title: Amino acid sequence of the ligand-binding domain of the aryl hydrocarbon receptor 1 predicts sensitivity of wild birds to effects of dioxin-like compounds.
abstract: The sensitivity of avian species to the toxic effects of dioxin-like compounds (DLCs) varies up to 1000-fold among species, and this variability has been associated with interspecies differences in aryl hydrocarbon receptor 1 ligand-binding domain (AHR1 LBD) sequence. We previously showed that LD(50) values, based on in ovo exposures to DLCs, were significantly correlated with in vitro EC(50) values obtained with a luciferase reporter gene (LRG) assay that measures AHR1-mediated induction of cytochrome P4501A in COS-7 cells transfected with avian AHR1 constructs. Those findings suggest that the AHR1 LBD sequence and the LRG assay can be used to predict avian species sensitivity to DLCs. In the present study, the AHR1 LBD sequences of 86 avian species were studied, and differences at amino acid sites 256, 257, 297, 324, 337, and 380 were identified. Site-directed mutagenesis, the LRG assay, and homology modeling highlighted the importance of each amino acid site in AHR1 sensitivity to 2,3,7,8-tetrachlorodibenzo-p-dioxin and other DLCs. The results of the study revealed that (1) only amino acids at sites 324 and 380 affect the sensitivity of AHR1 expression constructs of the 86 avian species to DLCs and (2) in vitro luciferase activity of AHR1 constructs containing only the LBD of the species of interest is significantly correlated (r  (2) = 0.93, p < 0.0001) with in ovo toxicity data for those species. These results indicate promise for the use of AHR1 LBD amino acid sequences independently, or combined with the LRG assay, to predict avian species sensitivity to DLCs.
authors.affiliation: Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: Reza
authors.initials: R
authors.lastname: Farmahin
authors.forename: Gillian E
authors.initials: GE
authors.lastname: Manning
authors.forename: Doug
authors.initials: D
authors.lastname: Crump
authors.forename: Dongmei
authors.initials: D
authors.lastname: Wu
authors.forename: Lukas J
authors.initials: LJ
authors.lastname: Mundy
authors.forename: Stephanie P
authors.initials: SP
authors.lastname: Jones
authors.forename: Mark E
authors.initials: ME
authors.lastname: Hahn
authors.forename: Sibel I
authors.initials: SI
authors.lastname: Karchner
authors.forename: John P
authors.initials: JP
authors.lastname: Giesy
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Bursian
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Zwiernik
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Fredricks
authors.forename: Sean W
authors.initials: SW
authors.lastname: Kennedy
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D001665:Binding Sites; D001717:Birds; D015153:Blotting, Western; D019556:COS Cells; D018929:Cell Culture Techniques; D002522:Chlorocebus aethiops; D004147:Dioxins / Q000737:chemistry / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D007928:Lethal Dose 50; D008024:Ligands; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008156:Luciferases / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011237:Predictive Value of Tests; D011485:Protein Binding; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013045:Species Specificity; D014162:Transfection
chemical_list: D004147:Dioxins; D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; D008156:Luciferases; D001189:Aryl Hydrocarbon Hydroxylases; C108015:cytochrome P-450 CYP1A5