A thyroid hormone receptor mutation that dissociates thyroid hormone regulation of gene expression in vivo

Abstract

Resistance to thyroid hormone (RTH) is most often due to point mutations in the ␤-isoform of the thyroid hormone (TH) receptor (TR-␤). The majority of mutations involve the ligand-binding domain, where they block TH binding and receptor function on both stimulatory and inhibitory TH response elements. In contrast, a few mutations in the ligand-binding domain are reported to maintain TH binding and yet cause RTH in certain tissues. We introduced one such naturally occurring human RTH mutation (R429Q) into the germline of mice at the TR-␤ locus. R429Q knock-in (KI) mice demonstrated elevated serum TH and inappropriately normal thyroid-stimulating hormone (TSH) levels, consistent with hypothalamic-pituitary RTH. In contrast, 3 hepatic genes positively regulated by TH (Dio1, Gpd1, and Thrsp) were increased in R429Q KI animals. Mice were then rendered hypothyroid, followed by graded T 3 replacement. Hypothyroid R429Q KI mice displayed elevated TSH subunit mRNA levels, and T 3 treatment failed to normally suppress these levels. T3 treatment, however, stimulated pituitary Gh levels to a greater degree in R429Q KI than in control mice. Gsta, a hepatic gene negatively regulated by TH, was not suppressed in R429Q KI mice after T 3 treatment, but hepatic Dio1 and Thrsp mRNA levels increased in response to TH. Cardiac myosin heavy chain isoform gene expression also showed a specific defect in TH inhibition. In summary, the R429Q mutation is associated with selective impairment of TH-mediated gene repression, suggesting that the affected domain, necessary for TR homodimerization and corepressor binding, has a critical role in negative gene regulation by TH.corepressor ͉ homodimer ͉ negative regulation ͉ resistance to thyroid hormone T hyroid-stimulating hormone (thyrotropin or TSH) is a heterodimeric glycoprotein consisting of 2 non-covalently linked protein subunits (TSH-␣ and TSH-␤), synthesized in the pituitary thyrotroph, which regulates the thyroid. TSH-releasing hormone (TRH) is synthesized in the paraventricular nucleus of the hypothalamus and released into the portal circulation, where it regulates the synthesis and glycosylation pattern (bioactivity) of pituitary TSH. The hypothalamic-pituitary-thyroid (HPT) axis is regulated by negative feedback involving thyroid hormones (THs) (T 4 and T 3 ), which are produced by the thyroid gland. The major negative regulator of TSH secretion is T 3 , which directly inhibits the transcription of the TSH-␣ and -␤ subunit genes (1-5) and TRH (6-8).TH action is mediated by different isoforms of the TH receptor (TR), which are members of the nuclear receptor superfamily of ligand-modulated transcription factors. Two genes, by alternative splicing and transcriptional start site utilization, express the known ligand-binding TR isoforms, TR-␣1, TR-␤1, TR-␤2, and TR-␤3. Negative regulation of the HPT axis is principally mediated by the ␤ isoform of the TR (9-13).On genes with a positive TH response element, TR interacts with corepressor proteins (CoRs) in the absence of ligand, and this...

Novel Mechanism of Positive versus Negative Regulation by Thyroid Hormone Receptor β1 (TRβ1) Identified by Genome-wide Profiling of Binding Sites in Mouse Liver

“…7B). There were relatively fewer T3-down-regulated genes that had both TR␤1 and RXR␣ ChIP peaks (41% for TR␤1-PTU ChIP peaks), which is in agreement with an earlier report that demonstrated that TR homodimers might be more important for negative regulation (35). These FIGURE 6.…”

Circadian Regulation of Tshb Gene Expression by Rev-Erbα (NR1D1) and Nuclear Corepressor 1 (NCOR1)

“…2). On the Gh gene, THR is bound to a Ϫ220 bp site (28,29). NCOR1 was enriched in this region and released upon T 3 treatment, consistent with reports on Gh regulation (Fig.…”

Syndromes of Reduced Sensitivity to Thyroid Hormone

“…On some occasions, mut TRβs may show greater impairment of transactivation on genes negatively rather than positively regulated by T 3 [41,54]. Recent work suggests that the mut TRβ R429Q affects predominantly the TRβ2 mediated action [55] while mut TRβ R338W, through its association with a single nucleotide polymorphism in the enhancer region, produces over expression of the mut TRβ allele [56]. These two mechanisms give credence to the existence of predominantly pituitary RTH.…”