探討一去泛素酶藉由調控VPS34複合物進而促進細胞自噬之機轉

Abstract

細胞自噬為一演化上具保守性的細胞作用。藉由分解及回收細胞質中的物質，細胞自噬在維持細胞恆定及對抗環境壓力上扮演了不可或缺的角色。目前已有許多研究證實了泛素連接系統於調控細胞自噬作用的重要性，然而去泛素酶如何參與這條路徑尚未被透徹了解。在這篇研究中，我們發現一去泛素化酶可透過對細胞自噬中的關鍵因子VPS34脂質激酶執行去泛素化進而促進細胞自噬。藉由水解VPS34上所帶有以離胺酸29/48連接的異質泛素鏈，此去泛素酶能使VPS34免於被降解並穩定VPS34-VPS15-Beclin1複合物。更重要的是，我們的研究顯示了此去泛素酶不論在細胞養分充足狀態或養分缺乏所引發的壓力下與VPS34都有持續的交互作用並皆能促進細胞自噬，因而暗示了此去泛素酶在維持基礎水平的細胞自噬方面有一定的角色。此外，我們亦發現此去泛素酶和兩種分別與ATG14L或UVRAG結合的VPS34複合物皆有交互作用，且也調控了胞吞作用。綜觀來說，我們的研究指出此去泛素酶藉由去泛素化並穩定VPS34蛋白進而正向調控細胞自噬及胞吞作用。

Autophagy, an evolutionary conserved process, is pivotal for maintaining cell homeostasis and adapting to environmental stresses through degrading or recycling cytoplasmic components. While the involvement of E3-ubiquitin conjugation system in regulating autophagy was unveiled by various studies, how deubiquitinases (DUBs) participate in this process receives less attention. Here, we discovered that a promising deubiquitinase mediates autophagy induction through deubiquitinating VPS34, a lipid kinase that functions at nucleation stage. Through hydrolyzing Lys29/Lys48-linked heterotypic ubiquitin chains on VPS34, this deubiquitinase prevents degradation of VPS34 and concomitantly stabilizes VPS34-VPS15-Beclin1 complexes. Importantly, this deubiquitinase constitutively interacts with VPS34 to promote autophagy at both nutrient-rich and starved conditions, indicating its potential role in maintaining basal level of autophagy. In addition, further explorations indicate that this deubiquitinase interacts with both ATG14L and UVRAG-containing VPS34 complexes to modulates both autophagy and endocytic pathway. Together, this study revealed that this deubiquitinase positively regulates autophagic and endocytic pathways via deubiquitinating and stabilizing VPS34.