Mechanism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated decrease of the nuclear estrogen receptor in MCF-7 human breast cancer cells.
Treatment of MCF-7 cells with 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 1 nM [3H]17 beta-estradiol resulted in decreased radiolabeled nuclear estrogen receptor (ER) levels as determined by velocity sedimentation analysis. In parallel studies, nuclear extracts from TCDD-treated cells also exhibited decreased binding to a consensus 32P-genomic estrogen responsive element (ERE) as determined in a gel mobility shift assay. Time-course studies showed that the decreases in nuclear ER and ER-ERE binding in TCDD-treated cells were observed within 1 to 3 h after treatment, respectively, and persisted for up to 24 h. Cycloheximide (10 microM) did not affect the TCDD-mediated response, whereas 1 microM alpha-naphthoflavone, an aryl hydrocarbon (Ah) receptor antagonist, partially blocked downregulation of nuclear ER binding by TCDD. TCDD did not significantly affect steady state ER mRNA levels as determined by Northern analysis or the rate of ER gene transcription in a nuclear run-on assay. These results suggest that the TCDD-mediated decrease in nuclear ER levels is an Ah receptor-mediated response which occurs at the translational or post-translational level.
Wang
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Department of Veterinary Physiology and Pharmacology, Texas A&M University, College Station 77843-4466.
Porter
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Krishnan
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Narasimhan
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Safe
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D000704:Analysis of Variance; D000818:Animals; D001483:Base Sequence; D001571:Benzoflavones / Q000494:pharmacology; D015152:Blotting, Northern; D001943:Breast Neoplasms; D002467:Cell Nucleus / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011485:Protein Binding; D011960:Receptors, Estrogen / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D001571:Benzoflavones; D000072317:Polychlorinated Dibenzodioxins; D011960:Receptors, Estrogen; C011512:alpha-naphthoflavone; D004247:DNA; D003513:Cycloheximide