Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence regarding the nature of the regulatory factors which directly act upon liver cells and extra-hepatic tissues to alter CBG synthesis is scarce. The present study used cultured rat fetal hepatocytes to investigate the involvement and possible interplay in this process of several members of the nuclear receptors superfamily: vitamin D (VDR), retinoic acids (RAR/RXR) and thyroid hormones (TR). Treatment of cells with 1alpha,25-(OH)2D3 (1,25-D) elicited a dose-dependent inhibition of basal CBG concentration in culture medium. Maximum inhibition to about 15% of control level was achieved with 0.1-1.0 nM, with an IC50 of 3.8 x 10(-12) M and with no significant change in binding affinity. Differential activation of RAR and RXR with either 9-cis-retinoic acid (9-cis-RA) or the RAR-selective synthetic retinoid TTNPB revealed that high doses of both drugs diminished CBG expression, though the former proved about 10-times more potent than the latter in this regard. Amplification by triiodothyronine (T3) of CBG synthesis failed to block the inhibitory effects of either 1,25-D or retinoids, as revealed by both binding capacity and mRNA measurements. Relative to CBG, 1,25-D similarly depressed the synthesis of alpha-fetoprotein (AFP), while on the contrary, retinoids and T3 were shown to cause opposite effects, as 9-cis-RA and TTNPB elevated and T3 decreased AFP expression. The present findings identify for the first time ligands of VDR and RAR/RXR as powerful negative regulators of both basal and T3-stimulated CBG biosynthesis in fetal hepatocytes and suggest lack of a functional interplay between TR and VR or RAR/RXR in these processes.
J Steroid Biochem Mol Biol 1996 Jan
PMID:Regulation of corticosteroid-binding globulin synthesis by 1alpha,25-dihyroxy-vitamin D3 (calcitriol), 9-cis-retinoic acid and triiodothyronine in cultured rat fetal hepatocytes. 864 9

Following the cloning and deletion analysis of the vitamin D receptor, most recent advances have been in the isolation and characterization of the DNA response elements found in the promoter region of target genes of vitamin D. Vitamin D, like the thyroid and retinoid hormones, binds to repeat sequences, but the repeats are separated by three nonspecified bases. The action of the VDR requires the presence of the RXR proteins and evidently other proteins that are involved in regulating transcriptions. A possible role of phosphorylation of the ligand binding domain of the VDR in transcription has also appeared. Very likely, the molecular events involved in vitamin D stimulation or suppression of a target gene will include its interaction with a number of transcription factors, both in the regulation of transcription and in the actual machinery involved in the transcription process through polymerase II. Although likely, it is not entirely clear whether the genomic action of vitamin D can account for all of its biological activities. Nongenomic actions of the vitamin D hormone have been reported, but convincing evidence that this is of biological importance in vivo is lacking. Advances in our understanding of the vitamin D mechanism of action can clearly be expected from physical studies of cloned and expressed vitamin D receptor and its subdomains, elucidation of the transcription factors in vitamin D-modulated transcription of target genes, elucidation of the role of phosphorylation in the transcription process, and the identification of important genes that are regulated in the specific target tissues responsive to vitamin D. This will definitely remain as a very active field of investigation well into the future.
Prog Nucleic Acid Res Mol Biol 1996
PMID:Recent advances in the molecular biology of vitamin D action. 865 Mar 7

We identified and characterized a novel rat vitamin D receptor isoform (rVDR1), which retains intron 8 of the canonical VDR (rVDR0) during alternative splicing. In this isoform protein directed by the stop codon in this newly identified exon, a part of the ligand binding domain (86 amino acids) is truncated at the C-terminal end but contains 19 extra amino acids. The rVDR1 transcript was expressed at a level 1/15 to 1/20 of that of rVDR0 in the kidney and intestine in adult rats but not in embryos. The recombinant rVDR1 protein showed no ligand binding activity. Homo- and heterodimers of the recombinant rVDR0 and rVDR1 proteins bound to a consensus vitamin D response element (VDRE) but not to consensus response elements for thyroid hormone and retinoic acid. However, unlike rVDR0, rVDR1 did not form a heterodimeric complex with RXR on the VDRE. A transient expression assay showed that this isoform acted as a dominant negative receptor against rVDR0 transactivation. Interestingly, the dominant negative activities of rVDR1 differed among VDREs. Thus, the present study indicates that this new VDR isoform negatively modulates the vitamin D signaling pathway, through a particular set of target genes.
Mol Cell Biol 1996 Jul
PMID:Intron retention generates a novel isoform of the murine vitamin D receptor that acts in a dominant negative way on the vitamin D signaling pathway. 866 54

Transcriptional and DNA binding activities of the human vitamin D receptor (hVDR) were examined in the yeast Saccharomyces cerevisiae. In the studies described here, VDR itself exhibited little transcriptional activity regardless of the nature of the vitamin D-responsive elements (VDREs) used. Consistent with its lack of functional activity, recombinant VDR was unable to bind to VDREs in vitro using bandshift analysis. Interestingly, VDR was able to bind to VDREs with high affinity and to fully activate transcription in intact yeast cells in the presence of the retinoid X receptor (RXR). Although RXR subtypes displayed a similar capacity to induce heterodimer formation with VDR on VDREs, RXR gamma was the strongest of the subtypes in potentiating VDR-dependent transactivation. We also evaluated both DNA binding and transcriptional activities of VDR alone and VDR plus RXR on directly repeated response elements whose half-sites were separated by three and six base pairs. DNA-binding assays together with functional assays revealed that VDR was active only in the presence of RXR, regardless of spacing. Using a domain-swap approach, we constructed a chimeric receptor in which the DNA-binding domain of VDR was replaced with that of the glucocorticoid receptor. Interaction of both wild type and chimeric receptors with a hybrid-responsive element in the presence of RXR revealed that RXR and VDR bound to the 5'- and 3'-half-sites of VDRE, respectively. Finally, we show that the fifth position in the 3'-half-site (C) of the VDRE strongly influences the binding of VDR/RXR heterodimer to its cognate cis-elements. Cumulatively, our studies demonstrate, using an eukaryotic yeast system, that the functional VDR unit includes RXR or an equal partner.
Mol Endocrinol 1996 Feb
PMID:Human vitamin D receptor-dependent transactivation in Saccharomyces cerevisiae requires retinoid X receptor. 882 59

Analysis of the 5'-flanking region of the avian (chicken) PTH (cPTH) gene has revealed a DNA segment between -74 and -60 that is analogous to the consensus sequence for the vitamin D3 response element (VDRE). The DNA segment consists of two imperfect direct repeats, GGGTCA and GGGTGT, which are separated by a 3-bp spacer. The functionality of the putative VDRE was verified by transfection studies in opossum kidney cells using plasmid constructs that contained various regions of the cPTH gene 5'-flanking sequence and promoter fused to the gene for chloramphenicol acetyl transferase (CAT). Likewise, negative regulation of gene transcription by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] was detected when the cPTH VDRE was inserted immediately upstream from truncated forms of the cPTH or the SV40 early promoter. Using gel mobility shift assays, the cPTH VDRE was compared with the human osteocalcin (hOC) VDRE, which activates gene transcription in the presence of 1,25-(OH)2D3. With a partially purified nuclear extract from dog intestine, the two VDREs produced gel shift patterns that were remarkably similar, with the exception that the binding affinity for the hOC sequence was notably greater. Both VDREs produced two major bound complexes (B1 and B2), which could be completely abolished by the addition of an excess of unlabeled hOC VDRE or a monoclonal antibody specific for the VDR protein. Furthermore, similar protein:DNA complexes were observed when either the cPTH or hOC VDRE were incubated with a mixture of purified preparations of recombinant VDR and retinoid X receptor alpha proteins. Ethylation interference analysis showed that the base contacts made by complexes B1 and B2 with the cPTH VDRE were essentially the same and were restricted primarily to the two half-site sequences.
Mol Endocrinol 1996 Feb
PMID:Characterization of a response element in the 5'-flanking region of the avian (chicken) PTH gene that mediates negative regulation of gene transcription by 1,25-dihydroxyvitamin D3 and binds the vitamin D3 receptor. 882 60

The C-terminal domain of the human vitamin D receptor (hVDR) is essential for dimerization with retinoid X receptors and for transcriptional activation. To define the dimerization domain of the hVDR, a series of internal deletion mutants of the receptor were prepared beginning within the E domain and extending through the F domain to the C terminus. These mutant receptors were tested for dimerization and transcriptional activities by means of gel shift assay and beta-galactosidase assay, respectively, in a yeast system. The dimerization domain of the hVDR was localized to two separate but adjacent regions of the receptor molecule. In these experiments, the activation domain colocalized with dimerization. To more precisely delineate a relationship between these domains, region-specific random mutagenesis was carried out to detect mutants using error-prone PCR and a functional screen strategy employed using transformed yeast. Two classes of inactive receptors were identified: one in which both transcriptional activation and dimerization were compromised and a second in which only transcriptional activation was abolished. Most of the mutations responsible for these phenotypes were single. The studies suggest a separation between dimerization and transactivation domains. We reconstituted each of these hVDR mutants in a mammalian expression vector and evaluated them individually in COS-1 cells. All VDR mutants were transcriptionally active in this cellular background in response to 1,25-dihydroxyvitamin D3 although the potency of the hormone was reduced. The latter observation coincided with the observation that each mutant was compromised to some extent in binding affinity. These data clearly demonstrate the existence of an activation domain in hVDR that is separable from the domain involved in dimerization. Factors that couple hVDR to the general transcription apparatus in yeast through the activation domain in the hVDR, however, appear to be unrelated or dissimilar to those used in COS-1 cells.
Mol Endocrinol 1996 Aug
PMID:Transcriptional activation and dimerization functions in the human vitamin D receptor. 884 11

The nature of the DNA binding interactions of the human vitamin D receptor (hVDR) with the murine osteopontin vitamin D response element (mOP VDRE) was examined. Both recombinant hVDR and human retinoid X receptor beta (hRXRbeta) proteins were obtained from baculovirus-infected Sf9 insect cells. Mixing extracts of the two recombinant proteins resulted in the strong, specific formation of a slower migrating complex in the electrophoretic mobility shift assay. Crude extracts of the expressed hVDR alone were also capable of binding with high affinity to the mOP sequence, and this binding was enhanced in the presence of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). Competition experiments confirmed the specificity of this interaction and revealed that the human osteocalcin VDRE was a poor competitor for this binding. Ethylation interference footprint analyses of hVDR/hRXRbeta and hVDR complexes revealed only subtle differences in how these two different VDR-containing complexes interacted with the mOP VDRE. The footprints displayed contact points in both halves of the direct repeat format, confirming the dimeric and major groove interactions of both types of complexes. DNA affinity chromatography of labelled hVDR extracts revealed a peak eluting at ca. 290 mM KC1 that was capable of rebinding to the mOP sequence in gel shift experiments. Ultraviolet (UV) light-crosslinking experiments of hVDR extracts alone to radiolabelled DNA were consistent with the existence of a homodimeric hVDR interaction. Additionally, these experiments confirmed the direct interaction of a hVDR/hRXRbeta heterodimer when mixed extracts were utilized. From these results we infer that homodimers of the hVDR which respond with enhanced DNA binding to particular vitamin D response elements when exposed to 1,25-(OH)2D3 are possible. This may be of functional significance when RXR proteins are limiting or RXR ligand is present within a cell.
J Steroid Biochem Mol Biol 1996 Dec
PMID:Vitamin D receptor interactions with the murine osteopontin response element. 901 Mar 43

The sequences in the rat osteocalcin gene that lie 3' to the vitamin D response element (VDRE) have been shown to augment transcriptional activation by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. These DNA sequences, however, are unable to bind the VDR or mediate 1,25-(OH)2D3 responsiveness independently of the VDRE. To further characterize this region, the functional properties of a series of mutant oligonucleotides were examined in transiently transfected ROS 17/2.8 cells. When these mutant oligonucleotides were expressed upstream of the heterologous herpes simplex virus thymidine kinase promoter, the bases between -420 and -414 of the rat osteocalcin gene were identified as critical for maximal transactivation by 1,25-(OH)2D3. Furthermore, mutation of these sequences in the context of the native osteocalcin promoter and enhancer totally abolished the ability of the VDRE to mediate 1,25-(OH)2D3 responsiveness. These bases, which are essential for the 1,25-(OH)2D3 responsiveness of the rat osteocalcin gene, are also present in a similar position, relative to the VDRE, in the human osteocalcin gene. To explore whether these sequences could enhance transactivation by other inducible transcription factors, they were examined for their ability to synergize with the chick vitellogenin estrogen response element and the rat somatostatin cAMP response element. When placed upstream to the herpes simplex virus thymidine kinase promoter and transfected into ROS 17/2.8 cells, these sequences were able to enhance transcriptional responsiveness to 17beta-estradiol and forskolin, respectively, demonstrating that they also contribute to transactivation by other inducible transcription factors.
Mol Endocrinol 1997 Feb
PMID:DNA sequences downstream from the vitamin D response element of the rat osteocalcin gene are required for ligand-dependent transactivation. 901 68

The numerous members of the steroid/nuclear hormone receptor superfamily act as direct transducers of circulating signals, such as steroids, thyroid hormone, and vitamin or lipid metabolites, and modulate the transcription of specific target genes, primarily as dimeric complexes. The receptors for 9-cis retinoic acid and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], RXR and VDR, respectively, as members of this superfamily, form a heterodimeric complex and bind cooperatively to vitamin D responsive elements (VDREs) to activate or repress the transcription of a multitude of genes which regulate a variety of physiological functions. To directly investigate RXR- and VDR-mediated transactivation, we developed a cell-free transcription system for 1,25(OH)2D3 signaling by utilizing crude nuclear extracts and a G-free cassette-based assay. Transcriptional enhancement in vitro was dependent on purified, exogenous RXR and VDR and was responsive to physiological concentrations of 1,25(OH)2D3. We found that RXR and VDR transactivated selectively from VDRE-linked templates exclusively as a heterodimeric complex, since neither receptor alone enhanced transcription in vitro. By the addition of low concentrations of the anionic detergent Sarkosyl to limit cell-free transcription to a single round and the use of agarose gel mobility shift experiments to assay factor complex assembly, we observed that 1,25(OH)2D3 enhanced RXR:VDR-mediated stabilization or assembly of preinitiation complexes to effect transcriptional enhancement from VDRE-linked promoter-containing DNA.
Mol Cell Biol 1997 Apr
PMID:Retinoid X receptor:vitamin D3 receptor heterodimers promote stable preinitiation complex formation and direct 1,25-dihydroxyvitamin D3-dependent cell-free transcription. 912 40

With receptor immunocytochemistry, neurons receptive for the steroidhormone 1.25-dihydroxyvitamin D3 have been observed in hypothalamic nuclei. In the present paper we report that a fraction of 1.25-dihydroxyvitamin D3 receptor (VDR) immunoreactive neurons in the hypothalamus of male rats are immunoreactive for oxytocin (OT), suggesting a direct genomic action of this steroid on OT expression. While only 10% of neurons with OT immunofluorescence in the periventricular nucleus contained nuclear VDR immunostaining, up to 50% of the OT neurons in the supraoptic nucleus and 30% in the magnocellular portion of the paraventricular nucleus were VDR positive. VDR immunostaining in the magnocellular nuclei was in many cases confined to the perinuclear cytoplasm. We assume that 1.25-dihydroxyvitamin D3 has effects on hypothalamic peptidergic systems similar to other steroid hormones.
Cell Mol Biol (Noisy-le-grand) 1997 Jun
PMID:1.25-Dihydroxyvitamin D3 receptor is partly colocalized with oxytocin immunoreactivity in neurons of the male rat hypothalamus. 922 Jan 47


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