Quélo I, Kahlen J P, Rascle A, Jurdic P, Carlberg C
Laboratoire de Biologie Moléculaire et Cellulaire, Ecole Normale Supérieure de Lyon, France.
DNA Cell Biol. 1994 Dec;13(12):1181-7. doi: 10.1089/dna.1994.13.1181.
1,25-Dihydroxyvitamin D3 (VD) controls multiple aspects of homeostasis, cell growth, and differentiation by the action of its nuclear receptor (VDR), which binds to, and activates transcription from, response elements in the promoter region of its target genes. Carbonic anhydrase-II (CA-II), an enzyme important to osteoclast function, has been shown to be regulated by VD. We screened the promoter of chicken CA-II for VDR binding sites and identified a functional VDRE, between positions -1,203 and -1,187. Like the majority of the VDREs described to date, this response element consists of two directly repeated hexameric core binding motifs spaced by three nucleotides and is bound by a heterodimer formed by the VDR and the retinoid X receptor (RXR). We show that the polarity of the binding of this heterodimer is 5'-VDR-RXR-3' in the CA-II VDRE, whereas on a "classical" DR3-type VDRE, such as that of the mouse osteopontin gene, this polarity is reversed to 5'-RXR-VDR-3'. We also show that the polarity of the heterodimeric complex in relation to the basic transcriptional machinery influences the sensitivity of the transcriptional activity to VD. This suggests that the orientation of a hormone response element in its natural promoter context constitutes an additional level of gene regulation.
1,25-二羟基维生素D3（VD）通过其核受体（VDR）的作用来控制体内稳态、细胞生长和分化的多个方面，VDR可与靶基因启动子区域的反应元件结合并激活其转录。碳酸酐酶-II（CA-II）是破骨细胞功能的一种重要酶，已被证明受VD调控。我们筛选了鸡CA-II启动子中的VDR结合位点，并在-1203至-1187位之间鉴定出一个功能性VDRE。与迄今描述的大多数VDRE一样，该反应元件由两个直接重复的六聚体核心结合基序组成，中间间隔三个核苷酸，并由VDR和视黄酸X受体（RXR）形成的异二聚体结合。我们发现，在CA-II VDRE中，这种异二聚体的结合极性为5'-VDR-RXR-3'，而在“经典”的DR3型VDRE（如小鼠骨桥蛋白基因的VDRE）上，这种极性则相反，为5'-RXR-VDR-3'。我们还表明，异二聚体复合物相对于基本转录机制的极性会影响转录活性对VD的敏感性。这表明激素反应元件在其天然启动子环境中的方向构成了基因调控的一个额外层面。
