Induction of secreted type IIA phospholipase A(2) gene transcription by interleukin-1 beta - Role of C/EBP factors

Secreted type IIA phospholipase A(2), which is involved in arachidonic acid release, is abundantly produced by chondrocytes and secreted in the synovi al fluids of patients affected by rheumatoid arthritis. Transfection experi ments showed that interleukin-1 beta stimulates the phospholipase A(2) [-16 14; +20] promoter activity by 6-7-fold and that the [-210; -176] fragment i s critical for this stimulation. CAAT enhancer-binding protein (C/EBP) beta and C/EBP delta transcription factors bind to this element as shown by ban dshift experiments. Interleukin-1 beta increased the levels of C/EBP delta mRNA as soon as 2 h and up to 24 h without affecting those of C/EBP delta, Higher amounts of C/EBP delta proteins correlate with the stimulation of C/ EBP delta mRNA Mutations or 5' deletions in the upstream [-247; -210] regio n reduced by 2-fold the basal and interleukin-1 beta-stimulated transcripti on activities. Two types of factors bind to overlapping sequences on this f ragment: NF1-like proteins and the glucocorticoid receptor. The glucocortic oid receptor is responsible for a moderate stimulation of the promoter acti vity by dexamethasone and may interact with C/EBP factors to achieve a full transcription activity in basal conditions and in the presence of interleu kin-1 beta. A [-114; -85] proximal regulatory element forms three complexes in bandshift experiments, the slowest mobility one involving the Sp1 zinc finger factor. Mutation of this sequence reduced to 2-fold the stimulation of the promoter activity by interleukin-1 beta or the C/EBP factors. Induct ion of the transcription of secreted type IIA phospholipase A(2) gene by in terleukin-1 beta in chondrocytes absolutely requires C/EBP beta and C/EBP d elta factors but does not involve NF-kappa B.