School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
Biochem Biophys Res Commun. 2018 May 15;499(3):635-641. doi: 10.1016/j.bbrc.2018.03.202. Epub 2018 Mar 31.
Nascent cargo proteins in the endoplasmic reticulum are transported to the Golgi by COPII carriers. Typical COPII vesicles are 60-70 nm in diameter, and much larger macromolecules, such as procollagen, are transported by atypical large COPII carriers in mammalian cells. The formation of large COPII carriers is enhanced by Cul3 ubiquitin ligase, which mono-ubiquitinates Sec31A, a COPII coat protein. However, the deubiquitinating enzyme for Sec31A was unclear. Here, we show that the deubiquitinating enzyme USP8 interacts with and deubiquitinates Sec31A. The interaction was mediated by the adaptor protein STAM1. USP8 overexpression inhibited the formation of large COPII carriers. By contrast, USP8 knockdown caused the accumulation of COPII coat proteins around the cis-Golgi, promoted the intracellular trafficking of procollagen IV from the endoplasmic reticulum to the Golgi, and increased collagen IV secretion. We concluded that USP8 deubiquitinates Sec31A and inhibits the formation of large COPII carriers, thereby suppressing collagen IV secretion.
内质网中新生的货物蛋白通过 COPII 载体运输到高尔基体。典型的 COPII 小泡直径为 60-70nm，而在哺乳动物细胞中，较大的大分子，如前胶原，是通过非典型的大 COPII 载体运输的。Cul3 泛素连接酶增强了大 COPII 载体的形成，该酶对 COPII 外壳蛋白 Sec31A 进行单泛素化。然而，Sec31A 的去泛素化酶尚不清楚。在这里，我们表明去泛素化酶 USP8 与 Sec31A 相互作用并使其去泛素化。这种相互作用是由衔接蛋白 STAM1 介导的。USP8 的过表达抑制了大 COPII 载体的形成。相比之下，USP8 的敲低导致 COPII 外壳蛋白在顺式高尔基体周围积累，促进了前胶原 IV 从内质网到高尔基体的细胞内运输，并增加了胶原 IV 的分泌。我们得出结论，USP8 去泛素化 Sec31A 并抑制大 COPII 载体的形成，从而抑制胶原 IV 的分泌。
