NADPH oxidase 1 (Nox1) is a multicomponent enzyme consisting of p22(phox), Nox 
organizer 1 (NOXO1), Nox1 activator 1, and Rac1. Interleukin-1beta, flagellin, 
interferon-gamma, and tumor necrosis factor alpha (TNF-alpha) similarly induced 
Nox1 in a colon cancer cell line (T84), whereas only TNF-alpha fully induced 
NOXO1 and upregulated superoxide-producing activity by ninefold. This 
upregulation was canceled by knockdown of NOXO1 with small interfering RNAs. 
TNF-alpha rapidly phosphorylated p38 mitogen-activated protein kinase and c-Jun 
N-terminal kinase 1/2, followed by phosphorylation of c-Jun and c-Fos and 
appearance of an AP-1 binding activity within 30 min. We cloned the 5' flank of 
the human NOXO1 gene (-3888 to +263 bp), and found that the region between -585 
and -452 bp, which contains consensus elements of YY-1, AP-1, and Ets, and the 
GC-rich region encoding three putative binding sites for SP-1, was crucial for 
TNF-alpha-dependent promoter activity. Serial mutation analysis of the elements 
identified an AP-1 binding site (from -561 to -551 bp, agtAAGtcatg) as a crucial 
element for TNF-alpha-stimulated transcription of the human NOXO1 gene, which 
was also confirmed by the AP-1 decoy experiments. Thus, TNF-alpha acts as a 
potent activator of Nox1-based oxidase in colon epithelial cells, suggesting a 
potential role of this oxidase in inflammation of the colon.