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Vol. 18, Issue 7, 2389-2399, July 2007

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MTOC Reorientation Occurs during FcR-mediated Phagocytosis in Macrophages

Edward W. Eng^*,, Adam Bettio, John Ibrahim, and Rene E. Harrison^*,

Departments of *Cell and Systems Biology and Biological Sciences, University of Toronto at Scarborough, Toronto, Ontario M1C 1A4, Canada

Submitted December 19, 2006; Revised April 2, 2007; Accepted April 9, 2007
Monitoring Editor: Patrick Brennwald

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 µm 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 FcR 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.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Rene E. Harrison (harrison{at}utsc.utoronto.ca)

Abbreviations used: APC, antigen-presenting cell; DIC, differential interference contrast; GSK-3, glycogen synthase kinase 3; MHC, major histocompatibility complex; MT, microtubule; MTOC, microtubule organizing center; PI3K, phosphatidylinositol 3-kinase; sRBC, sheep red blood cell; TIRFM, total internal reflection fluorescence microscopy.

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