The coupling of epidermal growth factor receptor down regulation by 1alpha,25-dihydroxyvitamin D3 to the hormone-induced cell cycle arrest at the G1-S checkpoint in ovarian cancer cells

1alpha,25-dihydroxyvitamin D3, 1,25(OH)(2)D-3, regulates gene expression through the vitamin D receptor. The present studies identify the epidermal growth factor receptor, EGFR, as a target gene suppressed by 1,25(OH)(2)D-3 in human ovarian cancer cells. The suppression was detected at both mRNA and protein levels in vitamin D-sensitive human ovarian cancer cells. A novel vitamin D response element was identified in intron 1 of the EGFR genome, a known hotspot for its transcriptional regulation. Chromatin immunoprecipitations and reporter gene analyses showed that the intronic DNA element bound to vitamin D receptor and a co-repressor and was functional in mediating transcriptional suppression of EGFR promoter by 1,25(OH)(2)D-3 under stable transfection conditions. Consistent with the EGFR down regulation, 1,25(OH)(2)D-3 suppressed activation of the external signal regulated kinase by epidermal growth factors. Over expression of an active EGFR in vitamin D sensitive ovarian cancer cells caused resistance to 1,25(OH)(2)D-3-induced growth suppression and diminished the hormonal regulation of cyclin D1, cyclin E, Skp2 and p27, a group of cell cycle regulators that mediate 1,25(OH)(2)D-3-induced cell cycle arrest at G1-S checkpoint. Taken together, our studies demonstrate that 1,25(OH)(2)D-3 suppresses the response of human ovarian cancer cells to mitogenic growth factors and couple the suppression to the cell cycle arrest at G1-S checkpoint by the hormone. (C) 2011 Elsevier Ireland Ltd. All rights reserved.