title: ARA9 modifies agonist signaling through an increase in cytosolic aryl hydrocarbon receptor.
abstract: The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the effects of agonists like 2,3, 7,8-tetrachlorodibenzo-p-dioxin. In the current model for AHR signaling, the unliganded receptor is found in the cytosol as part of a complex with a dimer of the 90-kDa heat shock protein and an immunophilin-like molecule, ARA9. In yeast, expression of ARA9 results in an increase in the maximal agonist response and a leftward shift in the AHR dose-response curve. To better understand the mechanism by which ARA9 modifies AHR signal transduction, we performed a series of coexpression experiments in yeast and mammalian cells. Our results demonstrate that ARA9's influence on AHR signaling is not due to inhibition of a membrane pump or modification of the receptor's transactivation properties. Using receptor photoaffinity labeling experiments, we were able to show that ARA9 enhances AHR signal transduction by increasing the available AHR binding sites within the cytosolic compartment of the cell. Our evidence suggests that ARA9's effects are related to its role as a cellular chaperone; i.e. we observed that expression of ARA9 increases the fraction of AHR in the cytosol and also stabilized the receptor under heat stress.
authors.affiliation: McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: LaPres
authors.forename: E
authors.initials: E
authors.lastname: Glover
authors.forename: E E
authors.initials: EE
authors.lastname: Dunham
authors.forename: M K
authors.initials: MK
authors.lastname: Bunger
authors.forename: C A
authors.initials: CA
authors.lastname: Bradfield
mesh_terms: D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones / Q000378:metabolism; D019920:Photoaffinity Labels; D011489:Protein Denaturation; D011506:Proteins; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D015398:Signal Transduction / Q000187:drug effects; D016559:Tacrolimus / Q000494:pharmacology; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D019920:Photoaffinity Labels; D011506:Proteins; D018336:Receptors, Aryl Hydrocarbon; D011993:Recombinant Fusion Proteins; C103265:aryl hydrocarbon receptor-interacting protein; D016559:Tacrolimus