Molecular machinery of the macropinosome and phagosome formation.

巨噬细胞表现出活跃的巨噬作用和吞噬作用，这是f -肌动蛋白依赖的细胞运动，分别摄取细胞外溶质和细菌等颗粒。这些细胞运动也需要各种肌动蛋白结合蛋白来调节f -肌动蛋白的聚合、解聚和重排。为了阐明巨噬细胞和吞噬的分子机制，我们研究了几种肌动蛋白结合蛋白在巨噬细胞和吞噬中的作用，并揭示了其中一些蛋白的功能贡献。在这项研究中，我们已经确定了肌球蛋白介导的收缩活动，关闭吞噬杯进入巨噬细胞内吞噬体。结果表明，尽管其他种类的肌球蛋白也分布在吞噬杯和/或吞噬体周围，但只有肌球蛋白lc定位于吞噬杯的远端边缘。然后，我们开发了一种新的应用荧光比成像技术来原位演示两个相关分子如f -肌动蛋白和肌动蛋白结合蛋白之间的功能关系。利用这种比值成像技术，我们发现肌动蛋白-4是α -肌动蛋白的一种新型异构体，它优先定位于巨噬细胞的早期巨肽小体圆形褶皱中。这些发现表明，肌动蛋白-4的f -actin捆绑可能在功能上与巨肽小体的形成和维持有关。此外，我们正在继续研究其他f -actin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.