The neutrophil participates in many aspects of the body's immune defense system and is an integral cellular component of the inflammatory response. An understanding of how neutrophil functions are activated and regulated is paramount for effective therapeutic intervention in these areas. The signal transduction process that is initiated by the binding of chemoattractant receptor ligands is known to involve GTP binding proteins (G proteins). We have identified a novel low molecular weight G protein In human neutrophils, termed rapl. Preliminary data indicates that rapl may interact with protein components of the neutrophil NADPH oxidase system and can produce effects on the activity of the oxidase in a reconstituted system. We have additionally shown rap1 to be a substrate for cAMP-dependent protein kinase and this phosphorylation is enhanced by conditions/agents which mimic liganded chemoattractant receptor. rap1 may be able to interact directly with the N-formyl peptide receptor, either to serve as an additional transducer of receptor signalling, or as a means to attenuate neutrophil activation via Gn. The regulatory roles of rapl phosphorylation have yet to be defined but are clearly relevant to the ability of endogenous mediators to inhibit neutrophil function. We propose to develop specific rapl probes and purified rapl protein preparations to study physical and functional macromolecular interactions of rap in the human neutrophil. Interactions of Lo with neutrophil N-formyl peptide receptor, NADPH oxidase system, and other potential effectors (GAP's) will be examined. The influence of covalent modifications of rap in regulating these interactions will be determined and defined mechanistically. The proposed studies will enable us to better understand the regulation of neutrophil activation, as well as to elucidate the normal cellular roles of rap and related G proteins.
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