The characterization of tyrosine phosphorylation of 78 and 92 kDa proteins in rat basophilic RBL-2H3 cells.

Previously, we have demonstrated that tyrosine phosphorylation of 78 and 92 kDa proteins in rat basophilic leukemia cells (RBL-2H3) is involved in a signal transduction system for high-affinity IgE receptor (Fc epsilon RI)-mediated histamine secretion. However, it is not clarified whether the tyrosine phosphorylation of 78 and 92 kDa proteins in RBL-2H3 cells is regulated by activation of protein kinase C (PKC) or phosphatidylinositol 3-kinase (PI3-kinase). In this study, therefore, the effect of depletion of PKC in RBL-2H3 cells, or the influence of PKC, PI3-kinase and tyrosine kinase inhibitors on histamine release from RBL-2H3 cells was examined. The elimination of PKC in RBL-2H3 cells induced significant suppression of histamine release, although the tyrosine phosphorylation of 78 and 92 kDa proteins was not inhibited. The inhibition of histamine release was also observed by the treatment with a PKC inhibitor such as H-7, calphostin C, a PI3-kinase inhibitor such as wortmannin or a tyrosine kinase inhibitor such as ST638, genistein, hervimycin A, although the tyrosine phosphorylation of both proteins was inhibited by only ST638. These results suggest that the 78 kDa protein in RBL-2H3 cells is not identical to the protein-tyrosine kinase PTK72 and the tyrosine phosphorylation of 78 and 92 kDa proteins in RBL-2H3 cells occurs upstream of PKC and PI3-kinase activation or is regulated independently of the PKC- and PI3-kinase-dependent signaling pathway.