Engagement of the high-affinity IgE receptor activates src protein-related tyrosine kinases

THE high-affinity IgE receptor (FcɛRI), which is expressed on the surface of mast cells and basophils, has a central role in immediate allergic responses. In the rat basophilic leukaemia cell line RBL-2H3, which is a model system for the analysis of FcɛRI-mediated signal transduction, surface engagement of FcɛRI induces histamine release and the tyrosine phosphorylation of several distinct proteins 1 . Although the α, β and γ subunits of FcɛRI lack intrinsic tyrosine protein kinase (TPK) activity, a kinase that copurifies with FcɛRI phosphorylates the β and γ subunits of the receptor on tyrosine residues 2,3 . We report here that in RBL-2H3 cells, p56 lyn and pp60 c-src are activated after FcɛRI crosslinking, and p56 lyn coimmunoprecipitates with FcɛRI. In the mouse mastcell line PT-18, another cell type used to study FCɛRI-mediated signalling, tyrosine phosphorylation of proteins is also an immediate consequence of receptor crosslinking. Notably, the only detectable src protein-related TPK in PT-18 cells is p62 c-yes , and it is this TPK that is activated on FcɛRI engagement and coimmunoprecipitates with the receptor. Therefore, it seems that different src protein-related TPKs can associate with the same receptor and become activated after receptor engagement.