Phosphoinositide-3-kinase-independent contractile activities associated with Fcgamma-receptor-mediated phagocytosis and macropinocytosis in macrophages

• Published in: Journal of cell science Vol. 116; no. Pt 2; pp. 247 - 257
• Main Authors: Araki, Nobukazu, Hatae, Tanenori, Furukawa, Aizo, Swanson, Joel A
• Format: Journal Article
• Language: English
• Published: England 15.01.2003
• Subjects: Actin Cytoskeleton - drug effects; Actin Cytoskeleton - genetics; Actin Cytoskeleton - metabolism; Actin Cytoskeleton - ultrastructure; Androstadienes - pharmacology; Animals; Azepines - pharmacology; Cell Surface Extensions - drug effects; Cell Surface Extensions - metabolism; Cell Surface Extensions - ultrastructure; Cells, Cultured; Contractile Proteins - drug effects; Contractile Proteins - metabolism; Enzyme Inhibitors - pharmacology; Erythrocytes - cytology; Erythrocytes - metabolism; Macrophages - drug effects; Macrophages - enzymology; Macrophages - ultrastructure; Mice; Microscopy, Electron, Scanning; Myosin-Light-Chain Kinase - antagonists & inhibitors; Myosin-Light-Chain Kinase - metabolism; Myosins - metabolism; Naphthalenes - pharmacology; Phagocytosis - drug effects; Phagocytosis - physiology; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; Pinocytosis - drug effects; Pinocytosis - physiology; Receptors, IgG - drug effects; Receptors, IgG - metabolism; Recombinant Fusion Proteins; Wortmannin
• ISSN: 0021-9533

Previous studies have shown that Fcgamma receptor (FcR)-mediated phagocytosis and macropinocytosis in macrophages consist of two dissociable activities: a phosphoinositide 3-kinase (PI3K)-independent extension of phagocytic cups and a PI3K-dependent contractile mechanism that closes phagosomes and ruffles into intracellular organelles. Here, we identify an additional contractile activity that persists in the presence of the PI3K inhibitor wortmannin. ML-7, an inhibitor of myosin-light-chain kinase (MLCK), inhibited FcR-mediated phagocytosis, macropinocytosis and cell movements associated with ruffling. Scanning electron microscopy demonstrated a striking difference in morphology between phagocytic cups in the different inhibitors: whereas phagocytic cups of control cells and wortmannin-treated cells conformed closely to particles and appeared to have constricted them, the phagocytic cups in cells treated with ML-7 were more open. Video microscopy of macrophages expressing green-fluorescent-protein (GFP)-actin fusions revealed that bound IgG-opsonized erythrocytes were squeezed during phagosome formation and closure. In ML-7, GFP-actin-rich protrusions extended outward but failed to squeeze particles. Moreover, in contrast to the effects of PI3K inhibitors, ML-7 markedly reduced ruffle movement, and perturbed circular ruffle formation. These PI3K-independent myosin-II-based contractile activities that squeeze phagocytic cups and curve ruffles therefore represent a third component activity of the actin cytoskeleton during phagocytosis and macropinocytosis.