TY - JOUR T1 - Regulation of Steroid Receptor Expression by 1α-Hydroxyvitamin D5 in Hormone-responsive Breast Cancer Cells JF - Anticancer Research JO - Anticancer Res SP - 3555 LP - 3561 VL - 29 IS - 9 AU - ERUM A. HUSSAIN-HAKIMJEE AU - RAJENDRA G. MEHTA Y1 - 2009/09/01 UR - http://ar.iiarjournals.org/content/29/9/3555.abstract N2 - Background: Vitamin D analog, 1α-hydroxy-24-ethyl-cholecalciferol (1α(OH)D5), is a less toxic VDR agonist that suppresses proliferation of breast cancer cells in vitro and in vivo. The present study assessed 1α(OH)D5-mediated regulation of VDR, and its potential anti-estrogenic activity in BT-474 cells. Materials and Methods: The mRNA and protein expression of steroid receptors were determined using RT-PCR and Western blot analyses, respectively. Results: VDR mRNA was up-regulated (180% of control) by 1α(OH)D5 within seven hours, whereas the expression of VDR protein increased by two-fold in 24 hours. This increase was abolished in presence of either actinomycin D or cyclohexamide. Additionally, there was a four-fold decrease in ERα mRNA and 40% decrease in ERα protein after 28 and 48 hours following 1α(OH)D5 treatment, respectively. Down-regulation of some of the estrogen-inducible genes was observed. Conclusion: Although no VDR stabilization by 1α(OH)D5 was observed, there was an increased expression of the VDR followed by partial anti-estrogenic activity in hormone-responsive BT-474 cells. ER -