Identification of liver X receptor-retinoid X receptor as an activator of the sterol regulatory element-binding protein 1c gene promoter
Identification of liver X receptor-retinoid X receptor as an activator of the sterol regulatory element-binding protein 1c gene promoter
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DOI：
10.1128/mcb.21.9.2991-3000.2001
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发表时间：
2001-05-01
影响因子：
5.3
通讯作者：
Yamada, N
中科院分区：
文献类型：
--
作者：
Yoshikawa, T;Shimano, H;Yamada, N
为了鉴定激活固醇调节元件结合蛋白Ic（SREBP-1c）转录的转录因子，我们使用含有2.6-kb小鼠SREBP-1基因启动子的报告基因从SREBP-1敲除小鼠的脂肪组织中筛选了表达cDNA文库。我们克隆并鉴定了氧固醇受体肝X受体（LXR α）和LXR β作为小鼠SREBP-1c启动子的强激活剂。在转染研究中，LXR α或β的表达以剂量依赖性方式激活SREBP-1c启动子-荧光素酶基因。缺失和突变的研究，以及凝胶迁移率变动分析，位于LXR反应元件复合物组成的两个新的LXR结合基序，显示出高度的相似性，最近发现的LXR反应元件在ABC 1基因启动子，反向胆固醇转运。添加LXR配体22（R）-羟基胆固醇增加了启动子活性。类维生素A X受体（RXR），异源二聚体的合作伙伴，及其配体9-顺式维甲酸的共表达也协同激活SREBP-1c启动子。在HepG 2细胞中，通过22（R）-羟基胆固醇和9-顺式-视黄酸处理诱导SREBP-1c mRNA和前体蛋白水平，证实内源性LXR-RXR激活可诱导内源性SREBP-1c表达。LXR对SREBP-1c的激活与细胞核SREBP-1c的轻微增加相关，导致脂肪酸合成酶基因（其下游基因之一）的激活，如荧光素酶测定所测量。这些数据表明，LXR-RXR可以通过调节SREBP-1c表达来修饰脂肪生成酶基因的表达，从而在脂肪酸和胆固醇代谢之间提供新的联系。
In an attempt to identify transcription factors which activate sterol-regulatory element-binding protein Ic (SREBP-1c) transcription, we screened an expression cDNA library from adipose tissue of SREBP-1 knockout mice using a reporter gene containing the 2.6-kb mouse SREBP-1 gene promoter. We cloned and identified the oxysterol receptors liver X receptor (LXR alpha) and LXR beta as strong activators of the mouse SREBP-1c promoter. In the transfection studies, expression of either LXR alpha or -beta activated the SREBP-1c promoter-luciferase gene in a dose-dependent manner. Deletion and mutation studies, as well as gel mobility shift assays, located an LXR response element complex consisting of two new LXR-binding motifs which showed high similarity to an LXR response element recently found in the ABC1 gene promoter, a reverse cholesterol transporter. Addition of an LXR ligand, 22(R)-hydroxycholesterol, increased the promoter activity. Coexpression of retinoid X receptor (RXR), a heterodimeric partner, and its ligand 9-cis-retinoic acid also synergistically activated the SREBP-1c promoter. In HepG2 cells, SREBP-1c mRNA and precursor protein levels were induced by treatment with 22(R)-hydroxycholesterol and 9-cis-retinoic acid, confirming that endogenous LXR-RXR activation can induce endogenous SREBP-1c expression. The activation of SREBP-1c by LXR is associated with a slight increase in nuclear SREBP-1c, resulting in activation of the gene for fatty acid synthase, one of its downstream genes, as measured by the luciferase assay. These data demonstrate that LXR-RXR can modify the expression of genes for lipogenic enzymes by regulating SREBP-1c expression, providing a novel link between fatty acid and cholesterol metabolism.