INHIBITION BY DEXAMETHASONE OF ANTIGEN-INDUCED C-JUN N-TERMINAL KINASE ACTIVATION IN RAT BASOPHILIC LEUKEMIA-CELLS

Antigen stimulation of IgE-sensitized rat basophilic leukemia RBL-2H3 cells induced activation of c-Jun N-terminal kinase (JNK) within a few minutes with maximum activity attained 40 min later. The increase in JNK activity was accompanied with an increase in phosphorylation of c- Jun in the cells. The dg-induced JNK activation was inhibited by the p hosphatidylinositol 3-kinase inhibitors wortmannin (10-100 nM) and LY 294002 (100 mu M) but not by the protein kinase C inhibitors calphosti n C (1 and 3 mu M) and Ro 31-8425 (1 and 3 mu M). Pretreatment with de xamethasone (10 and 100 nM) for 18 h inhibited the Ag-induced increase in JNK activity in a concentration-dependent manner. At least 6 h of preincubation with dexamethasone was necessary to inhibit the Ag-induc ed JNK activation. The phosphorylation of c-Jun induced by the Ag stim ulation was reduced by pretreatment with dexamethasone without reducti on of the content of c-Jun protein. The Ag-induced activation of the J NK kinase kinase mitogen-activated protein kinase-extracellular signal -regulated kinase kinase-l was also Inhibited by pretreatment with dex amethasone at 10 and 100 nM, These findings indicate that dexamethason e reduces JNK protein level and inhibits the Ag-induced activation of JNK resulting in the inhibition of c-Jun phosphorylation.