scholarly journals A core SMRT corepressor complex containing HDAC3 and TBL1, a WD40-repeat protein linked to deafness

2000 ◽  
Vol 14 (9) ◽  
pp. 1048-1057 ◽  
Author(s):  
Matthew G. Guenther ◽  
William S. Lane ◽  
Wolfgang Fischle ◽  
Eric Verdin ◽  
Mitchell A. Lazar ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Thyroid Hormone ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Histone H3 ◽  
Sensorineural Deafness ◽  
Loss Of Function ◽  
Wd40 Repeat ◽  
Corepressor Complex

The corepressor SMRT mediates repression by thyroid hormone receptor (TR) as well as other nuclear hormone receptors and transcription factors. Here we report the isolation of a novel SMRT-containing complex from HeLa cells. This complex contains transducin β-like protein 1 (TBL1), whose gene is mutated in human sensorineural deafness. It also contains HDAC3, a histone deacetylase not previously thought to interact with SMRT. TBL1 displays structural and functional similarities to Tup1 and Groucho corepressors, sharing their ability to interact with histone H3. In vivo, TBL1 is bridged to HDAC3 through SMRT and can potentiate repression by TR. Intriguingly, loss-of-function TRβ mutations cause deafness in mice and humans. These results define a new TR corepressor complex with a physical link to histone structure and a potential biological link to deafness.

scholarly journals Thyroid hormone-stimulated differentiation of primary rib chondrocytes in vitro requires thyroid hormone receptor β

2006 ◽  
Vol 191 (1) ◽  
pp. 221-228 ◽  
Author(s):  
Bénédicte Rabier ◽  
Allan J Williams ◽  
Frederic Mallein-Gerin ◽  
Graham R Williams ◽  
O Chassande
Keyword(s):  
Thyroid Hormone ◽  
Growth Plate ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Primary Cultures ◽  
Wild Type ◽  
Proliferation And Differentiation ◽  
Thyroid Hormone Receptor Β

The active thyroid hormone, triiodothyronine (T3), binds to thyroid hormone receptors (TR) and plays an essential role in the control of chondrocyte proliferation and differentiation. Hypo- and hyperthyroidism alter the structure of growth plate cartilage and modify chondrocyte gene expression in vivo, whilst TR mutations or deletions in mice result in altered growth plate architecture. Nevertheless, the particular roles of individual TR isoforms in mediating T3 action in chondrocytes have not been studied and are difficult to determine in vivo because of complex cellular and molecular interactions that regulate growth plate maturation. Therefore, we studied the effects of TRα and TRβ on chondrocyte growth and differentiation in primary cultures of neonatal rib chondrocytes isolated from TRα- and TRβ-deficient mice. T3 decreased proliferation but accelerated differentiation of rib chondrocytes from wild-type mice. T3 treatment resulted in similar effects in TRα-deficient chondrocytes, but in TRβ-deficient chondrocytes, all T3 responses were abrogated. Furthermore, T3 increased TRβ1 expression in wild-type and TRα-deficient chondrocytes. These data indicate that T3-stimulated differentiation of primary rib chondrocytes in vitro requires TRβ and suggest that the TRβ1 isoform mediates important T3 actions in mouse rib chondrocytes.

scholarly journals Preparation of unoccupied thyroid-hormone receptor

1994 ◽  
Vol 297 (1) ◽  
pp. 75-78 ◽  
Author(s):  
Q Li ◽  
A Inoue
Keyword(s):  
Thyroid Hormone ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Binding Capacity ◽  
Fatty Acyl ◽  
Receptor Complex ◽  
Simple Method ◽  
Sephadex Column

Thyroid hormone (3,5,3′-tri-iodothyronine; T3) regulates gene expression through binding to its specific receptor in the nucleus. In euthyroid animals, roughly half of all receptors are occupied by the hormone. Nuclear extracts thus yield mixtures of occupied and unoccupied receptors. We present here a simple method for transforming occupied receptors into unoccupied ones. In vitro, the T3-receptor complex dissociated in a half-dissociation time exceeding 100 h at 0 degrees C, and at temperatures that accelerated the dissociation the receptor was quickly inactivated. Long-chain-fatty-acyl-CoAs, on the other hand, greatly accelerated the dissociation of T3-receptor complex at 0 degree C. The receptor was extracted from rat liver nuclei, incubated with oleoyl-CoA to release the bound hormone, and passed through a small column of Lipidex, which strongly adsorbed both oleoyl-CoA and the dissociated hormone. The receptor was recovered in the flow-through fraction in its unoccupied form, as seen by the results of DEAE-Sephadex column chromatography and the loss of all previously bound [125I]T3. The maximum T3-binding capacity of the unoccupied receptor was about 1.5-fold that of the untreated sample, and the dissociation constant was unaltered. The results suggest that most nuclear thyroid-hormone receptors occupied by the hormone were transformed into unoccupied ones. From the T3-binding capacity before and after oleoyl-CoA treatment, the in vivo T3 occupancy of the receptor was estimated. The procedure is easy to perform, and the method should be useful for studies of unoccupied receptors.

scholarly journals Adipogenesis is differentially impaired by thyroid hormone receptor mutant isoforms

2010 ◽  
Vol 44 (4) ◽  
pp. 247-255 ◽  
Author(s):  
Alok Mishra ◽  
Xu-guang Zhu ◽  
Kai Ge ◽  
Sheue-Yann Cheng
Keyword(s):  
Thyroid Hormone ◽  
Hormone Receptors ◽  
Target Genes ◽  
Thyroid Hormone Receptor ◽  
Fold Increase ◽  
Dominant Negative ◽  
Peroxisome Proliferator ◽  
Loss Of Function ◽  
Peroxisome Proliferator Activated Receptor ◽  
Protein Levels

To understand the roles of thyroid hormone receptors (TRs) in adipogenesis, we adopted a loss-of-function approach. We generated 3T3-L1 cells stably expressing either TRα1 mutant (TRα1PV) or TRβ1 mutant (TRβ1PV). TRα1PV and TRβ1PV are dominant negative mutations with a frameshift in the C-terminal amino acids. In control cells, the thyroid hormone, tri-iodothyronine (T3), induced a 2.5-fold increase in adipogenesis in 3T3-L1 cells, as demonstrated by increased lipid droplets. This increase was mediated by T3-induced expression of the peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), which are master regulators of adipogenesis at both the mRNA and protein levels. In 3T3-L1 cells stably expressing TRα1PV (L1-α1PV cells) or TRβ1PV (L1-β1PV cells), adipogenesis was reduced 94 or 54% respectively, indicative of differential inhibitory activity of mutant TR isoforms. Concordantly, the expression of PPARγ and C/EBPα at the mRNA and protein levels was more repressed in L1-α1PV cells than in L1-β1PV cells. In addition, the expression of PPARγ downstream target genes involved in fatty acid synthesis – the lipoprotein lipase (Lpl) and aP2 involved in adipogenesis – was more inhibited by TRα1PV than by TRβ1PV. Chromatin immunoprecipitation assays showed that TRα1PV was more avidly recruited than TRβ1PV to the promoter to preferentially block the expression of the C/ebpα gene. Taken together, these data indicate that impaired adipogenesis by mutant TR is isoform dependent. The finding that induction of adipogenesis is differentially regulated by TR isoforms suggests that TR isoform-specific ligands could be designed for therapeutic intervention for lipid abnormalities.

scholarly journals Recruitment of N-CoR/SMRT-TBLR1 Corepressor Complex by Unliganded Thyroid Hormone Receptor for Gene Repression during Frog Development

2004 ◽  
Vol 24 (8) ◽  
pp. 3337-3346 ◽  
Author(s):  
Akihiro Tomita ◽  
Daniel R. Buchholz ◽  
Yun-Bo Shi
Keyword(s):  
Thyroid Hormone ◽  
Transcriptional Repression ◽  
Histone Deacetylases ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Histone Deacetylation ◽  
Gene Repression ◽  
Vertebrate Development ◽  
Inducible Promoters

ABSTRACT The corepressors N-CoR (nuclear receptor corepressor) and SMRT (silencing mediator for retinoid and thyroid hormone receptors) interact with unliganded nuclear hormone receptors, including thyroid hormone (T3) receptor (TR). Several N-CoR/SMRT complexes containing histone deacetylases have been purified. The best studied among them are N-CoR/SMRT complexes containing TBL1 (transducin beta-like protein 1) or TBLR1 (TBL1-related protein). Despite extensive studies of these complexes, there has been no direct in vivo evidence for the interaction of TBL1 or TBLR1 with TR or the possible involvement of such complexes in gene repression by any nuclear receptors in any animals. Here, we used the frog oocyte system to demonstrate that unliganded TR interacts with TBLR1 and recruits TBLR1 to its chromatinized target promoter in vivo, accompanied by histone deacetylation and gene repression. We further provide evidence to show that the recruitment of TBLR1 or related proteins is important for repression by unliganded TR. To investigate the potential role for TBLR1 complexes during vertebrate development, we made use of T3-dependent amphibian metamorphosis as a model. We found that TBLR1, SMRT, and N-CoR are recruited to T3-inducible promoters in premetamorphic tadpoles and are released upon T3 treatment, which induces metamorphosis. More importantly, we demonstrate that the dissociation of N-CoR/SMRT-TBLR1 complexes from endogenous TR target promoters is correlated with the activation of these genes during spontaneous metamorphosis. Taken together, our studies provide in vivo evidence for targeted recruitment of N-CoR/SMRT-TBLR1 complexes by unliganded TR in transcriptional repression during vertebrate development.

scholarly journals Constitutive activation of gene expression by thyroid hormone receptor results from reversal of p53-mediated repression.

1997 ◽  
Vol 17 (12) ◽  
pp. 7195-7207 ◽  
Author(s):  
J S Qi ◽  
V Desai-Yajnik ◽  
Y Yuan ◽  
H H Samuels
Keyword(s):  
Gene Expression ◽  
Thyroid Hormone ◽  
Hormone Receptor ◽  
Promoter Activity ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Gene Promoters ◽  
Wild Type ◽  
Constitutive Activation

Thyroid hormone receptor (T3R) is a member of the steroid hormone receptor gene family of nuclear hormone receptors. In most cells T3R activates gene expression only in the presence of its ligand, L-triiodothyronine (T3). However, in certain cell types (e.g., GH4C1 cells) expression of T3R leads to hormone-independent constitutive activation. This activation by unliganded T3R occurs with a variety of gene promoters and appears to be independent of the binding of T3R to specific thyroid hormone response elements (TREs). Previous studies indicate that this constitutive activation results from the titration of an inhibitor of transcription. Since the tumor suppresser p53 is capable of repressing a wide variety of gene promoters, we considered the possibility that the inhibitor is p53. Evidence to support this comes from studies indicating that expression of p53 blocks T3R-mediated constitutive activation in GH4C1 cells. In contrast with hormone-independent activation by T3R, p53 had little or no effect on T3-dependent stimulation which requires TREs. In addition, p53 mutants which oligomerize with wild-type p53 and interfere with its function also increase promoter activity. This enhancement is of similar magnitude to but is not additive with the stimulation mediated by unliganded T3R, suggesting that they target the same factor. Since p53 mutants are known to target wild-type p53 in the cell, this suggests that T3R also interacts with p53 in vivo and that endogenous levels of p53 act to suppress promoter activity. Evidence supporting both functional and physical interactions of T3R and p53 in the cell is presented. The DNA binding domain (DBD) of T3R is important in mediating constitutive activation, and the receptor DBD appears to functionally interact with the N terminus of p53 in the cell. In vitro binding studies indicate that the T3R DBD is important for interaction of T3R with p53 and that this interaction is reduced by T3. These findings are consistent with the in vivo studies indicating that p53 blocks constitutive activation but not ligand-dependent stimulation. These studies provide insight into mechanisms by which unliganded nuclear hormone receptors can modulate gene expression and may provide an explanation for the mechanism of action of the v-erbA oncoprotein, a retroviral homolog of chicken T3R alpha.

scholarly journals Triiodothyronine affects the alternative splicing of thyroid hormone receptor alpha mRNA

2003 ◽  
Vol 179 (2) ◽  
pp. 217-225 ◽  
Author(s):  
DC Timmer ◽  
O Bakker ◽  
WM Wiersinga
Keyword(s):  
Alternative Splicing ◽  
Thyroid Hormone ◽  
Hepg2 Cells ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Negative Relationship ◽  
High Serum ◽  
Hnrnp A1 ◽  
Hyperthyroid Patients

The c-erbAalpha gene encodes two thyroid hormone receptors, TRalpha1 and TRalpha2, that arise from alternative splicing of the TRalpha pre-mRNA. TRalpha2 is not able to bind triiodothyronine (T(3)) and acts as a weak antagonist of TRs. It has been suggested that the balance of TRalpha1 to TRalpha2 is important in maintaining homeostasis. Here, we study the effect of thyroid hormone on the splicing of TRalpha under various conditions in HepG2 cells. First, T(3) was added to HepG2 cells that endogenously express TRalpha. This resulted in a decrease in the TRalpha1:TRalpha2 mRNA ratio after the addition of 10(-)(8 )M or 10(-)(7 )M T(3). Then, HepG2 cells were incubated with sera from hypothyroid or hyperthyroid patients. Sera from hyperthyroid patients (n=6) decreased the TRalpha1:TRalpha2 ratio compared with HepG2 cells incubated with sera from euthyroid patients (n=8). Sera from hypothyroid patients (n=6) had no effect on the TRalpha1:TRalpha2 ratio but supplementation with T(3) caused a decrease in the ratio. Finally, we tested sera from patients with nonthyroidal illness (NTI; n=17) which showed no effect on TRalpha splicing when compared with controls. Free thyroxine levels in sera from hypo-, eu-, and hyperthyroid patients, but not that of NTI patients, were negatively correlated (P<0.01) to the TRalpha1:TRalpha2 ratio. We next studied the expression of the splicing factors hnRNP A1 and ASF/SF2 (SF2) in relation to the splicing of the TRalpha gene. In HepG2 cells incubated with NTI sera a negative relationship was found between the ratio of hnRNP A1:SF2 and the TRalpha1:TRalpha2 ratio. A high hnRNP A1:SF2 ratio is associated with the use of the distal 5'-splice site. The splicing direction should then change towards TRalpha2, which is indeed the case. Rev-ErbA, which is partly complementary to TRalpha2 and could therefore interfere in the splicing process, did not relate to the TRalpha1:TRalpha2 ratio.In conclusion, high T(3) levels induce a low TRalpha1:TRalpha2 ratio which could protect the cell from excessive T(3)-induced gene expression. In vivo, this might be a mechanism to keep tIssues relatively euthyroid during high serum T(3) levels.

scholarly journals The Thyroid Hormone Receptor Is a Suppressor of ras-Mediated Transcription, Proliferation, and Transformation

2004 ◽  
Vol 24 (17) ◽  
pp. 7514-7523 ◽  
Author(s):  
Susana García-Silva ◽  
Ana Aranda
Keyword(s):  
Thyroid Hormone ◽  
Cyclin D1 ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Neuroblastoma Cells ◽  
Transcriptional Response ◽  
Tumor Formation ◽  
Mitogen Activated Protein Kinase ◽  
Proximal Promoter

ABSTRACT The thyroid hormone triiodothyronine (T3) has a profound effect on growth, differentiation, and metabolism in higher organisms. Here we demonstrate that T3 inhibits ras-induced proliferation in neuroblastoma cells and blocks induction of cyclin D1 expression by the oncogene. The hormone, at physiological concentrations, strongly antagonizes the transcriptional response mediated by the Ras/mitogen-activated protein kinase/ribosomal-S6 subunit kinase (Rsk) signaling pathway in cells expressing thyroid hormone receptors (TRs). T3 blocks the response to the oncogenic forms of the three ras isoforms (H-, K-, and N-ras) and both TRα and TRβ can mediate this action. The main target for induction of cyclin D1 transcription by oncogenic ras in neuroblastoma cells is a cyclic AMP response element (CRE) located in proximal promoter sequences, and T3 represses the transcriptional activity of b-Zip transcription factors such as CREB (CRE-binding protein) or ATF-2 (activation transcription factor 2) that are direct targets of Rsk2 and bind to this sequence. The hormone also blocks fibroblast transformation by oncogenic ras when TR is expressed. Furthermore, TRs act as suppressors of tumor formation by the oncogene in vivo in nude mice. The TRβ isoform has stronger antitransforming properties than the α isoform and can inhibit tumorigenesis even in hypothyroid mice. These results show the existence of a previously unrecognized transcriptional cross talk between the TRs and the ras oncogene which influences relevant processes such as cell proliferation, transformation, or tumorigenesis.

scholarly journals Thyroid Hormone Action in Liver: A Coregulator Shift Rather Than the Canonical Switch

2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A980-A980
Author(s):  
Yehuda Shabtai ◽  
Nagaswaroop K Nagaraj ◽  
Kirill Batmanov ◽  
Young-Wook Cho ◽  
Yuxia Guan ◽  
...  
Keyword(s):  
Gene Expression ◽  
Thyroid Hormone ◽  
Hormone Receptors ◽  
Liver Fat ◽  
Creb Binding Protein ◽  
Corepressor Complex ◽  
Regulate Body Weight ◽  
Activated State ◽  
Precise Analysis

Abstract Thyroid hormone receptors (TR) are transcription factors that mediate the effects of thyroid hormones (TH) in development, physiology, and metabolism. TR canonically activates gene expression via a “switch” whereby TH converts chromatin-bound TR from a transcriptional repressor to an activator. In this model, the unliganded repressed state is mediated by binding of the nuclear receptor corepressor (NCoR), while the TH-activated state is caused by dismissal of NCoR and stabilization of binding of coactivators including CREB-binding protein (CBP). TH also negatively regulates gene expression, although the mechanism is controversial. Elucidation of the TR transcriptional mechanism in vivo has been hampered by the low concentration of endogenous TRs and the unavailability of high quality antibodies. To address this, we generated a mouse line in which endogenous TRβ1 was epitope-tagged to allow precise analysis at physiological levels, and explored TR function in liver where the actions of TR regulate body weight, cholesterol, and liver fat. ChIP-seq analysis revealed TRβ binding at genomic sites with epigenomic characteristics of enhancers, at sequences enriched for the canonical DR4 motif bound by TR with its RXR partner, at both positively- as well as negatively-regulated genes. The NCoR/HDAC3 corepressor complex was reduced but not completely dismissed by TH at positive enhancers and, surprisingly, at enhancers associated with negatively. CBP binding was also not “all or none” but, rather, shifted toward increased binding at enhancers in their active state, i.e., in the presence of TH for activated genes, but in the absence of TH for repressed genes. Thus, TH action is due to a shift, not an on/off switch, in coregulator association with TRβ-regulated enhancers determines their activity and transcriptional outcomes.

Estrogen and Thyroid Hormone Receptor Interactions: Physiological Flexibility by Molecular Specificity

2002 ◽  
Vol 82 (4) ◽  
pp. 923-944 ◽  
Author(s):  
Nandini Vasudevan ◽  
Sonoko Ogawa ◽  
Donald Pfaff
Keyword(s):  
Thyroid Hormone ◽  
Hormone Receptors ◽  
Thyroid Hormone Receptor ◽  
Hormone Signaling ◽  
Cell Type ◽  
Reproductive Behaviors ◽  
Receptor Interactions ◽  
Molecular Specificity

The influence of thyroid hormone on estrogen actions has been demonstrated both in vivo and in vitro. In transient transfection assays, the effects of liganded thyroid hormone receptors (TR) on transcriptional facilitation by estrogens bound to estrogen receptors (ER) display specificity according to the following: 1) ER isoform, 2) TR isoform, 3) the promoter through which transcriptional facilitation occurs, and 4) cell type. Some of these molecular phenomena may be related to thyroid hormone signaling of seasonal limitations upon reproduction. The various combinations of these molecular interactions provide multiple and flexible opportunities for relations between two major hormonal systems important for neuroendocrine feedbacks and reproductive behaviors.

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