Styrene and butadiene, used in the production of rubber and plastics, are implicated in the etiology of human cancer. Butadiene is classified by the USEPA as """"""""carcinogenic to humans by inhalation"""""""", by the NTP as a """"""""known human carcinogen"""""""". Chronic occupational exposures to mixtures of styrene and butadiene correlate with risk for leukemias. This project will examine the etiology of butadiene-induced mutagenesis, developing structure-activity relationships for DNA adducts arising from butadiene epoxides and associated with human genotoxicity.
The first aim will combine NMR, crystallography, and biochemical approaches to examine N1- deoxyinosine adducts arising from deamination of N1-deoxyadenosine alkylation products. We propose a role for Y-family Pol i utilizing the Hoogsteen face of dl for templating, allowing incorporation of protonated dCTP or dATP.
The second aim will employ NMR and crystallographic approaches to examine stereoisomeric N3-dU adducts of butadiene monoepoxide, which arise from deamination of N3-dC adducts. We propose that they do not undergo rotation about the glycosyl bond, into the syn conformation, thus leading to fundamentally different biological and mutagenic outcomes.
The third aim will use NMR, biochemical, and site-specific mutagenesis to examine N7-dG adducts arising from exposures to butadiene epoxides. Emphasis will be placed on relationships of N7-dG adduction to the formation of interstrand and intrastrand crosslinks by butadiene diepoxide;this depends upon DNA sequence and diepoxide stereochemistry. Interstrand crosslinks form in 5'-GNC-3'sequences. We propose that the orientations of N7-dG butadiene diol epoxide mono-adducts depend upon stereochemistry, differentially orienting the diol epoxides for interstrand vs. intrastrand crosslinking. The chemistry, mutational spectra, and replication bypass of N7-dG FAPy re-arrangement products will be examined. Overall, we will delineate mechanism(s) by which N1-dl and N3-dU butadiene adducts induce mutations, and why specific polymerase(s) mediate lesion bypass. Insight will be gained into DNA crosslinking chemistry of butadiene diepoxides. Insight will be gained into the chemistry of butadiene N7-dG FAPy lesions, their biological processing, and their structures. This is essential to understanding how occupational exposures to mixtures of styrene and butadiene contribute to human genotoxicity and cancer etiology.
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