Molecular machinery of the macropinosome and phagosome formation.

巨噬细胞表现出活跃的巨噬细胞吞噬作用和吞噬作用，这是F-肌动蛋白依赖的细胞运动，分别摄取细胞外的溶质和颗粒，如细菌。这些细胞运动还需要多种肌动蛋白结合蛋白来调节F-肌动蛋白聚合、解聚和重排。为了阐明巨噬细胞吞噬的分子机制，我们综述了几种肌动蛋白结合蛋白在巨噬细胞吞噬和吞噬过程中的作用，并揭示了其中一些蛋白的功能贡献。在这项研究中，我们发现了一种肌球蛋白介导的收缩活动，它使巨噬细胞内的吞噬小体关闭吞噬杯。结果表明，虽然其他类型的肌球蛋白也分布在吞噬细胞杯和/或吞噬小体周围，但只有肌球蛋白Lc定位于吞噬细胞杯的远端边缘。然后，我们发展了一种新的应用荧光比率成像技术来原位展示两个相关分子之间的功能关系，如F-肌动蛋白和肌动蛋白结合蛋白。利用这一比率成像技术，我们发现α-肌动蛋白的一种新的亚型肌动蛋白-4优先定位于巨噬细胞中的环状褶皱和早期的大胞体。这些发现表明，肌动蛋白与肌动蛋白结合可能在功能上与巨噬菌体的形成和维持有关。此外，我们目前正在继续研究其他的肌动蛋白结合蛋白，如cofilin和ERM蛋白。

Macrophages show active macropinocytosis and phagocytosis which are F-actin-dependent cell motilities to take up extracellular solute and particles such as bacteria, respectively. These cell motilities also require a variety of actin-binding proteins which regulate F-actin polymerization, depolymerization and rearrangement. In order to elucidate the molecular machinery of macropinocytosis and phagocytosis, we have surveyed the involvement of several actin-binding proteins in macropinocytosis and phagocytosis, and revealed functional contributions of some of them. In this study, we have identified a myosin-mediated contractile activity that closes phagocytic cups into intracellular phagosomes in macrophages. It was shown that only myosin lc localized on the distal margin of the phagocytic cup, although other classes of myosins also distributed around phagocytic cups and/or phagosomes.Then, we developed a new application of the fluorescence ratio imaging technique to in situ demonstration of the functional relationship between two related molecules such as F-actin and an actin-binding protein. Using this ratio imaging technique, we revealed that actinin-4, a novel isoform of alpha-actinin, was preferentially localized in circular ruffles, early macropinosomes in macrophages. These findings suggest that F-actin-bundling by actinin-4 may be functionally associated with macropinosomes formation and maintenance.Furthermore, we are now continuing studies on other F-actin-binding proteins such as cofilin and ERM proteins.