1 alpha 25-dihydroxyvitamin D-3 actions in LNCaP human prostate cancer cells are androgen-dependent

We and others have recently shown that 1 alpha,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] significantly inhibits cell proliferation and increases secretion of prostate-specific antigen (PSA) in LNCaP cells, an androgen-responsive human prostate cancer cell line. The present study was designed to investigate the possible interactions between 1.25-(OH)(2)D-3 and androgens in the regulation of LNCaP cellular function. LNCaP cell growth was dose-dependently inhibited by 1,25-(OH)(2)D-3 (60% inhibition at 10 nM) when cells were cultured in medium supplemented with FBS (FBS medium). 1,25-(OH)(2)D-3-treated cells showed a 5-fold increase in PSA secretion, similar to the increase seen in dihydrotestosterone (DHT)-treated cells. In combination, 1.25-(OH)(2)D-3 and DHT synergistically enhanced PSA secretion 22-fold. This synergistic effect was even greater when cells were cultured in medium supplemented with charcoal-stripped serum (CSS medium), where endogenous steroids are substantially depleted. Under these conditions, 1,25-(OH)(2)D-3 and DHT together stimulated PSA secretion up to 50-fold over the untreated control, Radioligand binding assays and Western blot analyses showed that the androgen receptor (AR) content was increased significantly by 1,25-(OH)(2)D-3 at 48 h. Furthermore, the steady-state mRNA level of AR was up-regulated approximately 2-fold by 1,25-(OH)(2)D-3 at 24 h. When cells were grown in CSS medium, 1,25-(OH)(2)D-3 alone no longer inhibited cell growth or induced PSA secretion, Titration experiments revealed that the addition of DHT at 1 nu to the medium restored the antiproliferative activity of 1,25-(OH)(2)D-3. Conversely, an antiandrogen, Casodex, completely blocked 1,25-(OH)(2)D-3 antiproliferative and PSA stimulation activities when cells were cultured in FBS medium. In conclusion, these results demonstrate that the antiproliferative and PSA induction activities of 1,25-(OH)(2)D-3 in LNCaP cells are dependent upon androgen action and that AR up-regulation by 1,25(OH)(2)D-3 likely contributes, to the synergistic actions of 1,25-(OH)(2)D-3 and DHT in these cells.