The molecular nature of calcium (Ca2+)-dependent mechanisms and the ion channels having a major role in the apoptosis of cancer cells remain a subject of debate. Here, we show that the recently identified Orai1 protein represents the major molecular component of endogenous store-operated Ca2+ entry (SOCE) in human prostate cancer (PCa) cells, and constitutes the principal source of Ca2+ influx used by the cell to trigger apoptosis. The downregulation of Orai1, and consequently SOCE, protects the cells from diverse apoptosis-inducing pathways, such as those induced by thapsigargin (Tg), tumor necrosis factor α, and cisplatin/oxaliplatin. The transfection of functional Orai1 mutants, such as R91W, a selectivity mutant, and L273S, a coiled-coil mutant, into the cells significantly decreased both SOCE and the rate of Tg-induced apoptosis. This suggests that the functional coupling of STIM1 to Orai1, as well as Orai1 Ca2+-selectivity as a channel, is required for its pro-apoptotic effects. We have also shown that the apoptosis resistance of androgen-independent PCa cells is associated with the downregulation of Orai1 expression as well as SOCE. Orai1 rescue, following Orai1 transfection of steroid-deprived cells, re-established the store-operated channel current and restored the normal rate of apoptosis. Thus, Orai1 has a pivotal role in the triggering of apoptosis, irrespective of apoptosis-inducing stimuli, and in the establishment of an apoptosis-resistant phenotype in PCa cells.

In recent years, the transient receptor potential melastatin member 8 (TRPM8) channel has emerged as a promising prognostic marker and putative therapeutic target in prostate cancer (PCa). However, the mechanisms of prostate-specific regulation and functional evolution of TRPM8 during PCa progression remain unclear. Here we show, for the first time to our knowledge, that only secretory mature differentiated human prostate primary epithelial (PrPE) luminal cells expressed functional plasma membrane TRPM8 ( PM TRPM8) channels. Moreover, PCa epithelial cells obtained from in situ PCa were characterized by a significantly stronger PM TRPM8-mediated current than that in normal cells. This PM TRPM8 activity was abolished in dedifferentiated PrPE cells that had lost their luminal secretory phenotype. However, we found that in contrast to PM TRPM8, endoplasmic reticulum TRPM8 ( ER TRPM8) retained its function as an ER Ca 2+ release channel, independent of cell differentiation. We hypothesize that the constitutive activity of ER TRPM8 may result from the expression of a truncated TRPM8 splice variant. Our study provides insight into the role of TRPM8 in PCa progression and suggests that TRPM8 is a potentially attractive target for therapeutic intervention: specific inhibition of either ER TRPM8 or PM TRPM8 may be useful, depending on the stage and androgen sensitivity of the targeted PCa.

Accumulating data point to K þ channels as relevant players in controlling cell cycle progression and proliferation of human cancer cells, including prostate cancer (PCa) cells. However, the mechanism(s) by which K þ channels control PCa cell proliferation remain illusive. In this study, using the techniques of molecular biology, biochemistry, electrophysiology and calcium imaging, we studied the expression and functionality of intermediate-conductance calcium-activated potassium channels (IK Ca1 ) in human PCa as well as their involvement in cell proliferation. We showed that IK Ca1 mRNA and protein were preferentially expressed in human PCa tissues, and inhibition of the IK Ca1 potassium channel suppressed PCa cell proliferation. The activation of IK Ca1 hyperpolarizes membrane potential and, by promoting the driving force for calcium, induces calcium entry through TRPV6, a cation channel of the TRP (Transient Receptor Potential) family. Thus, the overexpression of the IK Ca1 channel is likely to promote carcinogenesis in human prostate tissue.

One major clinical problem with prostate cancer is the cells' ability to survive and proliferate upon androgen withdrawal. Because Ca 2+ is central to growth control, understanding the mechanisms of Ca 2+ homeostasis involved in prostate cancer cell proliferation is imperative for new therapeutic strategies. Here, we show that agonist-mediated stimulation of A 1 -adrenergic receptors (A 1 -AR) promotes proliferation of the primary human prostate cancer epithelial (hPCE) cells by inducing store-independent Ca 2+ entry and subsequent activation of nuclear factor of activated T cells (NFAT) transcription factor. Such an agonist-induced Ca 2+ entry (ACE) relied mostly on transient receptor potential canonical 6 (TRPC6) channels, whose silencing by antisense hybrid depletion decreased both hPCE cell proliferation and ACE. In contrast, ACE and related growth arrest associated with purinergic receptors (P2Y-R) stimulation involved neither TRPC6 nor NFAT. Our findings show that A 1 -AR signaling requires the coupled activation of TRPC6 channels and NFAT to promote proliferation of hPCE cells and thereby suggest TRPC6 as a novel potential therapeutic target.