Regulation of Human Phagocyte Function by Rac Proteins

描述（由申请人提供）：由吞噬细胞的NADPH氧化酶形成的活性氧（ROS）在宿主防御和炎症中起主要作用。白细胞在遇到微生物产物时激活的一个中心特征是一个两阶段的反应，首先导致预激活，启动状态，在二次激活刺激下产生极大增强的反应。与微生物病原体相关的分子模式被toll样受体（TLRs）识别。这种识别导致TLR激活和信号事件，使中性粒细胞接受随后的化学引诱剂刺激。为了了解这种协调中性粒细胞反应在ROS生成方面的分子基础，我们将研究从参与NADPH氧化酶激活的受体到最终序列的信号通路。

DESCRIPTION (provided by applicant): Reactive oxygen species (ROS) formed by the NADPH oxidase of phagocytic cells play a primary role in host defense and inflammation. A central feature of leukocyte activation upon encountering microbial products is a two-phased response, leading at first to a pre-activated, primed state, which generates a vastly enhanced response upon a secondary, activating stimulus. The molecular patterns associated with microbial pathogens are recognized by Toll-like receptors (TLRs). This recognition leads to TLR activation and signaling events that prime neutrophils for subsequent stimulation by chemoattractants. To understand the molecular basis for this coordinated neutrophil response in respect to ROS generation, we will investigate the signaling pathways from the receptors involved to the final sequence of NADPH oxidase activation. We have shown that oxidase activity is regulated by the GTPase Rac2 and the effector p21-activated kinase (Pak). Our studies so far point to a role of Pak in several aspects of the fMLP-induced respiratory burst including multiple phosphorylation events and association with cytochrome b558. The involvement of Pak in NADPH oxidase assembly at the membrane will be investigated in detail. Studies with Pak-null or transgenic mice harboring a Pak kinase inhibitory fragment will define Pak function in vivo. The signaling sequences emanating from activated TLRs seem to diverge between monocytes and neutrophils, leading to ROS generation versus priming. We hypothesize that Rac-regulated pathways are key elements for understanding how different innate immune cells regulate bacterial killing and we will investigate the molecular mechanisms involved. A common trait connecting TLR2 activation, priming and chemoattractant-induced ROS generation is the dependence on tyrosine phosphorylations. We will elucidate potential associations of TLRs or formyl peptide receptors with tyrosine kinase receptors and evaluate how these complexes relay their signals in neutrophils and microglia. These studies will yield novel insights into the overall control of oxidant formation by innate immune cells.