Our long-term objective is to study the +___________________________________ chemopreventive effect of retinoids on chronic and excessive alcohol related carcinogenesis in the liver and peripheral organs. The present grant proposal focuses on cell proliferation, which plays a central role in hepatic carcinogenesis in both the initiation and promotion stages, particularly when chemical carcinogens are involved. Retinoic acid plays an important role in controlling carcinogenic progression in a variety of cancers, including liver cancer. One of the chemopreventive effects of retinoids is thought to be mediated through control of proliferation via delaying progression of damaged cells into S phase, which allows for DNA repair and induction of apoptosis, thereby reducing the risk of carcinogenic initiation. However, long term and excessive ethanol intake reduces hepatic retinoid levels. The observation that retinoid concentrations are decreased in both plasma and cancerous liver tissues of hepatocarcinoma patients, suggests a role for retinoid depletion in hepatocarcinogenesis. However, it is not known 1) whether chronic ethanol-induced hepatocellular proliferation (which could convert hepatocytes from a state of resistance to a carcinogen to a state of susceptibility) is due to alcohol-impaired retinoid metabolism and signaling, and if so, 2) whether restoration of retinoid status by either inhibiting ethanol-induced retinoid catabolism or supplementing retinoic acid can suppress both ethanol-induced cell hyperproliferation as well as ethanol-promoted (diethylnitrosamine induced) hepatocellular carcinogenesis. We will investigate the possible role of diminished retinoid signaling and/or the up-regulation of the Jun N-terminal kinases-dependent (JNK) signaling pathway by chronic ethanol treatment on alcohol induced hepatocellular cell proliferation as well as alcohol-promoted hepatocellular carcinogenesis (induced by diethylnitrosamine). Simultaneously, we will test whether treatment with either chlormethiazole (an inhibitor of retinoic acid catabolism) and all-trans retinoic acid in ethanol-fed rats can inhibit alcohol-induced hepatocellular cell proliferation as well as alcohol-promoted hepatocellular carcinogenesis via either restoring normal retinoid signaling and/or inhibiting the JNK dependent signaling pathway. This study will be the first to link the regulation of retinoid signaling with Jun N-terminal kinases-dependent pathway, cell proliferation and apoptosis in an alcohol-treated, chemically induced carcinogenesis animal model, which would have implications for the prevention and treatment of alcohol related human cancers.
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