title: ERK kinase inhibition stabilizes the aryl hydrocarbon receptor: implications for transcriptional activation and protein degradation.
abstract: The ultimate carcinogen and metabolite of benzo-[a]pyrene-7,8-dihydrodiol, benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide (+/-), stimulates apoptosis, and this process can be blocked by extracellular signal-regulated kinase (Erk) kinase inhibitors. However, we show here that Erk kinase inhibitors were unable to prevent B[a]P-7,8-dihydrodiol-induced apoptosis, leading us to speculate that Erk kinases are linked to regulation of the aryl hydrocarbon (Ah) receptor. Cotreatment of hepa1c1c7 cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and Erk kinase inhibitor PD98059, U0126, or SL327 led to enhanced nuclear accumulation of Ah receptor but with a reduced capacity to complement TCDD induction of Cyp1a1. This is explained in part by the ability of Erk kinase inhibitors to alter the steady-state levels of cellular Ah receptor, a result that leads to a dramatic induction in detectable receptor levels. These changes in cellular Ah receptor levels are associated with delayed degradation of the Ah receptor because TCDD-initiated degradation is reversed when cells are co-treated with TCDD and Erk kinase inhibitors. Erk kinase is linked to Ah receptor expression, as demonstrated by reductions in total Ah receptor levels after overexpression of constitutively active MEK1. In addition, Erk kinase activity modulates the transcriptional response because MEK1 overexpression enhances TCDD-initiated transactivation potential of the receptor. Thus, Erk kinase activity facilitates ligand-initiated transcriptional activation while targeting the Ah receptor for degradation. Immunoprecipitation experiments of the Ah receptor indicate that Erk kinase activity is associated with the receptor. It is interesting that the carboxyl region of the Ah receptor is associated with the transactivation region as well as the site for ubiquitination, indicating that Erk kinase-dependent phosphorylation targets the carboxyl region of the receptor.
authors.affiliation: Laboratory of Environmental Toxicology, Department of Pharmacology, Chemistry & Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Chen
authors.forename: Theresa
authors.initials: T
authors.lastname: Operaña
authors.forename: Jessica
authors.initials: J
authors.lastname: Bonzo
authors.forename: Nghia
authors.initials: N
authors.lastname: Nguyen
authors.forename: Robert H
authors.initials: RH
authors.lastname: Tukey
mesh_terms: D000607:Aminoacetonitrile / Q000031:analogs & derivatives; D017209:Apoptosis; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D008956:Models, Chemical; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry*; D015398:Signal Transduction; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D002070:Butadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D008024:Ligands; D009570:Nitriles; D000072317:Polychlorinated Dibenzodioxins; D011480:Protease Inhibitors; D011506:Proteins; D018336:Receptors, Aryl Hydrocarbon; C424127:SL 327; C113580:U 0126; D025801:Ubiquitin; D000607:Aminoacetonitrile; D013395:Sucrose; D012313:RNA; D008156:Luciferases; D019363:Cytochrome P-450 CYP1A1; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one