Transmembrane mutations to FcγRIIA alter its association with lipid rafts:: Implications for receptor signaling

Many immunoreceptors have been reported to associate with lipid rafts upon ligand binding. The way in which this association is regulated is still obscure. We investigated the roles for various domains of the human immumoreceptor Fc gamma YRIIA in regulating its association with lipid rafts by determining the resistance of unligated, or ligated and cross-linked, receptors to solubilization by the nonionic detergent Triton X-100, when expressed in RBL-2H3 cells. Deletion of the cytoplasmic domain, or destruction of the cytoplasmic pahnitoylation site, had no effect on the association of the receptor with lipid rafts. A transmembrane mutant, A224S, lost the ability to associate with lipid rafts upon receptor cross-linking, whereas transmembrane mutants VA231-2MM and VVAL234-7GISF showed constitutive lipid raft association. Wild-type (WT) Fc gamma RIIA and all transmembrane mutants activated Syk, regardless of their association with lipid rafts. WT Fc gamma RIIA and mutants that associated with lipid rafts efficiently activated NF-kappa 3, in an ERK-dependent manner. In contrast, WT Fc gamma RIIA and the A224S mutant both presented efficient phagocytosis, while VA231-2MM and VVAL234-7GISF mutants presented lower phagocytosis, suggesting that phagocytosis may proceed independently of lipid raft association. These data identify the transmembrane domain of Fc gamma RIIA as responsible for regulating its inducible association with lipid rafts and suggest that Fc gamma RIIA-mediated responses, like NF-kappa B activation or phagocytosis, can be modulated by lipid raft association of the ligated receptor.