Calcitriol inhibits growth response to Platelet-Derived Growth Factor-BB in human prostate cells.

Calcitriol, a hormonal form of Vitamin D, regulates growth of normal and cancer cells of various origins by modulation of peptide growth factors signaling. Platelet-Derived Growth Factor (PDGF) signaling pathway is involved in prostate cancer progression. We studied the expression of PDGF receptors in human prostate primary stromal cells and cancer epithelial cell lines and growth response to PDGF-BB isoform. We found that the expression of PDGF receptors and PDGF-BB-mediated cell growth are regulated by calcitriol in prostate cells. Quantitative RT-PCR analysis revealed a lower level of mRNA for PDGF receptors in LNCaP and PC-3 cells than in primary stromal cells. Western blotting showed a high amount of PDGFRalpha and beta proteins in primary stromal cells that could not be detected in LNCaP, which may explain the resistance of LNCaP cells to growth-promoting effect of PDGF-BB. Addition of Epidermal Growth Factor (EGF) to the culture medium induces the expression of PDGFRbeta and restores responsiveness of LNCaP to PDGF-BB to some extent. Calcitriol down-regulates PDGFRbeta expression and negatively regulates PDGF-mediated cell growth. Calcitriol does not affect PDGFRalpha and PDGF-B mRNA expression. We suggest that inhibition of PDGFRbeta expression by calcitriol might reduce responsiveness of prostate cells to mitogenic action of PDGF-BB.

A20 gene expression is regulated by TNF, Vitamin D and androgen in prostate cancer cells.

A20 is a TNF-inducible primary response gene and its product, a zinc finger protein, has antiapoptotic function in several cancer cells. We studied A20 gene expression in the Vitamin D- and TNF-sensitive LNCaP cell line and in the Vitamin D- and TNF-resistant PC-3 cell line. The results of the quantitative real-time RT-PCR analyses demonstrated that the basal level of A20 mRNA production in PC-3 cells was considerably higher than in LNCaP cells that is associated with the resistance of PC-3 cells. TNF induced A20 gene expression in both cell lines, but with different effect. A20 mRNA expression was down-regulated by 10nM calcitriol within 3-9h after treatment and up-regulated by androgen reaching maximal values by 6h after stimulation in LNCaP cells. We conclude that A20 may be involved in the regulation of cell proliferation by TNF, Vitamin D, and androgen in prostate cancer.

Vitamin D-induced up-regulation of tumour necrosis factor alpha (TNF-alpha) in prostate cancer cells.

1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3 or calcitriol) is an active hormone that regulates cellular proliferation and induces apoptosis in cancer cells. Here we report on a new calcitriol target gene in prostate cancer cells, tumour necrosis factor alpha (TNF-alpha). Calcitriol and its analogue CB1093 up-regulate TNF-alpha mRNA expression in LNCaP and PC-3 cells. The stimulation is dose-dependent in both of these cell lines, demonstrated by the quantitative real-time polymerase chain reaction. Calcitriol and CB1093 act synergistically with human recombinant TNF-alpha in activation of TNF-alpha mRNA expression in LNCaP but not in PC-3 cells. Transcriptional activation of TNF-alpha gene by calcitriol or CB1093 does not lead to TNF-alpha protein secretion, however calcitriol and CB1093 enhance TPA-stimulated TNF-alpha production in LNCaP cells. We did not observe any significant effect of calcitriol on regulation of TNFR1 at the level of gene expression. Nor does calcitriol affect transcriptional regulation of cytokine (IL-1, IL-6) and cytokine receptor genes in LNCaP and PC-3 prostate cancer cell lines. Calcitriol and its analogue CB1093 at 10 nM concentration induce programmed cell death in LNCaP cells. Combined addition of human recombinant TNF-alpha with calcitriol or CB1093 cause enhanced effect in induction of apoptosis. We conclude that under physiological conditions vitamin D activates only the transcription of TNF-alpha gene, for TNF-alpha protein synthesis additional cofactors are required. Therefore a cooperation of vitamin D and TNF-alpha may play an important role in the control of cell growth in prostate cancer.

Calcitriol-induced prostate-derived factor: autocrine control of prostate cancer cell growth.

Calcitriol (1alpha,25-dihydroxycholecalciferol) seems to play an important role in the complex control of prostate cell growth. It inhibits proliferation and induces differentiation and apoptosis in prostate cancer cells. However, the molecular mechanisms of the antiproliferative activity of calcitriol are not completely understood. The expression of prostate-derived factor (PDF), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to be associated with proapoptotic and antimitotic activities. We show that calcitriol induces PDF expression in LNCaP human prostate cancer cells in a concentration- and time-dependent manner. In LNCaP cells, the suppression of cell growth by calcitriol is accompanied by stimulation of PDF mRNA and protein synthesis. Human recombinant PDF inhibits LNCaP cell growth. We do not detect any effect of PDF-specific antibody on the basal growth of LNCaP cells, but this antibody partially reverses the suppression of LNCaP cell growth by calcitriol, suggesting that the effect of calcitriol on cell growth is at least partially mediated by PDF. In PC-3 cells, which are less responsive to the growth-inhibitory effect of calcitriol, it has no effect on PDF expression. We do not detect an effect of recombinant PDF on SMAD phosphorylation in LNCaP cells, but ERK1/2 kinases are transiently phosphorylated in response to PDF, which suggests that in LNCaP cells PDF may exert its action through pathway alternative to the classical TGF-beta signaling pathway. The present study describes the regulation of PDF, the proapoptotic protein of the TGF-beta superfamily, by calcitriol in androgen-responsive prostate cancer cells. This is a new link between calcitriol and growth factors of TGF-beta superfamily in the control of prostate cell growth.