ANTIOXIDANTS & REDOX SIGNALING Volume 10, Number 6, 2008 © Mary Ann Liebert, Inc. DOI: 10.1089/ars.2007.2011 Forum Review Novel Role of Protein Disulfide Isomerase in the Regulation of NADPH Oxidase Activity: Pathophysiological Implications in Vascular Diseases FRANCISCO R. M. LAURINDO, 1 DENISE C. FERNANDES, 1 ANGÉLICA M. AMANSO, 1 LUCIA R. LOPES, 2 and CÉLIO X. C. SANTOS 1 ABSTRACT Vascular cell NADPH oxidase complexes are key sources of signaling reactive oxygen species (ROS) and con- tribute to disease pathophysiology. However, mechanisms that fine-tune oxidase-mediated ROS generation are incompletely understood. Besides known regulatory subunits, upstream mediators and scaffold platforms reportedly control and localize ROS generation. Some evidence suggest that thiol redox processes may coor- dinate oxidase regulation. We hypothesized that thiol oxidoreductases are involved in this process. We focused on protein disulfide isomerase (PDI), a ubiquitous dithiol disulfide oxidoreductase chaperone from the endo- plasmic reticulum, given PDI’s unique versatile role as oxidase/isomerase. PDI is also involved in protein traf- fic and can translocate to the cell surface, where it participates in cell adhesion and nitric oxide internaliza- tion. We recently provided evidence that PDI exerts functionally relevant regulation of NADPH oxidase activity in vascular smooth muscle and endothelial cells, in a thiol redox-dependent manner. Loss-of-function exper- iments indicate that PDI supports angiotensin II-mediated ROS generation and Akt phosphorylation. In ad- dition, PDI displays confocal co-localization and co-immunoprecipitates with oxidase subunits, indicating close association. The mechanisms of such interaction are yet obscure, but may involve subunit assembling stabi- lization, assistance with traffic, and subunit disposal. These data may clarify an integrative view of oxidase activation in disease conditions, including stress responses. Antioxid. Redox Signal. 10, 1101–1113. 1101 INTRODUCTION R EDOX PATHWAYS ADD AN IMPORTANT DIMENSION to cell sig- naling networks regulating physiological and pathologi- cal events, particularly cardiovascular disorders such as hyper- tension (16, 99). However, mechanisms providing fine-tuning of redox equilibrium are complex and yet incompletely under- stood. Indeed, it has been shown that redox signaling can oc- cur in the absence of overall changes in redox status of the ma- jor intracellular reductants glutathione or thioredoxin (37), and thus can be separated from oxidative stress, which is a disrup- tion of redox signaling requiring some type of cellular adapta- tion (49). Accordingly, most intra- and extracellular redox buffer pairs are not in equilibrium, suggesting their indepen- dent regulation (49), and further indicating that oxidative stress is more complex than a simple overall imbalance between ox- idants and antioxidants in favor of the former. In turn, oxida- tive stress activates vicious signaling circuits in several disease conditions, not only as a result of direct free radical-mediated damage to biomolecules, but—perhaps mostly—from disor- dered activation and/or expression of subcellular signaling tar- gets due to excessive, uncompensated, or decompartmentalized 1 Vascular Biology Laboratory, Heart Institute (InCor), University of São Paulo School of Medicine; and 2 Department of Pharmacology, Biomedical Sciences Institute, University of São Paulo, Brazil.