INTERLEUKIN-1-ALPHA AND TUMOR-NECROSIS-FACTOR-ALPHA SYNERGISTICALLY STIMULATE PROSTAGLANDIN E-2-DEPENDENT PRODUCTION OF INTERLEUKIN-11 IN RHEUMATOID SYNOVIAL FIBROBLASTS

Objective. In terleukin-11 (IL-11), an IL-6-type cytokine, is thought to be involved in bone resorption cia osteoclast differentiation. Here , we characterized the combined effect of IL-1 alpha and tumor necrosi s factor alpha (TNF alpha), major cytokines in the rheumatoid synovium , on the production of IL-11 by cultured rheumatoid synovial fibroblas ts (RSFs), Methods. The amounts of IL-11, IL-6, and prostaglandin E-2 (PGE(2)) were measured by enzyme-linked immunosorbent assay. IL-11 mes senger RNA (mRNA) levels were determined by Northern blotting. Protein expression of cytosolic phospholipase A(2) (cPLA(2)), cyclooxygenase 2 (COX-2), and protein kinase C (PKC) isoforms were determined by West ern blotting. Results. 1L-1 alpha and TNF alpha synergistically stimul ated RSFs to produce IL-11 at both the mRNA and protein levels. This s ynergistic effect was completely inhibited by indomethacin, The inhibi tion was prevented by PGE(2), indicating that the synergistic effect o f IL-1 alpha and TNF alpha was PGE(2)-mediated, The cooperative effect s of these 2 cytokines were also observed in the production of PGE(2) and the expression of 2 regulatory enzymes in PGE(2) production, cPLA( 2) and COX-2, The synergistic induction of IL-11 by IL-1 alpha and TNF alpha was completely inhibited by a potent inhibitor of all isoforms of PKC, GF109203X. In contrast, phorbol myristate acetate, which induc ed a down-regulation of PKC, degrading all PKC isoforms except atypica l PKC, did not affect the induction of IL-11, Conclusion. These findin gs suggest that IL-1 alpha and TNF alpha synergistically stimulate the production of IL-11 via their effects on PGE(2) production in the rhe umatoid joint, and that atypical PKC may be another target for down-re gulation of IL-11, the bone resorption-associated cytokine.