Regulation of estrogen receptor-alpha gene expression by 1,25-dihydroxyvitamin D in MCF-7 cells

This report describes an investigation of the role of 1,25-dihydroxyvitamin a (VD3) in the regulation of estrogen receptor-or (ER) in the ER-positive breast cancer cell line, MCF-7. Treatment of cells with 10 nM VD3 resulted in a 50% decline in the concentration of ER protein at 24 h. Scatchard anal ysis showed a corresponding decrease in the number of estradiol binding sit es and no alteration in the binding affinity of estradiol for the ER (K-d = 0.08 nM in VD3-treated cells compared with K-d = 0.07 nM in control cells) . Vitamin D treatment also caused a 50% decrease in the steady state amount of ER mRNA, which was maximal by 18 h. In vitro transcription run-on exper iments demonstrated a decrease of approximately 60% in transcription of the estrogen receptor gene. Transient transfections using an ER promoter-CAT c onstruct also demonstrated a 40% decrease in CAT activity after VD3 treatme nt. Sequence analysis identified a potential vitamin D response element (nV DRE) within the ER promoter. When this element was mutated, the ability of VD3 to block transcription from the ER promoter was lost. When the nVDRE wa s placed upstream of a heterologous promoter, nVDRE-SV40-CAT, treatment wit h VD3 resulted in a 50% decrease in CAT activity. Interestingly, co-transfe ction of either the ER promoter-CAT or the nVDRE-SV40-CAT construct and a v itamin D receptor expression vector into COS-1 or CV-1 cells showed an appr oximately 4-fold increase in CAT activity after VD3 treatment. Taken togeth er these data suggest that VD3: inhibition of ER gene transcription is medi ated through a nVDRE in the ER promoter. Inhibition appears to be cell spec ific. (C) 1999 Wiley-Liss, Inc.