You Hui, Ge Yamei, Zhang Jian, Cao Yizhi, Xing Jing, Su Dongming, Huang Yujie, Li Min, Qu Shen, Sun Fei, Liang Xiubin
Renal Division, Sir Run Run Hospital, Department of Pathophysiology, Nanjing Medical University, Nanjing, Jiangsu Province, 211166, China.
Department of Endocrinology and Metabolism, Shanghai Tenth People's Hospital, Tong-Ji University, Shanghai, 200072, China.
J Cell Sci. 2017 Mar 15;130(6):1027-1036. doi: 10.1242/jcs.198242. Epub 2017 Jan 30.
Ubiquitylation of the epithelial Na channel (ENaC) plays a critical role in cellular functions, including transmembrane transport of Na, Na and water balance, and blood pressure stabilization. Published studies have suggested that ENaC subunits are targets of ER-related degradation (ERAD) in yeast systems. However, the molecular mechanism underlying proteasome-mediated degradation of ENaC subunits remains to be established. Derlin-1, an E3 ligase mediator, links recognized target proteins to ubiquitin-mediated proteasomal degradation in the cytosol. In the present study, we found that derlin-1 suppressed the expression of ENaC at the protein level and that the subunit α-ENaC (also known as SCNN1A) physically interacted with derlin-1 at the membrane-anchored domains or the loop regions, and that derlin-1 initiated α-ENaC retrotranslocation. In addition, HUWE1, an endoplasmic reticulum (ER)-resident E3 ubiquitin ligase, was recruited and promoted K11-linked polyubiquitylation of α-ENaC and, hence, formation of an α-ENaC ubiquitin-mediated degradation complex. These findings suggest that derlin-1 promotes ENaC ubiquitylation and enhances ENaC ubiquitin- mediated proteasome degradation. The derlin-1 pathway therefore may represent a significant early checkpoint in the recognition and degradation of ENaC in mammalian cells.
上皮钠通道（ENaC）的泛素化在细胞功能中起着关键作用，包括钠的跨膜转运、钠和水平衡以及血压稳定。已发表的研究表明，在酵母系统中，ENaC亚基是内质网相关降解（ERAD）的靶点。然而，蛋白酶体介导的ENaC亚基降解的分子机制仍有待确定。Derlin-1是一种E3连接酶介质，可将识别的靶蛋白与胞质溶胶中泛素介导的蛋白酶体降解联系起来。在本研究中，我们发现Derlin-1在蛋白质水平上抑制ENaC的表达，并且亚基α-ENaC（也称为SCNN1A）在膜锚定结构域或环区域与Derlin-1发生物理相互作用，并且Derlin-1启动α-ENaC的逆向转运。此外，内质网（ER）驻留的E3泛素连接酶HUWE1被招募并促进α-ENaC的K11连接的多聚泛素化，从而形成α-ENaC泛素介导的降解复合物。这些发现表明，Derlin-1促进ENaC泛素化并增强ENaC泛素介导的蛋白酶体降解。因此，Derlin-1途径可能代表了哺乳动物细胞中ENaC识别和降解的一个重要早期检查点。
