A role of Nox1 in epithelial cell‐initiated inflammation and innate immunity of the colon

Guinea pig gastric mucosal cells respond to LPS from type I Helicobacter pylori and induce NADPH oxidase 1 (Nox1) and its organizer protein (NOXO1) in association with activation of rac1, resulting in enhanced superoxide production 10‐fold (Am J Physiol 2005). In contrast, human colonic epithelial cells (T84 cells) preferentially use the flagellin‐TLR5 pathway for priming of Nox1 oxidase and they were insensitive to LPS, peptidoglycan, and CpG DNA. Thus, gastric and colonic epithelial cells discern pathogenecities among bacteria to appropriately operate Nox1 for the host defense (J Immunol 2004). In this study, we show that IFN‐γ stimulates transcription of the Nox1 gene and enhances superoxide generation by T84 cells, which were completely blocked with Nox1 siRNA. We cloned −5.0 kbp of 5′‐frank of the human Nox1 gene. This region contains several potential binding sites for IFN‐γ‐responsive transcriptional factors, such as NF‐κB, Sp1, AP‐1, GATA, STAT1, and IRF‐1. IFN‐γ phososphorylated STAT1 and produced a STAT1‐GAS complex. GAS located at −3960 bp and −3645 bp was crucial for transcription of the Nox1 gene. The introduction of three point mutations of the GAS completely abolished the IFN‐γ‐stimulated promoter activity of the human Nox1 gene. These results suggest a potential role of Nox1‐derived oxygen radicals in inflammation and innate immune responses of the gastrointestinal tract.