AGGREGATION OF THE FC-EPSILON-RI ON MAST-CELLS STIMULATES C-JUN AMINO-TERMINAL KINASE-ACTIVITY - A RESPONSE INHIBITED BY WORTMANNIN

Aggregation of the high-affinity Fc receptors for immunoglobulin E (Ig E) (Fc epsilon RI) on the surface of mast cells initiates intracellula r signal transduction pathways including the tyrosine phosphorylation of cellular proteins, phosphoinositide hydrolysis, an increase in intr acellular calcium, and protein kinase C activation. These signals are believed to be involved in the exocytic release of inflammatory mediat ors such as vasoactive amines, cytokines, and lipid metabolites. Howev er, the downstream consequences of these early activation events are n ot well defined. One exception is the activation of the extracellular signal-regulated kinases/mitogen-activated protein kinases. One member of the mitogen-activated protein kinase superfamily, designated c-Jun amino-terminal kinase (JNK), has been recently identified. JNK is act ivated following dual phosphorylation at a Thr-Pro-Tyr motif in respon se to diverse stimuli including tumor necrosis factor-alpha, heat shoc k, or ultraviolet irradiation. We found that JNK was strongly activate d by antigen cross-linking in a mouse mast cell line passively sensiti zed with ovalbumin-specific IgE. Anti-mouse IgE antibody also activate d JNK. MEK kinase 1 (MEKK1) which activates the JNK activator, JNK kin ase (JNKK), was similarly activated by antigen stimulation. JNK but no t p42(erk2) activation induced by antigen was significantly inhibited in the presence of wortmannin, a known inhibitor of phosphatidylinosit ol 3-kinase. These results indicate that in response to the aggregatio n of Fc epsilon RI on mast cells, phosphatidylinositol 3-kinase activa tion is involved in the stimulation of the MEKK1, JNKK, JNK pathway.