LIGAND-SENSITIVE BINDING OF ACTIN-BINDING PROTEIN TO IMMUNOGLOBULIN-G FC RECEPTOR-I (FC-GAMMA-RI)

The high affinity receptor that binds the Fc domain of immunoglobulin G (IgG) subclasses 1 and 3 (Fc-gamma-RI) mediates important immune defense functions by inducing cell surface changes on human leukocytes. In this article, we document direct high affinity binding of Fc-gamma-RI to the actin filament cross-linking protein, actin-binding protein (ABP). In the absence of IgG, all Fc-gamma-RI molecules in undifferentiated cells of myeloid line U937 bound to ABP over a 9-fold range of Fc-gamma-RI expression induced by human IFN-gamma. Binding of IgG to U937 cells constitutively expressing Fc-gamma-RI or to COS cells genetically transfected to express Fc-gamma-RI rapidly decreased the avidity of Fc-gamma-RI for ABP. This finding suggests the existence of a pathway communicating a signal between a functional IgG receptor and intracellular components involved in the effector responses to Fc-gamma-RI-ligand interaction.