Yersinia-induced deregulation of cellular life and death signals in macrophages

宿主细胞死亡是微生物病原体与宿主免疫系统相互作用的一个显著特征。细胞死亡的数量和方式对宿主的免疫反应和感染结果有重要影响。然而，在感染期间参与细胞活力和死亡调节的途径尚不清楚。在我们的研究中，我们使用革兰氏阴性肠致病菌小肠结肠炎耶尔森氏菌作为工具来深入了解细菌感染的宿主免疫细胞中细胞死亡诱导和预防信号的调控。耶尔森菌可抑制感染细胞的中枢促炎信号通路并诱导巨噬细胞凋亡。这些事件依赖于一种特定的细菌Yop毒力蛋白，该蛋白通过乙酰化丝氨酸和苏氨酸残基来修饰关键的宿主细胞激酶，从而阻断上游信号对激酶的磷酸化和激活。我们的研究表明，耶尔森菌的免疫调节活性也针对感染巨噬细胞的激酶受体相互作用蛋白-1 （RIP1）。RIP1是多细胞命运决定的主要调控因子。它是细胞存活、死亡和炎症之间的分子开关。在巨噬细胞中，耶尔森菌修饰RIP1的磷酸化模式并参与RIP1诱导凋亡。然而，耶尔森菌靶向RIP1的分子机制及其生理后果尚未明确。目前的项目旨在从生物化学、分子和功能上表征耶尔森菌对RIP1诱导的翻译后修饰（磷酸化、乙酰化），并将鉴定的RIP1修饰与生物反应联系起来。我们期望从这些研究中获得对先天免疫细胞程序性细胞死亡途径调控的基本新见解。此外，由于RIP1是多种细胞应激条件下细胞活力的中心控制元件，因此这项工作的含义可能对理解人类生物学中的死亡和生命决定以及相关疾病的干预策略具有普遍重要性。

Death of host cells is a prominent characteristic in the crosstalk of a microbial pathogen with the host immune system. Quantity and mode of cell death have substantial impact on the host immune response and the outcome of infection. The pathways involved in the regulation of cell vitality and death during infection are, however, poorly understood. In our studies we use the gram-negative enteropathogenic bacterium Yersinia enterocolitica as tool to gain insights into the regulation of cell death-inducing and -preventing signals in bacteria-infected host immune cells. Yersinia suppresses central proinflammatory signaling pathways in infected cells and elicits apoptosis in macrophages. These events depend on a specific bacterial Yop virulence protein which modifies key host cell kinases by acetylating serine and threonine residues to block phosphorylation and activation of the kinases by upstream signals. Our studies indicate that the immunomodulatory activities of Yersinia also target the kinase Receptor-interacting protein-1 (RIP1) in infected macrophages. RIP1 is a master regulator of multiple cell fate decisions. It acts as a molecular switch between cell survival, death and inflammation. Yersinia modifies the phosphorylation pattern of RIP1 and engages RIP1 for apoptosis induction in macrophages. The molecular mechanisms by which Yersinia targets RIP1 and the physiological consequences thereof are, however, not yet defined. The current project aims to biochemically, molecularly and functionally characterize the posttranslational modifications induced by Yersinia on RIP1 (phosphorylation, acetylation) and to link the identified RIP1 modifications to biological responses. We expect from these studies basic new insights into the regulation of programmed cell death pathways in innate immune cells. Furthermore, since RIP1 is a central control element of cell vitality under multiple cellular stress conditions, the implications of this work could be of general importance for understanding death and life decisions in human biology and for intervention strategies in associated diseases.