Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Laboratory of Malaria Immunology, Immunology Frontier Research Centre, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Sci Rep. 2017 Mar 20;7:44795. doi: 10.1038/srep44795.
The evolutionarily conserved processes of endosome-lysosome maturation and macroautophagy are established mechanisms that limit survival of intracellular bacteria. Similarly, another emerging mechanism is LC3-associated phagocytosis (LAP). Here we report that an intracellular vacuolar pathogen, Legionella dumoffii, is specifically targeted by LAP over classical endocytic maturation and macroautophagy pathways. Upon infection, the majority of L. dumoffii resides in ER-like vacuoles and replicate within this niche, which involves inhibition of classical endosomal maturation. The establishment of the replicative niche requires the bacterial Dot/Icm type IV secretion system (T4SS). Intriguingly, the remaining subset of L. dumoffii transiently acquires LC3 to L. dumoffii-containing vacuoles in a Dot/Icm T4SS-dependent manner. The LC3-decorated vacuoles are bound by an apparently undamaged single membrane, and fail to associate with the molecules implicated in selective autophagy, such as ubiquitin or adaptors. The process requires toll-like receptor 2, Rubicon, diacylglycerol signaling and downstream NADPH oxidases, whereas ULK1 kinase is dispensable. Together, we have discovered an intracellular pathogen, the survival of which in infected cells is limited predominantly by LAP. The results suggest that L. dumoffii is a valuable model organism for examining the mechanistic details of LAP, particularly induced by bacterial infection.
内体溶酶体成熟和巨自噬的进化保守过程是限制细胞内细菌存活的既定机制。同样，另一种新兴机制是 LC3 相关吞噬作用 (LAP)。在这里，我们报告了一种细胞内液泡病原体，军团菌 dumoffii，通过 LAP 而不是经典的内吞成熟和巨自噬途径被特异性靶向。感染后，大多数军团菌 dumoffii 存在于 ER 样液泡中，并在这个小生境中复制，这涉及到经典内体成熟的抑制。复制小生境的建立需要细菌的 Dot/Icm 型 IV 型分泌系统 (T4SS)。有趣的是，其余部分的军团菌 dumoffii 以依赖 Dot/Icm T4SS 的方式瞬时获得 LC3 到军团菌 dumoffii 包含的液泡。LC3 修饰的液泡被显然未受损的单个膜结合，并且不能与参与选择性自噬的分子，如泛素或衔接子结合。该过程需要 Toll 样受体 2、Rubicon、二酰基甘油信号和下游 NADPH 氧化酶，而 ULK1 激酶是可有可无的。总之，我们发现了一种细胞内病原体，其在感染细胞中的存活主要受到 LAP 的限制。结果表明，军团菌 dumoffii 是研究 LAP 机制细节的有价值的模式生物，特别是由细菌感染诱导的 LAP。
