Retinoid-Related Receptor (ROR) α mRNA Expression Is Altered in the Brain of Male Mice Lacking All Ligand-Binding Thyroid Hormone Receptor (TR) Isoforms (original) (raw)
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ROR Augments Thyroid Hormone Receptor-Mediated Transcriptional Activation
Endocrinology, 1999
This study is designed to clarify the role of an orphan nuclear hormone receptor, ROR␣, on thyroid hormone (TH) receptor (TR)mediated transcription on a TH-response element (TRE). A transient transfection study using various TREs [i.e., F2 (chick lysozyme TRE), DR4 (direct repeat), and palindrome TRE] and TR and ROR␣1 was performed. When ROR␣1 and TR were cotransfected into CV1 cells, ROR␣1 enhanced the transactivation by liganded-TR on all TREs tested without an effect on basal repression by unliganded TR. By electrophoretic mobility shift assay, on the other hand, although ROR␣ bound to all TREs tested as a monomer, no (or weak) TR and ROR␣1 heterodimer formation was observed on various TREs except when a putative ROR-response element was present. The transactivation by ROR␣1 on a ROR-response element, which does not contain a TRE, was not enhanced by TR. The effect of ROR␣1 on the TREs is unique, because, whereas other nuclear hormone receptors (such as vitamin D receptor) may competitively bind to TRE to exert dominant negative function, ROR␣1 augmented TR action. These results indicate that ROR␣1 may modify the effect of liganded TR on TH-responsive genes. Because TR and ROR␣ are coexpressed in cerebellar Purkinje cells, and perinatal hypothyroid animals and ROR␣-disrupted animals show similar abnormalities of this cell type, cross-talk between these two receptors may play a critical role in Purkinje cell differentiation.
Journal of Molecular Endocrinology, 2005
In vivo assessment of the cellular impact of thyroid hormones on target tissues might be of help for physiological studies and to evaluate the consequences of various diseases of the thyroid gland in humans. Given the tenuous relationship between retinoid and tri-iodothyronine (T 3 ) status and that retinoids have also intracellular roles, the aim of this study was to determine the effect of hypothyroidism on the expression of T 3 nuclear receptors (TR) and retinoic acid nuclear receptors (RAR, RXR) in human peripheral blood mononuclear cells (PBMC). Using real time RT-PCR, we quantified the relative amount of mRNA of the thyroid (TR and TR ) and retinoid (RAR , RAR , and RXR ) nuclear receptors in PBMC of euthyroid (n=22) compared with hypothyroid (n=22) subjects. Classical plasma parameters (free T 3 (FT 3 ), free thyroxine (T 4 ) (FT 4 ), thyroid-stimulating hormone (TSH), retinol (ROH), retinol-binding protein (RBP) and transthyretin (TTR)) were also measured. In hypothyroid subjects, the concentration of TSH was elevated, and dramatically low T 3 and T 4 concentrations were associated with a decrease in the expression of TR . Expression of RAR and RAR significantly decreased in hypothyroid versus control subjects, while an increased concentration of ROH was emphasised by hypothyroidism. These results first indicated that primary hypothyroidism induces hypoactivation of the retinoid nuclear pathway in PBMC, which was not predicted by the plasma ROH level. Further investigations will be necessary to evaluate these parameters in very small changes in thyroid hormone production such as mild (subclinical) hypothyroidism.
RORα Augments Thyroid Hormone Receptor-Mediated Transcriptional Activation*
Endocrinology, 1999
This study is designed to clarify the role of an orphan nuclear hormone receptor, RORα, on thyroid hormone (TH) receptor (TR)-mediated transcription on a TH-response element (TRE). A transient transfection study using various TREs [i.e., F2 (chick lysozyme TRE), DR4 (direct repeat), and palindrome TRE] and TR and RORα1 was performed. When RORα1 and TR were cotransfected into CV1 cells, RORα1 enhanced the transactivation by liganded-TR on all TREs tested without an effect on basal repression by unliganded TR. By electrophoretic mobility shift assay, on the other hand, although RORα bound to all TREs tested as a monomer, no (or weak) TR and RORα1 heterodimer formation was observed on various TREs except when a putative ROR-response element was present. The transactivation by RORα1 on a ROR-response element, which does not contain a TRE, was not enhanced by TR. The effect of RORα1 on the TREs is unique, because, whereas other nuclear hormone receptors (such as vitamin D receptor) may c...
Molecular and Cellular Biochemistry, 2005
The aim of this study was to determine whether changes in the circulating thyroid hormone (TH) and brain synaptosomal TH content affected the relative levels of mRNA encoding different thyroid hormone receptor (TR) isoforms in adult rat brain. Northern analysis of polyA + RNA from cerebral cortex, hippocampus and cerebellum of control and hypothyroid adult rats was performed in order to determine the relative expression of all TR isoforms. Circulating and synaptosomal TH concentrations were determined by radioimmunoassay. Region-specific quantitative differences in the expression pattern of all TR isoforms in euthyroid animals and hypothyroid animals were recorded. In hypothyroidism, the levels of TRα2 mRNA (non-T 3 -binding isoform) were decreased in all brain regions examined. In contrast the relative expression of TRα1 was increased in cerebral cortex and hippocampus, whereas in cerebellum remained unaffected. The TRβ1 relative expression in cerebral cortex and hippocampus of hypothyroid animals was not affected, whereas this TR isoform was not detectable in cerebellum. The TR isoform mRNA levels returned to control values following T 4 intraperitoneal administration to the hypothyroid rats. The obtained results show that in vivo depletion of TH regulates TR gene expression in adult rat brain in a region-specific manner. (Mol Cell Biochem 278: [93][94][95][96][97][98][99][100] 2005)
Regulation of thyroid hormone receptor β-2 mRNA levels by retinoic acid
Molecular and Cellular Endocrinology, 1993
The thyroid hormone receptor, TR p-2, whose expression is limited to the pituitary and parts of the central nervous system, is strongly negatively regulated at the pre-translational level by thyroid hormone (T3). We have investigated whether retinoic acid (RA), whose receptors (RARs) share a high degree of homology with the thyroid hormone receptors (TRs), can regulate this gene in a manner simiIar to T3, as has been shown for the growth hormone (GH) gene. GH3 cells were incubated with 10 nM T3,l FM RA or both for 48 h and then TR p-2 mRNA levels determined by RNA blot hybridization analysis. We observed a 73% decrease in TR p-2 mRNA levels after incubation with T3 and a twofold increase in TR p-2 mRNA levels after incubation with RA alone. In the presence of RA, the T3 effect on TR p-2 mRNA levels was blunted with mRNA levels decreasing by only 20%. We investigated the mechanism by which retinoic acid increases and opposes the effects of T3 on levels of TR p-2 mRNA. In transient transfection experiments using a reporter plasmid containing the TR p-2 promoter and in nuclear run on assays, we found no effect of RA on TR p-2 gene transcription. We then investigated whether the effects of RA were mediated at the post-transcriptional level. Determination of the apparent half-life of TR p-2 mRNA using the transcriptional inhibitor, a~tinomycin D, showed that RA had no effect on TR p-2 mRNA stability. Therefore, we conclude that RA regulates another post-transcriptional event, either processing or transport of the TR p-2 mRNA.
Journal of Molecular Endocrinology, 2002
Thyroid hormone receptors (TRs) often modulate transcriptional activity of target genes by heterodimerization with the 9-cis retinoic acid receptor (RXR). On positive thyroid response elements (TREs), RXR favors binding of the TR-RXR complex to DNA and stimulates transcription. RXR action on negative TREs is unclear. Furthermore, the single half-site configuration of many negative TREs does not favor the binding of a classic TR-RXR heterodimer. In a comparative study using CV-1 cells (relatively RXR- and TR-deficient) and JEG-3 cells (relatively TR-deficient), we demonstrate the importance of RXR in the negative transcriptional regulation of genes of the hypothalamo-pituitary axis by tri-iodothyronine. While RXR has variable effects on ligand-independent activation produced by TRs, it was required for efficient ligand-dependent repression of the TRH gene for TRalpha1 and TRbeta1 and of the TSH genes by all TRs. Using different RXR constructs we also observed the importance of the C-...
Journal of Molecular Endocrinology, 2009
Transcriptional regulation is mediated by thyroid hormone (tri-iodothyronine, T3) receptors (TR), which bind to T3 response elements as heterodimers with retinoid X receptors (RXR). TR binds to corepressor proteins (CoR) in the absence of T3, which mediate transcriptional repression and to coactivator proteins (CoA) in the presence of T3, which mediate transcriptional stimulation, by recruiting additional proteins to the promoter. To determine the relationship between TR functions and cofactor bindings, we selected 13 single-point mutants on the ligand binding domain of TR, of which T3 bindings were well preserved and created VP16 chimeric receptors. Using mammalian two-hybrid assays, RXR binding in the absence of T3 was almost abolished for Y406K (helix; H10) and L422R (H11), while it was preserved for most other TR mutants. RXR binding was increased for I280K, V284R (H3), and C309K (H6). Addition of T3 enhanced RXR binding and T3 restored the RXR binding to Y406K but not to L422R....
Journal of Biological Chemistry, 1994
The thyroid hormone receptors (TR) form heterodimers with the retinoid X receptors (RXR) and activate target genes through thyroid-responsive elements (TRE). Heterodimerization elevates the DNA binding efficiency and thus can result in functional synergism between TR and RXR. Here we demonstrate that DNA sequences dictate the cooperative activation between TR and RXR despite the high affinity binding of the heterodimer to those TREs. We provide evidence that the C-terminal activation domain of RXR can modulate the triiodothyronine (T,) responsiveness of TWRXR heterodimers on reporter genes without altering the DNA binding properties of the heterodimers. The modulation function of this relatively small region is under the control of specific TRE sequences and promoter context. These data indicate that this C-terminal region of RXR is likely involved in receptor-cellular factorb) interactions. Finally, we propose that the synergistic activation by TR and RXR is achieved through elevated DNA binding and, dependent on the DNA sequence, the interaction of RXR with other transcription factors. Members of the nuclear receptor superfamily are ligandactivated transcription factors which interact with their cognate response elements in target genes and thereby regulate diverse aspects of homeostasis, differentiation, and development (1-3). Included in this family of proteins are receptors for steroids, retinoids (RAR and RXR),' thyroid hormone (TR), vitamin D, (VDR), ecdysone (EcR), and a large number of receptor-like proteins with unknown ligands (orphan receptors). Unlike steroid receptors which usually bind to palindromic response elements as homodimers, TR, RAR, and VDR bind to DNA sequences composed of various arrays of the PuGGT(C/ A)A core motif, primarily as heterodimers with RXR (4-8). Characterization of these degenerate response elements led to the conclusion that the orientation and spacing of the core sequence dictates the elective transcription properties for each of these receptors (9-13). Although TR and RAR can bind to complex response elements (HREs) as monomers and homodimers (14-17), heterodimerization with RXR greatly enhances DNA binding in vitro, and expression of exogenous RXR elevates the hormone *This research was supported by National Institutes of Health grants (to M.-J. T. and B. W. 0.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Molecular and Cellular Biology, 1994
The steroid/hormone nuclear receptor superfamily comprises several subfamilies of receptors that interact with overlapping DNA sequences and/or related ligands. The thyroid/retinoid hormone receptor subfamily has recently attracted much interest because of the complex network of its receptor interactions. The retinoid X receptors (RXRs), for instance, play a very central role in this subfamily, forming heterodimers with several receptors. Here we describe a novel member of this subfamily that interacts with RXR. Using a v-erbA probe, we obtained a cDNA which encodes a novel 445-amino-acid protein, RLD-1, that contains the characteristic domains of nuclear receptors. Northern (RNA) blot analysis showed that in mature rats, the receptor is highly expressed in spleen, pituitary, lung, liver, and fat. In addition, weaker expression is observed in several other tissues. Amino acid sequence alignment and DNA-binding data revealed that the DNA-binding domain of the new receptor is related ...