title: Distinct conformational changes induced by 20-epi analogues of 1 alpha,25-dihydroxyvitamin D3 are associated with enhanced activation of the vitamin D receptor.
abstract: The relative affinities of the 1 alpha,25-dihydroxyvitamin D3 (1,25-D3) analogues 20-epi-1 alpha,25-dihydroxyvitamin D3 (IE) and 20-epi-22-oxa-24a,26a,27a-tri-homo-1 alpha,25-dihydroxyvitamin D3 (ID) to the nuclear vitamin D receptor (VDR) are similar to that of 1,25-D3, but their antiproliferative action is 1000-fold greater. We tested whether the greater antiproliferative effect of these analogues is due to a differential activation of the VDR. In ROS 17/2.8 cells, the effective doses required to produce 50% maximal stimulation (ED50) of transfected reporter genes driven by either the osteocalcin or the osteopontin vitamin D-response elements (VDRE) were 5 x 10(-9) M, 10(-10) M, and 10(-11) M for 1,25-D3, ID, and IE, respectively. Similar results were obtained when recombinant human VDR was cotransfected into CV-1 cells with an osteocalcin VDRE-reporter plasmid. We found that in vitro the sensitivity of 1,25-D3-induced and analogue-induced receptors to proteases was different. The ED50 for binding to VDRE, as determined by electrophoretic mobility shift assays, was significantly higher for 1,25-D3-induced than for analogue-induced VDR. The concentration of retinoid X receptor (RXR) was significantly lower in 1,25-D3-induced than analogue-induced VDR complexes with VDRE. We therefore conclude that IE and ID augment transcriptional activity of VDR more than 1,25-D3 does, by producing conformational changes that enhance dimerization of VDR with RXR. We suggest that these conformational changes are due to differences in the contact sites of the 20-epi analogues and 1,25-D3 with the VDR.
authors.affiliation: Department of Medical Specialties, University of Texas, M.D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: S
authors.initials: S
authors.lastname: Peleg
authors.forename: M
authors.initials: M
authors.lastname: Sastry
authors.forename: E D
authors.initials: ED
authors.lastname: Collins
authors.forename: J E
authors.initials: JE
authors.lastname: Bishop
authors.forename: A W
authors.initials: AW
authors.lastname: Norman
mesh_terms: D000818:Animals; D001483:Base Sequence; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology; D002474:Cell-Free System; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism; D053495:Osteopontin; D051381:Rats; D018167:Receptors, Calcitriol / Q000502:physiology*; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D047488:Retinoid X Receptors; D012795:Sialoglycoproteins / Q000235:genetics; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014357:Trypsin / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D014157:Transcription Factors; D053495:Osteopontin; D014357:Trypsin; D002117:Calcitriol