Abstract 5496: Intratumor estradiol increment mediated by CtBP1/CYP19A1 decreases the proliferation of androgen insensitive prostate tumor cells

The normal growth and development of the prostate requires the action of estrogens and estrogens receptors (ER) a and ß. Estrogen-related pathways are clearly important in the development and progression of hormone-dependent cancers such as prostate cancer (PCa), but the role of ERß remains controversial. The production of estrogens from androgens is mediated by the aromatase enzyme. Aberrant expression of aromatase plays a critical role in PCa development and progression. Metabolic syndrome (MeS) causes sex hormone imbalance and has been identified as a risk factor for PCa. Recently, we found that C-terminal binding protein (CtBP1), a transcriptional co-repressor of tumor suppressor genes, is a novel molecular link between MeS and PCa. We developed a MeS mice model that were inoculated with PC3 stable CtBP1 depleted or control cells. MeS mice showed hormone imbalance and high levels of intratumor estradiol. Interestingly, CtBP1 strongly repressed aromatase expression in these xenografts. The aim of this study was to understand the transcriptional regulation mechanism of aromatase mediated by CtBP1 in a MeS/PCa model. To fulfill our aim, PC3 cells were co-transfected with a CtBP1 expression plasmid and a panel of ten reporter vectors containing different lengths (27-1,004 bp) of CYP19A1 promoter, cloning upstream to the luciferase gene. CtBP1 significantly repressed the activity of all the studied promoters. By chromatin inmunoprecipitation (ChIP) and RT-qPCR we determined that CtBP1 associated to CYP19A1 promoter and repressed its transcription. To identify possible CtBP1 partners in CYP19A1 expression regulation we investigated several transcription cofactors. By ChIP, we found that p300 (histone acetyl transferase) and ERß associated to aromatase promoter in PC3 cells. Using gene reporter assays, we established that CtBP1 and p300 synergistically repressed, while ER ß activated, aromatase promoter activity. Interestingly, estradiol exposure of PC3 cells, released CtBP1 from the aromatase promoter triggering its expression. Furthermore, we found that estradiol dramatically increased the viability and the S phase percentage of the androgen sensitive LNCaP and, its derivative, C4-2 cells; dramatically reducing apoptosis. Accordingly, estradiol decreased androgen insensitive PC3 cell viability and G1 phase arrest. In summary, CtBP1 represses aromatase expression in PCa. Nevertheless, MeS increases intratumor estradiol, which releases CtBP1 from aromatase pr