沙门菌致病岛2 Ⅲ型分泌系统研究进展

沙门菌(Salmonella)是革兰氏阴性的兼性胞内菌,可引起其广泛宿主的一系列疾病,严重时可导致全身性感染,威胁生命安全。沙门菌致病岛2(SPI2)是与沙门菌全身性感染密切相关的重要毒力基因簇,其编码的Ⅲ型分泌系统2(T3SS2)在沙门菌侵入宿主细胞后开始组装合成,经该装置分泌的多种效应蛋白对沙门菌在宿主细胞内的生存和增殖起着重要作用。近些年来,与沙门菌T3SS2相关的研究一直都是病原微生物领域关注的焦点之一。本文简要综述了SPI2的基因特征、SPI2基因表达的调控、T3SS2的结构和组成、T3SS2的效应蛋白及与T3SS2相关的疫苗研究等方面的主要研究进展。     

沙门菌毒力岛引发持续性感染机制的研究进展

沙门菌是一种重要的人兽共患食源性病原菌。其感染宿主后可以凭借独特的免疫逃逸机制逃避宿主免疫系统的清除,潜伏在宿主体内1年至终身不等,从而建立持续性感染。沙门菌持续性感染与毒力岛密切相关,尤其是沙门菌毒力岛（Salmonella pathogenicity islands,SPIs） SPI-1和SPI-2。SPI-1效应蛋白SipB和SipC等以不同的途径影响细菌入侵,诱导细胞自噬或者凋亡;而SPI-2效应蛋白SseI和SseL等可以通过调控不同的信号通路协助沙门菌的胞内存活,为沙门菌持续性感染的发生和发展提供条件。本文主要阐述SipB和SseI等毒力岛效应蛋白在沙门菌持续性感染过程中的作用,同时总结了SPI-6、SPI-7和SPI-19等毒力岛的作用,以期为研究沙门菌持续性感染提供新思路。     

胞内菌与细胞骨架

许多病毒微生物能侵入人体细胞,在囊泡或胞质中增殖,并导致疾病。细胞骨架在该过程中发挥着中心作用,一些特殊蛋白及信号传递系统也至关重要。本文就胞内菌进入宿主细胞的两个机制：“拉链”和“触发”机制,胞内菌在宿主细胞内肌动蛋白依赖性的运动等方面进行综述。     

沙门菌毒力效应蛋白对宿主NF-κB信号通路的调控

沙门菌(Salmonella)通过向宿主细胞分泌毒力效应蛋白(effector protein)来调控细胞内一系列的信号传导通路,从而有利于沙门菌的侵染和繁殖。NF-κB信号通路在宿主对病原菌的炎症反应及免疫应答中发挥着重要的作用,也是很多毒力效应蛋白调控的靶点。沙门菌致病岛(Salmonella pathogenicity island,SPI)-1上的毒力效应蛋白Sip A、Sop E、Sop E2和Sop B都能激活宿主细胞的NF-κB信号通路,而毒力效应蛋白Spt P、Avr A、Ssp H1以及SPI-2上的Sse L能有效地抑制NF-κB信号通路。研究这些毒力效应蛋白对NF-κB信号通路的时相调控和协同作用,将进一步揭示沙门菌的致病机制。     

沙门菌对酸压力的应答及其与毒力的关系

沙门菌(Salmonella spp.)作为肠道细菌,必须克服胃中酸性环境,才能进一步入侵宿主肠道上皮细胞。已有的研究表明,沙门菌通过进化出多种应答机制,增强自身在酸性环境下的生存。本文回顾了沙门菌的耐酸特性,阐述了抵御酸压力时的几种应答机理,包括胞内pH的维持、调控酸激蛋白的时序表达以及细胞膜特性的改变。这些研究对人类了解和控制沙门菌的感染具有重要的指导意义。     

沙门菌侵袭研究进展

鼠伤寒沙门菌表达两个不同的Ⅲ型分泌系统(typeⅢsecretion/translocation systems, TTSS),分别由致病岛1和2(pathogenicityi slands 1 and 2, SPI-1 and SPI-2)编码。细菌依赖TTSS将效应蛋白转运至宿主细胞,通过“触发”机制诱导细菌进入宿主细胞。这些效应蛋白可诱导细胞骨架重排,导致“巨吞饮”,促使细菌入侵。本综述依据多种沙门菌效应蛋白的功能,建立沙门菌侵袭模型。TTSS活化并转运效应蛋白进入宿主细胞发挥功能(Ⅰ)。小G蛋白交换因子SopE和肌醇磷酸酯酶SopB通过激活CDC42和Rac1,诱导内陷相关的蛋白聚集(Ⅱ)。SipA和SipC通过降低肌动蛋白临界浓度、刺激网素成束、稳定纤维状肌动蛋白(fibrousactin, F-actin)以及使肌动蛋白核化等功能,促使细菌入侵(Ⅲ)。SopB可使膜内陷区PIP2的浓度降低以及VAMP8聚集,促使细胞膜分裂(Ⅳ)。这些效应蛋白的联合作用,使膜皱褶在局部向外显著延伸,使沙门菌被细胞内形成的特殊膜结构包裹。沙门菌的另一种效应蛋白SptP,通过刺激小G蛋白内源性GTPase的活性,抑制小G蛋白的活化,使细胞膜恢复至原有状态(Ⅴ)。     

茄科雷尔氏菌的蛋白分泌系统及其特征

茄科雷尔氏菌利用自身的分泌系统能向胞外分泌上百种蛋白, 其中Ⅱ型和Ⅲ型分泌系统通过不同机制将分泌蛋白靶定到胞外或宿主细胞, 是决定茄科雷尔氏菌对宿主产生致病性的主要因素。其中Ⅲ型分泌系统不依赖Sec信号转导系统但必须依赖于宿主细胞的识别激活, 并在病原菌对宿主细胞的特异性识别和细菌在宿主细胞的生长增殖中发挥功能。到目前为止, 已经从茄科雷尔氏菌的GMI1000株系中鉴定出两类在宿主细胞中存在靶标, 并由Ⅲ型分泌系统分泌的效应蛋白Pop2和Gala蛋白家族。主要就茄科雷尔氏菌Ⅲ型分泌系统的基本特征以及效应蛋白及其宿主靶标的相互作用进行综述。     

细菌侵入宿主细胞的分子基础

本文对细菌侵入宿主细胞时所涉及的分子间相互作用进行了简要综述,概述了耶氏菌、肠致病性大肠杆菌、产单核细胞李氏菌、沙门菌及志贺菌等侵入哺乳动物细胞时相关分子的性质、结构与功能,并对宿主细胞上的受体分子进行了分析。     

禽沙门菌诱导宿主免疫应答的特性

沙门菌病(Salmonellosis)是全世界最普遍的食源性疾病之一,不仅对养殖业造成经济损失,还对人类安全构成威胁。禽沙门菌感染肠道后,可诱导肠上皮细胞表达多种TLRs和炎症反应的发生,在分泌的趋化因子作用下免疫效应细胞迁移到感染部位。细菌通过肠上皮细胞屏障后被巨噬细胞或树突状细胞吞噬,其中巨噬细胞是沙门菌的主要定殖场所。天然免疫系统将抗原递呈给淋巴细胞后,机体能够在2–3周内通过以Th1为主的免疫应答清除在肠道和深层组织中的沙门菌。而宿主特异性血清型鸡白痢沙门菌从肠道侵入后,在肝脾和其他器官中定殖,进而引发全身感染。早期感染阶段不会引起肠道炎症反应,主要诱导以Th2为主的免疫应答,而Th1型应答相对较弱,有利于鸡白痢沙门菌在机体内的持续存在和感染。本文围绕禽沙门菌的致病机理和免疫应答特性进行阐述,尤其对鸡白痢沙门菌免疫逃逸和持续载菌的特性进行深入分析,为禽沙门菌病的防控提供新靶标和新见解。     

SipC的C端能结合并促使纤维型肌动蛋白成束从而促进鼠伤寒沙门菌入侵

鼠伤寒沙门菌通过效应蛋白注入,利用宿主细胞的肌动蛋白骨架网络入侵非吞噬细胞。已知SipC能使肌动蛋白成核,使纤维型肌动蛋白成束,并转运鼠伤寒沙门菌Ⅲ型分泌系统的效应蛋白。但SipC如何使纤维型肌动蛋白成束的分子机制及发挥此活性功能域的作用仍不清楚。该研究利用一系列SipC删除/插入突     

Involvement of TIP60 acetyltransferase in intracellular <Emphasis Type="Italic">Salmonella</Emphasis>replication

Background  

Salmonella enterica is a facultative intracellular pathogen that replicates within a membrane-bound compartment termed Salmonella containing vacuole (SCV). The biogenesis of SCV requires Salmonella type III protein secretion/translocation system and their effector proteins which are translocated into host cells to exploit the vesicle trafficking pathways. SseF is one of these effectors required for SCV formation and Intracellular Salmonella replication through unknown mechanisms.     

Diversity of bacterial manipulation of the host ubiquitin pathways

Ubiquitination is generally considered as a eukaryotic protein modification, which is catalysed by a three‐enzyme cascade and is reversed by deubiquitinating enzymes. Ubiquitination directs protein degradation and regulates cell signalling, thereby plays key roles in many cellular processes including immune response, vesicle trafficking and cell cycle. Bacterial pathogens inject a series of virulent proteins, named effectors, into the host cells. Increasing evidence suggests that many effectors hijack the host ubiquitin pathways to benefit bacterial infection. This review summarizes the known functions and mechanisms of effectors from human bacterial pathogens including enteropathogenic Escherichia coli, Salmonella, Shigella, Chlamydia and Legionella, highlighting the diversity in their mechanisms for manipulating the host ubiquitin pathways. Many effectors adopt the molecular mimicry strategy to harbour similar structures or functional motifs with those of the host E3 ligases and deubiquitinases. On the other hand, a few of effectors evolve novel structures or new enzymatic activities to modulate various steps of the host ubiquitin pathways. The diversity in the mechanisms enhances the efficient exploitation of the host ubiquitination signalling by bacteria.     

Salmonella exploits host Rho GTPase signalling pathways through the phosphatase activity of SopB

Salmonella uses Type 3 secretion systems (T3SSs) to deliver virulence factors, called effectors, into host cells during infection. The T3SS effectors promote invasion into host cells and the generation of a replicative niche. SopB is a T3SS effector that plays an important role in Salmonella pathogenesis through its lipid phosphatase activity. Here, we show that SopB mediates the recruitment of Rho GTPases (RhoB, RhoD, RhoH, and RhoJ) to bacterial invasion sites. RhoJ contributes to Salmonella invasion, and RhoB and RhoH play an important role in Akt activation. R‐Ras1 also contributes to SopB‐dependent Akt activation by promoting the localised production of PI(3,4)P₂/PI(3,4,5)P₃. Our studies reveal new signalling factors involved in SopB‐dependent Salmonella infection.     

Formin‐mediated actin polymerization promotes Salmonella invasion

Salmonella invade host cells using Type 3 secreted effectors, which modulate host cellular targets to promote actin rearrangements at the cell surface that drive bacterial uptake. The Arp2/3 complex contributes to Salmonella invasion but is not essential, indicating other actin regulatory factors are involved. Here, we show a novel role for FHOD1, a formin family member, in Salmonella invasion. FHOD1 and Arp2/3 occupy distinct microdomains at the invasion site and control distinct aspects of membrane protrusion formation. FHOD1 is phosphorylated during infection and this modification is required for promoting bacterial uptake by host cells. ROCK II, but not ROCK I, is recruited to the invasion site and is required for FHOD1 phosphorylation and for Salmonella invasion. Together, our studies revealan important phospho‐dependent FHOD1 actin polymerization pathway in Salmonella invasion.     

Intracellular Salmonella metabolism

Growth of Salmonella inside infected host cells is a key aspect of their ability to cause local enteritis or systemic disease. This growth depends on exploitation of host nutrients through a large Salmonella metabolism network with hundreds of metabolites and enzymes. Studies in cell culture infection models are unravelling more and more of the underlying molecular and cellular mechanisms but also show striking Salmonella metabolic plasticity depending on host cell line and experimental conditions. In vivo studies have revealed a qualitatively diverse, but quantitatively poor, host‐Salmonella nutritional interface, which on one side makes Salmonella fitness largely resilient against metabolic perturbations, but on the other side severely limits Salmonella biomass generation and growth rates. This review discusses goals and techniques for studying Salmonella intracellular metabolism, summarises main results and implications, and proposes key issues that could be addressed in future studies.     

Unveiling ubiquitinome rearrangements induced by Salmonella infection

Ubiquitination plays a critical role in the activation of host immune responses to infection and serves as a signal for pathogen delivery to phagophores along the xenophagy pathway. We recently performed systematic ubiquitination site profiling of epithelial cells infected with Salmonella Typhimurium. Our findings specifically highlight components of the NFKB, membrane trafficking pathways and RHO GTPase systems as ubiquitination hubs during infection. In addition, a broad spectrum of bacterial effectors and several outer membrane proteins are ubiquitinated in infected cells. This comprehensive resource of ubiquitinome dynamics during Salmonella infection enables further understanding of the complex host-pathogen interplay and may reveal novel targets for the inhibition of Salmonella invasion and inflammation.     

Mass spectrometry-based quantitative proteomic analysis of <Emphasis Type="Italic">Salmonella enterica</Emphasis> serovar Enteritidis protein expression upon exposure to hydrogen peroxide

Background  

Salmonella enterica, a common food-borne bacterial pathogen, is believed to change its protein expression profile in the presence of different environmental stress such as that caused by the exposure to hydrogen peroxide (H₂O₂), which can be generated by phagocytes during infection and represents an important antibacterial mechanism of host cells. Among Salmonella proteins, the effectors of Salmonella pathogenicity island 1 and 2 (SPI-1 and SPI-2) are of particular interest since they are expressed during host infection in vivo and are important for invasion of epithelial cells and for replication in organs during systemic infection, respectively. However, the expression profiles of these proteins upon exposure to H₂O₂ or to host cells in vivo during the established phase of systemic infection have not been extensively studied.     

Typhoidal Salmonella: Distinctive virulence factors and pathogenesis

Although nontyphoidal Salmonella (NTS; including Salmonella Typhimurium) mainly cause gastroenteritis, typhoidal serovars (Salmonella Typhi and Salmonella Paratyphi A) cause typhoid fever, the treatment of which is threatened by increasing drug resistance. Our understanding of S. Typhi infection in human remains poorly understood, likely due to the host restriction of typhoidal strains and the subsequent popularity of the S. Typhimurium mouse typhoid model. However, translating findings with S. Typhimurium across to S. Typhi has some limitations. Notably, S. Typhi has specific virulence factors, including typhoid toxin and Vi antigen, involved in symptom development and immune evasion, respectively. In addition to unique virulence factors, both typhoidal and NTS rely on two pathogenicity‐island encoded type III secretion systems (T3SS), the SPI‐1 and SPI‐2 T3SS, for invasion and intracellular replication. Marked differences have been observed in terms of T3SS regulation in response to bile, oxygen, and fever‐like temperatures. Moreover, approximately half of effectors found in S. Typhimurium are either absent or pseudogenes in S. Typhi, with most of the remaining exhibiting sequence variation. Typhoidal‐specific T3SS effectors have also been described. This review discusses what is known about the pathogenesis of typhoidal Salmonella with emphasis on unique behaviours and key differences when compared with S. Typhimurium.