Downregulation of the Ah receptor in mouse hepatoma cells treated in culture with 2,3,7,8-tetrachlorodibenzo-p-dioxin.
The aromatic hydrocarbon (Ah) receptor behaves as a ligand-dependent transcription factor in the induction of cytochrome P450IA1. In cells exposed to the Ah receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the Ah receptor undergoes a transformation from a form with low affinity for nucleic acids (cytosolic receptor) into a form that preferentially associates with the cell nucleus (nuclear receptor). We followed the fate of the Ah receptor in mouse hepatoma cells during short-term exposure to [3H]TCDD by analyzing both cytosolic and nuclear fractions for specific binding. Nuclear Ah receptor levels increased over the first 2 h of treatment and then decreased to about 50% of maximal concentrations by 5 h after start of treatment. The decrease in nuclear receptor was not accompanied by a reappearance of detectable Ah receptor in the cytosolic fraction; further incubation with [3H]TCDD in cytosols from lysed cells did not label any additional receptor sites in cytosolic extract. By the 6th h of incubation, the total receptor population in the cell was only about 15-20% of that detected at the start of the incubation. The levels of specific binding detected were unaffected by up to 20 h of incubation with the vehicle DMSO, confirming that the presence of TCDD is required for the observed downregulation to occur. These results indicate that there is a substantial ligand-dependent loss in total Ah receptor during short-term exposure of cells to TCDD in culture.
Prokipcak
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RD
Department of Pediatrics, Hospital for Sick Children, Toronto, Ont., Canada.
Okey
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AB
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation; D066298:In Vitro Techniques; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051379:Mice; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism / Q000494:pharmacology*; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug