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 incre ases secretion of prostate-specific antigen (PSA) in LNCaP cells, an a ndrogen-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. LN CaP 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 i ncrease in PSA secretion, similar to the increase seen in dihydrotesto sterone (DHT)-treated cells. In combination, 1.25-(OH)(2)D-3 and DHT s ynergistically 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 s ubstantially depleted. Under these conditions, 1,25-(OH)(2)D-3 and DHT together stimulated PSA secretion up to 50-fold over the untreated co ntrol, Radioligand binding assays and Western blot analyses showed tha t 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 inhib ited cell growth or induced PSA secretion, Titration experiments revea led that the addition of DHT at 1 nu to the medium restored the antipr oliferative 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 conc lusion, these results demonstrate that the antiproliferative and PSA i nduction activities of 1,25-(OH)(2)D-3 in LNCaP cells are dependent up on 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.