INFLUENCE OF CLOSTRIDIUM-BOTULINUM C2 TOXIN ON FC-EPSILON-RI-MEDIATEDSECRETION AND TYROSINE PHOSPHORYLATION IN RBL CELLS

We studied the effects of the binary Clostridium botulinum C2 toxin on stimulated [H-3]serotonin release and protein tyrosine phosphorylatio n in RBL 2H3 hm1 cells. Actin was specifically ADP-ribosylated by C2 t oxin in intact cells resulting in a 2-3 fold increase in antigen-or ca lcium ionophore (A23187)-induced degranulation. The effects of C2 toxi n were time-and concentration-dependent. Toxin treatment, which dramat ically changes the morphology of RBL cells, was not sufficient to indu ce mediator release in the absence of activators of secretion. Antigen -and A23187-stimulated tyrosine phosphorylation of 60-80 kDa and 110-1 20 kDa proteins was reduced or blocked after C2 toxin incubation. Trea tment of RBL cells with the tyrosine phosphatase inhibitor pervanadate reversed the inhibitory effect of C2 toxin on stimulated protein tyro sine phosphorylation indicating activation of phosphatases by C2 toxin . The data indicate that disassembly of the actin cytoskeleton by C2 t oxin facilitates Fc epsilon RI-mediated signal-secretion coupling and suggest a role of the actin cytoskeleton in phosphatase regulation in RBL cells.