Mycobacterium tuberculosis (Mtb), as an important intracellular pathogen, can invade and survive in macrophages and is capable of escaping the clearance of immune system. Despite decades of research efforts, the precise mechanism of immune escape and the virulence factors encoded by Mtb involved remain to be explored. Mtb-specific genomic regions of deletion (RD)-encoded proteins and PE/PPE family proteins have been implicated in immune evasion. Here, we screened more than forty RD-encoded proteins which might be involved in facilitating bacterial survival in macrophages, and found that a Mtb PPE68/Rv3873 protein, encoded by Mtb-RD1, is essential for efficient Mtb intracellular survival in macrophages. In terms of mechanism, we found that the ubiquitin ligase (E3) Makorin Ring Finger Protein 1 (MKRN1) of macrophage interacted with PPE68 and promoted the attachment of lysine (K)-63-linked ubiquitin chains to the K166 site of PPE68. K63-ubiquitination of PPE68 further bound src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1) to suppress K63-linked polyubiquitin chains of tumor necrosis factor receptor-associated factor 6 (TRAF6), and then remarkably suppressed TRAF6-driven NF-κB and AP-1 signaling and TNF-α, IL-6 and NO production. We demonstrate that the K63-linked ubiquitination of PPE68 by MKRN1 contributed to the PPE68-mediated mycobacterial immune escape. Our finding identifies a previously unrecognized mechanism by which host MKRN1-mediated-ubiquitination of mycobacterial PPE protein suppresses innate immune responses. Disturbing the interaction between host MKRN1 ubiquitin system and mycobacterial PPE protein might be a potential therapeutic target for tuberculosis.

中文翻译：

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宿主 MKRN1 介导的分枝杆菌 PPE 蛋白泛素化抑制先天免疫反应。

结核分枝杆菌（Mtb）作为一种重要的细胞内病原体，可以侵入并在巨噬细胞中生存，并且能够逃避免疫系统的清除。尽管经过数十年的研究努力，免疫逃逸的精确机制和结核分枝杆菌编码的毒力因子仍有待探索。Mtb 特异性基因组区域的缺失 (RD) 编码蛋白和 PE/PPE 家族蛋白与免疫逃避有关。在这里，我们筛选了四十多种可能参与促进巨噬细胞中细菌存活的RD编码蛋白，并发现由Mtb-RD1编码的Mtb PPE68/Rv3873蛋白对于Mtb在巨噬细胞中的有效胞内存活至关重要。在机制方面，我们发现巨噬细胞的泛素连接酶（E3）Makorin环指蛋白1（MKRN1）与PPE68相互作用，促进赖氨酸（K）-63连接的泛素链附着到PPE68的K166位点。PPE68 的 K63 泛素化进一步结合含有 src 同源 2 结构域的蛋白酪氨酸磷酸酶 1 (SHP1)，抑制肿瘤坏死因子受体相关因子 6 (TRAF6) 的 K63 连接的多聚泛素链，然后显着抑制 TRAF6 驱动的 NF-κB AP-1 信号传导和 TNF-α、IL-6 和 NO 产生。我们证明 MKRN1 对 PPE68 的 K63 连接泛素化有助于 PPE68 介导的分枝杆菌免疫逃逸。我们的发现确定了一种以前未被认识的机制，宿主 MKRN1 介导的分枝杆菌 PPE 蛋白泛素化可抑制先天免疫反应。干扰宿主 MKRN1 泛素系统和分枝杆菌 PPE 蛋白之间的相互作用可能是结核病的潜在治疗靶点。