A role for PKC-ε in FcγR-mediated phagocytosis by RAW 264.7 cells

Protein kinase C (PKC) plays a prominent role in immune signaling, and the paradigms for isoform selective signaling are beginning to be elucidated. Real-time microscopy was combined with molecular and biochemical approaches to demonstrate a role for PKC-epsilon in Fcgamma receptor (FcgammaR)-dependent phagocytosis. RAW 264.7 macrophages were transfected with GFP-conjugated PKC isoforms, and GFP movement was followed during phagocytosis of fluorescent IgG-opsonized beads. PKC-epsilon, but not PKC-delta, concentrated around the beads. PKC-epsilon accumulation was transient; apparent as a flash on target ingestion. Similarly, endogenous PKC-epsilon was specifically recruited to the nascent phagosomes in a time-dependent manner. Overexpression of PKC-epsilon, but not PKC-alpha, PKC-delta, or PKC-gamma enhanced bead uptake 1.8-fold. Additionally, the rate of phagocytosis in GFP PKC-epsilon expressors was twice that of cells expressing GFP PKC-delta. Expression of the regulatory domain (ERD) and the first variable region (epsilonV1) of PKC-epsilon inhibited uptake, whereas the corresponding PKC-delta region had no effect. Actin polymerization was enhanced on expression of GFP PKC-epsilon and ERD, but decreased in cells expressing epsilonV1, suggesting that the epsilonRD and epsilonV1 inhibition of phagocytosis is not due to effects on actin polymerization. These results demonstrate a role for PKC-epsilon in FcgammaR-mediated phagocytosis that is independent of its effects on actin assembly.