Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne 3000, Australia.
Department of Molecular Infection Biology, Helmholtz-Centre for Infection Research, 38124 Braunschweig, Germany.
Nat Microbiol. 2017 Jan 13;2:16258. doi: 10.1038/nmicrobiol.2016.258.
Cell death signalling pathways contribute to tissue homeostasis and provide innate protection from infection. Adaptor proteins such as receptor-interacting serine/threonine-protein kinase 1 (RIPK1), receptor-interacting serine/threonine-protein kinase 3 (RIPK3), TIR-domain-containing adapter-inducing interferon-β (TRIF) and Z-DNA-binding protein 1 (ZBP1)/DNA-dependent activator of IFN-regulatory factors (DAI) that contain receptor-interacting protein (RIP) homotypic interaction motifs (RHIM) play a key role in cell death and inflammatory signalling. RHIM-dependent interactions help drive a caspase-independent form of cell death termed necroptosis. Here, we report that the bacterial pathogen enteropathogenic Escherichia coli (EPEC) uses the type III secretion system (T3SS) effector EspL to degrade the RHIM-containing proteins RIPK1, RIPK3, TRIF and ZBP1/DAI during infection. This requires a previously unrecognized tripartite cysteine protease motif in EspL (Cys47, His131, Asp153) that cleaves within the RHIM of these proteins. Bacterial infection and/or ectopic expression of EspL leads to rapid inactivation of RIPK1, RIPK3, TRIF and ZBP1/DAI and inhibition of tumour necrosis factor (TNF), lipopolysaccharide or polyinosinic:polycytidylic acid (poly(I:C))-induced necroptosis and inflammatory signalling. Furthermore, EPEC infection inhibits TNF-induced phosphorylation and plasma membrane localization of mixed lineage kinase domain-like pseudokinase (MLKL). In vivo, EspL cysteine protease activity contributes to persistent colonization of mice by the EPEC-like mouse pathogen Citrobacter rodentium. The activity of EspL defines a family of T3SS cysteine protease effectors found in a range of bacteria and reveals a mechanism by which gastrointestinal pathogens directly target RHIM-dependent inflammatory and necroptotic signalling pathways.
细胞死亡信号通路有助于组织内稳态，并为免受感染提供先天保护。衔接蛋白，如受体相互作用丝氨酸/苏氨酸蛋白激酶 1（RIPK1）、受体相互作用丝氨酸/苏氨酸蛋白激酶 3（RIPK3）、TIR 结构域包含衔接子诱导干扰素-β（TRIF）和 Z-DNA 结合蛋白 1（ZBP1）/DNA 依赖性干扰素调节因子激活物（DAI），它们都含有受体相互作用蛋白（RIP）同源相互作用基序（RHIM），在细胞死亡和炎症信号中发挥关键作用。RHIM 依赖性相互作用有助于驱动一种称为坏死性凋亡的无胱天蛋白酶依赖性细胞死亡形式。在这里，我们报告肠道致病性大肠杆菌（EPEC）利用 III 型分泌系统（T3SS）效应蛋白 EspL 在感染过程中降解含有 RHIM 的蛋白质 RIPK1、RIPK3、TRIF 和 ZBP1/DAI。这需要 EspL 中以前未被识别的三部分半胱氨酸蛋白酶基序（Cys47、His131、Asp153），该基序在这些蛋白质的 RHIM 内切割。细菌感染和/或 EspL 的异位表达导致 RIPK1、RIPK3、TRIF 和 ZBP1/DAI 的快速失活，并抑制肿瘤坏死因子（TNF）、脂多糖或聚肌苷酸：聚胞苷酸（poly（I：C））诱导的坏死性凋亡和炎症信号。此外，EPEC 感染抑制 TNF 诱导的混合谱系激酶结构域样伪激酶（MLKL）的磷酸化和质膜定位。在体内，EspL 半胱氨酸蛋白酶活性有助于 EPEC 样鼠病原体鼠柠檬酸杆菌对小鼠的持续定植。EspL 半胱氨酸蛋白酶活性定义了一类存在于多种细菌中的 T3SS 半胱氨酸蛋白酶效应子，并揭示了胃肠道病原体直接靶向 RHIM 依赖性炎症和坏死性凋亡信号通路的机制。
