CALCIUM SIGNALING BY THE HIGH-AFFINITY MACROPHAGE FC-GAMMA RECEPTOR REQUIRES THE CYTOSOLIC DOMAIN

Hematopoietic cells express multiple receptors which bind the Fc domain of IgG. We utilized transfection of COS-1 cells, a cell line which lacks endogenous Fc receptors, to study the expression and function of Fc-gamma-RI, the high affinity Fc-gamma receptor in the absence of other Fc-gamma receptors. Fc-gamma-RI was efficiently expressed in transiently transfected COS-1 cells as measured by flow cytometry and the binding of IgG sensitized RBCs (EA). In addition, analysis at the single cell level demonstrated that individually transfected COS-1 cells release cytosolic free Ca2+ [(Ca2+)i] upon activation with anti-Fc-gamma-RI antibody. The calcium response required Fc-gamma-RI cross-linking. COS-1 cells transfected with mutant Fc-gamma-RI lacking the cytosolic domain expressed Fc-gamma receptors and bound EA as well as wild type receptors, but failed to induce an increase in [Ca2+]i. These data indicate that Fc-gamma-RI in the absence of other Fc-gamma-RI receptors mediates a calcium signal and that the cytoplasmic domain of Fc-gamma-RI contains the elements required for calcium dependent signal transduction.