The p38 mitogen-activated protein kinase pathway regulates interleukin-6 synthesis in response to tumor necrosis factor in osteoblasts

The induction of interleukin-6 (IL-6), using a proinflammatory cytokine (tumor necrosis factor-α), was studied in a human osteoblast cell line (MG-63) in relation to p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB transcription factor. When added to MG-63 cells, tumor necrosis factor-α (TNF-α) had a stimulatory effect on the production of IL-6, and this elevation was significantly reduced by SB203580, a specific p38 MAPK inhibitor. In addition, the stimulation of IL-6 release was also reduced by pyrrolidine dithiocarbamate (PDTC) or NF-κB SN50, which has been reported to be a potent NF-κB inhibitor. Both the NF-κB inhibitors in the presence of SB203580 had a more inhibitory effect on IL-6 release. In this study, TNF-α stimulated NF-κB binding affinity as well as p38 MAP kinase activation, leading to the release of IL-6. However, the specific inhibitor of p38 MAPK, SB203580, had no effect on TNF-α-induced NF-κB activation and both NF-κB inhibitors failed to reduce the p38 MAPK activation in the TNF-α-stimulated osteoblasts. In addition, inhibition of p38 MAPK partially, but significantly, impaired TNF-α-regulated release of osteocalcin, an important differentiation marker in osteoblasts. These results strongly suggest that both p38 MAPK and NF-κB are required in TNF-α-induced IL-6 synthesis and that these two TNF-α-activated pathways can be primarily dissociated. Furthermore, p38 MAPK may play a significant role in differentiation in MG-63 cells.