Inter-related in vitro effects of androgens, fatty acids and oxidative stress in prostate cancer: a mechanistic model supporting prevention strategies.

Oxidation of mitochondrial fatty acids (FA) results in the generation of reactive oxygen species (ROS) which have been postulated to play a key role in the initiation and progression of prostate cancer (PC). We previously reported that androgens increase FA uptake into PC cells. We thus examined if androgens that are known to induce ROS generation regulate FA oxidation in PC cells. The effects of the androgen-depleted medium, R1881 (synthetic androgen) and/or androgen receptor blocker, bicalutamide were examined in the human androgen-responsive but not dependent 22rv1 cells. R1881 supplementation significantly increased mitochondrial FA oxidation ((14)C-radiolabeled FA degradation studies), resulting in increased ROS production. Androgens increased the mRNA levels of carnitine palmitoyltransferase (CPT1), the rate limiting enzyme in the process of mitochondrial FA oxidation. Treatment with R1881 and bicalutamide inhibited these androgen regulated effects. Inhibition of mitochondrial ROS generation by two different inhibitors, rotenone and thenoyltrifluoroacetone, eliminated the androgen-induced ROS generation, to the same level as in cells deprived of androgens or treated with R1881 and bicalutamide. Taken together, androgens increase the mitochondrial oxidation of FA, leading to increased production of ROS that is associated with prostate cell proliferation and mutagenesis. These results therefore support the rationale for PC prevention using 5-alpha reductase inhibitors, dietary restrictions or anti-oxidants, each of which has different inhibitory but complementary effects.

Calcitriol-induced prostate-derived factor: autocrine control of prostate cancer cell growth.

Calcitriol (1alpha,25-dihydroxycholecalciferol) seems to play an important role in the complex control of prostate cell growth. It inhibits proliferation and induces differentiation and apoptosis in prostate cancer cells. However, the molecular mechanisms of the antiproliferative activity of calcitriol are not completely understood. The expression of prostate-derived factor (PDF), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to be associated with proapoptotic and antimitotic activities. We show that calcitriol induces PDF expression in LNCaP human prostate cancer cells in a concentration- and time-dependent manner. In LNCaP cells, the suppression of cell growth by calcitriol is accompanied by stimulation of PDF mRNA and protein synthesis. Human recombinant PDF inhibits LNCaP cell growth. We do not detect any effect of PDF-specific antibody on the basal growth of LNCaP cells, but this antibody partially reverses the suppression of LNCaP cell growth by calcitriol, suggesting that the effect of calcitriol on cell growth is at least partially mediated by PDF. In PC-3 cells, which are less responsive to the growth-inhibitory effect of calcitriol, it has no effect on PDF expression. We do not detect an effect of recombinant PDF on SMAD phosphorylation in LNCaP cells, but ERK1/2 kinases are transiently phosphorylated in response to PDF, which suggests that in LNCaP cells PDF may exert its action through pathway alternative to the classical TGF-beta signaling pathway. The present study describes the regulation of PDF, the proapoptotic protein of the TGF-beta superfamily, by calcitriol in androgen-responsive prostate cancer cells. This is a new link between calcitriol and growth factors of TGF-beta superfamily in the control of prostate cell growth.