Elevated levels of cyclooxygenase-2 in antigen-stimulated mast cells is associated with minimal activation of p38 mitogen-activated protein kinase

We have investigated possible factors that underlie changes in the producti on of eicosanoids after prolonged exposure of mast cells to Ag. Ag stimulat ion of cultured RBL-2H3 mast cells resulted in increased expression of cycl ooxygenase (COX-2) protein and message. Other eicosanoid-related enzymes, n amely COX-1, 5-lipoxygenase, and cytosolic phospholipase A(2) were not indu ced. Activation of extracellular signal-regulated kinase, e-Jun N-terminal kinase, and p38 mitogen-activated protein (MAP) kinase preceded the inducti on of COX-2, whereas phosphatidylinositol 3' kinase and its substrate, Akt, were constitutively activated in RBL-2H3 cells. Studies with pharmacologic inhibitors indicated that of these kinases, only p38 MAP kinase regulated expression of COX-2. The induction of COX-2 was blocked by the p38 MAP kina se inhibitor SB202190, even when added 12-16 h after stimulation with Ag wh en p38 MAP kinase activity had returned to near basal, but still minimally elevated, levels. Interestingly, expression of COX-2 as well as cytosolic p hospholipase A(2) and 5-lipoxygenase were markedly reduced by SB202190 in u nstimulated cells. Collectively, the results imply that p38 MAP kinase regu lates expression of eicosanoid-related enzymes, passively or actively, at v ery low levels of activity in RBL-2H3 cells. Also, comparison with publishe d data suggest that different MAP kinases regulate induction of COX-2 in in flammatory cells of different and even similar phenotype and suggest cautio n in extrapolating results from one type of cell to another.