mRNA expression through the VDR in ERα-negative breast cancer cells. A) Cultured tumor-derived cells from five patients (1-5) with ERα-negative breast cancer and the ER-negative SUM-229PE (S) and ER-positive BT-474 (B) established cell lines were incubated with calcitriol (1X10-7 M) or its vehicle (C, ethanol) for 24 hr. Subsequently, mRNA was extracted and real time RT-PCR (qPCR) was performed. B) Cultured breast tumor-derived cells were treated with increasing calcitriol concentrations (1X10-10 M and 1X10-7 M) for 24 hr. C) Cells were incubated in the absence (C) or presence of calcitriol (Cal, 1X10-8 M), without or with a VDR antagonist (TEI, 1X10-6 M). Results shown are the mean ± S.D. of ERα/GAPDH mRNA normalized ratio of two independent experiments per triplicate. Data were normalized to 1 for vehicle-treated cells. *P ≤ 0.05 vs. C. **P ≤ 0.05 vs. calcitriol alone.