title: Pituitary specific retinoid-X receptor ligand interactions with thyroid hormone receptor signaling revealed by high throughput reporter and endogenous gene responses.
abstract: Disruption of thyroid hormone (TH) signaling can compromise vital processes both during development and in the adult. We previously reported on high-throughput screening experiments for man-made TH disruptors using a stably integrated line of rat pituitary cells, GH3.TRE-Luc, in which a thyroid hormone receptor (TR) response element drives luciferase (Luc) expression. In these experiments, several retinoid/rexinoid compounds activated the reporter. Here we show that all-trans and 13-cis retinoic acid appear to function through the heterodimer partners of TRs, retinoid-X receptors (RXRs), as RXR antagonists abrogated retinoid-induced activation. The retinoids also induced known endogenous TR target genes, showing good correlation with Luc activity. Synthetic RXR-specific agonists significantly activated all tested TR target genes, but interestingly, retinoid/rexinoid activation was more consistent between genes than the extent of T3-induced activation. In contrast, the retinoids neither activated the Luc reporter construct in transient transfection assays in the human hepatocarcinoma cell line HuH7, nor two of the same T3-induced genes examined in pituitary cells. These data demonstrate the suitability and sensitivity of GH3.TRE-Luc cells for screening chemical compound libraries for TH disruption and suggest that the extent of disruption can vary on a cell type and gene-specific bases, including an underappreciated contribution by RXRs.
authors.affiliation: Department of Neurobiology, Physiology and Behavior, 1 Shields Avenue, University of California Davis, Davis, CA 95616, United States.
authors.forename: Brenda J
authors.initials: BJ
authors.lastname: Mengeling
authors.affiliation: Department of Neurobiology, Physiology and Behavior, 1 Shields Avenue, University of California Davis, Davis, CA 95616, United States. Electronic address: jdfurlow@ucdavis.edu.
authors.forename: J David
authors.initials: JD
authors.lastname: Furlow
mesh_terms: D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D017930:Genes, Reporter; D057166:High-Throughput Screening Assays; D006801:Humans; D008024:Ligands; D010902:Pituitary Gland; D051381:Rats; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism*; D047488:Retinoid X Receptors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012176:Retinoids / Q000494:pharmacology; D015398:Signal Transduction; D013963:Thyroid Hormones / Q000494:pharmacology
chemical_list: D008024:Ligands; D011988:Receptors, Thyroid Hormone; D047488:Retinoid X Receptors; D012176:Retinoids; D013963:Thyroid Hormones
keywords: Endocrine disruption; Reporter gene assay; Retinoids; Rexinoids; Thyroid hormone receptors