title: Antagonism of aryl hydrocarbon receptor signaling by 6,2',4'-trimethoxyflavone.
abstract: The aryl hydrocarbon receptor (AHR) is regarded as an important homeostatic transcriptional regulator within physiological and pathophysiological processes, including xenobiotic metabolism, endocrine function, immunity, and cancer. Agonist activation of the AHR is considered deleterious based on toxicological evidence obtained with environmental pollutants, which mediate toxic effects through AHR. However, a multitude of plant-derived constituents, e.g., polyphenols that exhibit beneficial properties, have also been described as ligands for the AHR. It is conceivable that some of the positive aspects of such compounds can be attributed to suppression of AHR activity through antagonism. Therefore, we conducted a dioxin response element reporter-based screen to assess the AHR activity associated with a range of flavonoid compounds. Our screen identified two flavonoids (5-methoxyflavone and 7,4'-dimethoxyisoflavone) with previously unidentified AHR agonist potential. In addition, we have identified and characterized 6,2',4'-trimethoxyflavone (TMF) as an AHR ligand that possesses the characteristics of an antagonist having the capacity to compete with agonists, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo[a]pyrene, thus effectively inhibiting AHR-mediated transactivation of a heterologous reporter and endogenous targets, e.g., CYP1A1, independent of cell lineage or species. Furthermore, TMF displays superior action by virtue of having no partial agonist activity, in contrast to other documented antagonists, e.g., alpha-napthoflavone, which are partial weak agonists. TMF also exhibits no species or promoter dependence with regard to AHR antagonism. TMF therefore represents an improved tool allowing for more precise dissection of AHR function in the absence of any conflicting agonist activity.
authors.affiliation: Center for Molecular Toxicology and Carcinogenesis, Department of Veterinary Sciences, The Pennsylvania State University, Pennsylvania 16802, USA.
authors.forename: Iain A
authors.initials: IA
authors.lastname: Murray
authors.forename: Colin A
authors.initials: CA
authors.lastname: Flaveny
authors.forename: Brett C
authors.initials: BC
authors.lastname: DiNatale
authors.forename: Chris R
authors.initials: CR
authors.lastname: Chairo
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Schroeder
authors.forename: Ann
authors.initials: A
authors.lastname: Kusnadi
authors.forename: Gary H
authors.initials: GH
authors.lastname: Perdew
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000494:pharmacology; D001667:Binding, Competitive; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D047309:Flavones / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D008024:Ligands; D008156:Luciferases / Q000235:genetics; D051379:Mice; D015394:Molecular Structure; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D011869:Radioligand Assay; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000235:genetics; D048348:Reverse Transcription; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: C546607:6,2',4'-trimethoxyflavone; D047309:Flavones; D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D001564:Benzo(a)pyrene; D003577:Cytochrome P-450 Enzyme System; D008156:Luciferases