Modulation of apoptosis by Legionella Pneumophila

描述(由申请人提供)：嗜肺军团菌是一种细胞内病原体，它逃避细胞内融合，劫持ER到高尔基体的囊泡交通，将其吞噬小体重塑为ER衍生的隔室，允许细胞内复制。嗜肺乳杆菌的Dot/LCM IV型分泌系统对于调节吞噬小体的生物发生和调节巨噬细胞的凋亡途径是必不可少的，它通过激活caspase-3而不依赖于内源性和外源性的凋亡途径。Dot/LCM介导的caspase-3激活导致Rabaptin-5的切割，Rabaptin-5是早期内体调节因子Rab5的效应器。使用caspase-3肽抑制剂抑制caspase-3可以阻止嗜肺乳杆菌在细胞内的复制，并导致有机体向吞噬溶酶体的运输，类似于Dot/ICM突变体。我们的假设是：caspase-3介导的Rabaptin-5的切割是含军团菌吞噬小体(LCP)受阻生物发生和细胞内复制的核心。为了验证这一假说，我们的特定目的是检验以下几个方面：特定目的I.caspase-3激活在LCP生物发生中的作用；特定目的II：caspase-3介导的Rabaptin-5裂解在LCP生物发生中的作用；特定目的III.鉴定参与Caspase-3激活的嗜肺乳杆菌效应子。意义：我们提出的研究是我们理解这种病原体侵占宿主细胞的分子和细胞机制的关键，并将揭示这种病原体在宿主细胞中的凋亡途径和囊泡运输之间进行串扰以重塑宿主细胞的细胞机制。参与这一过程的细菌效应物是治疗和预防该病的潜在靶点。

DESCRIPTION (provided by applicant): Legionella pneumophila is an intracellular pathogen that evades endocytic fusion and hijacks ER-to-golgi vesicle traffic to remodel its phagosome into an ER-derived compartment permissive for intracellular replication. The Dot/lcm type IV secretion system of L. pneumophila is essential for both modulation of phagosome biogenesis and modulation of the macrophage apoptotic pathways through robust early and novel activation of caspase-3, independent of the intrinsic and extrinsic pathways of apoptosis. The Dot/lcm- mediated activation of caspase-3 results in cleavage of Rabaptin-5, which is an effector of the early endosome regulator Rab5. Inhibition of caspase-3 using caspase-3 peptide inhibitors blocks intracellular replication of L. pneumophila and results in trafficking of the organism to phagolysosomes, similar to dot/icm mutants. Our hypothesis is: Caspase-3-meditaed cleavage of Rabaptin-5 is central to the arrested biogenesis of the Legionella-containing phagosome (LCP) and to intracellular replication. To test this hypothesis, our specific aims are to examine the following: Specific aim I. Role of caspase-3 activation in biogenesis of the LCP; Specific aim II: Role of caspase-3-mediated cleavage of Rabaptin-5 in biogenesis of the LCP; Specific aim III. Identification of the L. pneumophila effector involved in caspase-3 activation. Significance: Our proposed studies are the crux of our understanding of the molecular and cellular mechanisms by which this pathogen commandeer the host cell, and will she light on the cellular mechanism by which this pathogen engages a cross talk between the apoptotic pathways and vesicle traffic in the host cell to remodel it to its liking. The bacterial effector involved in this process is a potential target for therapy and prevention of the disease.