Membrane ruffles capture C3bi-opsonized particles in activated macrophages

• Published in: Molecular biology of the cell Vol. 19; no. 11; pp. 4628 - 4639
• Main Authors: Patel, Prerna C, Harrison, Rene E
• Format: Journal Article
• Language: English
• Published: United States The American Society for Cell Biology 01.11.2008
• Subjects: Animals; Cell Adhesion - drug effects; Cell Line; Cell Membrane Structures - drug effects; Cell Membrane Structures - immunology; Cell Membrane Structures - ultrastructure; Complement C3b - immunology; Endosomes - drug effects; Endosomes - metabolism; Humans; Kinesin - metabolism; Lipopolysaccharides - pharmacology; Macrophage Activation - drug effects; Macrophage Activation - immunology; Macrophage-1 Antigen - metabolism; Macrophages - cytology; Macrophages - drug effects; Macrophages - immunology; Macrophages - ultrastructure; Mice; Mice, Inbred C57BL; Microtubules - drug effects; Microtubules - metabolism; Models, Biological; Opsonin Proteins - immunology; Phagocytosis - drug effects; Pinocytosis - drug effects; rab GTP-Binding Proteins - metabolism; Sheep; Talin - metabolism; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E08-02-0223

A widespread belief in phagocyte biology is that FcgammaR-mediated phagocytosis utilizes membrane pseudopods, whereas Mac-1-mediated phagocytosis does not involve elaborate plasma membrane extensions. Here we report that dynamic membrane ruffles in activated macrophages promote binding of C3bi-opsonized particles. We identify these ruffles as components of the macropinocytosis machinery in both PMA- and LPS-stimulated macrophages. C3bi-particle capture is facilitated by enrichment of high-affinity Mac-1 and the integrin-regulating protein talin in membrane ruffles. Membrane ruffle formation and C3bi-particle binding are cytoskeleton dependent events, having a strong requirement for F-actin and microtubules (MTs). MT disruption blunts ruffle formation and PMA- and LPS-induced up-regulation of surface Mac-1 expression. Furthermore, the MT motor, kinesin participates in ruffle formation implicating a requirement for intracellular membrane delivery to active membrane regions during Mac-1-mediated phagocytosis. We observed colocalization of Rab11-positive vesicles with CLIP-170, a MT plus-end binding protein, at sites of particle adherence using TIRF imaging. Rab11 has been implicated in recycling endosome dynamics and mutant Rab11 expression inhibits both membrane ruffle formation and C3bi-sRBC adherence to macrophages. Collectively these findings represent a novel membrane ruffle "capture" mechanism for C3bi-particle binding during Mac-1-mediated phagocytosis. Importantly, this work also demonstrates a strong functional link between integrin activation, macropinocytosis and phagocytosis in macrophages.