Regulation of interleukin-β-induced interleukin-6 gene expression in human fibroblast-like synoviocytes by p38 mitogen-activated protein kinase

Involvement of p38 mitogen-activated protein (MAP) kinase in interleukin (IL)-6 gene expression of human fibroblast-like synoviocytes (FLSs) was assessed. p38 MAP kinase was constitutively expressed in human FLSs and activated in response to IL-1 beta. A pyridinylimidazole compound, SB203580, inhibited p38 MAP kinase activity in vivo, since the activity of MAPKAP kinase-2 (a substrate of p38 MAP kinase) in IL-1 beta-stimulated FLSs was totally suppressed by it. SB203580 concentration-dependently inhibited protein production and gene expression of IL-6 by human FLSs. The effect of SB203580 was dependent on de novo protein synthesis. SB203580 significantly reduced the stability of IL-6 mRNA without affecting the rate of IL-6 gene transcription. Here, we provide evidence that p38 MAP kinase is activated in response to IL-1 beta in human FLSs and is involved in IL-6 synthesis by stabilizing IL-6 mRNA.