Effects of cycloheximide on the induction of cyp1a1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (tcdd) in three human breast cancer cell lines

Treatment of MCF-7, MDA-MB-231 and Hs578-T human breast cancer cell lines with 10_-9 M 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces CYP1A1 gene expression in the MCF-7 but not in the MDA-MB-231 or Hs578-T cells. Pretreatment of the cells with 10_-5 M cycloheximide results in significantly increased P4501A1 mRNA levels in all three cells lines. However, in cells co-treated with 10_-5 M cycloheximide plus 10_-9 M TCDD, an induced response by TCDD was observed in the MCF-7 and MDA-MB-231 but not in Hs578-T cells. Gel-retardation assays of nuclear extracts from the three cell lines complexed with a ³²P-labeled dioxin-responsive element (DRE) gave a TCDD-inducible retarded band only in the MCF-7 and MDA-MB-231 cells. A retarded band with a similar mobility was observed in nuclear extracts from Hs578-T cells treated with either 10_-9 M TCDD or DMSO (solvent control). These results suggest that aryl hydrocarbon non-responsive MDA-MB-231 and Hs578-T human breast cancer cell lines contain the CYP1A1 gene and treatment with cycloheximide increases both constitutive and TCDD-induced CYP1A1 gene expression.