Androgen Receptor Mutations and Estrogen Receptor-β Modulate Genistein Effects on Prostate Cancer Cells
thesisposted on 28.06.2013, 00:00 authored by Abeer M. Mahmoud
Genistein is the most abundant and potent isoflavone in soy and it has an estradiol-like structure. Results from previous studies examining genistein effects on androgen receptor (AR) expression and prostate cancer (PCa) cell proliferation have been contradictory. In this study, we demonstrated that these mixed results can be attributed to the use of LNCaP cells that has a promiscuous AR attributed to the presence of the T877A mutation, without comparison to cells with wild-type AR (WT-AR). We demonstrated using in silico modeling that genistein is able to bind with higher affinity to the promiscuously mutant AR than to the WT-AR. Our in vitro studies showed that low, physiological concentrations of genistein inhibited cell proliferation and AR expression and activity in presence of WT-AR. However, in the presence of mutant type of AR (MT-AR), corresponding doses induced stimulatory effects on AR expression and cell proliferation. We also demonstrated that the effects of physiological doses of genistein are mediated by ER-β activation in the presence of WT-AR while the presence of MT-AR neutralizes this mediating role of ER-β in genistein’s inhibitory activity. In contrast, cell growth inhibitory effects of higher, pharmacological doses of genistein were preserved in the presence of both types of AR, due to inhibition of protein tyrosine kinase observed at these high doses. It has been reported that the ER-β promoter is hypermethylated and its expression declines with the progression of localized PCa. We observed that genistein reversed ER-β promoter hypermethylation and increased ER-β expression in LNCaP and LAPC-4 cells, but not PC-3 cells which have low basal levels of ER-β promoter methylation. We also found that genistein increased ER-β transcriptional activity in LAPC-4 and PC-3 cells, but not in LNCaP cells which may be attributable to the override of ER-β activity by the activated MT-AR in the latter cell line. This study yields information about the possible beneficial versus harmful effects of dietary genistein as a function of dose and AR mutational status. Since AR mutations tend to occur in advanced PCa following failure of androgen ablation therapy, the outcome of this study identifies potential harmful effects of genistein-rich soy diets on the subset of PCa patients who have promiscuous mutations in their AR.