NF-κB regulates phagocytic NADPH oxidase by inducing the expression of gp91phox

The superoxide-generating phagocytic NADPH oxidase is an important component of the innate immune response against microbial agents, and is involved in shaping the cellular response to a variety of physiological and pathological signals. One of the downstream targets of NADPH oxidase-derived radicals is the ubiquitous transcription factor NF-kappa B, which controls the expression of a large array of genes involved in immune function and cell survival. Here we show that NF-kappa B itself is a key factor in controlling NADPH oxidase expression and function. In monocytic and microglial cell lines, the expression of the NADPH oxidase subunit gp91(phox) was induced by lipopolysaccharide/interferon gamma treatment and was inhibited in cells constitutively expressing I kappa B alpha. Furthermore, inducible reactive oxygen species production was inhibited in I kappa B alpha overexpressing cells. gp91(phox) expression was very low in RelA(-/-) fibroblasts and could be induced by reconstituting these cells with p65/RelA. Thus, gp91(phox) expression is dependent on the presence of p65/RelA. We also found that gp91(phox) transcription is dependent on NF-kappa B and we identified two potential cis-acting elements in the murine gp91(phox) promoter that control NF-kappa B-dependent regulation. The findings raise the possibility of a positive feedback loop in which NF-kappa B activation by oxidative stress leads to further radical production via NADPH oxidase.