title: Aryl hydrocarbon receptor repressor and TiPARP (ARTD14) use similar, but also distinct mechanisms to repress aryl hydrocarbon receptor signaling.
abstract: The aryl hydrocarbon receptor (AHR) regulates the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The AHR repressor (AHRR) is an AHR target gene and functions as a ligand-induced repressor of AHR; however, its mechanism of inhibition is controversial. Recently, we reported that TCDD-inducible poly (ADP-ribose) polymerase (TiPARP; ARTD14) also acts as a repressor of AHR, representing a new player in the mechanism of AHR action. Here we compared the ability of AHRR- and TiPARP-mediated inhibition of AHR activity. TCDD increased AHRR mRNA levels and recruitment of AHRR to cytochrome P450 1A1 (CYP1A1) in MCF7 cells. Knockdown of TiPARP, but not AHRR, increased TCDD-induced CYP1A1 mRNA and AHR protein levels. Similarly, immortalized TiPARP(-/-) mouse embryonic fibroblasts (MEFs) and AHRR(-/-) MEFs exhibited enhanced AHR transactivation. However, unlike TiPARP(-/-) MEFs, AHRR(-/-) MEFs did not exhibit increased AHR protein levels. Overexpression of TiPARP in AHRR(-/-) MEFs or AHRRΔ8, the active isoform of AHRR, in TiPARP(-/-) MEFs reduced TCDD-induced CYP1A1 mRNA levels, suggesting that they independently repress AHR. GFP-AHRRΔ8 and GFP-TiPARP expressed as small diffuse nuclear foci in MCF7 and HuH7 cells. GFP-AHRRΔ8_Δ1-49, which lacks its putative nuclear localization signal, localized to both the nucleus and the cytoplasm, while the GFP-AHRRΔ8_Δ1-100 mutant localized predominantly in large cytoplasmic foci. Neither GFP-AHRRΔ8_Δ1-49 nor GFP-AHRRΔ8_Δ1-100 repressed AHR. Taken together, AHRR and TiPARP repress AHR transactivation by similar, but also different mechanisms.
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada. l.macpherson@mail.utoronto.ca.
authors.forename: Laura
authors.initials: L
authors.lastname: MacPherson
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada. shaimaa.ahmed@utoronto.ca.
authors.forename: Shaimaa
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada. laura.tamblyn@utoronto.ca.
authors.forename: Laura
authors.initials: L
authors.lastname: Tamblyn
authors.affiliation: IUF-Leibniz Research Institute for Environmental Medicine gGmbH, Auf'm Hennekamp 50, 40225 Düsseldorf, Germany. krutmann@uni-duesseldorf.de.
authors.forename: Jean
authors.initials: J
authors.lastname: Krutmann
authors.affiliation: Immunology and Environment, Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straβe 31, 53115 Bonn, Germany. irmgard.foerster@uni-bonn.de.
authors.forename: Irmgard
authors.initials: I
authors.lastname: Förster
authors.affiliation: IUF-Leibniz Research Institute for Environmental Medicine gGmbH, Auf'm Hennekamp 50, 40225 Düsseldorf, Germany. hwei@uni-bonn.de.
authors.forename: Heike
authors.initials: H
authors.lastname: Weighardt
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada. jason.matthews@utoronto.ca.
authors.forename: Jason
authors.initials: J
authors.lastname: Matthews
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D017353:Gene Deletion; D055785:Gene Knockdown Techniques; D006801:Humans; D051379:Mice; D033703:Nucleoside Transport Proteins; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism*; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation; D015854:Up-Regulation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D033703:Nucleoside Transport Proteins; D011065:Poly(ADP-ribose) Polymerases; D018336:Receptors, Aryl Hydrocarbon; D012097:Repressor Proteins; C492162:AHRR protein, human; C117300:Ahrr protein, mouse; C579717:TiPARP protein, human; C000594530:2,3,7,8-tetrachlorodibenzo-p-dioxin poly(ADP-ribose) polymerase, mouse