Convergence of Fc gamma receptor IIA and Fc gamma receptor IIIB signaling pathways in human neutrophils.
Human neutrophils (PMNs) express two receptors for the Fc domain of IgG: the transmembrane FcgammaRIIA, whose cytosolic sequence contains an immunoreceptor tyrosine-based activation motif, and the GPI-anchored FcgammaRIIIB. Cross-linking of FcgammaRIIIB induces cell activation, but the mechanism is still uncertain. We have used mAbs to cross-link selectively each of the two receptors and to assess their signaling phenotypes and functional relation. Cross-linking of FcgammaRIIIB induces intracellular Ca2+ release and receptor capping. The Ca2+ response is blocked by wortmannin and by N,N-dimethylsphingosine, inhibitors of phosphatidylinositol 3-kinase and sphingosine kinase, respectively. Identical dose-response curves are obtained for the Ca2+ release stimulated by cross-linking FcgammaRIIA, implicating these two enzymes in a common signaling pathway. Wortmannin also inhibits capping of both receptors, but not receptor endocytosis. Fluorescence microscopy in double-labeled PMNs demonstrates that FcgammaRIIA colocalizes with cross-linked FcgammaRIIIB. The signaling phenotypes of the two receptors diverge only under frustrated phagocytosis conditions, where FcgammaRIIIB bound to substrate-immobilized Ab does not elicit cell spreading. We propose that FcgammaRIIIB signaling is conducted by molecules of FcgammaRIIA that are recruited to protein/lipid domains induced by clustered FcgammaRIIIB and, thus, are brought into juxtaposition for immunoreceptor tyrosine-based activation motif phosphorylation and activation of PMNs.
Chuang
F Y
FY
Department of Biochemistry, Mount Sinai School of Medicine, New York 10029, USA.
Sassaroli
M
M
Unkeless
J C
JC
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D007941:Leukemia P388; D008024:Ligands; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D051379:Mice; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D010587:Phagocytosis / Q000187:drug effects / Q000276:immunology; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011940:Receptor Aggregation / Q000187:drug effects / Q000276:immunology; D017452:Receptors, IgG / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D007166:Immunosuppressive Agents; D008024:Ligands; D020033:Protein Isoforms; D017452:Receptors, IgG; C061800:N,N-dimethylsphingosine; D013110:Sphingosine; D002118:Calcium; D000077191:Wortmannin