ATG5 provides host protection acting as a switch in the atg8ylation cascade between autophagy and secretion

ATG5 is a part of the E3 ligase directing lipidation of ATG8 proteins, a process central to membrane atg8ylation and canonical autophagy. Loss of Atg5 in myeloid cells causes early mortality in murine models of tuberculosis. This in vivo phenotype is specific to ATG5. Here we show using human cell lines that absence of ATG5 but not of other ATGs directing canonical autophagy promotes lysosomal exocytosis and secretion of extracellular vesicles, and, in murine Atg5fl/fl LysM-Cre neutrophils, their excessive degranulation. This is due to lysosomal disrepair in ATG5 knockout cells and the sequestration by an alternative conjugation complex, ATG12-ATG3, of ESCRT protein ALIX which acts in membrane repair and exosome secretion. These findings reveal a previously undescribed function of ATG5 in its host-protective role in murine experimental models of tuberculosis and emphasize the significance of the branching aspects of the atg8ylation conjugation cascade beyond the canonical autophagy.

ATG5是E3连接酶的一部分，负责指导ATG8蛋白的脂化过程，这一过程对于膜atg8化及经典自噬途径至关重要。在髓系细胞中ATG5的缺失会导致小鼠结核病模型中的早期死亡。这一体内表型专属于ATG5。在本研究中，我们利用人细胞系证实，ATG5的缺失而非其他调控经典自噬的ATGs的缺失，促进了溶酶体外排及细胞外囊泡的分泌，并且在ATG5fl/fl LysM-Cre中性粒细胞中，导致了其过度脱颗粒。这一现象归因于ATG5敲除细胞中的溶酶体损伤以及由替代性共价复合物ATG12-ATG3捕获的ESCRT蛋白ALIX的隔离，该蛋白在膜修复及外泌体分泌中发挥作用。这些发现揭示了ATG5在宿主保护作用中在结核病小鼠实验模型中的先前未描述的功能，并强调了atg8化共价级联反应分支方面的意义，这一意义超越了经典自噬途径。