Yen P M, Liu Y, Sugawara A, Chin W W
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Biol Chem. 1996 May 3;271(18):10910-6. doi: 10.1074/jbc.271.18.10910.
We have examined vitamin D receptor (VDR), thyroid hormone receptor (TR), and retinoid X receptor beta (RXR beta) binding to vitamin D response elements (VDREs), two thyroid hormone response elements (TREs) (DR4 and F2), and a retinoic acid response element (DR5). VDR/RXR bound well to the VDREs and to DR4 and DR5 using the electrophoretic mobility shift assay. Surprisingly, VDR/RXR also bound well to F2, which contains half-sites arranged as an inverted palindrome. In co-transfection experiments using CV-1 cells, we observed that VDR repressed basal transcription in the absence of ligand on DR3 and osteopontin VDREs and F2, but had no effect on DR4 or DR5. VDR selectively mediated ligand-dependent transcription on only VDREs. VDR also exhibited dominant negative activity as it blocked triiodothyronine (T3)-mediated transcriptional activity on DR4 and F2. These results demonstrate that VDR/RXR heterodimers can bind promiscuously to a wide range of hormone response elements, including inverted palindromes. Moreover, they show that unliganded VDRs, similar to TRs and retinoic acid receptors, can repress basal transcription. Last, they also suggest a novel repressor function of VDR on T3-mediated transcription which may be significant in tissues where VDR and TR are co-expressed.
我们检测了维生素D受体（VDR）、甲状腺激素受体（TR）和视黄酸X受体β（RXRβ）与维生素D反应元件（VDREs）、两个甲状腺激素反应元件（TREs）（DR4和F2）以及一个视黄酸反应元件（DR5）的结合情况。利用电泳迁移率变动分析，VDR/RXR能很好地与VDREs、DR4和DR5结合。令人惊讶的是，VDR/RXR也能很好地与F2结合，F2包含呈反向回文排列的半位点。在使用CV-1细胞的共转染实验中，我们观察到在无配体情况下，VDR能抑制DR3、骨桥蛋白VDREs和F2上的基础转录，但对DR4或DR5没有影响。VDR仅在VDREs上选择性地介导配体依赖性转录。VDR还表现出显性负性活性，因为它能阻断三碘甲状腺原氨酸（T3）介导的DR4和F2上的转录活性。这些结果表明，VDR/RXR异二聚体可杂乱地结合多种激素反应元件，包括反向回文序列。此外，结果表明，与TR和视黄酸受体类似，未结合配体的VDR能抑制基础转录。最后，结果还提示VDR对T3介导的转录具有一种新的抑制功能，这在VDR和TR共表达的组织中可能具有重要意义。
