The E3 Ubiquitin Ligase gp78 Protects against ER Stress in Zebrafish Liver
The E3 Ubiquitin Ligase gp78 Protects against ER Stress in Zebrafish Liver
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DOI：
10.1016/j.jgg.2014.05.005
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发表时间：
2014-07-20
影响因子：
5.9
通讯作者：
Fang, Shengyun
中科院分区：
文献类型：
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作者：
Chen, Zhiliang;Ballar, Petek;Fang, Shengyun
通过未折叠蛋白反应（UPR）增强内质网（ER）相关蛋白降解（ERAD）活性是恢复ER稳态的机制之一。体外证据表明，哺乳动物gp 78蛋白是一种E3泛素连接酶，其通过在生理和应激条件下使蛋白多泛素化和靶向蛋白进行蛋白酶体降解来促进ERAD。然而，gp 78在维持ER蛋白稳态中的体内功能仍然未经测试。在这里，我们表明，像它的哺乳动物的对应物，斑马鱼gp 78也是E3泛素连接酶在体外泛素化试验所揭示的。表达分析发现，gp 78在几个器官中高度表达，包括肝脏和脑，无论是仔鱼还是成鱼。用衣霉素处理幼鱼或成鱼诱导ER应激并上调肝脏中gp 78 ERAD复合物的几个关键组分的表达。此外，肝脏特异性过表达的gp 78（gp 78-R2 M）的显性负性形式，使肝脏更敏感衣霉素诱导的内质网应激，并增强表达的固醇反应元件结合蛋白（Srebp）的靶基因，这在很大程度上抑制鱼类过表达野生型gp 78。总之，这些数据表明，gp 78在保护肝脏免受ER应激方面起着关键作用。
Enhanced endoplasmic reticulum (ER)-associated protein degradation (ERAD) activity by the unfolded protein response (UPR) represents one of the mechanisms for restoring ER homeostasis. In vitro evidence indicates that the mammalian gp78 protein is an E3 ubiquitin ligase that facilitates ERAD by polyubiquitinating and targeting proteins for proteasomal degradation under both physiologic and stress conditions. However, the in vivo function of gp78 in maintaining ER protein homeostasis remains untested. Here we show that like its mammalian counterpart, the zebrafish gp78 is also an E3 ubiquitin ligase as revealed by in vitro ubiquitination assays. Expression analysis uncovered that gp78 is highly expressed in several organs, including liver and brain, of both larval and adult fish. Treatment of larvae or adult fish with tunicamycin induces ER stress and upregulates the expression of several key components of the gp78 ERAD complex in the liver. Moreover, liver-specific overexpression of the dominant-negative form of gp78 (gp78-R2M) renders liver more sensitive to tunicamycin-induced ER stress and enhances the expression of sterol response element binding protein (Srebp)-target genes, which was largely suppressed in fish overexpressing wild-type gp78. Together, these data indicate that gp78 plays a critical role in protecting against ER stress in liver.