The goal of this application is to investigate the mechanism by which nitroaromatic carcinogens cause mutations. We shall focus on the major DNA adducts formed by the nitropyrenes, the primary mutagenic pollutants in diesel exhaust, but also plan to initiate work on the DNA adducts of 3-nitrobenzanthrone, a recently discovered potent mutagenic and carcinogenic contaminant in diesel. We hypothesize that a group of DNA adducts formed by these nitroarenes play important roles in the etiology of human cancer via the mutagenic effects in crucial sequences of cancer genes (e.g., p53). We also hypothesize that most of these mutations occur via error-prone bypass of the lesions by Y-family DNA polymerases. In order to test these hypotheses, we shall synthesize and characterize oligonucleotides containing the major guanine adducts of 1-nitropyene, 1,6- and 1,8-dinitropyere, and 3-nitrobenzanthrone in important gene sequences. These adduct-containing oligonucleotides will be used to construct single-stranded plasmid or viral vectors and mutagenicity and genotoxicity will be evaluated in Escherichia coli and mammalian cells. The effect of specific repair or replication proteins will be assessed by using repair-proficient and -deficient cell lines or inhibitors. The cellular studies will be complemented by investigating in vitro kinetics and fidelity of polymerization catalyzed by Dpo4 and four human Y- family DNA polymerases. Initially, we shall focus on the C8 guanine adduct of 1-nitropyrene. The translesion synthesis products will be sequenced to determine the mutagenic pattern caused by each DNA polymerase. Finally, duplex plasmid vectors with these adducts will be constructed, and progression of replication fork will be examined in human cell extracts to determine if each adduct is significant block to fork progression. Mutational types and frequencies in double-stranded DNA will be determined. Together, these studies will provide a deeper understanding of the mechanism of mutagenesis induced by the DNA adducts of these nitroaromatic carcinogens.
Nitroaromatic compounds have been detected in a variety of environmental samples, including diesel exhaust. These compounds are potent mutagens and carcinogens, and it has been suggested that some of these pollutants play a role in human lung and breast cancer. Therefore, investigation of the mechanism by which the nitroaromatic carcinogens cause mutations has high significance to public health.
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