Epigenetic repression of transcription by the Vitamin D 3 receptor in prostate cancer cells

Abstract

Normal prostate epithelial cells are acutely sensitive to the antiproliferative action of 1α,25-dihydroxyvitamin D 3 (1α,25(OH) 2D 3), whilst prostate cancer cell lines and primary cultures display a range of sensitivities. We hypothesised that key antiproliferative target genes of the Vitamin D receptor (VDR) were repressed by an epigenetic mechanism in 1α,25(OH) 2D 3-insensitive cells. Supportively, we found elevated nuclear receptor co-repressor and reduced VDR expression correlated with reduced sensitivity to the antiproliferative action of 1α,25(OH) 2D 3. Furthermore, the growth suppressive actions of 1α,25(OH) 2D 3 can be restored by co-treatment with low doses of histone deacetylation inhibitors, such as trichostatin A (TSA) to induce apoptosis. Examination of the regulation of VDR target genes revealed that co-treatment of 1α,25(OH) 2D 3 plus TSA co-operatively upregulated GADD45α. Similarly in a primary cancer cell culture, the regulation of appeared GADD45α repressed. These data demonstrate that prostate cancer cells utilise a mechanism involving deacetylation to suppress the responsiveness of VDR target genes and thus ablate the antiproliferative action of 1α,25(OH) 2D 3.