title: In vitro and in silico evaluation of transactivation potencies of avian AHR1 and AHR2 by endogenous ligands: Implications for the physiological role of avian AHR2.
abstract: Aryl hydrocarbon receptor (AHR) is well conserved from invertebrates to vertebrates, and it mediates the toxic effects of exogenous ligands, including dioxins. Recent studies reported that AHRs activated by endogenous ligands play critical roles in mammalian physiological homeostasis. Avian species possess at least two AHR isoforms (AHR1 and AHR2), which exhibit species- and isoform-specific transactivation potencies to exogenous ligands, whereas mammals possess a single AHR. To delineate the profiles and roles of endogenous ligands for avian AHR isoforms, we investigated in vitro transactivation potencies of avian AHRs (AHR1 and AHR2 from the jungle crow, Corvus macrorhynchos; common cormorant, Phalacrocorax carbo; and black-footed albatross, Phoebastria nigripes) treated with the endogenous tryptophan metabolites 6-formylindolo [3,2-b] carbazole (FICZ), l-kynurenine (l-Kyn), kynurenic acid (KYNA), and indoxyl sulfate (IS). Furthermore, we analyzed the binding mode of these ligands to each avian AHR isoform by in silico docking simulations. The EC50 of FICZ (0.009-0.032nM) was similar regardless of the species or isoform of AHR. The estimated in silico binding mode of FICZ to AHRs was well conserved in both isoforms. The transactivation potencies of avian AHRs to other tryptophan metabolites were 10(5)-10(7) fold lower than those for FICZ, and EC50 values varied in a species- and isoform-specific manner. This was consistent with poor conservation of the binding mode of l-Kyn, KYNA, and IS predicted in in silico docking simulations. Our results suggest that in avian species, FICZ is the most potent endogenous AHR ligand, and that AHR1 and AHR2 are physiologically functional.
authors.affiliation: Department of Biology, Kyung Hee University, Hoegi Dong, Dongdaemun-Gu, Seoul 130-701, Republic of Korea.
authors.forename: In-Sung
authors.initials: IS
authors.lastname: Kim
authors.affiliation: Department of Biology, Kyung Hee University, Hoegi Dong, Dongdaemun-Gu, Seoul 130-701, Republic of Korea; Department of Life and Nanopharmaceutical Science, Kyung Hee University, Hoegi Dong, Dongdaemun-Gu, Seoul 130-701, Republic of Korea.
authors.forename: Ji-Hee
authors.initials: JH
authors.lastname: Hwang
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama 790-8577, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Hirano
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama 790-8577, Japan.
authors.forename: Hisato
authors.initials: H
authors.lastname: Iwata
authors.affiliation: Department of Biology, Kyung Hee University, Hoegi Dong, Dongdaemun-Gu, Seoul 130-701, Republic of Korea; Department of Life and Nanopharmaceutical Science, Kyung Hee University, Hoegi Dong, Dongdaemun-Gu, Seoul 130-701, Republic of Korea. Electronic address: eykim08@khu.ac.kr.
authors.forename: Eun-Young
authors.initials: EY
authors.lastname: Kim
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D019556:COS Cells; D002227:Carbazoles / Q000378:metabolism / Q000494:pharmacology; D002522:Chlorocebus aethiops; D046368:Crows / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D007200:Indican / Q000378:metabolism / Q000494:pharmacology; D007736:Kynurenic Acid / Q000378:metabolism / Q000494:pharmacology; D007737:Kynurenine / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D062105:Molecular Docking Simulation; D011485:Protein Binding; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D014158:Transcription, Genetic / Q000187:drug effects*; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection
chemical_list: C111855:6-formylindolo(3,2-b)carbazole; D030161:Avian Proteins; D002227:Carbazoles; D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; D007737:Kynurenine; D007736:Kynurenic Acid; D007200:Indican
keywords: Aryl hydrocarbon receptor; Bird; FICZ; Indoxyl sulfate; Kynurenic acid; l-Kynurenine