TRPV6 Determines the Effect of Vitamin D3 on Prostate Cancer Cell Growth

Abstract

Despite remarkable advances in the therapy and prevention of prostate cancer it is still the second cause of death from cancer in industrialized countries. Many therapies initially shown to be beneficial for the patients were abandoned due to the high drug resistance and the evolution rate of the tumors. One of the prospective therapeutical agents even used in the first stage clinical trials, 1,25-dihydroxyvitamin D3, was shown to be either unpredictable or inefficient in many cases. We have already shown that TRPV6 calcium channel, which is the direct target of 1,25-dihydroxyvitamin D3 receptor, positively controls prostate cancer proliferation and apoptosis resistance (Lehen'kyi et al., Oncogene, 2007). However, how the known 1,25-dihydroxyvitamin D3 antiproliferative effects may be compatible with the upregulation of pro-oncogenic TRPV6 channel remains a mystery. Here we demonstrate that in low steroid conditions 1,25-dihydroxyvitamin D3 upregulates the expression of TRPV6, enchances the proliferation by increasing the number of cells entering into S-phase. We show that these pro-proliferative effects of 1,25-dihydroxyvitamin D3 are directly mediated via the overexpression of TRPV6 channel which increases calcium uptake into LNCaP cells. The apoptosis resistance of androgen-dependent LNCaP cells conferred by TRPV6 channel is drastically inversed when 1,25-dihydroxyvitamin D3 effects were combined with the successful TRPV6 knockdown. In addition, the use of androgen-deficient DU-145 and androgen-insensitive LNCaP C4-2 cell lines allowed to suggest that the ability of 1,25-dihydroxyvitamin D3 to induce the expression of TRPV6 channel is a crucial determinant of the success or failure of 1,25-dihydroxyvitamin D3-based therapies.

TRPV6 channel modulates proliferation of insulin secreting INS-1E beta cell line

“…In LNCaP prostate cancer cells, TRPV6 stimulates cell proliferation and survival [34], which was inferred from experiments using TRPV6 siRNA. Notably, the extent of suppression of LNCaP cell proliferation by TRPV6 siRNA (approximately 25% three days after siRNA transfection) [23,34] was highly comparable to that detected in our experiments using INS-1E cells (30% percent vs. nt siRNAtransfected cells after three days).…”

“…However, this limitation is also a hallmark of earlier studies [34,51]. Nevertheless, it is worth to notice that TRPV6 can be activated by vitamin D as well as estrogen [23,52,53]. These TRPV6 modulators were shown to improve human and rodent pancreatic beta cells endocrine and metabolic ).…”

“…For calibration of free [Ca 2+ ] i , the fluorescence level in the presence of EGTA (2 mM) (R min ) or calcium (1.5 mM) (R max ) was measured. For functional detection of TRPV6, a similar protocol was used as described in the literature [23]. In brief, measurements of the basal levels of [Ca 2+ ] i were obtained during the first 3 min, followed by an isoosmotic replacement with Ca 2+ -free Ringer-like solution (2 mM EGTA).…”

“…Three minutes later, 1.5 mM Ca 2+ was added to increase [Ca 2+ ] i . The reversibility of Ca 2+ changes is an indicator of cell viability and functional relevance of the Ca 2+ sensing TRPV6 channel [23][24][25][26].…”

TRPV6 Channels

“…In prostate cancer, Trpv6 transcripts are overexpressed and the expression pattern correlates with the aggressiveness of the disease Peng et al 2001;Fixemer et al 2003). Likewise, in the human lymph node prostate cancer cell line LNCaP, upregulation of Trpv6 transcripts by vitamin D treatment enhanced proliferation rate and resistance to apoptosis (Lehen'kyi et al 2007(Lehen'kyi et al , 2011(Lehen'kyi et al , 2012. The proliferation rate of HEK293 cells expressing the Trpv6 cDNA was also enhanced (Schwarz et al 2006).…”