The metabolism of retinoids and the regulation of gene expression by retinoids via nuclear receptors are profoundly altered in human prostate cancer cells and we hypothesize that these changes contribute to the characteristics of these malignant cells. To define the molecular bases for the failure of many human prostate carcinoma cell lines to express genes involved in retinoid metabolism (e.g. lecithin:retinol acyl transferase), and genes involved in retinoid signaling (e.g. RARs and RXRs), we will study their transcriptional regulation using chromatin immunoprecipitation (ChIP) and real-time RT-PCR assays (AIM 1a). To attempt to restore normal retinoid signaling and growth inhibition pathways in human prostate cancer cells, we will use pharmacological doses of retinoids in combination with other drugs, including RXR (retinoid X receptor) agonists (the omega-3 fatty acid docosahexaenoic acid, phytanic acid), and histone deacetylase inhibitors such as valproic acid (AIM 1b). We will also determine if these drug combinations can restore normal vitamin A (retinol) uptake and metabolism in the human prostate cancer cells (AIM 1c). The functions of enzymes and nuclear receptors in the retinoid signaling pathway will also be tested in two models of prostate cancer: a xenograft model of human tumors and a transgenic model of spontaneous prostate cancer development, the TRAMP model (AIM 2). These animal models will allow us to determine whether retinoid signal transduction abnormalities develop during the process of prostate tumorigenesis, and whether the modulation of retinol uptake and esterification prevents tumors from forming and/or slows tumor progression by altering cell differentiation in the TRAMP model. These experiments will provide insights into the basic mechanisms underlying prostate cancer progression. The knowledge generated from these studies should allow us to devise better pharmacological strategies to reverse specific gene repression and to restore more normal retinoid signaling in malignant cells.
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