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.

No abstract

Neuroendocrine (NE) differentiation is a hallmark of advanced, androgen-independent prostate cancer, for which there is no successful therapy. NE tumor cells are nonproliferating and escape apoptotic cell death; therefore, an understanding of the apoptotic status of the NE phenotype is imperative for the development of new therapies for prostate cancer. Here, we report for the first time on alterations in intracellular Ca 2 þ homeostasis, which is a key factor in apoptosis, caused by NE differentiation of androgen-dependent prostate cancer epithelial cells. NEdifferentiating regimens, either cAMP elevation or androgen deprivation, resulted in a reduced endoplasmic reticulum Ca 2 þ -store content due to both SERCA 2b Ca 2 þ ATPase and luminal Ca 2 þ binding/storage chaperone calreticulin underexpression, and to a downregulated store-operated Ca 2 þ current. NE-differentiated cells showed enhanced resistance to thapsigargin-and TNF-a-induced apoptosis, unrelated to antiapoptotic Bcl-2 protein overexpression. Our results suggest that targeting the key players determining Ca 2 þ homeostasis in an attempt to enhance the proapoptotic potential of malignant cells may prove to be a useful strategy in the treatment of advanced prostate cancer.

No abstract

No abstract

No abstract

BACKGROUND.Very little is known about the functional expression and the physiological role of ryanodine receptors in nonexcitable cells, and in prostate cancer cells in particular.Nonetheless, different studies have demonstrated that calcium is a major factor involved in apoptosis. Therefore, the calcium-regulatory mechanisms, such as ryanodine-mediated calcium release, may play a substantial role in the regulation of apoptosis. METHODS.We assessed the presence of such functional receptors in LNCaP prostate cancer cells, using fluorimetric measurements of intracellular calcium and expression assays of mRNA encoding ryanodine receptors. RESULTS. We show here that LNCaP cells responded to caffeine, a ryanodine receptor agonist, by mobilizing calcium. Another ryanodine receptor agonist, 4-chloro-m-cresol, had a similar effect and promoted calcium release. These effects were inhibited by pretreatment with ryanodine or thapsigargin. In addition to a calcium release, caffeine was able to produce a calcium entry blocked by nickel. We used a reverse transcription-polymerase chain reaction assay to investigate the expression of ryanodine receptors in LNCaP cells. Two types of ryanodine receptor mRNAs were expressed in LNCaP cells: RyR1 and RyR2 mRNAs. Finally, we show that ryanodine receptor activation by caffeine slightly stimulates apoptosis of prostate cancer cells, and that the inhibition of these receptors by ryanodine protects the cells against apoptosis. CONCLUSIONS. The combination of results showed that LNCaP cells, derived from a human prostate cancer, express functional RyRs able to mobilize Ca 2+ from intracellular stores and which might control apoptosis.

Neuroendocrine differentiation (NED) is a hallmark of advanced androgen-independent prostate cancer, for which no successful therapy exists. NED tumour cells escape apoptotic cell death by alterations of Ca2+ homeostasis where the store-operated Ca2+ entry (SOCE) is known to be a key event. We have previously shown that the downregulation of Orai1 protein representing the major molecular component of endogenous SOCE in human prostate cancer cells, and constituting the principal source of Ca2+ influx used by the cell to trigger apoptosis, contributes to the establishment of an apoptosis-resistant phenotype (Cell Death Dis. 2010 Sep 16;1:e75.). Here, we report for the first time that the decrease of SOCE during NED may be caused by alternative NED-induced mechanism involving cytoskeleton reorganisation. NED induced by androgen deprivation resulted in a decrease of SOCE due to cortical F-actin over-polymerization which inhibits thapsigargin-induced SOCE. The disruption of F-actin polymerization by Cytochalasin D in NED cells restored SOCE, while the induction of F-actin polymerization by jasplakinolide or calyculin A diminished SOCE without changing the expression of key SOCE players: Orai1, STIM1, and TRPC1. Our data suggest that targeting cytoskeleton-induced pathways of malignant cells together with SOCE-involved channels may prove a useful strategy in the treatment of advanced prostate cancer.