Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P19793 (retinoid X receptor alpha)
 391 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mouse peroxisome proliferator-activated receptor alpha (mP-PAR alpha) can activate transcription from the CYP4A6 promoter in transient cotransfection experiments in the absence (intrinsic transactivation) or presence of added peroxisome proliferator. However, mPPAR alpha-G, in which glycine is substituted for Glu282, exhibits very low intrinsic transactivation and responds fully to added peroxisome proliferators. The two receptors, when expressed in COS-1 cells, are nuclear in localization, are expressed at similar levels, have similar stability, and bind DNA in vitro with similar efficiency. The phenotypic difference in intrinsic transactivation is not altered by overexpression of the human retinoid X receptor alpha. The mPPAR alpha-G mutant receptor displays a higher EC50 for pirinixic acid and for 5,8,11,14-eicosatetraynoic acid than the wild-type PPAR alpha. This difference in the apparent EC50 value is independent of the cell lines used and indicates that the Glu282 to glycine substitution alters the response of mPPAR alpha to peroxisome proliferators. The EC50 values obtained for each receptor with the CYP4A6 reporter construct are lower than those for a reporter derived from the acyl-CoA oxidase gene. In general, an inverse relation is evident between the apparent EC50 values and the extent of intrinsic transactivation observed. The difference in intrinsic transactivation may reflect the presence of an endogenous activator at a concentration that is not sufficient to activate the mPPAR alpha-G but that is sufficient to effect the intrinsic transactivation seen for the wild-type mPPAR alpha.
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PMID:A single amino acid change in the mouse peroxisome proliferator-activated receptor alpha alters transcriptional responses to peroxisome proliferators. 756 38

Hepatocyte nuclear factor 4 (HNF-4), a highly conserved member of the steroid hormone receptor superfamily critical for development and liver-specific gene expression, is very similar to another superfamily member, retinoid X receptor alpha (RXR alpha), in overall amino acid sequence and DNA binding specificity. Since RXR alpha is known to heterodimerize with many other nuclear receptors, the formation of heterodimers between HNF-4 and RXR alpha was examined. With the electrophoretic mobility shift assay, coimmunoprecipitation, and transient transfection assays, it is shown that, unlike other nuclear receptors, HNF-4 does not form heterodimers with RXR alpha either in the presence or in the absence of DNA. We also show that in vitro-translated HNF-4 does not form heterodimeric complexes on DNA with a number of other receptors, including RXR beta, RXR gamma, retinoic acid receptor alpha, or thyroid hormone receptor alpha. To investigate the hypothesis that the lack of heterodimerization between HNF-4 and RXR alpha is due to a strong homodimerization activity of HNF-4, glycerol gradient sedimentation and kinetic analysis were used to show that HNF-4 is in fact a stable homodimer in solution. Finally, immunohistochemistry is used to show that the HNF-4 protein is found exclusively in the nuclei in both HepG2 cells, which express endogenous HNF-4, and transfected COS cells, which overexpress HNF-4. These findings lead us to propose that HNF-4 defines a new subclass of nuclear receptors which reside primarily in the nucleus and which bind DNA and regulate transcription as homodimers.
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PMID:Exclusive homodimerization of the orphan receptor hepatocyte nuclear factor 4 defines a new subclass of nuclear receptors. 765 30

Mouse retinoid X receptor alpha (RXR alpha) lacking the amino-terminal region A/B (RXR alpha delta AB) has been purified to more than 98% purity and functional homogeneity from bacterial and baculovirus-based recombinant expression systems with yields of 2-8 mg/liter of culture. The purified protein is soluble, and fluorescence quenching analysis demonstrated that it binds its cognate ligand 9-cis-retinoic acid (9-cis-RA) stoichiometrically, and with high affinity. Compared with RXR delta AB expressed in COS-1 cells, bacterially and baculovirus-expressed proteins bind approximately 10 and 5 times less efficiently to direct repeat 1 (DR1) DNA elements, respectively, suggesting that animal cell-specific modification of RXR or interaction with other animal cell-specific factors may modulate DNA binding. 9-cis-RA did not stimulate DR1 binding of functional RXR delta AB expressed in Escherichia coli, Sf9 or COS-1 cells. The previously reported ligand effect that can be observed with in vitro made receptor may therefore be a consequence of a conformational stabilization of improperly folded in vitro synthesized protein.
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PMID:Pure and functionally homogeneous recombinant retinoid X receptor. 792 81

The cDNA for a member of the nuclear receptor family was cloned and named ubiquitous receptor (UR), since UR protein and mRNA are detected in many cell types. Rat UR/human retinoid X receptor alpha (hRXR alpha) heterodimers bound preferentially to double-stranded oligonucleotide direct repeats having the consensus half-site sequence AGGTCA and 4-nt spacing (DR-4). Coexpression of UR in COS-1 cells inhibited the stimulation of chloramphenicol acetyltransferase (CAT) reporter gene expression by hRXR alpha and human retinoic acid receptor alpha in the presence of all-trans-retinoic acid when DR-4 (but not DR-5) was present upstream of the promoter of a CAT reporter gene (DR-4-CAT). UR expression also inhibited the activation of a DR-4-CAT reporter gene by hRXR alpha and 9-cis-retinoic acid or by thyroid hormone receptor beta in the presence of thyroid hormone. However, in the absence of 9-cis-retinoic acid, UR in combination with hRXR alpha stimulation DR-4-CAT expression. Coexpression of thyroid hormone receptor markedly reduced this stimulation in the absence of thyroid hormone. UR may play an important role in normal growth and differentiation by modulating gene activation in retinoic acid and thyroid hormone signaling pathways.
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PMID:Ubiquitous receptor: a receptor that modulates gene activation by retinoic acid and thyroid hormone receptors. 797 66

In order to study the structural details of ligand protein interactions of the human retinoid X receptor alpha (hRXR alpha), the DEF and EF domains of the receptor were expressed as glutathione S-transferase (GST) fusion proteins in Escherichia coli. The fusion proteins were expressed at high levels and were affinity-purified by chromatography over glutathione-agarose. The DEF and EF domains were cleaved from the fusion proteins by digestion with thrombin. Retinoic acid binding was quantitated using two different methods. The apparent dissociation constant (Kd) and the stoichiometry of 9-cis-retinoic acid binding were performed by monitoring quenching of protein fluorescence. To directly compare the binding affinity of the E. coli-derived truncated hRXR alpha with full-length hRXR alpha expressed in transiently transfected COS cells, Scatchard analyses of [3H]9-cis-retinoic acid binding assays were performed. Both methods of analysis indicate that while the cleaved DEF peptide bound 9-cis-retinoic acid tightly, the cleaved EF peptide exhibited variable binding activity between preparations. By fluorimetric analysis, the Kd of the cleaved DEF peptide was estimated to be 3 +/- 0.5 nM with a stoichiometry of 1:1.1 +/- 0.1. By Scatchard analysis, the Kd values for [3H]9-cis-retinoic acid to the GST-hRXR alpha (DEF) peptide and the cleaved DEF peptide were estimated to be 1.8 nM and 5.6 nM, respectively. The estimated molecular mass from high speed sedimentation equilibrium experiments was 36 +/- 2 kDa for the apo-DEF peptide alone and 38 +/- 3 kDa for the holo-DEF peptide complexed with 9-cis-retinoic acid. This suggests that the recombinant ligand binding domain was predominantly in the monomer form. However, dimers of the cleaved DEF peptides were detected in chemical cross-linking experiments both in the presence and absence of 9-cis-retinoic acid. Since the purified E. coli-derived truncated hRXR alpha DEF peptide appears to fully retain its ligand binding activity, it should provide a useful model system for further structural analysis of ligand-protein interactions.
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PMID:Characterization of the ligand binding domain of human retinoid X receptor alpha expressed in Escherichia coli. 803 15

The ability of peroxisome proliferator-activated receptors (PPARs) to induce expression of a reporter gene linked to a peroxisome proliferator-responsive element (PPRE) from either the rat enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase gene or acyl-CoA oxidase [acyl-CoA:oxygen 2-oxidoreductase, EC 1.3.3.6] gene was examined by transient transfection assays in COS cells. Mouse and rat PPARs, as well as Xenopus PPAR alpha (xPPAR alpha) could induce expression of a reporter gene linked to the hydratase/dehydrogenase PPRE in the presence of the peroxisome proliferators ciprofibrate or Wy-14,643, whereas xPPAR beta and xPPAR gamma were ineffective. A similar induction of expression of a reporter gene linked to the acyl-CoA oxidase PPRE was observed with all PPARs except xPPAR beta. Extracts from cells transfected with PPAR-encoding genes contained factors that bound to both PPREs. In vitro synthesized PPARs could interact weakly with both PPREs; however, binding of each PPAR to both PPREs was significantly increased by the addition of COS cell nuclear extracts, demonstrating that efficient PPAR/DNA binding requires auxiliary cofactors. One cofactor was identified as the 9-cis-retinoic acid receptor, RXR alpha (retinoid X receptor alpha). Cooperative DNA binding and heteromerization between RXR alpha and each of the PPARs could be seen with both PPREs. Our results demonstrate that PPAR/PPRE binding and cooperativity with RXR alpha (and other cofactors) are obligatory but not necessarily sufficient for peroxisome proliferator-dependent transcription induction and that distinct PPREs can selectively mediate induction by particular PPARs.
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PMID:Diverse peroxisome proliferator-activated receptors bind to the peroxisome proliferator-responsive elements of the rat hydratase/dehydrogenase and fatty acyl-CoA oxidase genes but differentially induce expression. 839 Jun 76

The nuclear receptor mouse retinoid X receptor alpha (mRXRalpha) was shown to be constitutively phosphorylated in its NH2-terminal A/B region, which contains potential phosphorylation sites for proline-directed Ser/Thr kinases. Mutants for each putative site were generated and overexpressed in transfected COS-1 cells. Constitutively phosphorylated residues identified by tryptic phosphopeptide mapping included serine 22 located in the A1 region that is specific to the RXRalpha1 isoform. Overexpression and UV activation of the stress-activated kinases, c-Jun NH2-terminal kinases 1 and 2 (JNK1 and JNK2), hyperphosphorylated RXRalpha, resulting in a marked decrease in its electrophoretic mobility. This inducible hyperphosphorylation involved three residues (serines 61 and 75 and threonine 87) in the B region of RXRalpha and one residue (serine 265) in the ligand binding domain (E region). Binding assays performed in vitro with purified recombinant proteins demonstrated that JNKs did not interact with RXRalpha but bound to its heterodimeric partners, retinoic acid receptors alpha and gamma (RARalpha and RARgamma). Hyperphosphorylation by JNKs did not affect the transactivation properties of either RXRalpha homodimers or RXRalpha/RARalpha heterodimers in transfected cultured cells.
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PMID:Hyperphosphorylation of the retinoid X receptor alpha by activated c-Jun NH2-terminal kinases. 1038 91

Friend of GATA (FOG)-2 is a multi-zinc finger transcriptional corepressor protein that binds specifically to GATA4. Gene targeting studies have demonstrated that FOG-2 is required for normal cardiac morphogenesis, including the development of the coronary vasculature, left ventricular compact zone, and heart valves. To better understand the molecular mechanisms by which FOG-2 regulates these cardiac developmental programs, we screened a mouse day 11 embryo library using a yeast two-hybrid interaction trap with the fifth and sixth zinc fingers of FOG-2 as bait. Using this approach, we isolated clones encoding the orphan nuclear receptors chicken ovalbumin upstream promoter-transcription factor (COUP-TF) 2 and COUP-TF3. COUP-TF2-null embryos die during embryonic development with defective angiogenesis and cardiac defects, a pattern that partly resembles the FOG-2-null phenotype. The interaction between COUP-TF2 and FOG-2 in mammalian cells was confirmed by co-immunoprecipitation of these proteins from transfected COS-7 cells. The sites of binding interaction between COUP-TF2 and FOG-2 were mapped to zinc fingers 5 and 6 and fingers 7 and 8 of FOG-2 and to the carboxyl terminus of the COUP-TF proteins. Binding to COUP-TF2 was specific because FOG-2 did not interact with the ligand-binding domains of retinoid X receptor alpha, glucocorticoid receptor, and peroxisome proliferating antigen receptor gamma, which are related to the COUP-TF proteins. Full-length FOG-2 markedly enhanced transcriptional repression by GAL4-COUP-TF2(117-414), but not by a COUP-TF2 repression domain mutant. Moreover, FOG-2 repressed COUP-TF2dependent synergistic activation of the atrial natriuretic factor promoter by both GATA4 and the FOG-2-independent mutant GATA4-E215K. Taken together, these findings suggest that FOG-2 functions as a corepressor for both GATA and COUP-TF proteins.
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PMID:Friend of GATA 2 physically interacts with chicken ovalbumin upstream promoter-TF2 (COUP-TF2) and COUP-TF3 and represses COUP-TF2-dependent activation of the atrial natriuretic factor promoter. 1138 75

DNA binding and mutagenesis in vitro established that the -67/-55 region of the apoA-II (apolipoprotein A-II) promoter contains a thyroid HRE (hormone response element), which strongly binds RXRalpha (retinoid X receptor alpha)/T(3)Rbeta (thyroid receptor beta) heterodimers and weakly T(3)Rbeta homodimers, but does not bind other homo- or heterodimers of RXRalpha or orphan nuclear receptors. Transactivation was abolished by point mutations in the thyroid HRE. In co-transfection experiments of HEK-293 (human embryonic kidney 293) cells, the -911/+29 human apoA-II promoter was transactivated strongly by RXRalpha/T(3)Rbeta heterodimers in the presence of RA (9- cis retinoic acid) or T(3) (tri-iodothyronine). Homopolymeric promoters containing either three copies of the -73/-40 (element AIIAB) or four copies of the -738/-712 (element AIIJ) apoA-II promoter could be transactivated by RXRalpha/T(3)Rbeta heterodimers in COS-7 cells only in the presence of T(3) or RA respectively. RXRalpha/T(3)Rbeta heterodimers and USF2a (upstream stimulatory factor 2a) synergistically transactivated the -911/+29 apoA-II promoter in the presence of T(3). USF2a also enhanced the activity of a GAL4-T(3)Rbeta fusion protein in the presence of T(3) and suppressed the activity of a GAL4-RXRalpha fusion protein in the presence of RA. These findings suggest a functional specificity of the two HREs of the apoA-II promoter for retinoids and thyroids, which is modulated by synergistic or antagonistic interactions between RXRalpha/T(3)Rbeta heterodimers and the ubiquitous transcription factor USF2a.
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PMID:Functional specificity of two hormone response elements present on the human apoA-II promoter that bind retinoid X receptor alpha/thyroid receptor beta heterodimers for retinoids and thyroids: synergistic interactions between thyroid receptor beta and upstream stimulatory factor 2a. 1295 42