Molecular machinery and signal transduction of phagocytosis and macropinocytosis

吞噬作用和巨噬作用是细胞的内吞性表面运动，分别摄取细胞外颗粒和液体，在先天免疫和抗原呈递中起重要作用。这些细胞表面运动是由驱动f -肌动蛋白重组和膜运输的分子机制介导的，这些分子机制由复杂的信号转导途径巧妙地控制。本课题的主要目的是研究细胞吞噬和巨噬过程中磷酸肌肽信号与分子机制之间的关系。在本研究中，我们通过生物成像和图像分析发现，大肌动蛋白小体形成膜中PI(4,5)P2和PI(3,4,5)P3的水平与肌动蛋白细胞骨架的变化密切相关。形成巨红细胞杯的膜褶中PI(4,5)P2的浓度比其他区域增加了一倍以上。PI(4,5)P2水平在接近大蛋白酶体前达到最大值，在大蛋白酶体内化后迅速下降。相比之下，PI(3,4,5)P3是在大醇溶体内化前后在大醇溶体形成部位局部产生的。我们的研究结果表明，由I类pi3激酶局部控制的磷酸肌苷水平对于调节影响细胞膜结构变化的肌动蛋白结合蛋白的功能是重要的。此外，我们已经证明PI(3)P是III类PI3kinase的主要产物，对于形成的大蛋白酶体的融合是必不可少的。

Phagocytosis and macropinocytosis are endocytic cell surface movements for taking extracellular particles such and fluid, respectively, and play important roles in innate immunity and antigen presentation. These cell surface movements are mediated by molecular machineries driving F-actin reorganization and membrane traffic, which are ingeniously controlled by complicated signal transduction pathways. The main aim of this research project is to resolve the relationship between molecular machineries and phosphoinositide signal during phagocytosis and macropinocytosis.In this study using bioimaging and image analysis, we revealed that levels of PI(4,5)P2 and PI(3,4,5)P3 in the membrane of forming macropinosomes were closely linked to the changes in actin cytoskeleton. The concentrations of PI(4,5)P2 in the membrane ruffles forming macropinocytic cups increased more than double that in other areas. The PI(4,5)P2 levels reached its maximum just before closing into macropinosomes, and rapidly fell after macropinosome internalization. In contrast, the PI(3,4,5)P3 was locally produced at the site of macropionosome formation around the time of macropinosome internalization. Our findings suggest that locally controlled levels of phosphoinositides by class I PI3kinase are important for regulating the function of actin-binding proteins which affect changes in the cell surface membrane architecture. Furthermore, we have shown that PI(3)P which is the main product of class III PI3kinase is essential for the fusion of formed macropinosomes.