Role of Protein Kinase C in Macrophage Activation

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Macrophage phagocytosis is the first line of defense against infection. Normally, Fc¿R-mediated phagocytosis efficiently clears pathogens and presents antigen to the adaptive immune system. However, dysregulation of FcR signaling contributes to chronic inflammatory diseases such as rheumatoid arthritis and atherosclerosis. Thus, understanding the molecular mechanisms of macrophage phagocytosis is essential to the discovery of novel targets for regulation of chronic inflammation. Mice lacking protein kinase C-epsilon (PKC-¿) are highly susceptible to bacteria infections and fail to mount an effective inflammatory response. We have shown that PKC-¿ is necessary for efficient Fc¿R-mediated phagocytosis and for production of pro-inflammatory genes. The mechanism of PKC-¿ action requires localization to phagosomes and catalytic activity. However, how PKC-¿ is activated and signals for phagocytosis and gene induction are unknown. Functionally, we have shown that PKC-¿ is involved in pseudopod extension, a process that requires fusion of intracellular vesicles into the phagosome. Structurally, we have identified the pseudosubstrate domain as critical for PKC-¿ translocation and shown that it preferentially interacts with polyphosphoinositides. This novel finding has implications for the mechanism of PKC-¿ activation, which is currently unknown. Based on our research and that of others, we propose that catalytically active PKC-¿ is necessary for the focal delivery of vesicles into the forming phagosome. PKC-¿ is activated by diacylglycerol and a phosphoinositide monophosphate (PIP). Active PKC-¿ phosphorylates proteins involved in the vesicle fusion necessary for membrane delivery and pseudopod extension. PKC-¿ is also necessary for the induction of genes required for resolution of infection. This model will be tested using bone marrow-derived macrophages from wild type and PKC-¿ null mice. Specifically, we will I) Identify the PIP required for PKC-¿ translocation to phagosomes, II) Determine the role of PKC-¿ in vesicle trafficking and fusion, III) Use conventional and traceable PKC techniques to identify PKC-¿ substrates, and IV) Use an unbiased, qPCR array approach to identify PKC-¿-regulated genes. Defining the mechanisms by which PKC-¿ transduces Fc¿R-initiated signals in phagocytosis and gene induction is critical to our understanding of host defense and the defects that contribute to chronic inflammatory diseases. The proposed studies use cutting edge technologies, coupled with classical approaches, in primary macrophages. We will rigorously test hypotheses supported by preliminary data and reach beyond current paradigms to identify PKC-¿-regulated genes and substrates. The information gained will provide insight into the role of PKC-¿ in Fc¿R-mediated signal transduction and how its loss impacts innate immunity.