EFFECTS OF CYCLOHEXIMIDE ON THE INDUCTION OF CYP1A1 GENE-EXPRESSION BY 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) IN 3 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 P-32-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.