2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polynuclear aromatic hydrocarbons are ubiquitous environmental contaminants with adverse effects on human health. These compounds cause toxicity by activating the aryl hydrocarbon receptor (AHR). The AHR also has physiological roles regulating vascular development, immune function, and cell growth, suggesting a role in human disease. To understand these diverse functions and the possible role of AHR in human disease, it is important to determine how AHR signaling is regulated. The negative regulation of AHR signaling is poorly understood. An inhibitor of AHR transcriptional activation function, AHR repressor (AHRR), has been identified, but its role in regulating AHR signaling remains enigmatic, and possible functions beyond the AHR pathway have been virtually ignored. Recent epidemiological studies have linked AHRR Pro185 and Ala185 polymorphisms to human reproductive disorders and AHRR has been identified as a likely tumor suppressor gene in humans. However, fundamental questions concerning the biochemical and functional characteristics of the AHRR and its variants remain unresolved, preventing a full understanding of its roles in human disease. The studies proposed here will utilize established vertebrate model systems (human cells and zebrafish embryos) to determine the transcription factor specificity and gene selectivity of AHRR and its polymorphic variants, the mechanism by which AHRR represses AHR and hypoxia inducible factors (HIFs), and the role of AHRR in regulating embryonic development and the response to TCDD and hypoxia in vivo. The central hypothesis is that AHRR acts through a transrepression mechanism to regulate the transcriptional activity of several transcription factors.
In Aim 1, we will test the hypothesis that human AHRR can repress a variety of constitutively active and conditional transcription factors. We will also use gain-of-function (Tet-On) and loss-of- function (siRNA) experiments in human cell lines to determine the AHR and HIF target gene specificity of repression by AHRR.
In Aim 2, we will use AHRR mutants, co-immunoprecipitation and chromatin immunoprecipitation assays, and ARNT-deficient cells to test several hypotheses: a) that the human AHRR and its variants act by a transrepression mechanism;b) that AHRR repression is ARNT-dependent;and c) that AHRR represses by binding to AHR and HIF or their transcription complexes.
In Aim 3, we will investigate the in vivo function of AHRR in the powerful zebrafish embryo model system. We will generate germ-line null mutants for each of the two zebrafish AHRR paralogs. With these AHRR-null fish combined with AHRR overexpression experiments, we will assess the in vivo transcription factor and gene target specificity of AHRRs, the role of transrepression in the mechanism of action, and the roles of AHRR in embryonic development and the response to activators of AHR and HIF.
The aryl hydrocarbon receptor repressor (AHRR), a protein found in humans and other Vertebrate Animals functions to regulate the ability of toxicants such as dioxin and carcinogenic polycyclic aromatic hydrocarbons to cause altered gene expression and toxicity. AHRR polymorphisms have been linked to male infertility and endometriosis in women, and the AHRR has been proposed to function as a tumor suppressor gene. The proposed research will elucidate the mechanisms by which human AHRR and its polymorphic variants regulate the activity of signaling pathways involved in the response to hypoxia and toxicants such as dioxin, providing new insight into its role in human disease.
|Wincent, Emma; Kubota, Akira; Timme-Laragy, Alicia et al. (2016) Biological effects of 6-formylindolo[3,2-b]carbazole (FICZ) in vivo are enhanced by loss of CYP1A function in an Ahr2-dependent manner. Biochem Pharmacol 110-111:117-29|
|Shoots, Jenny; Fraccalvieri, Domenico; Franks, Diana G et al. (2015) An Aryl Hydrocarbon Receptor from the Salamander Ambystoma mexicanum Exhibits Low Sensitivity to 2,3,7,8-Tetrachlorodibenzo-p-dioxin. Environ Sci Technol 49:6993-7001|
|DeGroot, Danica E; Franks, Diana G; Higa, Tatsuo et al. (2015) Naturally occurring marine brominated indoles are aryl hydrocarbon receptor ligands/agonists. Chem Res Toxicol 28:1176-85|
|Rousseau, Michelle E; Sant, Karilyn E; Borden, Linnea R et al. (2015) Regulation of Ahr signaling by Nrf2 during development: Effects of Nrf2a deficiency on PCB126 embryotoxicity in zebrafish (Danio rerio). Aquat Toxicol 167:157-71|
|Hahn, Mark E; McArthur, Andrew G; Karchner, Sibel I et al. (2014) The transcriptional response to oxidative stress during vertebrate development: effects of tert-butylhydroquinone and 2,3,7,8-tetrachlorodibenzo-p-dioxin. PLoS One 9:e113158|
|Lowe, Margaret M; Mold, Jeff E; Kanwar, Bittoo et al. (2014) Identification of cinnabarinic acid as a novel endogenous aryl hydrocarbon receptor ligand that drives IL-22 production. PLoS One 9:e87877|
|Parks, Ashley J; Pollastri, Michael P; Hahn, Mark E et al. (2014) In silico identification of an aryl hydrocarbon receptor antagonist with biological activity in vitro and in vivo. Mol Pharmacol 86:593-608|
|Aluru, Neelakanteswar; Jenny, Matthew J; Hahn, Mark E (2014) Knockdown of a zebrafish aryl hydrocarbon receptor repressor (AHRRa) affects expression of genes related to photoreceptor development and hematopoiesis. Toxicol Sci 139:381-95|
|Reitzel, Adam M; Passamaneck, Yale J; Karchner, Sibel I et al. (2014) Aryl hydrocarbon receptor (AHR) in the cnidarian Nematostella vectensis: comparative expression, protein interactions, and ligand binding. Dev Genes Evol 224:13-24|
|Amemiya, Chris T; AlfÃ¶ldi, Jessica; Lee, Alison P et al. (2013) The African coelacanth genome provides insights into tetrapod evolution. Nature 496:311-6|
Showing the most recent 10 out of 36 publications