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Cross-Talk between PPARs and the Partners of RXR: A Molecular Perspective. PPAR Res 2009; 2009:925309. [PMID: 20052392 PMCID: PMC2801013 DOI: 10.1155/2009/925309] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Accepted: 09/07/2009] [Indexed: 11/23/2022] Open
Abstract
The PPARs are integral parts of the RXR-dependent signaling networks. Many other nuclear receptor subfamily 1 members also require RXR as their obligatory heterodimerization partner and they are often co-expressed in any given tissue. Therefore, the PPARs often complete with other RXR-dependent nuclear receptors and this competition has important biological implications. Thorough understanding of this cross-talk at the molecular level is crucial to determine the detailed functional roles of the PPARs. At the level of DNA binding, most RXR heterodimers bind selectively to the well-known “DR1 to 5” DNA response elements. As a result, many heterodimers share the same DR element and must complete with each other for DNA binding. At the level of heterodimerization, the partners of RXR share the same RXR dimerization interface. As a result, individual nuclear receptors must complete with each other for RXR to form functional heterodimers. Cross-talk through DNA binding and RXR heterodimerization present challenges to the study of these nuclear receptors that cannot be adequately addressed by current experimental approaches. Novel tools, such as engineered nuclear receptors with altered dimerization properties, are currently being developed. These tools will enable future studies to dissect specific RXR heterodimers and their signaling pathways.
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Whitfield GK, Remus LS, Jurutka PW, Zitzer H, Oza AK, Dang HT, Haussler CA, Galligan MA, Thatcher ML, Encinas Dominguez C, Haussler MR. Functionally relevant polymorphisms in the human nuclear vitamin D receptor gene. Mol Cell Endocrinol 2001; 177:145-59. [PMID: 11377830 DOI: 10.1016/s0303-7207(01)00406-3] [Citation(s) in RCA: 297] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The functional significance of two unlinked human vitamin D receptor (hVDR) gene polymorphisms was evaluated in twenty human fibroblast cell lines. Genotypes at both a Fok I restriction site (F/f) in exon II and a singlet (A) repeat in exon IX (L/S) were determined, and relative transcription activities of endogenous hVDR proteins were measured using a transfected, 1,25-dihydroxyvitamin D(3)-responsive reporter gene. Observed activities ranged from 2--100-fold induction by hormone, with higher activity being displayed by the F and the L biallelic forms. Only when genotypes at both sites were considered simultaneously did statistically significant differences emerge. Moreover, the correlation between hVDR activity and genotype segregated further into clearly defined high and low activity groups with similar genotypic distributions. These results not only demonstrate functional relevance for both the F/f and L/S common polymorphisms in hVDR, but also provide novel evidence for a third genetic variable impacting receptor potency.
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Affiliation(s)
- G K Whitfield
- Department of Biochemistry, College of Medicine, 1501 N. Campbell Ave., University of Arizona, Tucson, AZ 85724, USA
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Liu YY, Nguyen C, Ali Gardezi SA, Schnirer I, Peleg S, Ali Gradezi S. Differential regulation of heterodimerization by 1alpha,25-dihydroxyvitamin D(3) and its 20-epi analog. Steroids 2001; 66:203-12. [PMID: 11179727 DOI: 10.1016/s0039-128x(00)00151-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Twenty-epi analogs of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) are 100-1000 times more potent transcriptionally than the natural hormone. To determine to what extent this enhanced activity is mediated through modulation of the dimerization process, we performed quantitative dimerization assays with in vitro translated vitamin D receptor (ivtVDR) and fusion proteins containing glutathione-S-transferase (GST) and either the ligand-binding domain of VDR (GST-VDR) or retinoid X receptor (RXR)alpha (GST-RXR). We found that VDR did not form homodimers in either the presence or absence of ligand, but heterodimerization of the ligand-binding domains of RXRalpha and VDR was primarily deltanoid-dependent. The ED(50) for induction of heterodimerization was 1-2 x 10(-)(9) M for 1alpha,25(OH)(2)D(3) and 0.5 x 10(-)(11) M for 20-epi 1alpha,25(OH)(2)D(3). Mutations in VDR's activation function 2 domain (AF-2) diminished the abilities of 1alpha,25(OH)(2)D(3) to induce a protease-resistant conformation and heterodimerization. These mutations changed neither the potency of 20-epi-1alpha,25(OH)(2)D(3) to induce protease-resistant conformation nor its potency to induce dimerization. Mutations in heptad 9/helix 10 abolished the ability of both 1alpha,25(OH)(2)D(3) and the 20-epi analog to induce dimerization, but not their potency to fold VDR into a protease-resistant conformation. We hypothesize that both the hormone and the analog stabilize receptor conformations that expose VDR's dimerization interface, and that interfaces exposed by these ligands are probably not significantly different. However, the mechanisms by which the two ligands expose the dimerization interface are different with respect to participation of the AF-2 domain.
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Affiliation(s)
- Y Y Liu
- Department of Medical Specialties, Section of Endocrinology, Box 15, The University of Texas M.D. Anderson Cancer Center, Texas Medical Center, Houston 77030, USA
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Nakajima S, Yamagata M, Sakai N, Ozono K. Effect of cyclic adenosine 3',5'-monophosphate and protein kinase A on ligand-dependent transactivation via the vitamin D receptor. Mol Cell Endocrinol 2000; 159:45-51. [PMID: 10687851 DOI: 10.1016/s0303-7207(99)00202-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
We examined the effects of cyclic adenosine 3',5'-monophosphate (cAMP) and protein kinase A (PKA) on the ligand-dependent transactivation mediated via the 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) receptor (VDR). A human VDR expression plasmid was transfected into HeLa, Saos-2 and MG63 cells with a luciferase reporter gene construct containing the vitamin D responsive element. With the addition of 0.5 mM 8 bromo-cAMP, the response to 1,25(OH)2D3 was suppressed to 61 and 78% in the HeLa and Saos-2 cells, respectively. The suppressive effect of 8 bromo-cAMP was observed without the introduction of the VDR expression plasmid in the MG63 cells. In the HeLa cells the co-expression of PKA reduced the ligand-inducible transactivation to 61% and the fold induction by 1,25(OH)2D3 to 89% of that without PKA. The CREB binding protein (CBP) was recently reported to integrate the intracellular signals via the cAMP/PKA cascade and nuclear hormone receptors. However, the suppressive effect of cAMP was not influenced by the co-expression of CBP. Lastly, we introduced point mutations at possible PKA phosphorylation sites into the VDR expression vector at serine-172 and threonine-175, but both mutant receptors still exhibited reduced transactivation with the co-expression of PKA. These results indicate that the phosphorylation of proteins other than the VDR may also be involved in the inhibitory effect mediated by the cAMP/PKA cascade.
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Affiliation(s)
- S Nakajima
- Department of Environmental Medicine, Research Institute, Osaka Medical Center for Maternal and Child Health, Izumi, Japan
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Lian JB, Stein GS, Stein JL, van Wijnen AJ. Regulated expression of the bone-specific osteocalcin gene by vitamins and hormones. VITAMINS AND HORMONES 1999; 55:443-509. [PMID: 9949687 DOI: 10.1016/s0083-6729(08)60941-3] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- J B Lian
- Department of Cell Biology, University of Massachusetts Medical Center, Worcester 01655, USA
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Nakajima S, Yamagata M, Sakai N, Ozono K. Characterization of the activation function-2 domain of the human 1,25-dihydroxyvitamin D3 receptor. Mol Cell Endocrinol 1998; 139:15-24. [PMID: 9705070 DOI: 10.1016/s0303-7207(98)00077-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In this study, we determined the ligand-dependent activation function domain 2 (AF-2) of the human vitamin D receptor (hVDR) and characterized it using site-directed mutagenesis. A single mutation at glutamic acid-420 (E420Q) and an additional mutation at leucine-417 (L417A-E420Q) eliminated ligand-dependent transcriptional activation. In addition, lysine-264 was also demonstrated to be vital for ligand-induced transactivation. However, bacterial-overexpressed transcriptional factor IIB (TFIIB) was able to bind to both AF-2 and lysine-264 mutant hVDRs in vitro. The ligand-dependent transactivation via wild type hVDR was interfered with weakly only when a 10-fold molar excess of L417A-E420Q plasmid was co-transfected. This suppressive effect was diminished by introducing an additional mutation at a cysteine residue in the DNA binding domain. Thus, we conclude that the AF-2 domain of the hVDR located between amino acids 417 and 420, as well as lysine-264, are essential for ligand-dependent transactivation, and that TFIIB was not necessary for the function of these two regions of the hVDR. Our finding that AF-2 mutant hVDRs exhibit only very weak suppressive effect may indicate a difference in the molecular mechanism of the VDR-mediated transactivation from other nuclear receptors.
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Affiliation(s)
- S Nakajima
- Department of Environmental Medicine, Research Institute, Osaka Medical Center for Maternal and Child Health, Izumi, Japan
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The vitamin D endocrine system and its therapeutic potential. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s0065-2490(96)80007-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
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Darwish HM, DeLuca HF. Recent advances in the molecular biology of vitamin D action. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1996; 53:321-44. [PMID: 8650307 DOI: 10.1016/s0079-6603(08)60149-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
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.
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Affiliation(s)
- H M Darwish
- Department of Biochemistry, University of Wisconsin-Madison 53706, USA
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Haussler MR, Jurutka PW, Hsieh JC, Thompson PD, Selznick SH, Haussler CA, Whitfield GK. New understanding of the molecular mechanism of receptor-mediated genomic actions of the vitamin D hormone. Bone 1995; 17:33S-38S. [PMID: 8579895 DOI: 10.1016/8756-3282(95)00205-r] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The nuclear vitamin D receptor (VDR) binds the 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]hormone with high affinity and elicits its actions to regulate gene expression in target cells by binding to vitamin D-responsive elements (VDREs). VDREs in positively controlled genes such as osteocalcin, osteopontin, beta 3-integrin, and vitamin D-24-OHase are direct hexanucleotide repeats with a spacer of three nucleotides. The VDR associates with these VDREs with the greatest affinity as a heterodimer with one of the family of retinoid X receptors (RXRs). VDR consists of an N-terminal zinc finger domain that determines DNA binding, a "hinge" segment and a C-terminal hormone binding domain which also contains two conserved regions that engage in heterodimerization with an RXR on the VDRE. The role of the 1,25(OH)2D3 ligand in transcriptional activation by the VDR-RXR heterodimer is to alter the conformation of the hormone-binding domain of VDR to facilitate strong dimerization with RXR, which results in ligand-enhanced association with the VDRE. Thus RXR is recruited into a heterocomplex by liganded VDR. The natural ligand for the RXR coreceptor, 9-cis retinoic acid, suppresses both VDR-RXR binding to the VDRE and 1,25(OH)2D3-stimulated transcription, indicating that 9-cis retinoic acid diverts RXR away from being the silent partner of VDR to instead form RXR homodimers. Recent data reveal that after binding RXR, a subsequent target for VDR in the vitamin D signal transduction cascade is basal transcription factor IIB (TFIIB).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M R Haussler
- Department of Biochemistry, College of Medicine, University of Arizona, Tucson 85724, USA
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Carlberg C. Mechanisms of Nuclear Signalling by Vitamin D3. Interplay with Retinoid and Thyroid Hormone Signalling. ACTA ACUST UNITED AC 1995. [DOI: 10.1111/j.1432-1033.1995.tb20727.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Hsieh JC, Nakajima S, Galligan MA, Jurutka PW, Haussler CA, Whitfield GK, Haussler MR. Receptor mediated genomic action of the 1,25(OH)2D3 hormone: expression of the human vitamin D receptor in E. coli. J Steroid Biochem Mol Biol 1995; 53:583-94. [PMID: 7626514 DOI: 10.1016/0960-0760(95)00112-d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The nuclear vitamin D receptor (VDR) binds the 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) hormone with high affinity and elicits its actions to stimulate gene expression in target cells by binding to the vitamin D-responsive element (VDRE). VDREs in such positively controlled genes as osteocalcin, osteopontin, beta 3 integrin and vitamin D-24-OHase are direct hexanucleotide repeats with a spacer of three nucleotides. The present studies of VDR/VDRE interaction utilized full-length human vitamin D receptor (hVDR) that was overexpressed in E. coli, purified to near homogeneity (> 95%), and its authenticity confirmed by demonstrating high affinity hormone binding and reactivity to monoclonal antibody 9A7 gamma. The expressed hVDR displays strict dependence on the family of retinoid X receptors (RXRs) for binding to the vitamin D-responsive element (VDRE) in the rat osteocalcin gene. Similar overexpression in E. coli of the DNA binding domain (delta 134), containing only residues 4-133 of hVDR, generated a receptor species that possesses intrinsic DNA binding activity. Both full-length and delta 134 hVDRs retain similar DNA binding specificities when tested with several natural hormone responsive elements, indicating that the N-terminal zinc finger region determines hVDR-DNA sequence selectivity. The C-terminal region of the molecule is required for hormone binding and confers the receptor with the property of very high affinity DNA binding, via heterodimerization between hVDR and RXR. A natural ligand for the RXR co-receptor, 9-cis retinoic acid, suppresses both VDR-RXR binding to the VDRE and 1,25(OH)2D3 stimulated transcription, indicating that 9-cis retinoic acid recruits RXR away from VDR to instead form RXR homodimers.
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Affiliation(s)
- J C Hsieh
- Department of Biochemistry, College of Medicine, University of Arizona, Tucson 85724, USA
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