Golgi-Associated Protein Kinase C-ε Is Delivered to Phagocytic Cups: Role of Phosphatidylinositol 4-Phosphate

Protein kinase C-epsilon (PKC-epsilon) at phagocytic cups mediates the membrane fusion necessary for efficient IgG-mediated phagocytosis. The C1B and pseudosubstrate (epsilon PS) domains are necessary and sufficient for this concentration. C1B binds diacylglycerol; the docking partner for epsilon PS is unknown. Liposome assays revealed that the epsilon PS binds phosphatidylinositol 4-phosphate (PI4P) and PI(3,5) P-2. Wortmannin, but not LY294002, inhibits PKC-epsilon concentration at cups and significantly reduces the rate of phagocytosis. As Wortmannin inhibits PI4 kinase, we hypothesized that PI4P mediates the PKC-epsilon concentration at cups and the rate of phagocytosis. PKC-epsilon colocalizes with the trans-Golgi network (TGN) PI4P reporter, P4M, suggesting it is tethered at the TGN. Real-time imaging of GFP-PKC-epsilon -expressing macrophages revealed a loss of Golgi-associated PKC-epsilon during phagocytosis, consistent with a Golgi-to-phagosome translocation. Treatment with PIK93, a PI4 kinase inhibitor, reduces PKC-epsilon at both the TGN and the cup, decreases phagocytosis, and prevents the increase in capacitance that accompanies membrane fusion. Finally, expression of the Golgi-directed PI4P phosphatase, hSac1-K2A, recapitulates the PIK93 phenotype, confirming that Golgiassociated PI4P is critical for efficient phagocytosis. Together these data are consistent with a model in which PKC-epsilon is tethered to the TGN via an epsilon PS-PI4P interaction. The TGN-associated pool of PKC-epsilon concentrates at the phagocytic cup where it mediates the membrane fusion necessary for phagocytosis. The novelty of these data lies in the demonstration that epsilon PS binds PI4P and PI(3,5) P-2 and that PI4P is necessary for PKC-epsilon localization at the TGN, its translocation to the phagocytic cup, and the membrane fusion required for efficient Fc [gamma] receptor-mediated phagocytosis.