Neutrophils play a key role in host defense by releasing reactive oxygen species (ROS). However, excessive ROS production by neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase can damage bystander tissues, thereby contributing to inflammatory diseases. Tumor necrosis factor-␣ (TNF-␣), a major mediator of inflammation, does not activate NADPH oxidase but induces a state of hyperresponsiveness to subsequent stimuli, an action known as priming. The molecular mechanisms by which TNF-␣ primes the NADPH oxidase are unknown. Here we show that Pin1, a unique cis-trans prolyl isomerase, is a previously unrecognized regulator of TNF-␣-induced NADPH oxidase hyperactivation. We first showed that Pin1 is expressed in neutrophil cytosol and that its activity is markedly enhanced by TNF-␣.
Inhibition of Pin1 activity with juglone or with a specific peptide inhibitor abrogated TNF-␣-induced priming of neutrophil ROS production induced by N-formylmethionyl-leucyl-phenylalanine peptide (fMLF). TNF-␣ enhanced fMLF-induced
IntroductionNeutrophils play an important role in host defense against invading pathogens and in inflammation. In response to stimulating agents, such as the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLF), neutrophils release large amounts of superoxide anions and other reactive oxygen species (ROS) in a phenomenon called the respiratory burst. ROS produced by the neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase play a key role in host defenses, 1-3 but excessive ROS production can damage healthy bystander tissues, thereby contributing to inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel diseases, and acute respiratory distress syndrome. 4,5 Neutrophil ROS production is mediated by the phagocyte NADPH oxidase, also called NOX2. NADPH oxidase is a multicomponent enzyme system that catalyzes NADPH-dependent reduction of oxygen to superoxide anion. 6,7 In resting cells, the NADPH oxidase is inactive and its components are distributed between the cytosol and membranes. When cells are activated, the cytosolic components (p47phox, p67phox, p40phox, and Rac2) migrate to the membranes, where they associate with the membranebound components (p22phox and gp91phox/NOX2, which form the flavocytochrome b558) to assemble the catalytically active oxidase. 7,8 During NADPH oxidase activation, p47phox, p67phox, p40phox, p22phox, and gp91phox/NOX2 become phosphorylated. 9-13 p47phox phosphorylation on several serines plays a pivotal role in oxidase activation in intact cells. 14,15 Neutrophil ROS production is enhanced or primed by a variety of mediators, including proinflammatory cytokines, such as tumor necrosis factor-␣ (TNF-␣). In vitro, TNF-␣ induces a very weak oxidative response by neutrophils but strongly enhances ROS release on exposure to a secondary stimulus, such as the bacterial peptide fMLF. [16][17][18] This "priming" of neutrophil ROS production plays a detrimental role in a variety of human inflammatory diseases, in which ROS hyperp...