The Rac effector p67^phox regulates phagocyte NADPH oxidase by stimulating Vav1 guanine nucleotide exchange activity

The phagocyte NADPH oxidase catalyzes the reduction of molecular oxygen to superoxide and is essential for microbial defense. Electron transport through the oxidase flavocytochrome is activated by the Rac effector p67^phox. Previous studies suggest that Vav1 regulates NADPH oxidase activity elicited by the chemoattractant formyl-Met-Leu-Phe (IMLP). We show that Vav1 associates with p67^phox and Rac2, but not Rac1, in fMLP-stimulated human neutrophils, correlating with superoxide production. The interaction of p67 ^phox with Vav1 is direct and activates nucleotide exchange on Rac, which enhances the interaction between p67^phox and Vav1. This provides new molecular insights into regulation of the neutrophil NADPII oxidase, suggesting that chemoattractant-stimulated superoxide production can be amplified by a positive feedback loop in which p67^phox targets Va1-mediated Rac activation.