Interleukin-1α and tumor necrosis factor α synergistically stimulate prostaglandin E2-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 necrosis factor alpha (TNF alpha), 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 E-2 (PGE(2)) were measured by enzyme-linked immunosorbent assay. IL-11 messenger 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 Western blotting. Results. 1L-1 alpha and TNF alpha 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 PGE(2), indicating that the synergistic effect of IL-1 alpha and TNF alpha was PGE(2)-mediated, The cooperative effects 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 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-1 alpha and TNF alpha synergistically stimulate the production of IL-11 via their effects on PGE(2) production in the rheumatoid joint, and that atypical PKC may be another target for down-regulation of IL-11, the bone resorption-associated cytokine.