Tumor necrosis factor α inhibits collagen α1(I) gene expression in rat hepatic stellate cells through a G protein

Abstract

Background and Aims: Tumor necrosis factor α (TNF-α) inhibits collagen gene expression in cultured fibroblasts. By binding to cell surface receptors, TNF-α promotes signals within the cells. The purpose of this study was to investigate the role played by G proteins in TNF-α-induced inhibition of collagen gene expression. Methods: Effect of TNF-α on collagen α1 (I) messenger RNA (mRNA) level was measured in cultured hepatic stellate cells in basal condition and after inhibiting or activating G proteins or the major intracellular signal transduction pathways. Results: TNF-α significantly decreased the level of α1(I) collagen mRNA. Treatment of cells with pertussis toxin inhibited this effect, whereas blocking adenylate cyclase or protein kinase A had no effect. Likewise, blocking phospholipase A2, phospholipase C, calcium channels, calmodulin, or protein kinase C did not eliminate the inhibitory effect of TNF-α on collagen mRNA. On the other hand, C2-ceramide and sphingomyelinase reproduced the effect of TNF-α on collagen gene expression, and TNF-α did not increase the effect of sphingomyelinase. Conclusions: TNF-α-induced inhibition of α1(I) collagen gene expression in a hepatic stellate cell line may be mediated by a pertussis toxin-sensitive G protein. TNF-α may inhibit this gene by using sphingomyelin/ceramide as an intracellular signal transduction pathway.