Anti-proliferative activity of 25-hydroxyvitamin D₃ in human prostate cells

1α-Hydroxylation of 25-hydroxyvitamin D₃ is believed to be essential for its biological effects. In this study, we evaluated the biological activity of 25(OH)D₃ itself comparing with the effect of cell-derived 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃). First, we measured the cell-derived 1α,25(OH)₂D₃ level in immortalized human prostate cell (PZ-HPV-7) using [³H]-25(OH)D₃. The effects of the cell-derived 1α,25(OH)₂D₃ on vitamin D₃ 24-hydroxylase (CYP24A1) mRNA level and the cell growth inhibition were significantly lower than the effects of 25(OH)D₃ itself added to cell culture. 25-Hydroxyvitamin D₃ 1α-hydroxylase (CYP27B1) gene knockdown had no significant effects on the 25(OH)D₃-dependent effects, whereas vitamin D receptor (VDR) gene knockdown resulted in a significant decrease in the 25(OH)D₃-dependent effects. These results strongly suggest that 25(OH)D₃ can directly bind to VDR and exerts its biological functions. DNA microarray and real-time RT-PCR analyses suggest that semaphorin 3B, cystatin E/M, and cystatin D may be involved in the antiproliferative effect of 25(OH)D₃.