Signal transduction in IgE receptor transfected mast cells

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We estabilshed the IgE receptor transfected-mouse mastocytoma P815 cells. The IgE receptors are composed of three types of polypeptides ; an IgE-biniding alpha subunit, a beta subunit, and two disulfide-linked gamma subunits. Three types of P815 transfectant were made ; cDNAs coding for each of whole three subunits were introduced (Wt) , cDNAs coding for whole alpha and gamma subunit and C-terminal depleted beta subunit were introduced (beta cd), cDNAs coding for whole alpha and beta subunit and C-terminal depleted gamma subunit were introduced (gamma cd). In Wt cells, endocytosis fo IgE receptors, tyrosine phosphorylation of beta and gamma subunit of IgE receptors, Lyn and Syk kinases and 42k protein ware increased. And the cytosolic Ca^<2+> concentration ([Ca^<2+>]i) and CD63 antigen expression on the cell surfaces were increased. However, in beta cd and gamma cd cells, the endocytosis of IgE receptor, tyrosine phosphorylation of above proteins, [Ca^<2+>]i increase and CD 63 antigen expression on the cells were not or little increased. In Wt cells, CD63 antigen expression on the cell surfaces was mostly blocked by the preteatment of herbimycin A.The surface expression of CD63 antigen reflected the degranulation in RBL-2H3 cells. Therefore, these results suggested that tyrosing phosphorylation of the C-terminal cytoplasmic domains of beta and gamma subunits was essential for IgE receptor endo cytosis, [Ca^<2+>]i increase and degranulation.