Effect of AhR knockdown on CYP1A1 and SULT1E1 expression in preconfluent MCF10A cells. A and B, MCF10A cells engineered for conditional knockdown of AhR were plated at low density, treated for 96 h with 0.1% DMSO or 1 μg/ml doxycycline (DOX), and harvested at ∼70% confluence for measurement of AhR mRNA (A) and immunoreactive protein (B) levels. In A, data are expressed relative to DMSO-treated cells as the mean ± S.E.M. of three independent cell culture experiments. ***, p < 0.001 compared with DMSO-treated cells. C and D, MCF10A cells plated at low density were treated for 96 h with DMSO or doxycycline; during the final 24 h of this treatment period, the cells were additionally treated with DMSO, 1 μM MNF, or 30 nM TCDD. The cells were then harvested at ∼70% confluence for measurement of CYP1A1 (C) and SULT1E1 (D) mRNA levels, and data are expressed as the mean ± S.E.M. of three independent cell culture experiments. ***, p < 0.001; **, p < 0.01 compared with DMSO-treated cells.