Single nucleotide polymorphism of human platelet-activating factor receptor impairs G-protein activation

Various proinflammatory and vasoactive actions of platelet-activating facto r (PAF) are mediated through a specific G-protein-coupled PAF receptor (PAF R). We identified a novel DNA variant in the human PAFR gene, which substit utes an aspartic acid for an alanine residue at position 224 (A224D) in the putative third cytoplasmic loop. This mutation was observed in a Japanese population at an allele frequency of 7.8%. To delineate the functional cons equences of this structural alteration, Chinese hamster ovary cells were st ably transfected with constructs encoding either wild-type or A224D mutated PAFR. No significant difference was observed in the expression level of th e receptor or the affinity to PAF or to an antagonist, WEB2086, between the cells transfected with wild-type and mutant PAFR. Chinese hamster ovary ce lls expressing A224D mutant PAFR displayed partial but significant reductio n of PAF-induced intracellular signals such as calcium mobilization, inosit ol phosphate production, inhibition of adenylyl cyclase, and chemotaxis. Th ese findings suggest that this variant receptor produced by a naturally occ urring mutation exhibits impaired coupling to G-proteins and may be a basis for interindividual variation in PAF-related physiological responses, dise ase predisposition or phenotypes, and drug responsiveness.