Berghöfer-Hochheimer Y, Zurek C, Wölfl S, Hemmerich P, Munder T
Hans-Knöll-Institut für Naturstoff-Forschung e.V., Department of Cell and Molecular Biology, Jena, Germany.
J Cell Biochem. 1998 Apr 1;69(1):1-12. doi: 10.1002/(sici)1097-4644(19980401)69:1<1::aid-jcb1>3.0.co;2-x.
The vitamin D receptor (VDR) heterodimerizes with the retinoid X receptor (RXR) and requires additional protein-protein interactions to regulate the expression of target genes. Using the yeast two-hybrid system, we identified the previously described protein L7, that specifically interacted with the VDR in the presence of vitamin D. Deletion analysis indicated, that the N-terminus of L7, which harbours a basic region leucine zipper like domain, mediated interaction with the VDR. Binding assays with purified GST-L7 demonstrated, that L7 specifically pulled down the VDR, that was either expressed in yeast or endogenously contained in the cell line U937. Interestingly, L7 inhibited ligand-dependent VDR-RXR heterodimerization, when constitutively expressed in yeast. We also demonstrate that L7 repressed binding of VDR-RXR heterodimers to a vitamin D response element. Surprisingly, L7 recruited RXR to the same response element in the presence of 9-cis retinoic acid. Ligand-dependent protein-protein interaction in the yeast two-hybrid system confirmed, that binding of L7 also was targeted at the RXR. Our data suggest, that protein L7 is a coregulator of VDR-RXR mediated transactivation of genes, that modulates transcriptional activity by interfering with binding of the receptors to genomic enhancer elements.
维生素D受体（VDR）与视黄酸X受体（RXR）形成异源二聚体，并需要额外的蛋白质-蛋白质相互作用来调节靶基因的表达。利用酵母双杂交系统，我们鉴定出了之前描述的蛋白质L7，它在维生素D存在的情况下与VDR特异性相互作用。缺失分析表明，L7的N端含有一个类似碱性区域亮氨酸拉链的结构域，介导了与VDR的相互作用。用纯化的GST-L7进行的结合试验表明，L7能特异性地拉下在酵母中表达或细胞系U937中内源性含有的VDR。有趣的是，当在酵母中组成性表达时，L7抑制配体依赖性的VDR-RXR异源二聚化。我们还证明L7抑制VDR-RXR异源二聚体与维生素D反应元件的结合。令人惊讶的是，在9-顺式视黄酸存在的情况下，L7将RXR招募到相同的反应元件上。酵母双杂交系统中配体依赖性的蛋白质-蛋白质相互作用证实，L7的结合也靶向RXR。我们的数据表明，蛋白质L7是VDR-RXR介导的基因反式激活的一个共调节因子，它通过干扰受体与基因组增强子元件的结合来调节转录活性。
