Cul3-KLHL20 泛素接合酶透過調控 ULK1 與 VPS34 複合體的降解來控制細胞自噬反應的終止

Cul3-KLHL20 ubiquitin ligase governs the turnover of ULK1 and VPS34 complexes to control autophagy termination

劉晉志(Chin-Chih Liu)

指導教授 ： 陳瑞華

國立臺灣大學/生命科學院/生化科學研究所/博士(2016年)

https://doi.org/10.6342/NTU201610307

摘要

當細胞面臨壓力時,會藉由細胞自噬反應降解胞內物質,以幫助細胞生存與 維持細胞及組織的恆定性。過去對細胞自噬的研究多聚焦於自噬的發生,對此過 程如何終止所知甚少。ULK1 是一個引發細胞自噬反應的絲氨酸/蘇氨酸蛋白激酶。 在本篇研究中我們發現 ULK1 是 Cul3-KLHL20 泛素接合酶的基質,在細胞自噬發 生後,KLHL20 會辨認被自我進行磷酸化修飾的 ULK1,對其進行泛素化修飾並造 成蛋白降解。因此,細胞自噬可以藉由引發 KLHL20 對 ULK1 的降解,來限制反應 的強度以及反應持續的時間。除了 ULK1 以外,在缺乏養分的環境下,細胞自噬反 應也會透過 KLHL20,直接或間接的造成 ATG13,VPS34,Beclin-1,以及 ATG14 蛋白的降解。因此,KLHL20 可以透過降解 ULK1 以及 VPS34 複合體的相關蛋白, 來促使細胞自噬反應的終止。在長期缺乏養分的環境下,若阻礙 KLHL20 對細胞 自噬的調控功能使反應無法終止,會造成細胞死亡的增加。另外,在小鼠的骨骼 肌中剔除 KLHL20 基因,則會加劇糖尿病所引發的肌肉萎縮。我們的研究發現了 KLHL20 在細胞自噬反應之終止以及病理上的重要性。

關鍵字

KLHL20 ； ULK1 ； Beclin-1 ； VPS34 ； 細胞自噬 ； 泛素化

並列摘要

Autophagy, a cellular self-eating mechanism, is important for maintaining cell survival and tissue homeostasis in various stressed conditions. Although the molecular mechanism of autophagy induction has been well studied, how cells terminate autophagy process remains elusive. Here, we show that ULK1, a serine/threonine kinase critical for autophagy initiation, is a substrate of the Cul3-KLHL20 ubiquitin ligase. Upon autophagy induction, ULK1 autophosphorylation facilitates its recruitment to KLHL20 for ubiquitination and proteolysis. This autophagy-stimulated, KLHL20-dependent ULK1 degradation restrains the amplitude and duration of autophagy. Additionally, KLHL20 governs the degradation of ATG13, VPS34, Beclin-1, and ATG14 in prolonged starvation through a direct or indirect mechanism. Impairment of KLHL20-mediated regulation of autophagy dynamics potentiates starvation-induced cell death and aggravates diabetes-associated muscle atrophy. Our study identifies a key role of KLHL20 in autophagy termination by controlling autophagy-dependent turnover of ULK1 and VPS34 complex subunits and reveals the pathophysiological functions of this autophagy termination mechanism.

並列關鍵字

KLHL20 ； ULK1 ； Beclin-1 ； VPS34 ； autophagy ； ubiquitination

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