NAD(P)H Oxidase 1, a Product of Differentiated Colon Epithelial Cells, Can Partially Replace Glycoprotein 91phox in the Regulated Production of Superoxide by Phagocytes

Abstract

Reactive oxygen species (ROS) serve several physiological functions; in some settings they act in host defense, while in others they function in cellular signaling or in biosynthetic reactions. We studied the expression and function of a recently described source of ROS, NAD(P)H oxidase 1 or Nox1, which has been associated with cell proliferation. In situ hybridization in mouse colon revealed high Nox1 expression within the lower two-thirds of colon crypts, where epithelial cells undergo proliferation and differentiation. Human multitumor tissue array analysis confirmed colon-specific Nox1 expression, predominantly in differentiated epithelial tumors. Differentiation of Caco2 and HT29 cells with 1α,25-dihydroxyvitamin D₃ or IFN-γ enhances Nox1 expression and decreases cell proliferation, suggesting that Nox1 does not function as a mitogenic oxidase in colon epithelial cells. Transduction with retrovirus encoding Nox1 restored activation and differentiation-dependent superoxide production in gp91^phox-deficient PLB-985 cells, indicating close functional similarities to the phagocyte oxidase (phox). Furthermore, coexpression of cytosolic components, p47^phox and p67^phox, augments Nox1 activity in reconstituted K562 cells. Finally, Nox1 partially restores superoxide production in neutrophils differentiating ex vivo from gp91^phox-deficient CD34⁺ peripheral blood-derived stem cells derived from patients with X-linked chronic granulomatous disease. These studies demonstrate a significant functional homology (cofactor-dependent and activation-regulated superoxide production) between Nox1 and its closest homologue, gp91^phox, suggesting that targeted up-regulation of Nox1 expression in phagocytic cells could provide a novel approach in the molecular treatment of chronic granulomatous disease.