SUMOylation of the Farnesoid X Receptor (FXR) Regulates the Expression of FXR Target Genes
SUMOylation of the Farnesoid X Receptor (FXR) Regulates the Expression of FXR Target Genes
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DOI：
10.1074/jbc.m112.443937
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发表时间：
2013-05-10
影响因子：
4.8
通讯作者：
Suchy, Frederick J.
中科院分区：
文献类型：
--
作者：
Balasubramaniyan, Natarajan;Luo, Yuhuan;Suchy, Frederick J.
法尼醇X受体（FXR）属于配体激活的转录因子家族，调节代谢的许多方面，包括胆汁酸稳态。在这里，我们表明，FXR是共价修饰的小泛素样修饰剂（Sumo 1），细胞信号传导和转录的重要调节。分别在FXR的AF-1和配体结合结构域的赖氨酸122和275处的高度保守的共有位点在体外和体内进行SUMO化。染色质免疫沉淀（ChIP）分析表明，Sumo 1被招募到胆盐输出泵（BSEP），小异源二聚体伴侣（SHP），和OST α-OST β有机溶质转运蛋白位点的配体依赖性的方式。连续染色质免疫沉淀（ChIP-ReChIP）验证了FXR和Sumo 1与BSEP和SHP启动子的同时结合。Sumo 1的过表达显著降低了FXR与ChIP-ReChIP上的BSEP和SHP启动子的结合和/或募集。SUMO化对FXR的核定位没有明显影响。Sumo 1的表达显著抑制HepG 2细胞中FXR/维甲酸X受体α（RXR α）对BSEP和SHP启动子的配体依赖性反式激活。相反，突变取消SUMO化FXR或siRNA敲低Sumo 1表达增强BSEP和SHP启动子的反式激活FXR。SUMO化途径在阻塞性胆汁淤积期间显著改变，差异Sumo 1募集到FXR靶基因的启动子。总之，FXR是SUMO化，调节其能力，反式激活其靶基因在正常肝脏和阻塞性胆汁淤积。
The farnesoid X receptor (FXR) belongs to a family of ligand-activated transcription factors that regulate many aspects of metabolism including bile acid homeostasis. Here we show that FXR is covalently modified by the small ubiquitin-like modifier (Sumo1), an important regulator of cell signaling and transcription. Well conserved consensus sites at lysine 122 and 275 in the AF-1 and ligand binding domains, respectively, of FXR were subject to SUMOylation in vitro and in vivo. Chromatin immunoprecipitation (ChIP) analysis showed that Sumo1 was recruited to the bile salt export pump (BSEP), the small heterodimer partner (SHP), and the OST alpha-OST beta organic solute transporter loci in a ligand-dependent fashion. Sequential chromatin immunoprecipitation (ChIP-ReChIP) verified the concurrent binding of FXR and Sumo1 to the BSEP and SHP promoters. Overexpression of Sumo1 markedly decreased binding and/or recruitment of FXR to the BSEP and SHP promoters on ChIP-ReChIP. SUMOylation did not have an apparent effect on nuclear localization of FXR. Expression of Sumo1 markedly inhibited the ligand-dependent, transactivation of BSEP and SHP promoters by FXR/retinoid X receptor alpha (RXR alpha) in HepG2 cells. In contrast, mutations that abolished SUMOylation of FXR or siRNA knockdown of Sumo1 expression augmented the transactivation of BSEP and SHP promoters by FXR. Pathways for SUMOylation were significantly altered during obstructive cholestasis with differential Sumo1 recruitment to the promoters of FXR target genes. In conclusion, FXR is subject to SUMOylation that regulates its capacity to transactivate its target genes in normal liver and during obstructive cholestasis.