LXR alpha transactivates mouse organic solute transporter alpha and beta via IR-1 elements shared with FXR
LXR alpha transactivates mouse organic solute transporter alpha and beta via IR-1 elements shared with FXR
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DOI：
10.1007/s11095-006-9163-6
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发表时间：
2007-02-01
影响因子：
3.7
通讯作者：
Suzuki, Hiroshi
中科院分区：
文献类型：
--
作者：
Okuwaki, Masae;Takada, Tappei;Suzuki, Hiroshi
目的.最近发现的有机溶质转运蛋白（Ost）α和β位于肠细胞的基底外侧膜上，可能负责包括胆汁酸在内的许多底物的肠道吸收。在本研究中，其表达的转录调控机制进行了调查。方法和结果。为了阐明Osts的转录调控，使用小鼠Ost α/β启动子-荧光素酶报告基因构建体进行报告基因测定。将具有法尼醇X受体（FXR）和类视黄醇X受体α（RXR α）或肝X受体α（LXR α）和RXR α的构建体共转染到Caco-2细胞中诱导Ost α和β的转录活性，并且在用每种激动剂处理后观察到进一步增加。序列分析表明Ost α和Ost β启动子中存在IR-1区域，这通过IR-1序列的缺失消除了对FXR和LXR α的反应的发现得到证实。此外，IR-1突变降低了Ost α/β的FXR和LXR α依赖性反式激活。连同检测到FXR/RXR α和LXR α/RXR α与IR-1元件的直接结合，在Ost α和Ost β的启动子区域中揭示了功能性FXRE/LXRE的存在。此外，HNF-4 α进一步增强了FXR/RXR α和LXR α/RXR α对Ost α的刺激作用，但对Ost β无此作用。由此得出结论，LXR α/RXR α通过与FXR/RXR α共享的IR-1元件转录调节小鼠Ost α/β。暴露于FXR/LXR α调节剂可能会影响Ost α/β底物的分布。
Purpose. Recently identified organic solute transporter (Ost) alpha and beta are located on the basolateral membrane of enterocytes and may be responsible for the intestinal absorption of many substrates including bile acids. In the present study, the mechanism governing the transcriptional regulation of their expression was investigated.Methods and Results. To clarify the transcriptional regulation of Osts, reporter gene assays were performed using mouse Ost alpha/beta promoter-luciferase reporter constructs. Co-transfection of the constructs with farnesoid X receptor (FXR) and retinoid X receptor alpha (RXR alpha) or liver X receptor alpha (LXR alpha) and RXR alpha into Caco-2 cells induced the transcriptional activities of both Ost alpha and beta and further increases were observed following treatment with each agonist. Sequence analyses indicated the presence of IR-1 regions in Ost alpha and Ost beta promoters, which was confirmed by the finding that the deletion of IR-1 sequences abolished the response to FXR and LXR alpha. Furthermore, mutations in IR-1 reduced the FXR- and LXR alpha-dependent transactivation of Ost alpha/beta. Together with the detection of direct binding of FXR/RXR alpha and LXR alpha/RXR alpha to the IR-1 elements, the presence of functional FXRE/LXRE was revealed in the promoter region of both Ost alpha and Ost beta. In addition, the stimulatory effect of FXR/RXR alpha and LXR alpha/RXR alpha on Ost alpha, but not on Ost beta, was further enhanced by HNF-4 alpha.Conclusions. It was concluded that LXR alpha/RXR alpha transcriptionally regulate mouse Ost alpha/beta via IR-1 elements shared with FXR/RXR alpha. Exposure to FXR/LXR alpha modulators may affect the disposition of Ost alpha/beta substrates.