The principle aim of our research is to define and delineate the molecular mechanisms underlying and specifying the relationship between environmental exposure and human disease. Metabolic detoxification of environmental carcinogens such as benzo[a]pyrene, as well as toxic plant products like aflatoxin, is generally accomplished by a two-step pathway involving an activation step (Phase I) and a conjugation step (Phase II), ultimately resulting in the formation of an excretable derivative of the parent compound. Paradoxically, the end products of Phase I metabolism are often much more toxic than their precursors, and tight coupling of Phase I and Phase II activities is necessary to avoid toxicity, mutagenesis and carcinogenesis induced by Phase I products. Our model system involves the study of the Phase I gene (Cyplal) encoding a cytochrome P450 monooxygenase and a Phase II gene (Nmo-1) encoding an NAD(P)H-dependent menadione oxidoreductase (DT diaphorase). We have shown that the transcription of these two genes is coordinately induced by environmental contaminants such as dioxin and other ligands of the aromatic hydrocarbon receptor, yet differentially regulated by butylated hydroxytoluene, DNA-damaging agents, protein kinase-C activators, and a genetic locus on mouse chromosome 7 that induce only the Phase II gene. In order to address the molecular mechanisms for these effects we propose: to identify and characterize the transcriptional and post-transcriptional regulatory signals controlling the mouse Nmo-1 gene; to identify and purify novel the DNA/RNA-binding proteins mediating these signals; and to clone the genes responsible for those Nmo-1 regulatory proteins. Characterization of these proteins should provide valuable tools for the intelligent design of drugs that could provide a protective effect from toxic and mutagenic environmental chemicals and natural toxins in our foodstuff.
