Induction of Androgen Receptor by 1α,25-Dihydroxyvitamin D₃and 9-cis Retinoic Acid in LNCaP Human Prostate Cancer Cells¹

Abstract

We have recently shown that 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] inhibits proliferation of LNCaP cells, an androgen-responsive human prostate cancer cell line. Also, 1,25-(OH)2D3 increases androgen receptor (AR) abundance and enhances cellular responses to androgen in these cells. In the current study, we have investigated the mechanism by which 1,25-(OH)2D3 regulates AR gene expression and the involvement of AR in the 1,25-(OH)2D3- and 9-cis retinoic acid (RA)-mediated growth inhibition of LNCaP cells. Northern blot analyses demonstrated that the steady-state messenger RNA (mRNA) level of AR was significantly increased by 1,25-(OH)2D3 in a dose-dependent manner. Time-course experiments revealed that the increase of AR mRNA by 1,25-(OH)2D3 exhibited delayed kinetics. In response to 1,25-(OH)2D3, AR mRNA levels were first detected to rise at 8 h and reached a maximal induction of 10-fold over the untreated control at 48 h; the effect was sustained at 72 h. Furthermore, the induction of AR mRNA by 1,25-(OH)2D3 was completely abolished by incubation of cells with cycloheximide, a protein synthesis inhibitor. 1,25-(OH)2D3 was unable to induce expression of an AR promoter-luciferase reporter. Together, these findings indicate that the stimulatory effect of 1,25-(OH)2D3 on AR gene expression is indirect. Western blot analyses showed an increase of AR protein in 1,25-(OH)2D3-treated cells. This increased expression of AR was followed by 1,25-(OH)2D3-induced inhibition of growth in LNCaP cells. Similar to 1,25-(OH)2D3, 9-cis RA also induced AR mRNA expression, and the effect of both hormones was additive. Moreover, 1,25-(OH)2D3 and 9-cis RA acted synergistically to inhibit LNCaP cell growth. These antiproliferative effects of 1,25-(OH)2D3 and 9-cis RA, alone or in combination, were blocked by the pure AR antagonist, Casodex. In conclusion, our results demonstrate that growth inhibition of LNCaP cells by 1,25-(OH)2D3 and 9-cis RA is mediated by an AR-dependent mechanism and preceded by the induction of AR gene expression. This finding, that differentiating agents such as vitamin D and A derivatives are potent inducers of AR, may have clinical implications in the treatment of prostate cancer.

Vitamin D and Endometrium: A Systematic Review of a Neglected Area of Research

“…The inhibitory effect of VD was more effective with a progesterone-induced 24-hydroxylase inhibition in line with the observation that 24-hydroxylase is upregulated in endometrial cancer cells and can control VD cellular responses [53]. This result is consistent with an enhanced anti-proliferative action following a combination of VD and 24-hydroxylase inhibitor treatment in in vitro and in vivo models of prostate and lung tumors [66,67]. …”

Mechanisms of the Anti-Cancer and Anti-Inflammatory Actions of Vitamin D

“…Interestingly, there is cross talk between calcitriol actions and androgen and estrogen signaling in PCa and BCa cells. Calcitriol upregulates AR expression in LNCaP PCa cells (61,62). The androgen-inducible, growth-inhibitory gene AS3/APRIN is also induced by calcitriol in LNCaP cells (63).…”

Interaction of vitamin D with membrane-based signaling pathways

“…Likewise, there is a complex and unresolved relationship between 1α,25(OH) 2 D 3 and androgen receptor (AR) synthesis and signaling. 1α,25(OH) 2 D 3 induces AR in LNCaP cells (Zhao et al, 1999) while AR reduces VDR transcriptional activity (Ting et al, 2005), perhaps in some cells by a mechanism mediated by prohibitin (Mooso et al, 2010). In addition, 1α,25(OH) 2 D 3 inhibits glucuronidation and so, inactivation of androgen in prostate cancer cells through the repression of UDP-glucuronosyltransferases (UGT) 2B15 and 2B17, which is counterintuitive given the growth promoting action of androgen and the antiproliferative effect of 1α,25(OH) 2 D 3 in prostate cancer cells (Kaeding et al, 2008).…”