Modulation of p47 ^<i>PHOX</i> activity by site-specific phosphorylation: Akt-dependent activation of the NADPH oxidase

Abstract

The leukocyte NADPH oxidase catalyzes the reduction of oxygen to O \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document} at the expense of NADPH. Extensive phosphorylation of the oxidase subunit p47 PHOX occurs during the activation of the enzyme in intact cells. p47 PHOX carrying certain serine-to-alanine mutations fails to support NADPH oxidase activity in intact cells, suggesting that the phosphorylation of specific serines on p47 PHOX is required for the activation of the oxidase. Earlier studies with both intact cells and a kinase-dependent, cell-free system have suggested that protein kinase C can phosphorylate those serines of p47 PHOX whose phosphorylation is necessary for its activity. Work with inhibitors suggested that a phosphatidylinositol 3-kinase-dependent pathway also can activate the oxidase. Phosphorylation of p47 PHOX by Akt (protein kinase B), whose activation depends on phosphatidylinositol 3-kinase, could be the final step in such a pathway. We now find that Akt activates the oxidase in vitro by phosphorylating serines S304 and S328 of p47 PHOX . These results suggest that Akt could participate in the activation of the leukocyte NADPH oxidase.