ESX Secretion-Associated Protein C From Mycobacterium tuberculosis Induces Macrophage Activation Through the Toll-Like Receptor-4/Mitogen-Activated Protein Kinase Signaling Pathway
ESX Secretion-Associated Protein C From Mycobacterium tuberculosis Induces Macrophage Activation Through the Toll-Like Receptor-4/Mitogen-Activated Protein Kinase Signaling Pathway
复制标题
来自结核分枝杆菌的 ESX 分泌相关蛋白 C 通过 Toll 样受体 4/丝裂原激活蛋白激酶信号通路诱导巨噬细胞激活
DOI：
10.3389/fcimb.2019.00158
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发表时间：
2019-05-10
影响因子：
5.7
通讯作者：
Zhang, Xuelian
中科院分区：
文献类型：
--
作者：
Guo, Qinglong;Bi, Jing;Zhang, Xuelian
结核分枝杆菌作为一种兼性胞内致病菌，可与宿主巨噬细胞相互作用，调节巨噬细胞功能，从而影响天然免疫和获得性免疫。由ESX-1分泌系统分泌的蛋白质参与这种关系。尽管ESX-1在宿主-病原体相互作用和毒力中的重要性是众所周知的，但在分枝杆菌发病机制中的主要作用归因于EsxA（EAST-6），并且病原体和巨噬细胞之间相互作用中的单个组分的功能仍不清楚。在这里，我们研究了EspC对巨噬细胞活化的影响。EspC蛋白由espA/C/D簇编码，其不与esx-1基因座相连，但对于ESX-1、EsxA和EsxB的主要毒力因子的分泌是必需的。我们的结果表明，在M.丝裂霉素诱导促炎细胞因子并增强表面标志物表达。这种机制依赖于Toll样受体4（TLR 4），如使用来自TLR 4 −/−小鼠的EspC处理的巨噬细胞所证明的，导致与野生型小鼠相比，促炎细胞因子分泌和表面标志物表达减少。免疫沉淀和免疫荧光实验表明EspC与TLR 4直接相互作用。此外，EspC还可通过诱导丝裂原活化蛋白激酶（MAPK）磷酸化和核因子-κB活化，激活巨噬细胞，促进抗原提呈。当巨噬细胞用抗TLR 4抗体阻断或用MAPK抑制剂预处理时，EspC诱导的细胞因子表达、表面标志物上调和MAPK信号传导激活被抑制。此外，我们的研究结果表明，EspC过表达增强了M.巨噬细胞内和应激条件下的smeglobulin。综上所述，我们的研究结果表明，EspC可能是另一种ESX-1毒力因子，不仅通过TLR 4依赖性MAPK信号转导激活巨噬细胞来调节宿主先天免疫应答，而且在宿主细胞中致病性分枝杆菌的存活中起重要作用。
Mycobacterium tuberculosis, as a facultative intracellular pathogen, can interact with host macrophages and modulate macrophage function to influence innate and adaptive immunity. Proteins secreted by the ESX-1 secretion system are involved in this relationship. Although the importance of ESX-1 in host-pathogen interactions and virulence is well-known, the primary role is ascribed to EsxA (EAST-6) in mycobacterial pathogenesis and the functions of individual components in the interactions between pathogens and macrophages are still unclear. Here, we investigated the effects of EspC on macrophage activation. The EspC protein is encoded by an espA/C/D cluster, which is not linked to the esx-1 locus, but is essential for the secretion of the major virulence factors of ESX-1, EsxA and EsxB. Our results showed that both EspC protein and EspC overexpression in M. smegmatis induced pro-inflammatory cytokines and enhanced surface marker expression. This mechanism was dependent on Toll-like receptor 4 (TLR4), as demonstrated using EspC-treated macrophages from TLR4−/− mice, leading to decreased pro-inflammatory cytokine secretion and surface marker expression compared with those from wild-type mice. Immunoprecipitation and immunofluorescence assays showed that EspC interacted with TLR4 directly. Moreover, EspC could activate macrophages and promote antigen presentation by inducing mitogen-activated protein kinase (MAPK) phosphorylation and nuclear factor-κB activation. The EspC-induced cytokine expression, surface marker upregulation, and MAPK signaling activation were inhibited when macrophages were blocked with anti-TLR4 antibodies or pretreated with MAPK inhibitors. Furthermore, our results showed that EspC overexpression enhanced the survival of M. smegmatis within macrophages and under stress conditions. Taken together, our results indicated that EspC may be another ESX-1 virulence factor that not only modulates the host innate immune response by activating macrophages through TLR4-dependent MAPK signaling but also plays an important role in the survival of pathogenic mycobacteria in host cells.