DIFFERENT RESPONSE OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD)-SENSITIVE GENES IN HUMAN BREAST-CANCER MCF-7 AND MDA-MB-231 CELLS

Human breast cancer cell lines are widely used to study the antiestrog enic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vitro. Li ke other groups we found that 10 nM TCDD inhibits cell growth and indu ces cytochrome P450 1A1 (CYP1A1)-associated 7-ethoxyresorufin-O-deethy lase (EROD) activity in MCF-7 cells expressing the estradiol receptor (ER). Neither cell growth nor EROD activity was affected in ER-negativ e MBA-MB 231 cells. Results of reverse transcription-polymerase chain reaction (RT-PCR) revealed a strong induction of CYP1A1 mRNA in MCF-7 but only a weak increase in MBA-MB 231 cells treated with 1, 10, or 10 0 nM TCDD. Transcripts of CYP1B1 were detected in both cell lines and mRNA content was enhanced 8- and 30-fold in MCF-7 and MDA-MB 231 cells treated with 1 nM TCDD, respectively. In gel mobility shift assay a s tronger signal of DNA-binding aryl hydrocarbon receptor (AhR) was obse rved in MDA-MB 231 than in MCF-7 cells treated with 10 nM TCDD. These results were confirmed by RT-PCR analyses which showed an approximatel y 40-fold higher AhR mRNA content in untreated MBA-MB 231 than in MCF7 cells. In contrast the mRNA of the AhR nuclear translocator was expre ssed in a similar range of magnitude. Treatment of the cells with TCDD did not change mRNA expression of both genes. Analysis of NADPH:quino ne oxidoreductase (NMO- 1) and plasminogen activator inhibitor-2 (PAI- 2) mRNA expression revealed a dose-dependent induction of both genes i n MDA-MB 231 cells after TCDD-treatment. From the results it was concl uded that AhR-mediated transactivation is not impaired in ER-negative MDA-MB 231 cells. In addition, the results confirm reported data that expression of ER seems to be important for regulation of CYP1A1 induct ion after TCDD in human breast cancer cell lines but the present data show that ER does not appear to have a function in TCDD-induced mRNA e xpression of CYP1B1, NMO-1, and PAI-2 in MDA-MB 231 cells. (C) 1995 Ac ademic Press, Inc.