Study of the role of ectokinase on the signal transduction in mast cells

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We examined the effects of K252b, an ectoprotein kinase inhibitor of microbial origin, on the activation of RBL-2H3 cells by cross-linking of IgB receptors or by the Ca^<2+> ionophore A23187. Analysis of phosphorylation of ectoproteins following IgE receptor cross-linking revealed that K252b mainly inhibited the phosphorylation of a 130-kDa protein. The inhibitor simultaneously inhibited the degranulation and the sustained increase in the cytosolic calcium ion concentration even afteraddition of Ag. In contrast, K252b did not inhibit the increase in degranulation and cytosolic calcium ion concentration caused by stimulation with A23187. Permeation of K252b into RBL-2H3 cells, assessed by fluorescence intensity, was very low. K252b also inhibited de-granulation caused by IgE receptor cross-linking in human basophils, but did not inhibit the de-granuation caused by A23187. Thus, our findings suggest that the effects of K252b may be mediated by outersurface-bound or -anchored K252b-sensitive molecules on RBL-2H3 cells and human basophils, and that the phosphorylation of ectoprotein may be involve a transmembrane influx of Ca^<2+> by IgE rece-ptor cross-linking.