Signal transduction in neutrophil chemotaxis

描述（由申请人提供）：中性粒细胞是循环白细胞中最丰富的细胞类型，是宿主抵御入侵细菌和其他病原体的第一道防线。它们通过对趋化剂梯度的反应向感染或炎症部位迁移，这一过程被称为趋化性。中性粒细胞趋化是由趋化信号转导途径介导的。本项目的长期目标是阐明趋化信号的分子基础。我们对肌醇磷脂Ptdlns(3,4,5)P3介导的信号通路特别感兴趣。这一途径已被证明对介导趋化反应至关重要，但其调控仍不明确。趋化刺激会在趋化细胞前缘的质膜上引发ptdln (3,4,5)P3的局部积累。随后，一组pleckstrin同源（PH）结构域的蛋白通过与Ptdlns(3,4,5)P3的特异性结合转移到膜上，并随后触发导致趋化的下游信号。以前认为ph结构域膜易位仅依赖于膜中ptdln (3,4,5)P3的浓度。最近，我们发现细胞内肌醇磷酸lns(1,3,4,5)P4与Ptdlns(3,4,5)P3竞争结合PH结构域，并减弱中性粒细胞中PH结构域的膜移位，为PH结构域功能的调节提供了一种新的模式。这一有趣的结果使我们假设lns(1,3,4,5)P4通过抑制PH结构域易位负调控中性粒细胞趋化性。与这一观点一致的是，我们的初步数据显示，在趋化过程中，lns(1,3,4,5)P4水平大大增加。此外，用膜渗透的lns(1,3,4,5)P4处理中性粒细胞可显著抑制其趋化运动。为了进一步了解lns(1,3,4,5)P4对Ptdlns(3,4,5)P3信号在趋化性中的调控作用，我们将描述通过趋化剂刺激增加lns(1,3,4,5)P4细胞内水平的分子机制（Aim I）。此外，将使用缺乏lns(1,3,4,5)P4的中性粒细胞来研究化学引诱剂诱导的lns(1,3,4,5)P4增强的生理后果（Aim II）。最后，将通过小鼠腹膜炎模型和背气囊模型研究lns(1,3,4,5)P4对活体动物中性粒细胞趋化的贡献（Aim III）。总之，这些研究将更好地理解lns(1,3,4,5)P4在中性粒细胞趋化中的作用，最终目标是建立lns(1,3,4,5)P4及其相关途径作为调节中性粒细胞功能的新治疗靶点。因此，可以开发出更有效的治疗方法来治疗各种传染病和炎症性疾病，如哮喘、多发性硬化症和类风湿性关节炎。

DESCRIPTION (provided by applicant): Neutrophils are the most abundant cell type among circulating white blood cells and constitute the first line of host defense against invading bacteria and other pathogens. They migrate toward sites of infection or inflammation by responding to gradients of chemoattractants, a process known as chemotaxis. Neutrophil chemotaxis is mediated by chemotactic signal transduction pathways. The long-term goal of this project is to elucidate the molecular basis of the chemotactic signaling. We are particularly interested in the signal pathway mediated by inositol phospholipid Ptdlns(3,4,5)P3. This pathway has proven to be essential for mediating chemotactic responses, while its regulation remains ill defined. Chemoattractant stimulation initiates localized accumulation of Ptdlns(3,4,5)P3 on the plasma membrane at the leading edge of chemotaxing cells. A set of pleckstrin homolog (PH) domain-containing proteins are then translocated onto the membrane via their specific binding to Ptdlns(3,4,5)P3 and subsequently trigger downstream signals leading to chemotaxis. The PH-domain membrane translocation was previously thought to be dependent solely upon concentrations of Ptdlns(3,4,5)P3 in the membrane. Recently, we discovered that an intracellular inositol phosphate, lns(1,3,4,5)P4, competes with Ptdlns(3,4,5)P3 for binding to the PH domain and attenuates PH-domain membrane translocation in neutrophils, providing a novel mode of regulation for PH domain function. This intriguing result led us to hypothesize that lns(1,3,4,5)P4, by suppressing PH- domain translocation, negatively regulates neutrophil chemotaxis. Consistent with this idea, our preliminary data show that lns(1,3,4,5)P4 level is greatly augmented during chemotaxis. In addition, treatment of neutrophils with membrane-permeant lns(1,3,4,5)P4 significantly inhibits their chemotactic movement. To further understand the regulation of Ptdlns(3,4,5)P3 signal by lns(1,3,4,5)P4 in chemotaxis, we will characterize the molecular mechanisms by which the intracellular level of lns(1,3,4,5)P4 is augmented by Chemoattractant stimulation (Aim I). Moreover, the physiological consequences of the chemoattractant- elicited augmentation of lns(1,3,4,5)P4 will be investigated using neutrophils lacking lns(1,3,4,5)P4 (Aim II). Finally, the contribution of lns(1,3,4,5)P4 to neutrophil chemotaxis in live animals will be investigated using a mouse peritonitis model and a dorsal air pouch model (Aim III). Together, these studies will provide a better understanding of the role of lns(1,3,4,5)P4 in neutrophil chemotaxis, with the ultimate goal of establishing lns(1,3,4,5)P4 and related pathways as novel therapeutic targets for modulating neutrophil functions. Accordingly, more efficient and effective therapies could be developed to treat a variety of infectious and inflammatory diseases, such as asthma, multiple sclerosis, and rheumatoid arthritis.