Laboratory of Biochemistry and Molecular Biology, Department of Medical Sciences, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki, 889-1692, Japan.
Department of Chemistry, Faculty of Sciences, Tadulako University, Kampus Bumi Tadulako Tondo, Palu, 94118, Indonesia.
Sci Rep. 2018 May 9;8(1):7317. doi: 10.1038/s41598-018-25724-x.
The maintenance of endoplasmic reticulum (ER) homeostasis is essential for cell function. ER stress-induced pre-emptive quality control (ERpQC) helps alleviate the burden to a stressed ER by limiting further protein loading. We have previously reported the mechanisms of ERpQC, which includes a rerouting step and a degradation step. Under ER stress conditions, Derlin family proteins (Derlins), which are components of ER-associated degradation, reroute specific ER-targeting proteins to the cytosol. Newly synthesized rerouted polypeptides are degraded via the cytosolic chaperone Bag6 and the AAA-ATPase p97 in the ubiquitin-proteasome system. However, the mechanisms by which ER-targeting proteins are rerouted from the ER translocation pathway to the cytosolic degradation pathway and how the E3 ligase ubiquitinates ERpQC substrates remain unclear. Here, we show that ERpQC substrates are captured by the carboxyl-terminus region of Derlin-1 and ubiquitinated by the HRD1 E3 ubiquitin ligase prior to degradation. Moreover, HRD1 forms a large ERpQC-related complex composed of Sec61α and Derlin-1 during ER stress. These findings indicate that the association of the degradation factor HRD1 with the translocon and the rerouting factor Derlin-1 may be necessary for the smooth and effective clearance of ERpQC substrates.
内质网（ER）稳态的维持对于细胞功能至关重要。内质网应激诱导的预先质量控制（ERpQC）有助于通过限制进一步的蛋白质加载来减轻应激内质网的负担。我们之前已经报道了 ERpQC 的机制，它包括重路由步骤和降解步骤。在 ER 应激条件下，内质网相关降解的组成部分 Derlin 家族蛋白（Derlins）将特定的 ER 靶向蛋白重路由到细胞质中。新合成的重路由多肽通过细胞质伴侣 Bag6 和泛素-蛋白酶体系统中的 AAA-ATPase p97 降解。然而，ER 靶向蛋白如何从 ER 易位途径重路由到细胞质降解途径，以及 E3 连接酶如何泛素化 ERpQC 底物仍不清楚。在这里，我们表明 ERpQC 底物被 Derlin-1 的羧基末端区域捕获，并在降解之前被 HRD1 E3 泛素连接酶泛素化。此外，HRD1 在 ER 应激期间形成一个由 Sec61α 和 Derlin-1 组成的大 ERpQC 相关复合物。这些发现表明，降解因子 HRD1 与易位体和重路由因子 Derlin-1 的结合对于 ERpQC 底物的顺利有效清除可能是必要的。
