Abstract
Tumor necrosis factor-α (TNF-α) stimulates osteoblast production of interleukin-6 (IL-6), an inflammatory cytokine implicated in osteoclastic bone resorption. Therefore, we tested the hypothesis that TNF-α-induced IL-6 production in MG-63 osteosarcoma cells occurs via the p38 mitogen-activated protein kinase (MAPK) pathway. TNF-α activated p38 MAPK and stimulated IL-6 secretion by MG-63 cells, and inhibitor abrogated TNF-α-dependent IL-6 secretion. Transfection of IL-6 full-length and 5'-deletion gene promoter reporter constructs indicated that p38 MAPK activation by TNF-α enhanced IL-6 gene expression, and that the p38 MAPK-responsive region resided in the proximal 260-bp segment. Transfection of NFκB and C/EBPβ-sensitive reporter promoter constructs demonstrated that NFκB activity was enhanced and that constitutive C/EBPβ was inhibited by TNF-α, with both effects being p38 MAPK-dependent. In conclusion, although p38 MAPK activation by TNF-α stimulates IL-6 secretion by MG-63 cells, it has opposing effects on c/EBPβ and NFκB activity.
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