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Stimulation of hyaluronan synthesis by tumor necrosis factor-alpha is mediated by the p50/p65 NF-kappa B complex in MRC-5 myofibroblasts.

The lesions of fibrocontractive diseases result from an excessive myofibroproliferative response to numerous forms of inflammatory stimuli, which elicit the net deposition of extracellular matrix (ECM) in the interstitium of the affected tissue. Hyaluronan (HA), reported to be a key player supporting cellular migration and adherence, is a major component of ECM that undergoes dynamic regulation during inflammation. The molecular regulation of HA biosynthesis by inflammatory cytokines on myofibroblasts is not yet completely understood. Here we report the biochemical characteristics of the lung myofibroblast cell line MRC-5, and we demonstrate that the production of HA by this cell line is inducible by the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), at the message level of HA synthase (HAS). In TNF-alpha-stimulated MRC-5 cells, DNA-binding and competition experiments indicated that the predominant NF-kappa B binding activity detected with nuclear extract-stimulated cells is mediated by the p50/p65 complex. Using antisense oligonucleotides, we confirmed that the TNF-alpha-stimulation of HA synthesis by MRC-5 cells is dependent on the activation of the p50/p65 NF-kappa B complex. These findings indicate that TNF-alpha production within inflamed tissues may enhance the HA synthesis via the transcriptional induction of HAS on myofibroblasts, thereby providing a provisional matrix for supporting cellular migration and adhesion, and that the p50/p65 NF-kappa B complex that plays an important role in the regulation of HA production by TNF-alpha might be an appropriate target for therapeutic compounds to treat tissue fibrosis accompanied by inflammation.