Eng Edward W, Bettio Adam, Ibrahim John, Harrison Rene E
Department of Cell and Systems Biology, University of Toronto at Scarborough, Toronto, Ontario, Canada.
Mol Biol Cell. 2007 Jul;18(7):2389-99. doi: 10.1091/mbc.e06-12-1128. Epub 2007 Apr 18.
Cell polarization is essential for targeting signaling elements and organelles to active plasma membrane regions. In a few specialized cell types, cell polarity is enhanced by reorientation of the MTOC and associated organelles toward dynamic membrane sites. Phagocytosis is a highly polarized process whereby particles >0.5 microm are internalized at stimulated regions on the cell surface of macrophages. Here we provide detailed evidence that the MTOC reorients toward the site of particle internalization during phagocytosis. We visualized MTOC proximity to IgG-sRBCs in fixed RAW264.7 cells, during live cell imaging using fluorescent chimeras to label the MTOC and using frustrated phagocytosis assays. MTOC reorientation in macrophages is initiated by FcgammaR ligation and is complete within 1 h. Polarization of the MTOC toward the phagosome requires the MT cytoskeleton and dynein motor activity. cdc42, PI3K, and mPAR-6 are all important signaling molecules for MTOC reorientation during phagocytosis. MTOC reorientation was not essential for particle internalization or phagolysosome formation. However Golgi reorientation in concert with MTOC reorientation during phagocytosis implicates MTOC reorientation in antigen processing events in macrophages.
细胞极化对于将信号元件和细胞器靶向至活跃的质膜区域至关重要。在少数特殊细胞类型中，微管组织中心（MTOC）及相关细胞器重新定向至动态膜位点可增强细胞极性。吞噬作用是一个高度极化的过程，大于0.5微米的颗粒在巨噬细胞表面的刺激区域被内化。在此，我们提供了详细证据，表明在吞噬作用期间MTOC会重新定向至颗粒内化位点。我们通过在固定的RAW264.7细胞中观察MTOC与IgG包被的绵羊红细胞（IgG-sRBCs）的接近程度、在活细胞成像期间使用荧光嵌合体标记MTOC以及使用受挫吞噬试验进行了研究。巨噬细胞中的MTOC重新定向由FcγR连接引发，并在1小时内完成。MTOC向吞噬体的极化需要微管（MT）细胞骨架和动力蛋白的运动活性。在吞噬作用期间，cdc42、磷脂酰肌醇-3激酶（PI3K）和膜相关PAR-6都是MTOC重新定向的重要信号分子。MTOC重新定向对于颗粒内化或吞噬溶酶体形成并非必不可少。然而，在吞噬作用期间高尔基体与MTOC重新定向协同发生，这表明MTOC重新定向参与了巨噬细胞中的抗原加工事件。
