Transcriptional regulation of the gyclooxygenase-2 gene in activated mast cells

Activation of mast cells by aggregation of their IgE receptors induces rapi d and transient synthesis of cyclooxygenase-2 (COX-2). In this study we inv estigated (i) the cis-acting response elements and transcription factors ac tive at the COX-2 promoter and (ii) the signal transduction pathways mediat ing COX-2 induction following aggregation of mast cell IgE receptors. Trans ient transfection assays with COX-2 promoter/luciferase constructs suggest that a consensus cyclic AMP response element is essential for induced COX-2 expression. Cotransfection studies with plasmids expressing c-Jun, dominan t negative Ras, dominant negative c-Jun NH2-terminal kinase, and dominant n egative MEKK1 demonstrate that activation of the Ras/MEKK1/c-Jun NH2-termin al kinase/c-Jun pathway is required for COX-2 promoter-mediated luciferase expression. Attenuation of COX-2 promoter activity by dominant negative con structs for Raf-1, ERK1, and ERK2 suggests that the Ras/Raf-1/extracellular signal-regulated kinase pathway is also necessary for COX-2 induction. Alt hough mutating the two NF-IL6 sites individually did not affect COX-2 promo ter activity, mutating both NF-IL6 sites substantially inhibits COX-2 promo ter activity. Moreover, overexpression of wild type CCAAT/enhancer-binding protein-beta (C/EBP beta) augments COX-2 promoter activity in activated mas t cells and cotransfection of a dominant negative C/EBP beta construct comp letely blocks COX-2 promoter/luciferase expression. Our data suggest that i n activated mast cells, a Ras/MEKKl/c-Jun NH,terminal kinase signal transdu ction pathway activating c-Jun, a Ras/Raf-1/extracellular signal-regulated kinase pathway, and activated C/EBP beta facilitate COX-2 induction via the cyclic AMP response element and NF-IL6 sites of the COX-2 promoter.