title: Transcriptional synergism between the vitamin D3 receptor and other nonreceptor transcription factors.
abstract: Small changes in the concentrations and/or combinations of trans-acting factors can result in profound alterations in gene expression. Synergistic interaction between different classes of transcription factors bound to distinct sites within a promoter/enhancer region is one mechanism by which this can occur. Reflecting this, hormone response elements, DNA recognition sites for steroid/nuclear receptors, are often found in promoter regions organized as multiple copies or are clustered among binding sites for other trans-acting factors. To systematically examine the potential interactions between one such receptor, the vitamin D3 receptor (VDR), and other nonreceptor transcription factors, we constructed a series of reporter plasmids containing one copy of the osteopontin (Spp1) vitamin D response element (VDRE), consisting of two direct repeats spaced by 3 base pairs, and one binding site for the transcription factors SP1, NF-1, Oct-1, or AP-1. We also generated reporters either under the control of two copies of Spp1 VDRE, or a distinct VDRE from the human osteocalcin gene promoter. The various reporters were used to transiently transfect HeLa or CV-1 cells in the presence and absence of 1,25-dihydroxyvitamin D3. Our results show that VDR transactivates 12-20 times more strongly from two Spp1-VDREs than from one, indicating that VDR synergizes with itself. VDR also synergizes with the other nonreceptor factors, since we observe a 6- to 12-fold degree of synergistic induction after ligand addition, depending on the particular factor. The functional basis for the transcriptional synergism appears to be at the level of cooperative DNA binding, at least for VDR alone and VDR-Oct-1, as demonstrated in vitro by gel mobility shift assays using purified factors. Consistent with this, we show that the minimal requirement for transcriptional synergism in vivo by VDR is its DNA-binding domain.
authors.affiliation: Department of Pharmacology, Cornell University Graduate School of Medical Sciences, New York, New York 10021.
authors.forename: M
authors.initials: M
authors.lastname: Liu
authors.forename: L P
authors.initials: LP
authors.lastname: Freedman
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002117:Calcitriol / Q000494:pharmacology; D002460:Cell Line; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004357:Drug Synergism; D017930:Genes, Reporter; D006367:HeLa Cells; D051863:Host Cell Factor C1; D006801:Humans; D008969:Molecular Sequence Data; D050811:Octamer Transcription Factor-1; D015675:Osteocalcin / Q000235:genetics; D053495:Osteopontin; D011401:Promoter Regions, Genetic; D018167:Receptors, Calcitriol / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D012795:Sialoglycoproteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; D051863:Host Cell Factor C1; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; D018167:Receptors, Calcitriol; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D014157:Transcription Factors; D015675:Osteocalcin; D053495:Osteopontin; D004247:DNA; D002117:Calcitriol