Platelet-activating factor (PAF) is a unique phospholipid mediator of acute allergic and inflammatory reactions that displays an impressive range of biological activities including powerful regulatory effects on the liver. The major objective of this proposal is to provide new insights into the molecular basis of PAF signaling. Dr. Fisher recently cloned a novel splice variant of the rat PAF receptor (rPAF) with ligand binding and G protein-coupling characteristics distinct from that of the rPAFR. This receptor variant, named rPAFRsv, arises by use of a minor AT-AC splicing mechanism previously described in only 9 genes. In the proposed studies, Dr. Fisher will identify the G proteins to which rPAFR and rPAFRsv couple and assess the relative roles of these two receptors in PAF signaling alone and in a receptor co-expression paradigm. He will determine the molecular basis of their distinct ligand binding and G protein-coupling phenotypes to provide new insights into the structure/function relationships of both receptor forms. He will assess the role of conserved negatively charged residues in extracellular receptor domains in ligand binding and the relative effects of receptor-mediated vs. RGS protein-mediated attenuation in PAF-stimulated signaling. RGS proteins are a recently described family of proteins that regulate G protein-coupled signaling and PAF signaling. Dr. Fisher has demonstrated that one of these proteins, RGS3, is involved in regulating PAF signaling. The proposed studies will provide novel insights into the molecular basis of action of PAF and should have broad implications in understanding PAF signaling in liver and other tissues.
