Thyroid Hormone Receptors Repress Estrogen Receptor Activation of a TRE (original) (raw)
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Molecular Endocrinology, 1998
We have employed a chimeric receptor system in which we cotransfected yeast GAL4 DNA-binding domain/retinoid X receptor β ligand-binding domain chimeric receptor (GAL4RXR), thyroid hormone receptor-β (TRβ), and upstream activating sequence-reporter plasmids into CV-1 cells to study repression, derepression, and transcriptional activation. In the absence of T3, unliganded TR repressed transcription to 20% of basal level, and in the presence of T3, liganded TRβ derepressed transcription to basal level. Using this system and a battery of TRβ mutants, we found that TRβ/RXR heterodimer formation is necessary and sufficient for basal repression and derepression in this system. Additionally, an AF-2 domain mutant (E457A) mediated basal repression but not derepression, suggesting that interaction with a putative coactivator at this site may be critical for derepression. Interestingly, a mutant containing only the TRβ ligand binding domain (LBD) not only mediated derepression, but also stimu...
Regulatory functions of a non-ligand-binding thyroid hormone receptor isoform
Cell regulation, 1991
Gene regulation by thyroid hormones is mediated through multiple nuclear receptors. Only some of these thyroid hormone receptor (TR) isoforms become transcriptional enhancers in the presence of the thyroid hormone T3. Here we analyze the regulatory function of the human TRa2 isoform. This protein does not bind T3 and is not a transcriptional activator of thyroid hormone-responsive elements (TRE). Transfected TRa2 functions as a constitutive repressor of the transcriptional activators TRal and TR,81 but also represses heterologous receptors, including the retinoic acid receptor and the estrogen receptor, which can activate TRE-controlled genes. TRa2 protein showed strongly reduced DNA binding to a palindromic TRE when compared with the active TRs. Hybrid receptor analysis revealed that the special properties of the TRa2 protein, including its repressor function and DNA binding characteristics, are intrinsic properties of its carboxyterminus and can be transferred to other receptors. Although it has been shown that the active TRs can act as repressors and silencers due to their strong DNA binding in the absence of hormone, our data show that TRa2 is unlikely to inhibit TRs and other receptors through a competitive DNA binding mechanism. Antibody gel shift experiments suggest that repression by TRa2 might result from interaction with active receptors. Thus, the receptorlike TRa2 isoform differs from typical nuclear receptors in its DNA-binding and ligand-binding properties and appears to regulate the activity of other receptors via protein-protein interaction.
Proceedings of the National Academy of Sciences, 1992
Steroid/TH receptors mediate transcriptional induction of promoters containing hormone response elements (HREs) through an unclear mechanism that involves receptor binding to both hormone and a HRE. Here we demonstrate that both HRE binding and the transcriptional inducing activities of one member of this family, TH receptor, were markedly enhanced by heterodimerization with H-2RIIBP, a non-TH-binding member of the steroid hormone receptor superfamily. H-2RIIBP, the mouse homologue of human retinoic acid-related receptor, was shown to form stable heterodimers with the TH receptor either in solution or when bound to a TH response element. The results presented indicate that it might be necessary for the TH receptor or other members of this superfamily to have specific partners for heterodimer formation to elicit maximal hormone-specific gene regulation from particular HREs.
Estrogen and thyroid hormone interaction on regulation of gene expression
Proceedings of the National Academy of Sciences, 1996
Estrogen receptor (ER) and thyroid hormone receptors (TRs) are ligand-dependent nuclear transcription factors that can bind to an identical half-site, AGGTCA, of their cognate hormone response elements. By in vitro transfection analysis in CV-1 cells, we show that estrogen induction of chloramphenicol acetyltransferase (CAT) activity in a construct containing a CAT reporter gene under the control of a minimal thymidine kinase (tk) promoter and a copy of the consensus ER response element was attenuated by cotransfection of TR alpha 1 plus triiodothyronine treatment. This inhibitory effect of TR was ligand-dependent and isoform-specific. Neither TR beta 1 nor TR beta 2 cotransfection inhibited estrogen-induced CAT activity, although both TR alpha and TR beta can bind to a consensus ER response element. Furthermore, cotransfection of a mutated TR alpha 1 that lacks binding to the AGGTCA sequence also inhibited the estrogen effect. Thus, the repression of estrogen action by liganded TR ...
Regulation of gene transcription by the thyroid hormone receptors
2006
Thyroid hormone (TH) has important effects on postnatal development as well as on adult metabolic homeostasis. TH meditates its effects through different isoforms of the thyroid hormone receptors (TRs) encoded by the TRalpha and TRbeta genes, respectively. TRs belong to the nuclear hormone receptor superfamily. These receptors are ligand-modulated transcription factors that bind to specific DNA elements located in the regulatory regions of target genes. The nature of these elements determines the effect TR will have on transcription. On what is called a positive TH response element (pTRE), the un-liganded receptor binds to DNA and represses transcription. Hormone binding induces a conformational change in the receptor, allowing for activation of transcription. In contrast, on a negative TH response element (nTRE), activation of transcription is mediated by the un-liganded receptor, whereas the liganded receptor represses transcription. The mechanism behind the regulation of a pTRE i...
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.
2016
Mutations in the human beta thyroid hormone receptor (h-TRB) gene are associated with the syndrome of generalized resistance to thyroid hormone. We investigated the interaction of three h-TR,61 mutants representing different types of func-tional impairment (kindreds ED, OK, and PV) with different response elements for 3,3',5-triiodothyronine(T3) and with reti-noid X receptor 13 (RXR,6). The mutant receptors showed an increased tendency to form homodimers on a palindromic T3-response element (TREpal), a direct repeat (DR + 4), and an inverted palindrome (TRElap). On TRElap, wild typeTR bind-ing was decreased by T3, while the mutant receptors showed a variably decreased degree of dissociation from TRElap in re-sponse to T3. The extent of dissociation was proportional to their T3 binding affinities. RXRf induced the formation of h-TRfi1:RXRf heterodimers equally well for mutants and the wild type h-TR$1 on these T3 response elements. However, the T3-dependent increase in heterodim...
PLoS ONE, 2014
Thyroid hormone (TH) exerts its effects by binding to the thyroid hormone receptor (TR), which binds to TH response elements (TREs) to regulate target gene expression. We investigated the relative ability of liganded homodimers TR and retinoid X receptor (RXR), and the heterodimer TR/RXR, to regulate gene expression for the TRE half-site organizations: direct repeat 4 (DR4), inverted repeat 0 (IR0) and everted repeat 6 (ER6). Luciferase reporter assays using a DR4 TRE suggest that both the TR homodimer and TR/RXR heterodimer regulate luciferase expression in the presence of their respective ligands. However, in the presence of the IR0 TRE, transfection with TR/RXR and RXR alone increased luciferase activity and there was no effect of TR alone. The presence of 9-cis-retinoic acid was necessary for luciferase expression, whereas TH treatment alone was insufficient. For the ER6 TRE, transfection with TR/RXR, TR alone and RXR alone (in the presence of their respective ligands) all caused a significant increase in luciferase activity. When both ligands were present, transfection with both TR/RXR caused more activation. Finally, we investigated the efficacy of the TR-antagonist 1-850 in inhibiting transcription by TR or TR/RXR at DR4 and ER6 TREs. We found that 1-850 did not suppress luciferase activation in the presence of TR/RXR for the ER6 TRE, suggesting conformational changes of the ligand binding domain of the TR when bound to different TRE half-site organizations. Collectively, the findings indicate that there are fundamental differences between TRE configurations that affect nuclear receptor interactions with the response element and ability to bind ligands and antagonists.