A cycloheximide-sensitive factor regulates TCDD-induced degradation of the aryl hydrocarbon receptor.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a prototype of environmental halogenated aromatic hydrocarbons, induces a rapid reduction in steady state aryl hydrocarbon receptor (AhR). Here, we analyzed the biochemical pathway and function of the downregulation. Our results reveal that TCDD downregulates the AhR protein by shortening the halflife of AhR. The TCDD-induced degradation of AhR is inhibited by MG132, a potent inhibitor of the 26S proteasome, indicating the ubiquitin-26S proteasome mediated proteolysis as a mechanism for the degradation of AhR. Furthermore, inhibition of protein synthesis by cycloheximide blocks the degradation of AhR by TCDD, suggesting a labile factor in controlling the stability of ligand-activated AhR (hence, designated as AhR degradation promoting factor, or ADPF). Analyses of nuclear AhR demonstrated that cycloheximide increases nuclear AhR protein and functional AhR/Arnt DNA-binding complex, resulting in superinduction of CYP1A1. Lastly, genetic analyses by using AhR- or Arnt-defective variant cells demonstrate that superinduction by cycloheximide requires the transcription activation (TA) domain of AhR, implicating the TA domain in the control of AhR turnover by ADPF. These findings provide new insights into the mechanism by which TCDD-activated AhR is regulated in nucleus through the 26S proteasome protein degradation pathway.
Ma
Qiang
Q
Molecular Toxicology Laboratory, Toxicology and Molecular Biology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV 26505, USA. qam1@cdc.gov
Baldwin
Kimberly T
KT
D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000494:pharmacology; D004247:DNA / Q000737:chemistry; D015536:Down-Regulation; D004785:Environmental Pollutants / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006207:Half-Life; D008024:Ligands; D051379:Mice; D010447:Peptide Hydrolases / Q000494:pharmacology*; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000502:physiology
D004785:Environmental Pollutants; D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D011500:Protein Synthesis Inhibitors; D018336:Receptors, Aryl Hydrocarbon; D004247:DNA; D003513:Cycloheximide; D019363:Cytochrome P-450 CYP1A1; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease