title: Protein kinase C modulates regulation of the CYP1A1 gene by the aryl hydrocarbon receptor.
abstract: Transcriptional activation of the human CYP1A1 gene by halogenated and polycyclic aromatic hydrocarbons is mediated by the aryl hydrocarbon receptor (AhR) complex, a ligand-dependent transcription factor. A competent AhR comprises at least two components following nuclear translocation and DNA binding, the AhR and the AhR nuclear translocator (Arnt) protein, whose combined action on human CYP1A1 gene transcription is shown to be dependent upon functional protein kinase C (PKC). In the present study, we examined the effects of phorbol 12-myristate 13-acetate, a potent PKC activator, on the ligand-induced transcriptional activation of the CYP1A1 gene and cellular function of the AhR in human HepG2 101L cells. The 101L cells carry a stable transgene consisting of 1800 bases of 5'-flanking DNA and the promoter of the human CYP1A1 gene linked to the firefly luciferase structural gene (Postlind, H., Vu, T. P., Tukey, R. H. & Quattrochi, L. C. (1993) Toxicol. Appl. Pharmacol. 118, 255-262). Pretreatment of cells with 12-myristate 13-acetate enhanced ligand-induced CYP1A1 gene expression 2-3-fold. Inhibition of PKC activity blocked directly the transcriptional activation and the transactivation of the CYP1A1 gene, indicating a role for PKC in the AhR-mediated transcriptional activation process. However, the DNA binding activities of the in vitro activated and the induced nuclear AhR as measured by electrophoretic mobility shift analysis were not affected when CYP1A1 transcription was inhibited, indicating the actions of PKC to be a nuclear event that works in concert with or precedes AhR binding to the gene. These results illustrate that PKC is absolutely essential for the cellular and molecular events that control induction of CYP1A1 gene transcription.
authors.affiliation: Department of Pharmacology and UCSD Cancer Center, University of California, San Diego, La Jolla, California 92093-0636, USA.
authors.forename: Y H
authors.initials: YH
authors.lastname: Chen
authors.forename: R H
authors.initials: RH
authors.lastname: Tukey
mesh_terms: D002273:Carcinogens / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics*; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D011493:Protein Kinase C / Q000378:metabolism*; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D002273:Carcinogens; D004791:Enzyme Inhibitors; D018336:Receptors, Aryl Hydrocarbon; D004247:DNA; D019363:Cytochrome P-450 CYP1A1; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate