title: Heat shock protein hsp90 regulates dioxin receptor function in vivo.
abstract: The dioxin (aryl hydrocarbon) receptor is a ligand-dependent basic helix-loop-helix (bHLH) factor that binds to xenobiotic response elements of target promoters upon heterodimerization with the bHLH partner factor Arnt. Here we have replaced the bHLH motif of the dioxin receptor with a heterologous DNA-binding domain to create fusion proteins that mediate ligand-dependent transcriptional enhancement in yeast (Saccharomyces cerevisiae). Previously, our experiments indicated that the ligand-free dioxin receptor is stably associated with the 90-kDa heat shock protein, hsp90. To investigate the role of hsp90 in dioxin signaling we have studied receptor function in a yeast strain where hsp90 expression can be down-regulated to about 5% relative to wild-type levels. At low levels of hsp90, ligand-dependent activation of the chimeric dioxin receptor construct was almost completely inhibited, whereas the activity of a similar chimeric construct containing the structurally related Arnt factor was not affected. Moreover, a chimeric dioxin receptor construct lacking the central ligand- and hsp90-binding region of the receptor showed constitutive transcriptional activity in yeast that was not impaired upon down-regulation of hsp90 expression levels. Thus, these data suggest that hsp90 is a critical determinant of conditional regulation of dioxin receptor function in vivo via the ligand-binding domain.
authors.affiliation: Department of Medical Nutrition, Karolinska Institutet, Novum, Huddinge, Sweden.
authors.forename: M L
authors.initials: ML
authors.lastname: Whitelaw
authors.forename: J
authors.initials: J
authors.lastname: McGuire
authors.forename: D
authors.initials: D
authors.lastname: Picard
authors.forename: J A
authors.initials: JA
authors.lastname: Gustafsson
authors.forename: L
authors.initials: L
authors.lastname: Poellinger
mesh_terms: D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D001571:Benzoflavones / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004147:Dioxins / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D007700:Kinetics; D051379:Mice; D011401:Promoter Regions, Genetic; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000032:analysis / Q000096:biosynthesis; D019324:beta-Naphthoflavone
chemical_list: C497396:ARNT protein, human; C497397:Arnt protein, mouse; D001571:Benzoflavones; D004268:DNA-Binding Proteins; D004147:Dioxins; D018841:HSP90 Heat-Shock Proteins; D018336:Receptors, Aryl Hydrocarbon; D011965:Receptors, Glucocorticoid; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D019324:beta-Naphthoflavone; D001616:beta-Galactosidase