Deciphering the function of actin remodeling in NLR-mediated innate immune sensing

先天免疫依赖于宿主细胞中的模式识别受体（PRR）对保守的病原体衍生结构（称为微生物相关分子模式（MAMP））的感测。NLR-蛋白家族的成员是重要的PRR，其涉及在被微生物刺激物激活后的炎症反应。我们对哺乳动物NLR蛋白的功能特性有着长期的兴趣。我们的工作的一个特别的重点在于NLR蛋白NOD 1，传感细菌肽聚糖。虽然NOD 1激活和信号转导的主要概念正在出现，但我们对NOD 1的细胞生物学及其精细调控的知识仍然非常有限。我们已经表明，NOD 1与宿主细胞中的F-肌动蛋白共定位，并且在最近的工作中使用HT筛选，我们现在已经确定了肌动蛋白调控网络的组成部分，这些组成部分有助于NOD 1介导的炎症反应。值得注意的是，许多侵入性细菌，可以激活NOD 1，可以同时影响肌动蛋白动力学的毒力蛋白的作用，往往靶向小GTP酶，间接调节F-肌动蛋白动力学。最近的研究结果表明，细菌效应子对宿主Rho GT3活性的破坏与NOD 1介导的炎症反应有关。我们最近的研究表明，F-actin动力学对人类细胞中的NOD 1信号传导很重要。我们已经确定了F-肌动蛋白动态调节的关键组成部分，即磷酸酶SSH 1及其底物cofilin，作为该功能的重要分子介质。这使我们提出，这些蛋白质参与整合细菌效应子和MAMP传感的肌动蛋白重塑的颠覆。在这里，我们将扩大我们最近的研究结果，并解决悬而未决的问题，如cofillin和SSH的不同直系同源物在NLR-冥想反应的作用。最重要的是，我们将通过鉴定参与这一新途径的蛋白质网络来阐明潜在的分子细节。最后，将解决如果激活NOD 1改变肌动蛋白聚合在人类细胞中，如果这有助于细胞自主抗菌反应。此外，我们将扩大我们的初步观察与福氏志贺菌作为感染模型，以其他临床相关的细菌病原体和分析SSH 1/cofilin对其他NOD 1介导的信号转导结果，如自噬的影响。通过保护宿主细胞肌动蛋白动力学间接传感细菌活性是哺乳动物先天免疫领域的新概念。解读F-actin重塑在NLR介导的先天免疫中的作用将为宿主-病原体相互作用的生物学提供重要的新见解，从长远来看，将为开发治疗炎症性疾病的新治疗策略奠定基础。

Innate immunity depends on sensing of conserved pathogen derived structures, referred to as microbe associated molecular patterns (MAMPs) by pattern-recognition receptors (PRRs) in the host cell. Members of the NLR-protein family are important PRRs that refer inflammatory responses upon activation by microbial stimuli. We have a long standing interesting in the functional characterization of mammalian NLR proteins. A particular focus of our work lies on the NLR-protein NOD1 that senses bacterial peptidoglycan. Although the main concepts of NOD1 activation and signaling are emerging, our knowledge on the cell biology of NOD1 and its fine regulation is still quite limited. We have shown that NOD1 co-localizes with F-actin in the host cell and in more recent work using HT-screening we now have identified components of the actin regulatory network that contribute to NOD1-mediated inflammatory responses. Notably, many invasive bacteria, that can activate NOD1, can simultaneously affect actin dynamics by the action of virulence proteins which often target small GTPases that indirectly regulate F-actin dynamics. Recent findings, show that subversion of host Rho GTPase activity by bacterial effectors is linked to NOD1-mediated inflammatory responses. Our recent study revealed that F-actin dynamic is important for NOD1 signaling in human cells. We have identified key components of the regulation of F-actin dynamic, namely the phosphatase SSH1 and its substrate cofilin, as important molecular mediators of this function. This leads us to propose that these proteins are involved in integrating subversion of actin remodeling by bacterial effectors and MAMP sensing. Here we will expand on our recent findings and address open questions, such as the role of the different orthologs of cofillin and SSH in NLR-meditated responses. Most importantly, we will elucidate the underlying molecular details by identification of the network of proteins involved in this novel pathway. Finally, will address if activation of NOD1 changes actin polymerization in human cells and if this contributes to cell-autonomous anti-bacterial responses. Moreover, we will expand our initial observation made with Shigella flexneri as infection model to other clinically relevant bacterial pathogens and analyze the effect of SSH1/cofilin on additional NOD1-mediated signalling outcomes such as autophagy. The indirect sensing of bacterial activity by guarding host cell actin dynamics is a novel concept in the field of innate immunity in mammals. Deciphering the role of F-actin remodelling in NLR-mediated innate immunity will provide important novel insights into the biology of host-pathogen interactions and in the long run will set the stage for the development of novel therapeutically strategies to treat inflammatory disorders.