Phagosomal targeting of CARD proteins

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Abstract: Phagosomal targeting of CARD proteins Phagocytosis is the process by which cells such as macrophages and dendritic cells bind, internalize, and kill microbes. Several different types of receptors are known to recognize microbes (either directly or through opsonization) and to trigger phagocytosis. The cell biological mechanisms by which these receptors drive phagocytosis are dependent the specific receptor. Thus, Fc-receptor mediated phagocytosis recruits a distinct set of cytoskeletal components than Dectin-1 (beta-glucan receptor) or complement receptor-mediated phagocytosis. Phagocytosis is tightly coupled to the initiation of inflammatory cytokine and chemokine production, although the mechanisms by which these processes are coupled are still being elucidated. Caspase Activation and Recruitment Domains (CARDs) are conserved protein-protein interaction domains found in a variety of cytoplasmic proteins key to microbial recognition and inflammatory signaling including Nod (nuclear oligomerization domain) proteins, Bcl10, Nalp1 and many others. We have observed that several CARD proteins are recruited to phagosomes. We hypothesize that CARD recruitment to phagosomes is a key mechanism by which signals for phagocytosis and inflammation are integrated. In this study, we will define the mechanism(s) by which CARD proteins are recruited to phagosomes and whether CARD proteins are recruited only to specific types of phagosomes (Aim1). We will determine what protein-protein interactions are required to get CARD proteins to phagosomes and whether these interactions are important for inflammatory signaling (Aim 2). We will determine whether activating a CARD protein (Nod2) on phagosomes alters its inflammatory signaling consequences, and whether such targeted activation influences antigen presentation and the type of adaptive immune response that is promoted. LAY SUMMARY: White blood cells eat and kill infectious microbes. They also initiate inflammatory responses that are crucial for defense against infection. We are defining how the molecular signaling pathways that control the processes of eating and killing microbes are connected to the signaling pathways required to activate inflammation. Clinical manipulation of these pathways may help suppress unwanted inflammation, or stimulate effective immune defenses.