Effects of herbimycin A and ST638 on Fc epsilon receptor-mediated histamine release and Ca2+ signals in rat basophilic leukemia (RBL-2H3) cells.

We examined the effect of the two protein tyrosine kinase inhibitors, alpha-cyano-3-ethoxy-4-hydroxy-5-phenylthiomethylcinnamide (ST638) and herbimycin A, on the activation processes of rat basophilic leukemia (RBL-2H3) cells by cross-linking of IgE receptors. RBL-2H3 cells sensitized with DNP-specific monoclonal IgE antibody were stimulated with multivalent antigen (DNP conjugate of bovine serum albumin). Analysis of phosphotyrosine-containing proteins in their lysates by SDS-PAGE and immunoblotting revealed that these two inhibitors efficiently inhibited the tyrosine phosphorylation of several proteins (32, 42, 56, 66, 72, 92, 150 kDa) including phospholipase C-gamma 1. The inhibitors also caused parallel inhibitions of the histamine release, the formation of inositol 1,4,5-trisphosphate, and the increase in cytosolic calcium ion concentration at the late sustained phase. A digital imaging fluorescence microscopic analysis of antigen-dependent calcium signals in individual cells showed that these two tyrosine kinase inhibitors inhibited the calcium influx from the external medium more powerfully than the mobilization of calcium ion from internal stores. In contrast, the inhibitors did not affect the increase in the cytosolic calcium ion concentration or the histamine release induced by the calcium ionophore A23187. Taken together, our results suggest that tyrosine phosphorylation following antigen stimulation regulates phosphatidylinositol hydrolysis and the influx of extracellular calcium.