Document Detail

Different structural requirements of the ligand binding domain of the aryl hydrocarbon receptor for high- and low-affinity ligand binding and receptor activation.
MedLine Citation:
PMID:  14742684     Owner:  NLM     Status:  MEDLINE    
The aryl hydrocarbon receptor (AhR) functions as a ligand-activated transcription factor that is responsible for the regulation of several response genes, of which the best characterized is the CYP1A1 gene. The present study was undertaken to elucidate the mechanism of activation of the AhR by omeprazole (OME), 2-mercapto-5-methoxybenzimidazole (MMB), and primaquine (PRQ), compounds that have previously been reported to induce CYP1A1 expression but that are not typical AhR ligands. All compounds caused a significant increase in luciferase activity in rat H4IIE and human HepG2 hepatoma cells transfected with a Gal4-AhR construct and the corresponding Gal4-Luc reporter gene. Furthermore, MMB and PRQ, but not OME, were capable of transforming cytosolic AhR to a DNA-binding form and displacing AhR-bound [3H]TCDD in rat hepatic cytosol in vitro. By performing site-directed mutagenesis of residues in the ligand-binding domain of the Gal4-AhR, a construct containing a Y320F substitution was found to be resistant to activation by OME, MMB, and PRQ, but not by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Comparable affinities of [3H]TCDD-binding to the wild-type and the Y320F mutant Gal4-proteins, expressed in human embryonic kidney 293 cells, were obtained in the ligand-binding assay. In contrast, the competition of receptor-bound [3H]TCDD by PRQ was absent from Gal4-Y320F but not from Gal4-AhR cell extracts. The results of this study confirm that MMB and PRQ are low-affinity ligands for the AhR and suggest that high- and low-affinity ligands interact with different residues of the AhR ligand-binding pocket. In addition, the data presented here indicate that Tyr320 plays an important role in AhR activation.
Maria Backlund; Magnus Ingelman-Sundberg
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Molecular pharmacology     Volume:  65     ISSN:  0026-895X     ISO Abbreviation:  Mol. Pharmacol.     Publication Date:  2004 Feb 
Date Detail:
Created Date:  2004-01-26     Completed Date:  2004-03-12     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0035623     Medline TA:  Mol Pharmacol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  416-25     Citation Subset:  IM    
Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
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MeSH Terms
Binding Sites / drug effects,  physiology
Cell Line
Omeprazole / chemistry,  metabolism,  pharmacology
Protein Binding / drug effects,  physiology
Receptors, Aryl Hydrocarbon / genetics,  metabolism*
Tetrachlorodibenzodioxin / chemistry,  metabolism,  pharmacology
Reg. No./Substance:
0/Ligands; 0/Receptors, Aryl Hydrocarbon; 1746-01-6/Tetrachlorodibenzodioxin; 73590-58-6/Omeprazole

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