L-type Calcium Channel α_1D Modulates Androgen Receptor Activities In Prostate Cancer Cells

Calcium (Ca2+) is the most common secondary messenger in intracellular cell signal transduction and is involved in several cellular processes such as apoptosis and proliferation, as well as carcinogenesis. Cellular Ca2+homeostasis is regulated by voltage-operated calcium channel and intracellular Ca2+pool. There are five major Ca2+permeable channels (L-, N-, P/Q-, R-, and T-type) mediate Ca2+entry. It has been shown that Ca2+signaling is involved in androgen-induced PSA secretion and cell proliferation in prostate cancer cells. Recent epidemiologic surveys indicated that L-type calcium channels might be involved in prostate cancer development because L-type blocker users showed a reduced prostate cancer incidence. Therefore, in the present study, we sought to conduct a pilot investigation for the role of voltage-gated calcium channels in androgen signaling and prostate cancer progression. A quantitative RT-PCR based screen showed that only L-type (Cav1.3) alpha-subunit gene CACNA1D is highly expressed in malignant prostate tissues compared to adjacent benign tissues derived. Meanwhile, semi-quantitative immunohisto-chemistry (IHC) analysis showed that α1D protein was highly expressed in malignant tissues compared to that in benign compartments. Consistently, the expression profiling analysis of the Oncomine Cancer Microarray database (http://www.oncomine.org) also showed that CACNA1D expression was significantly higher in prostate cancer compared to normal prostate. Nuclear localization of AR was visualized by immunofluorescent cell staining and confocal microscopy and the androgen-responsive element-luciferase reporter (ARE-LUC) plasmid transfection was used for AR transactivation. Blocking L-type channels with Nifedipine and Tetradrine or knocking down its protein expression using small interfering RNA (siRNA) significantly suppressed cell proliferation and androgen receptor-mediated gene expression (ARE-LUC) in prostate cancer cells. Furthermore, overexpression of CACNAID enhanced AR transactivation (ARE-LUC activity). Blocking L-type channels by Nifedipine and Tetradrine also reduced AR protein level and the expression of endogenous AR target genes, PSA and NKX3.1. In contrast, blocking T-type channel using Mibefradil enhanced AR transactivation and its target gene expression. Taken together, calcium channel L-type (Cav1.3) CACNA1D/α1D is overexpressed in prostate cancers and is positively involved in AR-mediated gene expression, while T-type channel might negatively modulated AR function. Further elucidating the pathogenesis between CACNA1D/α1D and the AR pathway could possibly contribute the development of a new therapeutic strategy for prostate cancer.