Abstract
FcγRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcγRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcγRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcγRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcγRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcγRIIIb. This effect was not restricted to FcγRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.
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