Aggregation of the FcεRI on Mast Cells Stimulates c-Jun Amino-terminal Kinase Activity

Aggregation of the high-affinity Fc receptors for immunoglobulin E (IgE) (FceRI) on the surface of mast cells initiates intracellular signal transduction pathways including the tyrosine phosphorylation of cellular proteins, phosphoinositide hydrolysis, an increase in intracellular calcium, and protein kinase C activation. These signals are believed to be involved in the exocytic release of inflammatory mediators such as vasoactive amines, cytokines, and lipid metabolites. However, the downstream consequences of these early activation events are not 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 activated following dual phosphorylation at a Thr-Pro-Tyr motif in response to diverse stimuli including tumor necrosis factor-α, heat shock, or ultraviolet irradiation. We found that JNK was strongly activated by antigen cross-linking in a mouse mast cell line passively sensitized with ovalbumin-specific IgE. Anti-mouse IgE antibody also activated JNK. MEK kinase 1 (MEKK1) which activates the JNK activator, JNK kinase (JNKK), was similarly activated by antigen stimulation. JNK but not p42erk2 activation induced by antigen was significantly inhibited in the presence of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase. These results indicate that in response to the aggregation of FceRI on mast cells, phosphatidylinositol 3-kinase activation is involved in the stimulation of the MEKK1, JNKK, JNK pathway.