Cytosolic Phospholipase A2 (cPLA2) Regulation of Human Monocyte NADPH Oxidase Activity: cPLA2 AFFECTS TRANSLOCATION BUT NOT PHOSPHORYLATION OF p67 phox AND p47 phox

Xiaoxian Zhao,Erik A Bey,Frans B Wientjes,Martha K Cathcart

doi:10.1074/jbc.m203630200

Abstract

The NADPH oxidase of human monocytes is activated upon exposure to opsonized zymosan and a variety of other stimuli to catalyze the formation of superoxide anion. Assembly of the NADPH oxidase complex is believed to be a highly regulated process, and molecular mechanisms responsible for this regulation have yet to be fully elucidated. We have previously reported that cytosolic phospholipase A(2) (cPLA(2)) expression and activity are essential for superoxide anion production in activated human monocytes. In this study, we investigated the mechanisms involved in cPLA(2) regulation of NADPH oxidase activation by evaluating the effects of cPLA(2) on translocation and phosphorylation of p67(phox) and p47(phox). We report that translocation and phosphorylation of p67(phox), as well as p47(phox), occur upon activation of human monocytes and that decreased cPLA(2) protein expression, mediated by antisense oligodeoxyribonucleotides (AS-ODN) specific for cPLA(2) mRNA, blocked the stimulation-induced translocation of p47(phox) and p67(phox) from the cytosol to the membrane fraction. Inhibition of translocation of both p47(phox) and p67(phox) by cPLA(2) AS-ODN was above 85%. Arachidonic acid (AA), a product of cPLA(2) enzymatic activity, completely restored translocation of both of these oxidase components in the AS-ODN-treated, cPLA(2)-deficient human monocytes. These results represent the first report that cPLA(2) activity or AA is required for p67(phox) and p47(phox) translocation in human monocytes. Although cPLA(2) was required for translocation of p47(phox) and p67(phox), it did not influence phosphorylation of these components. These results suggest that one mechanism of cPLA(2) regulation of NADPH oxidase activity is to control the arachidonate-sensitive assembly of the complete oxidase complex through modulating the translocation of both p47(phox) and p67(phox). These studies provide insight into the mechanisms by which activation signals are transduced to allow the induction of superoxide anion production in human monocytes.

Highlights

The phagocyte NADPH oxidase is a multicomponent enzyme that catalyzes the production of superoxide anion and plays a central role in the elimination of invading bacteria
To address the question of whether other fatty acids could restore the translocation of p67phox and p47phox in cytosolic phospholipase A2 (cPLA2)-deficient monocytes, we examined the effect of linoleic acid (LA) and palmitic acid (PA)
Monocytes and not neutrophils are present and activated in atherosclerotic lesions, and one atherogenic process that monocytes are believed to contribute to atherogenesis is the oxidation of low-density lipoprotein (LDL) by a mechanism requiring superoxide anion produced by NADPH oxidase [2,3]

Summary

Introduction

The phagocyte NADPH oxidase is a multicomponent enzyme that catalyzes the production of superoxide anion and plays a central role in the elimination of invading bacteria. We previously reported that treatment of human monocytes with such cPLA2 specific AS-ODN could substantially decrease ZOP-triggered superoxide anion production [36]. These results suggest that cPLA2 may regulate the superoxide anion production of monocytes via modulating the translocation of p67phox and p47phox from cytosol to membrane compartments, an essential step for formation of active complex of NADPH oxidase.

Results

Conclusion