title: Auto-induction mechanism of aryl hydrocarbon receptor 2 (AHR2) gene by TCDD-activated AHR1 and AHR2 in the red seabream (Pagrus major).
abstract: The toxic effects of dioxins and related compounds (DRCs) are mediated by the aryl hydrocarbon receptor (AHR). Our previous study identified AHR1 and AHR2 genes from the red seabream (Pagrus major). Moreover, we found that AHR2 mRNA levels were notably elevated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in the early life stage of red seabream embryos, while AHR1 mRNA level was not altered. In this study, to investigate the regulatory mechanism of these AHR transcripts, we cloned and characterized 5'-flanking regions of AHR1 and AHR2 genes. Both of the 5'-flanking regions in these AHR genes contained three potential xenobiotic-responsive elements (XREs). To assess whether the 5'-flanking region is transactivated by rsAHR1 and rsAHR2 proteins, we measured the transactivation potency of the luciferase reporter plasmids containing the 5'-flanking regions by AHR1 and AHR2 proteins that were transiently co-expressed in COS-7. Only reporter plasmid (pGL4-rsAHR2-3XREs) that contained three putative XRE sites in the 5'-flanking region of AHR2 gene showed a clear TCDD dose-dependent transactivation by AHR1 and AHR2 proteins. TCDD-EC50values for the rsAHR2-derived XRE transactivation were 1.3 and 1.4 nM for AHR1 and AHR2, respectively. These results suggest that the putative XREs of AHR2 gene have a function for AHR1- and AHR2-mediated transactivation, supporting our in ovo observation of an induction of AHR2 mRNA levels by TCDD exposure. Mutations in XREs of AHR2 gene led to a decrease in luciferase induction. Electrophoretic mobility shift assay showed that XRE1, the closest XRE from the start codon in AHR2 gene, is mainly responsible for the binding with TCDD-activated AHR. This suggests that TCDD-activated AHR1 and AHR2 up-regulate the AHR2 mRNA levels and this auto-induced AHR2 may amplify the signal transduction of its downstream targets including CYP1A in the red seabream.
authors.affiliation: Department of Life and Nanopharmaceutical Science, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 130-701, Korea.|Department of Biology, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 130-701, Korea.
authors.forename: Su-Min
authors.initials: SM
authors.lastname: Bak
authors.affiliation: Laboratory of Environmental Toxicology, Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Iida
authors.affiliation: Department of Environmental Toxicology, University of California, Davis, CA, 95616, USA.
authors.forename: Anatoly A
authors.initials: AA
authors.lastname: Soshilov
authors.affiliation: Department of Environmental Toxicology, University of California, Davis, CA, 95616, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Denison
authors.affiliation: Laboratory of Environmental Toxicology, Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577, Japan.
authors.forename: Hisato
authors.initials: H
authors.lastname: Iwata
authors.affiliation: Department of Life and Nanopharmaceutical Science, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 130-701, Korea. eykim08@khu.ac.kr.|Department of Biology, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 130-701, Korea. eykim08@khu.ac.kr.
authors.forename: Eun-Young
authors.identifier: http://orcid.org/0000-0002-9739-2324
authors.initials: EY
authors.lastname: Kim
mesh_terms: D024506:5' Flanking Region / Q000187:drug effects; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002999:Clone Cells; D024202:Electrophoretic Mobility Shift Assay; D029941:Fish Proteins / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006168:Guinea Pigs; D008024:Ligands; D009154:Mutation; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D020033:Protein Isoforms / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020218:Response Elements / Q000187:drug effects; D021541:Sea Bream / Q000502:physiology*; D017422:Sequence Analysis, DNA; D015533:Transcriptional Activation / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects*; D014873:Water Pollutants / Q000633:toxicity*
chemical_list: D029941:Fish Proteins; D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D020033:Protein Isoforms; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D011994:Recombinant Proteins; D014873:Water Pollutants
keywords: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD); Aryl hydrocarbon receptor (AHR); Auto-induction; Red seabream; Xenobiotic-responsive elements (XREs)