FC-EPSILON-R1-MEDIATED TYROSINE PHOSPHORYLATION OF MULTIPLE PROTEINS, INCLUDING PHOSPHOLIPASE C-GAMMA-1 AND THE RECEPTOR BETA-GAMMA-2 COMPLEX, IN RBL-2H3 RAT BASOPHILIC LEUKEMIA-CELLS

In basophils, mast cells, and the RBL-2H3 tumor mast cell line, cross-linking the high-affinity immunoglobulin E receptor (Fc-epsilon-R1) stimulates a series of responses, particularly the activation of phospholipase C (PLC), that lead to allergic and other immediate hypersensitivity reactions. The mechanism of activation of PLC, however, is not clear. Here, we show that cross-linking Fc-epsilon-R1 on RBL-2H3 cells causes the tyrosine phosphorylation of at least 12 cellular proteins, including PLC-gamma-1 (PLC-gamma-1) and the receptor-beta and gamma-subunits. P-32-labeled PLC-gamma-1 can be detected by anti-phosphotyrosine antibody as early as 10 s after the addition of antigen. The tyrosine-phosphorylated 33-kDa beta-subunit and 9- to 11-kDa gamma-subunit of the Fc-epsilon-R1 are additionally phosphorylated on serine and theonine residues, respectively, and are found as complexes with other phosphotyrosine-containing proteins in antigen-stimulated cells. Our results indicate a means by which the Fc-epsilon-R1 may control PLC activity in RBL-2H3 cells and raise the possibility that other receptor-mediated signalling events in mast cells may also be controlled through protein tyrosine phosphorylation.