title: Identification of amino acid residues in the ligand-binding domain of the aryl hydrocarbon receptor causing the species-specific response to omeprazole: possible determinants for binding putative endogenous ligands.
abstract: Omeprazole (OME) induces the expression of genes encoding drug-metabolizing enzymes, such as CYP1A1, via activation of the aryl hydrocarbon receptor (AhR) both in vivo and in vitro. However, the precise mechanism of OME-mediated AhR activation is still under investigation. While elucidating species-specific susceptibility to dioxin, we found that OME-mediated AhR activation was mammalian species specific. Moreover, we previously reported that OME has inhibitory activity toward CYP1A1 enzymes. From these observations, we speculated that OME-mediated AhR target gene transcription is due to AhR activation by increasing amounts of putative AhR ligands in serum by inhibition of CYP1A1 activity. We compared the amino acid sequences of OME-sensitive rabbit AhR and nonsensitive mouse AhR to identify the residues responsible for the species-specific response. Chimeric AhRs were constructed by exchanging domains between mouse and rabbit AhRs to define the region required for the response to OME. OME-mediated transactivation was observed only with the chimeric AhR that included the ligand-binding domain (LBD) of the rabbit AhR. Site-directed mutagenesis revealed three amino acids (M328, T353, and F367) in the rabbit AhR that were responsible for OME-mediated transactivation. Replacing these residues with those of the mouse AhR abolished the response of the rabbit AhR. In contrast, substitutions of these amino acids with those of the rabbit AhR altered nonsensitive mouse AhR to become sensitive to OME. These results suggest that OME-mediated AhR activation requires a specific structure within LBD that is probably essential for binding with enigmatic endogenous ligands.
authors.affiliation: Division of Cancer Development System, National Cancer Center Research Institute, Tokyo, Japan (K.S.); Division of Environmental Health Sciences, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan (S.O.); Department of Life Science, Dongguk University, Seoul, Korea (T.Y.); and Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan (M.K., T.Y.).
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Shiizaki
authors.forename: Seiichiroh
authors.initials: S
authors.lastname: Ohsako
authors.forename: Masanobu
authors.initials: M
authors.lastname: Kawanishi
authors.forename: Takashi
authors.initials: T
authors.lastname: Yagi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D006168:Guinea Pigs; D006801:Humans; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D009853:Omeprazole / Q000494:pharmacology*; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D054328:Proton Pump Inhibitors / Q000494:pharmacology*; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry* / Q000378:metabolism; D013045:Species Specificity
chemical_list: D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D054328:Proton Pump Inhibitors; D018336:Receptors, Aryl Hydrocarbon; C569463:CYP1A1 protein, human; D019363:Cytochrome P-450 CYP1A1; D009853:Omeprazole