Inhibition of degranulation of RBL-2H3 cells by casein kinase II substrate peptide

In a previous study, we demonstrated the existence of casein kinase II-like ectokinase activity on rat basophilic leukemia 2H3 (RBL-2H3) cells (Immunol. Let. 68, 369, 1999), and to determine the role of ectokinase in the degranulation of RBL-2H3 cells, in this study we investigated the effect of casein kinase II substrate peptide on the degranulation by the cells. Casein kinase II peptide (RRRDDDSDDD) dose-dependently (IC₅₀ = 50 μM) inhibited β-hexosaminidase release by IgE-sensitized antigen-stimulated RBL-2H3 cells, whereas casein kinase II peptide analogue (RRRDDDADDD) only partially inhibited β-hexosaminidase release by antigen-stimulated RBL-2H3 cells. Preincubation of RBL-2H3 cells with 200 μM of casein kinase II peptide significantly inhibited external 130 kDa protein phosphorylation, and casein kinase II peptide inhibited the sustained increase in cytosolic calcium ion concentration in response to antigen stimulation. Our findings suggest that casein kinase II acts as an ectokinase in RBL-2H3 cells and that casein kinase II peptide acts as a competitor for phosphorylation of ectoprotein, which involves degranulation and a transmembrane influx of Ca²⁺ by IgE receptor cross-linking. Another casein kinase II inhibitor, GT copolymer, also inhibited the degranulation of antigen-stimulated RBL-2H3 cells. Thus, the modulator of casein kinase II activity seems to be a good tool for the inhibitor of signal transduction in RBL-2H3 cells.