ENGAGEMENT OF THE HIGH-AFFINITY IGE RECEPTOR ACTIVATES SRC PROTEIN-RELATED TYROSINE KINASES

THE high-affinity IgE receptor (Fc-epsilon RI), 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 Fc-epsilon-RI-mediated signal transduction, surface engagement of Fc-epsilon-RI induces histamine release and the tyrosine phosphorylation of several distinct proteins 1. Although the alpha, beta and gamma-subunits of Fc-epsilon-RI lack intrinsic tyrosine protein kinase (TPK) activity, a kinase that copurifies with Fc-epsilon-RI phosphorylates the beta and gamma-subunits of the receptor on tyrosine residues 2,3. We report here that in RBL-2H3 cells, p56lyn and pp60c-src are activated after Fc-epsilon-RI crosslinking, and p56lyn coimmunoprecipitates with Fc-epsilon-RI. In the mouse mast-cell line PT-18, another cell type used to study FC-epsilon-RI-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 p62c-yes, and it is this TPK that is activated on Fc-epsilon-RI 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.