Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Isoform-specific transcriptional activity of overlapping targets that respond to thyroid hormone receptors a1 and b1

ABSTRACT: Thyroid hormone receptors (TRs) are hormone-regulated transcription factors that control multiple aspects of physiology and development. TRs are expressed in vertebrates as a series of distinct isoforms that exert distinct biological roles. We wished to determine if the two most widely expressed isoforms, TRa1 and TRb1, exert their different biological effects by regulating different sets of target genes. Using stably transformed HepG2 cells and a microarray analysis, we were able to demonstrate that TRa1 and TRb1 regulate a largely overlapping repertoire of target genes in response to T3 hormone. However, these two isoforms display very different transcriptional properties on each individual target gene, ranging from a much greater T3-mediated regulation by TRa1 than by TRb1, to near equal regulation by both isoforms. We also identified TRa1 and TRb1 target genes that were regulated by these receptors in a hormone-independent fashion. We suggest that it is this gene-specific, isoform-specific amplitude of transcriptional regulation that is the likely basis for the appearance and maintenance of TRa1 and TRb1 over evolutionary time. In essence, TRa1 and TRb1 adjust the magnitude of the transcriptional response at different target genes to different levels; by altering the ratio of these isoforms in different tissues or at different developmental times, the intensity of T3 response can be individually tailored to different physiological and developmental requirements. TRa1, TRb1, or empty plasmid control stably transfected HepG2 cells were treated with 100 nM T3 or with ethanol carrier alone for 6h. Three independent biological repeats were analyzed for each of the three transformant pools (empty plasmid control, TRa1, and TRb1).

ORGANISM(S): Homo sapiens

SUBMITTER: Martin Privalsky

PROVIDER: E-GEOD-17561 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Isoform-specific transcriptional activity of overlapping target genes that respond to thyroid hormone receptors alpha1 and beta1.

Chan Ivan H IH Privalsky Martin L ML

Molecular endocrinology (Baltimore, Md.) 20090723 11

Thyroid hormone receptors (TRs) are hormone-regulated transcription factors that control multiple aspects of physiology and development. TRs are expressed in vertebrates as a series of distinct isoforms that exert distinct biological roles. We wished to determine whether the two most widely expressed isoforms, TR alpha 1 and TR beta 1, exert their different biological effects by regulating different sets of target genes. Using stably transformed HepG2 cells and a microarray analysis, we were abl ...[more]

PMID: 19628582

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Project description:Thyroid hormone receptors (TRs) represent important regulators of development, homeostasis, cell proliferation and differentiation. Here we investigated the impact of thyroid hormone (T3) on growth and differentiation of human red blood cells. T3 was found to effectively accelerate differentiation of SCF/Epo dependent red cell progenitors in vitro concomitantly with inducing growth arrest. This T3 activity was further enhanced by 9-cis retinoic acid (9cRA) that activates retinoid X receptor (RXR), the obligate heterodimeric partner of TR. To identify molecular targets for T3 activity in red cells, we employed a genome wide approach with DNA microarrays. We demonstrate that T3 and 9cRA induces specific gene expression patterns of up-or down-regulated genes, including ALAD and GATA-2, respectively. This study also revealed gene clusters, indicating accelerated differentiation in response to treatment. Mining for T3 induced genes identified BTEB1 (KLF9) and GAR22 as TR target genes. BTEB1/ KLF9 (basic transcription element binding protein 1/ KrÃ¼ppel-like factor 9) is a known TR target gene. GAR22 (growth arrest specific 2 (GAS2)-related gene on chromosome 22), initially found as a putative tumor suppressor gene, was induced by T3 also in the presence of cycloheximide, identifying it as a direct target of TR. Thus, our study uncovers novel targets of TR action with a potential function in T3 induced differentiation and growth arrest of red cell progenitors. Experiment Overall Design: 13 hybridizations in two individual experiments. Experiment Overall Design: Experiment 1: Experiment Overall Design: 1_SCF/Epo, 1_Epo/insulin(8h), 1_Epo/insulin(24h), 1_Epo/insulin(48h) Experiment Overall Design: Experiment 2: Experiment Overall Design: 2_SCF/Epo, 2_Epo/insulin(8h), 2_Epo/insulin(24h), 2_Epo/insulin(48h) Experiment Overall Design: 2_Epo/insulin+T3(8h), 2_Epo/insulin+9cRA(8h) Experiment Overall Design: 2_Epo/insulin+T3+9cRA(8h), , 2_Epo/insulin+T3+9cRA(24h), 2_Epo/insulin+T3+9cRA(48h)

Project description:Synthetic selective thyroid hormone (TH) receptor (TR) modulators (STRMs) exhibit beneficial effects on dyslipidemias in animals and humans and reduce obesity, fatty liver and insulin resistance in preclinical animal models. STRMs differ from native THs in preferential binding to the TRβ subtype versus TRα, increased uptake into liver and reduced uptake into other tissues. However, selective modulators of other nuclear receptors (NRs) exhibit important gene-selective actions which have been attributed to differential effects on receptor conformation and dynamics and these effects can have profound influences in animals and humans. While there are suggestions that STRMs could exhibit such gene-specific actions, the extent to which these effects are actually observed in vivo has not been explored. Here, we show that saturating concentrations of the main active form of TH, triiodothyronine (T3), and the prototype STRM GC-1 induce identical gene-sets in livers of euthyroid and hypothyroid mice and a human cultured hepatoma cell line that only expresses TRβ, HepG2. We find one case in which GC-1 exhibits a modest gene-specific reduction in potency versus T3, at angiopoietin-like factor 4 (ANGPTL4) in HepG2. Investigation of the latter effect confirms that GC-1 acts through TRβ to directly induce this gene. However, this gene-selective GC-1 activity is not related to unusual T3 response element (TRE) sequence, unlike previously documented promoter-selective STRM actions. Together, our data suggest that T3 and GC-1 exhibit almost identical gene regulation properties and that gene-selective actions of GC-1 and similar STRMs will be subtle and rare. We treated HepG2 with vehicle or 10nM ligand (T3 or GC1; n=3 / treatment), analyzing mRNA 24h post treatment [Affymetrix]. We also treated 9-week old euthyroid male C57/Bl6 mice with vehicle or ligand (T3 or GC-1) by a single oral gavage (n=5 per treatment) and also performed a similar study in which mice were first made hypothyroid by two week feeding on iodine deficient diet (n=3-4 per treatment), analyzing mRNA 24h post treatment [Illumina].

Dataset Information

Isoform-specific transcriptional activity of overlapping targets that respond to thyroid hormone receptors a1 and b1

Publications

Isoform-specific transcriptional activity of overlapping target genes that respond to thyroid hormone receptors alpha1 and beta1.

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