title: Co-aggregation of FcgammaRII with FcepsilonRI on human mast cells inhibits antigen-induced secretion and involves SHIP-Grb2-Dok complexes.
abstract: Signaling through the high affinity IgE receptor FcepsilonRI on human basophils and rodent mast cells is decreased by co-aggregating these receptors to the low affinity IgG receptor FcgammaRII. We used a recently described fusion protein, GE2, which is composed of key portions of the human gamma1 and the human epsilon heavy chains, to dissect the mechanisms that lead to human mast cell and basophil inhibition through co-aggregation of FcgammaRII and FcepsilonRI. Unstimulated human mast cells derived from umbilical cord blood express the immunoreceptor tyrosine-based inhibitory motif-containing receptor FcgammaRII but not FcgammaRI or FcgammaRIII. Interaction of the mast cells with GE2 alone did not cause degranulation. Co-aggregating FcepsilonRI and FcgammaRII with GE2 1) significantly inhibited IgE-mediated histamine release, cytokine production, and Ca(2+) mobilization, 2) reduced the antigen-induced morphological changes associated with mast cell degranulation, 3) reduced the tyrosine phosphorylation of several cellular substrates, and 4) increased the tyrosine phosphorylation of the adapter protein downstream of kinase 1 (p62(dok); Dok), growth factor receptor-bound protein 2 (Grb2), and SH2 domain containing inositol 5-phosphatase (SHIP). Tyrosine phosphorylation of Dok was associated with increased binding to Grb2. Surprisingly, in non-stimulated cells, there were complexes of phosphorylated SHIP-Grb2-Dok that were lost upon IgE receptor activation but retained under conditions of Fcepsilon-Fcgamma co-aggregation. Finally, studies using mast cells from Dok-1 knock-out mice showed that IgE alone triggers degranulation supporting an inhibitory role for Dok degranulation. Our results demonstrate how human FcepsilonRI-mediated responses can be inhibited by co-aggregation with FcgammaRIIB and implicate Dok, SHIP, and Grb2 as key intermediates in regulating antigen-induced mediator release.
authors.affiliation: Department of Internal Medicine, Virginia Commonwealth University Health Systems, Richmond, Virginia 23298, USA. clkepley@mail1.vcu.edu
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Kepley
authors.forename: Sharven
authors.initials: S
authors.lastname: Taghavi
authors.forename: Graham
authors.initials: G
authors.lastname: Mackay
authors.forename: Daocheng
authors.initials: D
authors.lastname: Zhu
authors.forename: Penelope A
authors.initials: PA
authors.lastname: Morel
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.forename: John J
authors.initials: JJ
authors.lastname: Ryan
authors.forename: Leslie S
authors.initials: LS
authors.lastname: Satin
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: Pier P
authors.initials: PP
authors.lastname: Pandolfi
authors.forename: Andrew
authors.initials: A
authors.lastname: Saxon
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000276:immunology / Q000378:metabolism; D000941:Antigens / Q000276:immunology; D015550:Cell Degranulation / Q000276:immunology*; D004268:DNA-Binding Proteins / Q000276:immunology / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D006636:Histamine Release / Q000276:immunology; D006801:Humans; D008407:Mast Cells / Q000276:immunology / Q000502:physiology*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010750:Phosphoproteins / Q000276:immunology / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000276:immunology / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000276:immunology / Q000378:metabolism; D011940:Receptor Aggregation / Q000276:immunology; D017455:Receptors, IgE / Q000276:immunology* / Q000378:metabolism; D017452:Receptors, IgG / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000941:Antigens; D004268:DNA-Binding Proteins; C489560:DOK1 protein, human; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D017455:Receptors, IgE; D017452:Receptors, IgG; D010744:Phosphoric Monoester Hydrolases; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases