ABSTRACT

As one of the major, highly conserved catabolic pathways, autophagy delivers cytosolic components to lysosomes for degradation. It is essential for development, cellular homeostasis, and coping with stress. Reduced autophagy increases susceptibility to protein aggregation diseases and leads to phenotypes associated with aging. Of the three major forms of autophagy, macroautophagy (MA) can degrade organelles or aggregated proteins, and chaperone-mediated autophagy is specific for soluble proteins containing KFERQ-related targeting motifs. During endosomal microautophagy (eMI), cytoplasmic proteins are engulfed into late endosomes in an ESCRT machinery-dependent manner. eMI can be KFERQ-specific or occur in bulk and be induced by prolonged starvation. Its physiological regulation and function, however, are not understood. Here, we show that eMI in the Drosophila fat body, akin to the mammalian liver, is induced upon oxidative or genotoxic stress in an ESCRT and partially Hsc70-4-dependent manner. Interestingly, eMI activation is selective, as ER stress fails to elicit a response. Intriguingly, we find that reducing MA leads to a compensatory enhancement of eMI, suggesting a tight interplay between these degradative processes. Furthermore, we show that mutations in DNA damage response genes are sufficient to trigger eMI and that the response to oxidative stress is under the control of MAPK/JNK signaling. Our data suggest that, controlled by various signaling pathways, eMI allows an organ to react and adapt to specific types of stress and is thus likely critical to prevent disease.

Abbreviations: Atg: autophagy-related; CMA: chaperone-mediated autophagy; DDR: DNA damage repair; Df: deficiency (deletion); (E)GFP: (enhanced) green fluorescent protein; eMI: endosomal microautophagy; ER: endoplasmatic reticulum; ESCRT: endosomal sorting complexes required for transport; Eto: etoposide; FLP: flipase; Hsc: heat shock cognate protein; LAMP2A: lysosomal-associated membrane protein 2A; LE: late endosome; MA: macroautophagy; MI: microautophagy; MVB: multivesicular body; PA: photoactivatable; Para: paraquat; ROS: reactive oxygen species; SEM: standard error of means; Tor: target of rapamycin [serine/threonine kinase]; UPR: unfolded protein response; Vps: vacuolar protein sorting.

 抽象的

作为主要的、高度保守的分解代谢途径之一，自噬将胞质成分递送至溶酶体进行降解。它对于发育、细胞稳态和应对压力至关重要。自噬减少会增加对蛋白质聚集疾病的易感性，并导致与衰老相关的表型。在自噬的三种主要形式中，巨自噬 (MA) 可以降解细胞器或聚集蛋白，伴侣介导的自噬对含有 KFERQ 相关靶向基序的可溶性蛋白具有特异性。在内体微自噬 (eMI) 过程中，细胞质蛋白以 ESCRT 机制依赖性方式被吞噬到晚期内体中。 eMI 可以是 KFERQ 特异性的，也可以大量发生并由长期饥饿诱导。然而，其生理调节和功能尚不清楚。在这里，我们表明果蝇脂肪体中的 eMI（类似于哺乳动物肝脏）是在氧化或基因毒性应激下以 ESCRT 和部分 Hsc70-4 依赖的方式诱导的。有趣的是，eMI 激活是有选择性的，因为 ER 应激无法引起反应。有趣的是，我们发现减少 MA 会导致 eMI 的补偿性增强，这表明这些降解过程之间存在紧密的相互作用。此外，我们表明 DNA 损伤反应基因的突变足以触发 eMI，并且对氧化应激的反应受到 MAPK/JNK 信号传导的控制。我们的数据表明，在各种信号通路的控制下，eMI 允许器官对特定类型的压力做出反应并适应，因此可能对预防疾病至关重要。

缩写： Atg ：自噬相关； CMA：分子伴侣介导的自噬； DDR：DNA损伤修复； Df：缺乏（删除）； (E)GFP：（增强型）绿色荧光蛋白； eMI：内体微自噬； ER：内质网； ESCRT：运输所需的内体分选复合物； Eto：依托泊苷； FLP: 翻转酶； Hsc：热休克同源蛋白； LAMP2A：溶酶体相关膜蛋白2A； LE：晚期内体； MA：巨自噬； MI：微自噬； MVB：多泡体； PA：可光活化；对位：百草枯； ROS：活性氧； SEM：平均值的标准误差； Tor：雷帕霉素[丝氨酸/苏氨酸激酶]的靶标； UPR：未折叠蛋白反应； Vps：液泡蛋白质分选。