reverse transcriptase, Sequenase (version 2.0) and Klenow fragment of DNA polymerase I was strongly blocked at the nucleotide 3' to the adduct site. Only when a 3'-->5' exonuclease-deficient Klenow fragment was used was incorporation of a nucleotide opposite the adduct observed. Nevertheless, extension beyond the adduct site did not occur to a significant extent. Only a relatively small proportion of full-length product (< 5%) was detected. In the presence of Mn2+, the efficiency of bypass with this polymerase increased. When a 20mer primer was elongated in the presence of only one nucleotide triphosphate, deoxycytidylic acid was preferentially incorporated opposite the adduct. Deoxycytidine opposite the adduct was also preferred when a set of 21mer primers (containing each of the four nucleotides opposite dGAP) were elongated to a full-length product in the presence of all four deoxynucleotide triphosphates. In order to confirm these results, extension of a 15mer primer was carried out with all four deoxynucleotide triphosphates and the products were isolated. Maxam--Gilbert sequencing of each elongation product showed that primer extension occurred in an error-free manner. We conclude that dGAP is a strong block of DNA replication. However, when translesion synthesis occurs, it is largely accurate.

Topics: Base Sequence; Binding Sites; Deoxycytosine Nucleotides; Deoxyguanosine; DNA; DNA Adducts; DNA Replication; DNA-Directed DNA Polymerase; Molecular Sequence Data; Nucleotides; Oligonucleotides; Pyrenes; Sensitivity and Specificity; Templates, Genetic

1-Nitropyrene, the most abundant nitro-polycyclic aromatic hydrocarbon in the environment, is a known mammalian and bacterial mutagen and a tumorigen in animals. Early studies on DNA adduct characterization for 1-nitropyrene identified N-(deoxyguanosin-8-yl)-1-aminopyrene as the major product from the modification of calf thymus DNA with N-hydroxy-1-aminopyrene, the activated metabolite from nitroreduction of 1-nitropyrene. In this paper, we report the identification of two N2-deoxyguanosinyl adducts, in addition to N-(deoxyguanosin-8-yl)-1-aminopyrene, formed from the reaction of N-hydroxy-1-aminopyrene, prepared in situ, with calf thymus DNA. These DNA adducts were identified as 6-(deoxyguanosin-N2-yl)-1-aminopyrene and 8-(deoxyguanosin-N2-yl)-1-aminopyrene. The two N2-deoxyguanosinyl adducts were also identified in an ascorbic acid-catalyzed activation of 1-nitrosopyrene and in the mammary gland of female Sprague-Dawley rats administered 1-nitropyrene. The DNA adducts were also formed when 1-nitropyrene was metabolized by xanthine oxidase in the presence of calf thymus DNA, and when 1-nitropyrene was activated by rat liver microsomes and cytosols, as well as from DNA isolated from Salmonella typhimurium suspension cultures incubated with 1-nitropyrene.

Topics: Animals; Ascorbic Acid; Catalysis; Cattle; Chromatography, High Pressure Liquid; Deoxyguanosine; DNA Adducts; DNA, Bacterial; Environmental Pollutants; Epithelial Cells; Epithelium; Female; Mammary Glands, Animal; Microsomes, Liver; Mutagens; Nitrogen; Pyrenes; Rats; Rats, Sprague-Dawley; Salmonella typhimurium; Xanthine Oxidase

[3H]1-Nitropyrene was administered at a dose of 25 mg/kg by i.p. injection to female Wistar rats. Animals were killed 24 h later and DNA was isolated from kidney, liver and mammary gland, enzymically hydrolysed and analysed by reverse-phase h.p.l.c. A major adduct peak was detected in DNA from each of the three organs. Enzymic hydrolysates of DNA, which had been reacted in vitro with 1-nitropyrene in the presence of xanthine oxidase, were similarly analysed by h.p.l.c. One major adduct peak was obtained which had the same retention time as the in vivo product. Confirmatory evidence that the in vivo adduct and the in vitro adduct were structurally similar was obtained from the determination of the pH-dependent solvent partitioning profiles. Further, treatment of the in vivo adduct from liver, kidney or mammary gland DNA hydrolysates and the in vitro adduct with sodium hydroxide resulted in the formation of a more polar product which eluted earlier on h.p.l.c. This behaviour is consistent with scission of the imidazole ring of a deoxyguanosine adduct. The major DNA adduct formed in vitro following xanthine oxidase reduction of 1-nitropyrene has previously been identified by others as N-(deoxyguanosin-8-yl)-1-aminopyrene. The present data suggest that the in vivo 1-nitropyrene-DNA adduct has the same structure.

Topics: Animals; Chromatography, High Pressure Liquid; Deoxyguanosine; DNA; Female; Hydrolysis; In Vitro Techniques; Kidney; Liver; Mammary Glands, Animal; Pyrenes; Rats; Rats, Inbred Strains; Sodium Hydroxide; Xanthine Oxidase