Suppression of death receptor-mediated apoptosis by 1,25-dihydroxyvitamin D₃ revealed by microarray analysis

Recent studies suggest that growth inhibition by 1,25-dihydroxyvitamin D₃ represents an innovative approach to ovarian cancer therapy. To understand the molecular mechanism of 1,25-dihydroxyvitamin D₃ action, we profiled the hormone-induced changes in the transcriptome of ovarian cancer cells using microarray technology. More than 200 genes were identified to be regulated by 1,25-dihydroxyvitamin D₃. Reverse transcription-PCR analyses confirmed the regulation of a group of apoptosis-related genes, including the up-regulation of the decoy receptor that inhibits tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) action, TRAIL receptor 4, and the down-regulation of Fas, the receptor that mediates the action of Fas ligand. The regulation was further confirmed at the protein level. Consistent with the regulation of the death receptors, pretreatment with 1,25-dihydroxyvitamin D₃ decreased apoptosis induced by TRAIL and Fas ligand. Because persistent 1,25-dihydroxyvitamin D₃ treatment has been shown to induce apoptosis in ovarian cancer, the hormone appears to exert a dual effect on the death of ovarian cancer cells. Knock-down of TRAIL receptor 4 by RNA interference or ectopic expression of Fas relieved the suppressive effect of 1,25-dihydroxyvitamin D₃, showing that molecular manipulation of death receptors is a viable approach to overcome the protective effect of 1,25-dihydroxyvitamin D₃ on the apoptosis of ovarian cancer. These strategies may allow ovarian cancer patients to benefit from therapy with both 1,25-dihydroxyvitamin D₃ and ligands for death receptors, such as TRAIL, shown to selectively induce apoptosis in cancer but not normal cells.