Sequential translocation of tyrosine kinases Lyn and Syk to the activated Fcgamma receptors during phagocytosis.

Tyrosine phosphorylation of numerous proteins is one of the earliest events detectable during Fcgamma receptor-mediated phagocytosis. We demonstrate that IgG-coated particles associated with the surface of macrophages are enriched with numerous tyrosine-phosphorylated proteins. During particle internalization the proteins are still associated with particles but their phosphorylation is reduced. Lyn kinase is phosphorylated both at particle binding and internalization steps. The phosphorylated Syk kinase is the major kinase associated with engulfed particles. Imnunofluorescent studies confirm spatial and temporal distribution of Lyn and Syk kinases at different stages of phagocytosis. Our data indicate that ligation of Fcgamma receptors activates Lyn followed by Syk kinase and in the result multimolecular complex of the kinases and several accompanying tyrosine phosphorylated proteins with Fcgamma receptors is organized leading to local reorganization of actin-based skeleton and particle uptake.