Abstract 1215: Novel role of androgens: Involvement in mitochondrial fission and apoptosis in prostate cancer cells

Abstract

Abstract Novel role of androgens: Involvement in mitochondrial fission and apoptosis in prostate cancer cells The role of androgens on prostate cancer growth and proliferation is well known but very little is known about its pro-apoptotic roles. Here, we demonstrate a novel role of androgens in altering the shape and function of the mitochondria. Dynamin-related protein 1 (Drp1) is a key protein necessary for mitochondrial fragmentation or fission (MF). The expression of Drp1 (both protein and mRNA) correlated with the expression of androgen receptor (AR) in prostate cancer cell lines. Interestingly, Drp1 expression was very low in androgen refractory prostate metastatic tissues. Treatment of LNCaP cells with androgen agonist, R1881 increased the expression of Drp1 mRNA and protein. This increase was inhibited by androgen antagonist, bicalutamide. Androgen regulation of Drp1 was confirmed by knock out of AR (using siRNA), which resulted in decreased Drp1 expression. To measure mitochondrial fission (MF), cells were stably transfected with pAcGFP1-Mito, targeting the expression of GFP to mitochondria. Androgen treatment did not induce MF, although Drp1 was upregulated. However, treatment with CGP37157 (CGP), a mitochondrial Na+/Ca2+ channel blocker induced MF. Pre-treatment with R1881 significantly increased CGP-induced MF, suggesting that androgen-induced Drp1 facilitated CGP-induced MF. Androgens increased the proliferation of LNCaP, which was reduced by CGP treatment. Interestingly, treatment with CGP induced apoptosis which was further enhanced by pre-treatment with R1881. Drp1 dominant negative experiments showed that Drp1 was required for enhanced apoptosis, suggesting that androgen-induced Drp1 was responsible for increasing the apoptotic effects of CGP. Experiments to examine the paradoxical effects of androgens showed that induction of proliferation by androgens may be due to differential phosphorylation of Drp1. However, induction of apoptosis by CGP alone or in combination with androgens is due to the reduction of the expression of Mfn1, a protein that promotes mitochondrial fusion (opposite of fission). Use of proteasomal inhibitor, lactacystin, suggested that CGP treatment resulted in proteasome mediated degradation of Mfn1. In summary, our results demonstrated: i) transcriptional regulation of Drp1 by androgens, ii) androgen-induced Drp1 facilitated mitochondrial fission and apoptosis. Significance of these results: Clinical: we suggest that it is not necessary to block the function of androgens, instead administration of drugs (such as calcium channel blockers) that affect mitochondrial function induced death of cancer cells in the presence of androgens. Research: addresses a fundamental question about mechanisms involved in proliferation and apoptosis. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1215.