Possible involvement of phosphorylation of a 36,000-dalton protein of rat basophilic leukemia (RBL-2H3) cell membranes in serotonin release.

Phosphorylation of a 36,000-dalton (36k-Da) protein of rat basophilic leukemia (RBL-2H3) cell membranes was investigated. This phosphoprotein has been suggested to be the beta-subunit protein of the immunogloblin E (IgE) receptor of RBL-2H3 cells [Teshima et al., Biochem. biophys. Res. Commun. 125, 867-874 (1984)]. Phospholipids such as phosphatidyl serine, phosphatidyl inositol and phosphatidyl ethanolamine, which are known to be activators of protein kinase C, enhanced the phosphorylation of the 36K-Da protein. In contrast, 1-(5-isoquinoline sulfonyl)-2-methylpiperazine (H-7) which has been identified as a potent inhibitor of protein kinase C in vitro decreased incorporation of radioactive phosphate from [gamma-32P]ATP into this protein. These results indicate that the phosphorylation of the 36K-Da protein of RBL-2H3 cell membranes is catalyzed by protein kinase C. H-7 also inhibited the release of serotonin from RBL-2H3 cells stimulated with an antigen or calcium ionophore A23187 and 12-O-tetradecanoyl phorbol 13-acetate (TPA). Treatment of the antigen-stimulated cells with TPA caused a synergistic effect on the serotonin release. A similar effect was obtained by treatment of A23187-stimulated cells with TPA or 1-oleoyl-2-acetyl glycerol.