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Distinct Functions of the Fc∊R1 γ and β Subunits in the Control of Fc∊R1-mediated Tyrosine Kinase Activation and Signaling Responses in RBL-2H3 Mast Cells

1995; Elsevier BV; Volume: 270; Issue: 8 Linguagem: Inglês

10.1074/jbc.270.8.4013

1083-351X

Bridget S. Wilson, Nicholas Kapp, Rebecca Lee, Janet R. Pfeiffer, A. Marina Martinez, Yehudit Platt, François Letourneur, Janet M. Oliver,

Mast cells and histamine

In RBL-2H3 rat tumor mast cells, cross-linking the high affinity IgE receptor, Fc∊R1, activates the protein-tyrosine kinases Lyn and Syk and initiates a series of responses including protein-tyrosine phosphorylation, inositol 1,4,5-trisphosphate synthesis, Ca2+ mobilization, secretion, membrane ruffling, and actin plaque assembly. The development of chimeric receptors containing cytoplasmic domains of individual subunits of the heterotrimeric (αβγ2) Fc∊R1 has simplified analyses of early signaling events in RBL-2H3 cells. Here, RBL-2H3 cells were transfected with cDNAs encoding the extracellular and transmembrane domains of the interleukin-2 receptor α subunit (the Tac antigen) joined to the C-terminal cytoplasmic domains of the Fc∊R1 γ and β subunits (TTγ and TTβ). Both sequences contain tyrosine activation motifs implicated in antigen receptor signal transduction. TTγ and TTβ are expressed independently of the native Fc∊R1, as demonstrated by the ability of Tac cross-linking agents to trigger the clustering and internalization through coated pits of both chimeric receptors without co-clustering the Fc∊R1. A full range of signaling activities is induced by TTγ cross-linking; the TTγ-induced responses are slower and, except for Lyn activation, smaller than the Fc∊R1-induced responses. In striking contrast, TTβ cross-linking elicits no tyrosine phosphorylation or signaling responses, it impairs basal activities measured in secretion and anti-PY (anti-phosphotyrosine antibody) immune complex kinase assays, and it antagonizes Fc∊R1-induced Lyn and Syk activation, protein-tyrosine phosphorylation, and signaling responses. We hypothesize that the isolated β subunit binds a specific kinase or coupling protein(s) required for signaling activity, sequestering it from the signal-transducing γ subunit. Binding the same kinase or coupling protein to the β subunit of the intact Fc∊R1 may serve instead to present it to the adjacent γ subunit, resulting in enhanced kinase activation and signaling responses. In RBL-2H3 rat tumor mast cells, cross-linking the high affinity IgE receptor, Fc∊R1, activates the protein-tyrosine kinases Lyn and Syk and initiates a series of responses including protein-tyrosine phosphorylation, inositol 1,4,5-trisphosphate synthesis, Ca2+ mobilization, secretion, membrane ruffling, and actin plaque assembly. The development of chimeric receptors containing cytoplasmic domains of individual subunits of the heterotrimeric (αβγ2) Fc∊R1 has simplified analyses of early signaling events in RBL-2H3 cells. Here, RBL-2H3 cells were transfected with cDNAs encoding the extracellular and transmembrane domains of the interleukin-2 receptor α subunit (the Tac antigen) joined to the C-terminal cytoplasmic domains of the Fc∊R1 γ and β subunits (TTγ and TTβ). Both sequences contain tyrosine activation motifs implicated in antigen receptor signal transduction. TTγ and TTβ are expressed independently of the native Fc∊R1, as demonstrated by the ability of Tac cross-linking agents to trigger the clustering and internalization through coated pits of both chimeric receptors without co-clustering the Fc∊R1. A full range of signaling activities is induced by TTγ cross-linking; the TTγ-induced responses are slower and, except for Lyn activation, smaller than the Fc∊R1-induced responses. In striking contrast, TTβ cross-linking elicits no tyrosine phosphorylation or signaling responses, it impairs basal activities measured in secretion and anti-PY (anti-phosphotyrosine antibody) immune complex kinase assays, and it antagonizes Fc∊R1-induced Lyn and Syk activation, protein-tyrosine phosphorylation, and signaling responses. We hypothesize that the isolated β subunit binds a specific kinase or coupling protein(s) required for signaling activity, sequestering it from the signal-transducing γ subunit. Binding the same kinase or coupling protein to the β subunit of the intact Fc∊R1 may serve instead to present it to the adjacent γ subunit, resulting in enhanced kinase activation and signaling responses.