Association of IgG Fc receptor II with tyrosine kinases in the human basophilic leukemia cell line KU812F

Abstract

Background: We previously reported that crosslinking of IgG Fc receptor II (FcγRII) induces intracellular calcium mobilization, but not histamine release in human basophils. To clarify functional activities of FcγRII on human basophils, we analyzed the FcγRII-mediated signaling events in the human basophilic leukemia cell line KU812F. Methods: Flow cytometric methods were used to investigate the effect on intracellular calcium mobilization of cross-linking of FcγRII. KU812F cells were pre-incubated with anti-FcγRII monoclonal antibody (IV.3). After the addition of various concentrations of the tyrosine kinase inhibitor genistein or buffer alone, cells were stimulated with goat antimouse IgG F(ab') 2 (GAM) and analyzed with the flow cytometer. Next, in order to test the signaling events after cross-linking of FcγRII, we examined tyrosine kinase activity. The time-course of tyrosine phosphorylation after cross-linking of FcγRII and the effect of genistein on this tyrosine phosphorylation were tested by immunoblotting. Immunoprecipitation was also performed to identify the type of tyrosine kinase associated with signal transduction of FcγRII. Results: The tyrosine kinase inhibitor genistein inhibited intracellular calcium mobilization caused by cross-linking of FcγRII in a dose-dependent manner. Rapid tyrosine phosphorylation after FcγRII cross-linking was shown by immunoblot analysis and this phosphorylation was inhibited by genistein. Furthermore, tyrosine phosphorylation of Lyn and Syk was observed upon cross-linking of FcγRII. Conclusions: Tyrosine phosphorylation is necessary for the signaling pathway through FcγRII and tyrosine phosphorylation of Lyn and Syk, at least, is actively involved in this signal transduction.