Studies on the relationship between estrogen receptor content, glutathione S-transferase π expression, and induction by 2,3,7,8- tetrachlorodibenzo-p-dioxin and drug resistance in human breast cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces both phase I and phase II drug-metabolizing enzymes in rodent liver and hepatoma cell lines and this induction is mediated by the aryl hydrocarbon (Ah) receptor. Induction of CYP1A1 by TCDD in human breast cancer cells has been reported and results of several studies suggest that the estrogen receptor (ER) may be required for Ah responsiveness. This study investigates the induction of GSTΠ by TCDD in human breast cancer cells and the role of the ER in mediating this response. TCDD did not induce chloramphenicol acetyl transferase (CAT) activity in ER positive (ER⁺) MCF-7 and ER^- MDA-MB-468 and MDA-MB-231 human breast cancer cell lines transiently transfected with GSTΠ (human) or GSTP (rat) promoter-reporter constructs containing the - 291/+36 and -2.9/+59 region, respectively, of the GSTΠ and GSTP gene promoters. Furthermore, TCDD did not induce GSTΠ or GSTP in MDA-MB-468 and MDA-MB-231 human breast cancer cells stably transfected with the ER. RT-PCR confirmed that GSTπ mRNA levels were low in ER⁺ MCF-7 cells and high in ER^- MDA-MB-468 and MDA-MB-231 cells; however, in MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER GSTΠ mRNA levels remained elevated and were not inducible. MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER exhibited increased GST activity and decreased GSH content compared to wild-type cells; however, in MDA-MB-468 cells stably transfected with ER, the susceptibility to doxorubicin, ellipticine, chlorambucil, malphalan, or cisplatin was similar to that observed in wild-type cells. Adriamycin accumulation was similar in wild-type and ER stably transfected cells and verapamil did not affect this response, suggesting that ER expression did not influence p-glycoprotein activity. Taken together these data suggest that not all GST isoforms are responsive to TCDD and stable transfection of ER^- cells with ER is not sufficient to restore the ER⁺ phenotype in some breast cancer cell lines.