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The rat thyroid hormone receptor (TR) Deltabeta3 displays cell-, TR isoform-, and thyroid hormone response element-specific actions.

ABSTRACT: The THRB gene encodes the well-described thyroid hormone (T3) receptor (TR) isoforms TRbeta1 and TRbeta2 and two additional variants, TRbeta3 and TRDeltabeta3, of unknown physiological significance. TRbeta1, TRbeta2, and TRbeta3 are bona fide T3 receptors that bind DNA and T3 and regulate expression of T3-responsive target genes. TRDeltabeta3 retains T3 binding activity but lacks a DNA binding domain and does not activate target gene transcription. TRDeltabeta3 can be translated from a specific TRDeltabeta3 mRNA or is coexpressed with TRbeta3 from a single transcript that contains an internal TRDeltabeta3 translation start site. In these studies, we provide evidence that the TRbeta3/Deltabeta3 locus is present in rat but not in other vertebrates, including humans. We compared the activity of TRbeta3 with other TR isoforms and investigated mechanisms of action of TRDeltabeta3 at specific thyroid hormone response elements (TREs) in two cell types. TRbeta3 was the most potent isoform, but TR potency was TRE dependent. TRDeltabeta3 acted as a cell-specific and TRE-dependent modulator of TRbeta3 when coexpressed at low concentrations. At higher concentrations, TRDeltabeta3 was a TRE-selective and cell-specific antagonist of TRalpha1, -beta1, and -beta3. Both TRbeta3 and TRDeltabeta3 were expressed in the nucleus in the absence and presence of hormone, and their actions were determined by cell type and TRE structure, whereas TRDeltabeta3 actions were also dependent on the TR isoform with which it interacted. Analysis of these complex responses implicates a range of nuclear corepressors and coactivators as cell-, TR isoform-, and TRE-specific modulators of T3 action.

SUBMITTER: Harvey CB

PROVIDER: S-EPMC2681178 | biostudies-literature | 2007 Apr

REPOSITORIES: biostudies-literature

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The rat thyroid hormone receptor (TR) Deltabeta3 displays cell-, TR isoform-, and thyroid hormone response element-specific actions.

Harvey Clare B CB Bassett J H Duncan JH Maruvada Padma P Yen Paul M PM Williams Graham R GR

Endocrinology 20070111 4

The THRB gene encodes the well-described thyroid hormone (T3) receptor (TR) isoforms TRbeta1 and TRbeta2 and two additional variants, TRbeta3 and TRDeltabeta3, of unknown physiological significance. TRbeta1, TRbeta2, and TRbeta3 are bona fide T3 receptors that bind DNA and T3 and regulate expression of T3-responsive target genes. TRDeltabeta3 retains T3 binding activity but lacks a DNA binding domain and does not activate target gene transcription. TRDeltabeta3 can be translated from a specific ...[more]

PMID: 17218414

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Project description:The thyroid hormone receptor ? gene (THRA) transcript is alternatively spliced to generate either thyroid hormone receptor (TR)?1 or a non-hormone-binding variant protein, TR?2, the function of which is unknown. Here, we describe the first patients identified with a mutation in THRA that affects both TR?1 and TR?2, and compare them with patients who have resistance to thyroid hormone owing to a mutation affecting only TR?1, to delineate the relative roles of TR?1 and TR?2.We did clinical, biochemical, and genetic analyses of an index case and her two sons. We assessed physical and radiological features, thyroid function, physiological and biochemical markers of thyroid hormone action, and THRA sequence.The patients presented in childhood with growth failure, developmental delay, and constipation, which improved after treatment with thyroxine, despite normal concentrations of circulating thyroid hormones. They had similar clinical (macrocephaly, broad faces, skin tags, motor dyspraxia, slow speech), biochemical (subnormal ratio of free thyroxine:free tri-iodothyronine [T3], low concentration of total reverse T3, high concentration of creatine kinase, mild anaemia), and radiological (thickened calvarium) features to patients with TR?1-mediated resistance to thyroid hormone, although our patients had a heterozygous mis-sense mutation (Ala263Val) in both TR?1 and TR?2 proteins. The Ala263Val mutant TR?1 inhibited the transcriptional function of normal receptor in a dominant-negative fashion. By contrast, function of Ala263Val mutant TR?2 matched its normal counterpart. In vitro, high concentrations of T3 restored transcriptional activity of Ala263Val mutant TR?1, and reversed the dominant-negative inhibition of its normal counterpart. High concentrations of T3 restored expression of thyroid hormone-responsive target genes in patient-derived blood cells.TR?1 seems to be the principal functional product of the THRA gene. Thyroxine treatment alleviates hormone resistance in patients with mutations affecting this gene, possibly ameliorating the phenotype. These findings will help the diagnosis and treatment of other patients with resistance to thyroid hormone resulting from mutations in THRA.Wellcome Trust, NIHR Cambridge Biomedical Research Centre, Marie Curie Actions, Foundation for Development of Internal Medicine in Europe.

Project description:Pituitary GH-secretory profiles are sex dependent and regulate the sexually dimorphic expression of a large number of genes in the liver. The slow response of many sex-specific liver genes to changes in plasma GH status suggests that GH acts in the liver via both direct and indirect mechanisms organized in a hierarchical regulatory network. Presently, genome-wide liver transcription profiling was conducted to elucidate the global impact of pituitary hormone ablation on the sex specificity of rat liver gene expression and to identify sex-specific genes that respond rapidly to GH as candidates for direct targets of GH action. Hypophysectomy abolished the sex specificity of approximately 90% of 1032 sex-dependent genes, consistent with the dominant role of pituitary GH in regulating liver sexual dimorphism. Two major classes of sex-specific genes were identified: genes that were down-regulated after hypophysectomy and may be subject to positive GH regulation (461 class I genes), and genes that were up-regulated after hypophysectomy and may be subject to negative GH regulation (224 class II genes). Fifty class I sex-specific genes were induced, and 38 class II sex-specific genes were suppressed within 90 min of a physiological GH pulse, suggesting they are primary GH response genes. A further 71 sex-specific genes responded after a second GH treatment and may correspond to secondary response genes. Twenty four DNA-binding proteins were identified as early GH response genes, of which 15 were induced and nine were suppressed by GH. Five of these 24 genes displayed sex-specific expression, consistent with a hierarchical transcriptional network controlling sex-specific liver gene expression. Class II male-specific genes, such as Cyp2a2 and Cyp2c13, were down-regulated within 30 min of GH pulse treatment, as determined by heterogeneous nuclear RNA analysis, suggesting that transcription of these genes is restricted to the GH-free interpulse period in adult male rat liver. We conclude that GH acts via both positive and negative regulatory mechanisms to establish and maintain the sex specificity of liver gene expression.

Dataset Information

The rat thyroid hormone receptor (TR) Deltabeta3 displays cell-, TR isoform-, and thyroid hormone response element-specific actions.

Publications

The rat thyroid hormone receptor (TR) Deltabeta3 displays cell-, TR isoform-, and thyroid hormone response element-specific actions.

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