Tumor necrosis factor (TNF)-α-induced IL-8 expression in gastric epithelial cells: Role of reactive oxygen species and AP endonuclease-1/redox factor (Ref)-1

Abstract

TNF-α contributes to oxidative stress via induction of reactive oxygen species (ROS) and pro-inflammatory cytokines. The molecular basis of this is not well understood but it is partly mediated through the inducible expression of IL-8. As redox factor-1 (Ref-1), is an important mediator of redox-regulated gene expression we investigated whether ROS and Ref-1 modulate TNF-α-induced IL-8 expression in human gastric epithelial cells. We found that TNF-α treatment of AGS cells enhanced nuclear expression of Ref-1 and potently induced IL-8 expression. Overexpression of Ref-1 enhanced IL-8 gene transcription at baseline and after TNF-α treatment whereas Ref-1 suppression and antioxidant treatment inhibited TNF-α-stimulated IL-8 expression. TNF-α-mediated enhancement of other pro-inflammatory chemokines like MIP-3α and Gro-α was also regulated by Ref-1. Although TNF-α increased DNA binding activity of Ref-1-regulated transcription factors, AP-1 and NF-κB, to the IL-8 promoter, promoter activity was mainly mediated by NF-κB binding. Silencing of Ref-1 in AGS cells inhibited basal and TNF-α-induced AP-1 and NF-κB DNA binding activity, but not their nuclear accumulation. Collectively, we provide the first mechanistic evidence of Ref-1 involvement in TNF-α-mediated, redox-sensitive induction of IL-8 and other chemokines in human gastric mucosa. This has implications for understanding the pathogenesis of gastrointestinal inflammatory disorders.