Institute of Biochemistry, ETH Zürich, Switzerland.
EMBO J. 2012 Sep 12;31(18):3691-703. doi: 10.1038/emboj.2012.225. Epub 2012 Aug 10.
Autophagy is an intracellular trafficking pathway sequestering cytoplasm and delivering excess and damaged cargo to the vacuole for degradation. The Atg1/ULK1 kinase is an essential component of the core autophagy machinery possibly activated by binding to Atg13 upon starvation. Indeed, we found that Atg13 directly binds Atg1, and specific Atg13 mutations abolishing this interaction interfere with Atg1 function in vivo. Surprisingly, Atg13 binding to Atg1 is constitutive and not altered by nutrient conditions or treatment with the Target of rapamycin complex 1 (TORC1)-inhibitor rapamycin. We identify Atg8 as a novel regulator of Atg1/ULK1, which directly binds Atg1/ULK1 in a LC3-interaction region (LIR)-dependent manner. Molecular analysis revealed that Atg13 and Atg8 cooperate at different steps to regulate Atg1 function. Atg8 targets Atg1/ULK1 to autophagosomes, where it may promote autophagosome maturation and/or fusion with vacuoles/lysosomes. Moreover, Atg8 binding triggers vacuolar degradation of the Atg1-Atg13 complex in yeast, thereby coupling Atg1 activity to autophagic flux. Together, these findings define a conserved step in autophagy regulation in yeast and mammals and expand the known functions of LIR-dependent Atg8 targets to include spatial regulation of the Atg1/ULK1 kinase.
自噬是一种细胞内运输途径,它将细胞质隔离,并将多余和受损的货物输送到液泡中进行降解。Atg1/ULK1 激酶是核心自噬机制的一个必需组成部分,可能通过在饥饿时与 Atg13 结合而被激活。事实上,我们发现 Atg13 直接与 Atg1 结合,并且特异性的 Atg13 突变消除了这种相互作用,干扰了 Atg1 在体内的功能。令人惊讶的是,Atg13 与 Atg1 的结合是组成性的,不受营养条件或雷帕霉素(mTORC1 抑制剂)处理的影响。我们鉴定出 Atg8 是 Atg1/ULK1 的一种新的调节剂,它以 LC3 相互作用区域(LIR)依赖性的方式直接与 Atg1/ULK1 结合。分子分析表明,Atg13 和 Atg8 在不同的步骤合作来调节 Atg1 的功能。Atg8 将 Atg1/ULK1 靶向到自噬体,在那里它可能促进自噬体成熟和/或与液泡/溶酶体融合。此外,Atg8 结合触发酵母中 Atg1-Atg13 复合物的液泡降解,从而将 Atg1 活性与自噬通量偶联起来。总之,这些发现定义了酵母和哺乳动物中自噬调节的一个保守步骤,并将已知的 LIR 依赖性 Atg8 靶标的功能扩展到包括 Atg1/ULK1 激酶的空间调节。