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 [(3)H]-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.
Keywords: 1α,25(OH)(2)D(3); 1α,25-dihydroxy vitamin D(3); 1α,25-dihydroxyvitamin D(3); 25(OH) D(3); 25-hydroxyvitamin D(3); Anti-proliferative activity; BPE; CYP24A1; GAPDH; HPLC; LC–MS; Prostate; RXR; VDR; Vitamin D receptor; Vitamin D(3); bovine pituitary extract; glyceraldehyde-3-phosphate dehydrogenase; high performance liquid chromatography; liquid chromatography mass spectroscopy; retinoid X receptor; siRNA; small interfering RNA; vitamin D receptor.
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