Kishi-Itakura Chieko, Ktistakis Nicholas T, Buss Folma
Cambridge Institute for Medical Research, Keith Peters Building, University of Cambridge, Cambridge, UK.
Signalling Programme, Babraham Institute, Cambridge, UK.
Traffic. 2020 Apr;21(4):310-323. doi: 10.1111/tra.12723. Epub 2020 Mar 4.
Autophagy defends cells against proliferation of bacteria such as Salmonella in the cytosol. After escape from a damaged Salmonella-containing vacuole (SCV) exposing luminal glycans that bind to Galectin-8, the host cell ubiquitination machinery deposits a dense layer of ubiquitin around the cytosolic bacteria. The nature and spatial distribution of this ubiquitin coat in relation to other autophagy-related membranes are unknown. Using transmission electron microscopy, we determined the exact localisation of ubiquitin, the ruptured SCV membrane and phagophores around cytosolic Salmonella. Ubiquitin was not predominantly present on the Salmonella surface, but enriched on the fragmented SCV. Cytosolic bacteria without SCVs were less efficiently targeted by phagophores. Single bacteria were contained in single phagophores but multiple bacteria could be within large autophagic vacuoles reaching 30 μm in circumference. These large phagophores followed the contour of the engulfed bacteria, they were frequently in close association with endoplasmic reticulum membranes and, within them, remnants of the SCV were seen associated with each engulfed particle. Our data suggest that the Salmonella SCV has a major role in the formation of autophagic phagophores and highlight evolutionary conserved parallel mechanisms between xenophagy and mitophagy with the fragmented SCV and the damaged outer mitochondrial membrane serving similar functions.
自噬可保护细胞抵御诸如胞质中的沙门氏菌等细菌的增殖。在沙门氏菌从含有受损沙门氏菌的液泡（SCV）中逸出后，暴露于与半乳糖凝集素-8结合的腔内聚糖，宿主细胞泛素化机制在胞质细菌周围沉积一层致密的泛素。这种泛素包被相对于其他自噬相关膜的性质和空间分布尚不清楚。我们使用透射电子显微镜确定了泛素、破裂的SCV膜和胞质沙门氏菌周围吞噬泡的确切定位。泛素并非主要存在于沙门氏菌表面，而是富集于破碎的SCV上。没有SCV的胞质细菌被吞噬泡靶向的效率较低。单个细菌被单个吞噬泡包裹，但多个细菌可能存在于周长达到30μm的大型自噬泡内。这些大型吞噬泡沿着被吞噬细菌的轮廓分布，它们经常与内质网膜紧密相连，并且在其中，可以看到SCV的残余物与每个被吞噬颗粒相关联。我们的数据表明，沙门氏菌SCV在自噬吞噬泡的形成中起主要作用，并突出了异噬和线粒体自噬之间进化保守的平行机制，其中破碎的SCV和受损的线粒体外膜发挥类似的功能。
