The farnesoid X receptor controls gene expression in a ligand- and promoter-selective fashion
The farnesoid X receptor controls gene expression in a ligand- and promoter-selective fashion
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DOI：
10.1074/jbc.m306422200
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发表时间：
2004-03-05
影响因子：
4.8
通讯作者：
Cui, JS
中科院分区：
文献类型：
--
作者：
Lew, JL;Zhao, A;Cui, JS
Farnesoid X受体（FXR）是胆汁酸的核受体。配体激活的fxr调节基因的转录，从而反馈控制胆汁酸的合成和分泌。人体内有五种主要的胆汁酸。我们之前已经证明了胆酸盐作为FXR拮抗剂的作用，在这里我们展示了其他四种胆汁酸，鹅去氧胆酸（CDCA），去氧胆酸（DCA），胆酸（CA）和熊去氧胆酸（UDCA），以基因特异性的方式作为选择性FXR激动剂。在体外共激活物关联实验中，CDCA完全激活FXR，而CA部分激活FXR， DCA和UDCA的活性可以忽略不计。在谷胱甘肽s -转移酶下拉实验中也得到了类似的结果，只有CDCA和合成的FXR激动剂GW4064显著增加了SRC-1与FXR的相互作用。在用胆汁盐输出泵（BSEP）启动子驱动的荧光素酶结构进行的FXR转激活试验中，胆汁酸显示出不同的激活BSEP启动子的能力：CDCA、DCA、CA和UDCA分别将荧光素酶活性提高了25倍、20倍、18倍和8倍。一致地，CDCA在HepG2细胞中使BSEP mRNA增加750倍，而DCA、CA和UDCA分别诱导BSEP mRNA增加250倍、75倍和15倍。尽管BSEP mRNA部分诱导，CA、DCA和UDCA有效抑制胆固醇7 α -羟化酶（FXR的另一个靶点）的表达。我们进一步发现，所有四种胆汁酸都显著增加了FXR蛋白，这表明在FXR信号通路中存在一个自动调节回路。总之，这些结果表明，每种胆汁酸的结合导致不同的FXR构象，进而不同地调节单个FXR靶点的表达。
Farnesoid X receptor (FXR) is a nuclear receptor for bile acids. Ligand activated-FXR regulates transcription of genes to allow feedback control of bile acid synthesis and secretion. There are five major bile acids in humans. We have previously demonstrated that lithocholate acts as an FXR antagonist, and here we show that the other four bile acids, chenodeoxycholate (CDCA), deoxycholate (DCA), cholate (CA), and ursodeoxycholate (UDCA), act as selective FXR agonists in a gene-specific fashion. In an in vitro coactivator association assay, CDCA fully activated FXR, whereas CA partially activated FXR and DCA and UDCA had negligible activities. Similar results were also obtained from a glutathione S-transferase pull-down assay in which only CDCA and the synthetic FXR agonist GW4064 significantly increased the interaction of SRC-1 with FXR. In FXR transactivation assays with a bile salt export pump (BSEP) promoter-driven luciferase construct, bile acids showed distinct abilities to activate the BSEP promoter: CDCA, DCA, CA, and UDCA increased luciferase activity by 25-, 20-, 18-, and 8-fold, respectively. Consistently, CDCA increased BSEP mRNA by 750-fold in HepG2 cells, whereas DCA, CA, and UDCA induced BSEP mRNA by 250-, 75-, and 15-fold, respectively. Despite the partial induction of BSEP mRNA, CA, DCA, and UDCA effectively repressed expression of cholesterol 7alpha-hydroxylase, another FXR target. We further showed that all four bile acids significantly increased FXR protein, suggesting the existence of an auto-regulatory loop in FXR signaling pathways. In conclusion, these results suggest that the binding of each bile acid results in a different FXR conformations, which in turn differentially regulates expression of individual FXR targets.