Faculty Bibliography

Transcription factor NF-kappaB is normally sequestered in the cytoplasm, complexed with IkappaB inhibitory proteins. Tumor necrosis factor (TNF) and interleukin-1 induce IkappaB-alpha phosphorylation, leading to IkappaB-alpha degradation and translocation of NF-kappaB to the nucleus where it activates genes important in inflammatory and immune responses. TNF and interleukin-1 actions are typically terminated by desensitization, and IkappaB-alpha reappearance normally occurs within 30-60 min. We found that in normal human FS-4 fibroblasts maintained in the presence of TNF, IkappaB-alpha protein failed to return to base-line levels for up to 15 h. Removal of TNF at any time during the 15-h period resulted in complete IkappaB-alpha resynthesis, suggesting that IkappaB-alpha reappearance was prevented by continued TNF signaling. Long term exposure of FS-4 fibroblasts to TNF led to a persistent presence of IkappaB-alpha mRNA, sustained IkappaB kinase activation, continuous proteasome-mediated degradation of IkappaB-alpha, and sustained nuclear localization of NF-kappaB. Continuous exposure of FS-4 cells to TNF did not lead to a sustained activation of p38 or ERK mitogen-activated protein kinases, suggesting that not all TNF-induced signaling pathways are persistently activated. These findings challenge the notion that all cytokine-mediated signals are rapidly terminated by desensitization and illustrate the need to elucidate the process of deactivation of TNF-induced signaling

TNF-stimulated gene 6 (tsg6), encoding a 35-kDa secretory glycoprotein (TSG-6), is induced in fibroblasts, chondrocytes, synovial cells, and mononuclear cells by the proinflammatory cytokines TNF-alpha and IL-1, or by LPS. Large amounts of TSG-6 protein were found in synovial fluids of patients with rheumatoid arthritis. TSG-6 protein forms a stable complex with components of the serine protease inhibitor, inter-alpha-inhibitor (I alpha I). In this work, we show that TSG-6 potentiates the inhibitory effect of l alpha l on the protease activity of plasmin. The plasmin/plasminogen activator system is important in the protease network associated with inflammation. To test the hypothesis that through their cooperative inhibitory effect on plasmin TSG-6 and l alpha l can modulate the protease network and thus inhibit inflammation, we examined the effect of TSG-6 on experimentally induced inflammation. Human recombinant TSG-6 protein showed a potent anti-inflammatory activity in the murine air pouch model of carrageenan- or IL-1-induced acute inflammation. The inhibitory effect of locally administered TSG-6 on the IL-1-induced cellular infiltration was comparable with that of systemic dexamethasone treatment. Two mutant TSG-6 proteins with single amino acid substitutions close to the N terminus showed a complete or partial loss of anti-inflammatory activity. The anti-inflammatory effect of the TNF/IL-1-inducible TSG-6 protein, along with its ability to inhibit protease action through interaction with l alpha l, suggests that TSG-6 production during inflammation is part of a negative feedback loop operating through the protease network