Signal transduction in neutrophil chemotaxis

描述（由申请人提供）：中性粒细胞是循环白色血细胞中最丰富的细胞类型，构成宿主抵御入侵细菌和其他病原体的第一道防线。它们通过对趋化因子梯度的反应向感染或炎症部位迁移，这一过程称为趋化性。神经元的趋化性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。我们特别感兴趣的是肌醇磷脂Ptdlns（3，4，5）P3介导的信号通路。这一途径已被证明是必不可少的介导的趋化反应，而其调控仍然不明确。化学引诱物刺激引发PtdIns（3，4，5）P3在趋化细胞前缘的质膜上的局部积累。然后，一组含有普列克底物蛋白同源物（PH）结构域的蛋白质通过它们与Ptdlns（3，4，5）P3的特异性结合而易位到膜上，随后触发导致趋化性的下游信号。以前认为PH结构域膜转位仅依赖于膜中PtdIns（3，4，5）P3的浓度。最近，我们发现，细胞内的肌醇磷酸，lns（1，3，4，5）P4，竞争与Ptdlns（3，4，5）P3结合的PH结构域和减弱PH结构域的膜转位在中性粒细胞，提供了一种新的模式的调节PH结构域的功能。这一有趣的结果使我们推测lns（1，3，4，5）P4通过抑制PH-结构域转位负调节中性粒细胞趋化性.与此一致，我们的初步数据表明，lns（1，3，4，5）P4水平在趋化过程中大大增加。此外，用膜渗透性lns（1，3，4，5）P4处理中性粒细胞显著抑制其趋化运动。为了进一步了解在趋化性中lns（1，3，4，5）P4对Ptdlns（3，4，5）P3信号的调节，我们将表征通过化学引诱物刺激（Aim I）增加细胞内lns（1，3，4，5）P4水平的分子机制。此外，将使用缺乏lns（1，3，4，5）P4的嗜中性粒细胞研究化学引诱物引起的lns（1，3，4，5）P4增加的生理后果（目的II）。最后，将使用小鼠腹膜炎模型和背气囊模型（Aim III）研究lns（1，3，4，5）P4对活体动物中性粒细胞趋化性的贡献。总之，这些研究将提供一个更好的理解的作用，lns（1，3，4，5）P4在中性粒细胞趋化性，最终目标是建立lns（1，3，4，5）P4和相关途径作为新的治疗目标，调节中性粒细胞功能。因此，可以开发更有效和更有效的疗法来治疗各种感染性和炎性疾病，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.