Requirement of Fc Epsilon RI Gamma-subunit for IgE-mediated Up-regulation of Surface Fc Epsilon RI

Abstract

RATIONALE: Since FcεRIα cannot be expressed at the cell surface without the FcRγ-subunit, it has not been clarified whether the FcRγ and the transmembrane domain (TM) and cytoplasmic domain (CY) of FcεRIα are necessary for IgE-mediated FcεRIα up-regulation.METHODS: To clarify the role of the TM and CY of FcεRI in IgE-mediated cell surface expression of FcεRI, we constructed chimeric receptors and transduced them into a human mast cell line, HMC-1, with a viral vector system. To determine the contribution of the FcRγ to receptor up-regulation, an FcεRI chimera containing the TM and CY of FcγRIα was expressed in cell line NIH3T3 with or without co-transduction of the FcRγ. IgE-mediated FcεRI up-regulation of the chimeric receptors was examined by FACS.RESULTS: An FcεRI chimera containing the TM and CY or just the CY of FcγRIα was expressed on the cell surface, and they mediated efficient IgE-dependent up-regulation. Full-length FcγRI and an FcγRI chimera containing the TM and CY or just the CY of FcεRIα did not mediate IgG1-dependent up-regulation. The FcεRI chimera containing the TM and CY of FcγRIα failed to mediate IgE-dependent up-regulation. Co-transduction of either FcRγ, FcRγ ITAM mutant or a CY deletion mutant for FcRγ to the cells recovered its response to IgE.CONCLUSIONS: IgE-mediated up-regulation of FcγRIα requires FcRγ, but does not require activation signals by FcRγ ITAM. RATIONALE: Since FcεRIα cannot be expressed at the cell surface without the FcRγ-subunit, it has not been clarified whether the FcRγ and the transmembrane domain (TM) and cytoplasmic domain (CY) of FcεRIα are necessary for IgE-mediated FcεRIα up-regulation. METHODS: To clarify the role of the TM and CY of FcεRI in IgE-mediated cell surface expression of FcεRI, we constructed chimeric receptors and transduced them into a human mast cell line, HMC-1, with a viral vector system. To determine the contribution of the FcRγ to receptor up-regulation, an FcεRI chimera containing the TM and CY of FcγRIα was expressed in cell line NIH3T3 with or without co-transduction of the FcRγ. IgE-mediated FcεRI up-regulation of the chimeric receptors was examined by FACS. RESULTS: An FcεRI chimera containing the TM and CY or just the CY of FcγRIα was expressed on the cell surface, and they mediated efficient IgE-dependent up-regulation. Full-length FcγRI and an FcγRI chimera containing the TM and CY or just the CY of FcεRIα did not mediate IgG1-dependent up-regulation. The FcεRI chimera containing the TM and CY of FcγRIα failed to mediate IgE-dependent up-regulation. Co-transduction of either FcRγ, FcRγ ITAM mutant or a CY deletion mutant for FcRγ to the cells recovered its response to IgE. CONCLUSIONS: IgE-mediated up-regulation of FcγRIα requires FcRγ, but does not require activation signals by FcRγ ITAM.