MAST-CELL TUMOR-NECROSIS-FACTOR-ALPHA PRODUCTION IS REGULATED BY MEK KINASES

Mast cells synthesize and secrete specific cytokines and chemokines wh ich play an important role in allergic inflammation. Aggregation of th e high-affinity Fc receptor (Fc epsilon RI) for immunoglobulin E (IgE) in MC/9 mouse mast cells stimulates the synthesis and secretion of tu mor necrosis factor alpha (TNF-alpha). Fc epsilon RI aggregation activ ates several sequential protein kinase pathways, leading to increased activity of extracellular signal-regulated kinases (ERKs), c-Jun amino -terminal kinases (JNKs), and the p38 mitogen-activated protein (MAP) kinase, Inhibition of ERKs with the compound PD 098059 bad little effe ct on Fc epsilon RI-stimulated TNF-alpha production, Aggregation of Fc epsilon RI stimulated MEK kinase 1 (MEKK1) activity, which activates JNK kinase (JNKK), the kinase that phosphorylates and activates JNKs, Expression of activated MEKK1 (Delta MEKK1) in MC/9 cells strongly sti mulated JNK activity but only weakly stimulated p38 activity, and it i nduced a large activation of TNF-alpha promoter-regulated luciferase g ene expression, Inhibitory mutant JNK2 expressed in MC/9 cells signifi cantly blunted Fc epsilon RI stimulation of TNF-alpha promoter-driven luciferase expression, Wortmannin, an inhibitor of phosphatidylinosito l 3-kinase, diminished Fc epsilon RI-mediated TNF-alpha synthesis, sig nificantly blunted JNK activation and TNF-alpha promoter-driven lucife rase expression, and only weakly inhibited p38 kinase activation. inhi bition of NF kappa B activation resulting from Delta MEKK1 expression or Fc epsilon RI stimulation did not affect TNF-alpha promoter-driven luciferase expression. Our findings define a MEEK-regulated JNK pathwa y activated by Fc epsilon RI that regulates TNF-alpha production in ma st cells.