Role of NF-κB in the antiproliferative effect of endothelin-1 and tumor necrosis factor-α in human hepatic stellate cells: Involvement of cyclooxygenase-2

Abstract

During chronic liver diseases, hepatic stellate cells (HSC) acquire an activated myofibroblast-like phenotype and proliferate and synthesize fibrosis components. Endothelin-1 (ET-1), which inhibited the growth of human myofibroblastic HSC, increased the formation of two NF-κB DNA binding complexes; this effect was also observed with tumor necrosis factor-α (TNF- α). The complexes were identified as the p50/p50 and p50/p65 NF-κB dimers. Activation of NF-κB was associated with the degradation of the inhibitory protein IκB-α; no IκB-β was detected. Activation of NF-κB and degradation of IκB-α were prevented by the NF-κB inhibitors sodium salicylate and MG-132. In addition to cyclooxygenase-1 (COX-1), COX-2 is also constitutively expressed in human HSC, and the use of dexamethasone and of SC-58125, a selective COX-2 inhibitor, revealed that COX-2 accounts for basal COX activity. Moreover, COX-2 mRNA and protein were up-regulated by ET-1 and TNF-α, whereas COX-1 was unaffected. Induction of COX-2 and stimulation of COX activity by ET-1 and TNF-α were prevented by sodium salicylate and MG- 132, suggesting that activation of NF-κB by either factor is needed for stimulation of COX-2. Finally, SC-58125 and dexamethasone reduced the growth inhibitory effect of ET-1 and TNF-α, indicating that activation of COX-2 is required for inhibition of HSC proliferation. Taken together, our results suggest that NF-κB, by inducing COX-2 expression, may play an important role in the negative regulation of human myofibroblastic HSC proliferation.