宿主蛋白Syk在结核杆菌阻断宿主吞噬溶酶体融合中的作用及机制研究

As one of the most successful human pathogens, Mycobacterium tuberculosis (Mtb) has developed plethora strategies to counteract the bactericidal activities of the host macrophages. One of them is blocking the transfer of phagosomes containing Mtb to lysosomes directly or through the autophagy pathway. Both pathways are important for host immune responses to Mtb infections. During this blocking process, Mtb hijacks some host proteins besides of itself virulence factors. A key question to be addressed in this proposal is whether we can restore lysosome fusion to Mtb-containing phagosomes despite the presence of these virulence factors. Spleen tyrosine kinase (Syk) mediates the intracellular trafficking in immune cells. In macrophages infected with fungal and malarial pathogens, Syk is required in recruiting autophagy to phagosomes in the fungal and malarial-infected macrophages. In stark contrast and to our surprise, we found that inhibition of Syk restored phagosomes-lysosome fusion in Mtb-infected macrophages. Based on this preliminary result, we hypothesized that Syk play an active role in facilitating the ability of Mtb to block phagosomes-lysosome fusion. To verify the hypothesis, we will 1) determine whether Syk play a key role in blocking phagosomes-lysosome fusion, 2) explore whether the underlying mechanism for such blocking effect by Syk is mediated by the ability of Syk to phosphorylate a host phagosomal protein, and finally 3) investigate the functional significance of Syk activity during Mtb infections. Our proposal will show a new facet of counteracting host defending and might help to develop novel therapeutic strategy based on targeting Syk kinase.

结核分枝杆菌（Mtb）在细胞内存活的一个重要方式是直接或通过细胞自噬阻断含Mtb的吞噬体与溶酶体的融合。在此过程中，Mtb除了利用自身的毒力因子，也需要宿主蛋白的参与。本项目要研究的关键问题是即便存在这些毒力因子，是否也可以恢复吞噬体与溶酶体的融合。Syk（Spleen tyrosine kinase）调控免疫细胞内的物质运输，在真菌和疟疾感染的巨噬细胞中，对自噬体募集到吞噬体是必需的。然而我们发现加入Syk抑制剂恢复了Mtb感染的细胞中吞噬溶酶体的融合。因此我们推测Syk可能有助于Mtb阻断吞噬溶酶体的融合。为证实我们的推测，本研究拟利用细胞和分子生物学技术确定Syk是否参与Mtb阻断溶酶体融合，分析其是否通过调控与吞噬溶酶体相关蛋白的磷酸化来实现，最后分析Syk在Mtb感染中的意义。对该机制的探索将展现一个新的Mtb拮抗宿主防御的机制，有利于开发新的基于靶向Syk来治疗结核病的策略。