Cancer preventive agents found in the diet such as dithiolethiones can inhibit the initiation of cancer by increasing the expression of enzymes that inactivate tissue damaging chemicals. Using differential hybridization cloning techniques to find genes not previously characterized that are transcriptionally induced, a cDNA clone encoding dithiolethione-inducible gene-1 (DIG-1) was isolated and sequenced. Preliminary evidence hereby presented indicates that the enzyme might be able to inactivate quinone-containing carcinogens present in the environment, e.g. tobacco smoke. On a pilot scale, DIG-1 purified from rat hepatic tissue displayed high levels of quinone reductase activity. The hypothesis for the proposed research is that DIG-1 in inactivating the mutagenic and carcinogenic products of quinones. The specific objectives of the proposed studies are to purify larger quantities of DIG-1 from rat hepatic tissues and characterize its specific substrates, including quinone-containing carcinogens. The metabolism of the quinone-containing substrates of DIG-1 will be examined by over-expressing the enzyme in mammalian cell culture. The resulting inhibition of mutagenicity and cytotoxicity of quinones will then be monitored. The DIG-1 gene and its regulatory regions that respond to different classes of cancer chemoprotectors will be identified and the components of its regulatory pathway elucidated by standard molecular biological techniques. Altogether, these studies will define the protective role for DIG-1 in response to cancer preventive agents, and provide knowledge of the inducible cellular defense signals that control anticarcinogenesis.
