Transient recruitment of M-Ras GTPase to phagocytic cups in RAW264 macrophages during FcγR-mediated phagocytosis.

M-Ras, a member of the Ras superfamily, is known to be involved in diverse cellular processes. However, its involvement in FcγR-mediated phagocytosis remains unknown. We examined the spatiotemporal localization of M-Ras during the engulfment of IgG-opsonized erythrocytes (IgG-Es) in RAW264 macrophages. By the live-cell imaging of fluorescent protein-fused M-Ras, we found that M-Ras was localized to the membrane of phagocytic cups during the early stage of phagosome formation. Notably, ratiometric image analysis revealed that M-Ras was concentrated in the membrane of forming phagosomes. Moreover, our analysis of M-Ras mutant expression showed that phagosome formation was significantly inhibited in cells expressing GDP-locked mutant M-Ras-S27N. In contrast, the expression of wild-type M-Ras or GTP-locked mutant M-Ras-G22V facilitated the uptake of IgG-Es. These data suggest that M-Ras is a novel component of the FcγR-mediated phagocytic pathway and may regulate phagosome formation in macrophages.