Interleukin-1α and tumor necrosis factor α synergistically stimulate prostaglandin E2-dependent production of interleukin-11 in rheumatoid synovial fibroblasts

Abstract

Objective. Interleukin-11 (IL-11), an IL-6-type cytokine, is thought to be involved in bone resorption via osteoclast differentiation. Here, we characterized the combined effect of IL-1α and tumor necrosis factor α (TNFα), major cytokines in the rheumatoid synovium, on the production of IL- 11 by cultured rheumatoid synovial fibroblasts (RSFs). Methods. The amounts of IL-11, IL-6, and prostaglandin E2 (PGE2) were measured by enzyme-linked immunosorbent assay. IL-11 messenger RNA (mRNA) levels were determined by Northern blotting. Protein expression of cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2), and protein kinase C (PKC) isoforms were determined by Western blotting. Results. IL-1α and TNFα synergistically stimulated RSFs to produce IL-11 at both the mRNA and protein levels. This synergistic effect was completely inhibited by indomethacin. The inhibition was prevented by PGE2, indicating that the synergistic effect of IL-1α and TNFα was PGE2-mediated. The cooperative effects of these 2 cytokines were also observed in the production of PGE2 and the expression of 2 regulatory enzymes in PGE2 production, cPLA2 and COX-2. The synergistic induction of IL-11 by IL-1α and TNFα was completely inhibited by a potent inhibitor of all isoforms of PKC, GF109203X. In contrast, phorbol myristate acetate, which induced a down-regulation of PKC, degrading all PKC isoforms except atypical PKC, did not affect the induction of IL-11. Conclusion. These findings suggest that IL-1α and TNFα synergistically stimulate the production of IL- 11 via their effects on PGE2 production in the rheumatoid joint, and that atypical PKC may be another target for down-regulation of IL-11, the bone resorption-associated cytokine.