Comparative properties of the nuclear aryl hydrocarbon (Ah) receptor complex from several human cell lines

The aryl hydrocarbon (Ah) responsiveness of the T-47D, Hep G2, LS180, MCF-7, A431, C-4II and MDA-MB-231 human cancer cell lines was determined by the induction of CYP1A1 mRNA levels and ethoxyresorufin O-deethylase activity. With the exception of the MDA-MB-231 breast cancer cell line, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly induced CYP1A1 mRNA levels and ethoxyresorufin O-deethylase activity in the remaining six cell lines and, based on their EC₅₀ values, for ethoxyresorufin O-deethylase induction, their Ah responsiveness followed the order T-47D > C-4II > MCF-7 > LS180 > Hep G2 > A431. In contrast, all the cell lines expressed the nuclear Ah receptor complex (167.1-24.5 fmol/mg protein) which bound to a ³²P-labeled consensus dioxin responsive element (DRE) in a gel mobility shift assay. The results of gel permeation chromatography and sucrose density gradient centrifugation studies showed that the calculated M_r values for the nuclear Ah receptor complex varied from 175 kDa (MDA-MB-231 cells) to 221 kDa (MCF-7 cells). In contrast, the photoaffinity labeled nuclear Ah receptor from all the cell lines gave a specifically labeled 110 kDa band and the apparent molecular weight of the nuclear Ah receptor complex cross-linked to a bromodeoxyuridine-substituted DRE was 200 kDa. The data show that the molecular properties and levels of the nuclear Ah receptor complex from seven different human cancer cell lines do not predict Ah responsiveness.