Human Group V Phospholipase A2 Induces Group IVA Phospholipase A2-independent Cysteinyl Leukotriene Synthesis in Human Eosinophils

Nilda M Muñoz,Young Jun Kim,Angelo Y Meliton,Kwang Pyo Kim,Sang-Kyou Han,Evan Boetticher,Eileen O'Leary,Shigeharu Myou,Xiangdong Zhu,Joseph V Bonventre,Alan R Leff,Wonhwa Cho

doi:10.1074/jbc.m302476200

Abstract

We previously reported that exogenously added human group V phospholipase A2 (hVPLA2) could elicit leukotriene B4 biosynthesis in human neutrophils through the activation of group IVA phospholipase A2 (cPLA2) (Kim, Y. J., Kim, K. P., Han, S. K., Munoz, N. M., Zhu, X., Sano, H., Leff, A. R., and Cho, W. (2002) J. Biol. Chem. 277, 36479-36488). In this study, we determined the functional significance and mechanism of the exogenous hVPLA2-induced arachidonic acid (AA) release and leukotriene C4 (LTC4) synthesis in isolated human peripheral blood eosinophils. As low a concentration as 10 nm exogenous hVPLA2 was able to elicit the significant release of AA and LTC4 from unstimulated eosinophils, which depended on its ability to act on phosphatidylcholine membranes. hVPLA2 also augmented the release of AA and LTC4 from eosinophils activated with formyl-Met-Leu-Phe + cytochalasin B. A cellular fluorescent PLA2 assay showed that hVPLA2 had a lipolytic action first on the outer plasma membrane and then on the perinuclear region. hVPLA2 also caused the translocation of 5-lipoxygenase from the cytosol to the nuclear membrane and a 2-fold increase in 5-lipoxygenase activity. However, hVPLA2 induced neither the increase in intracellular calcium concentration nor cPLA2 phosphorylation; consequently, cPLA2 activity was not affected by hVPLA2. Pharmacological inhibition of cPLA2 and the hVPLA2-induced activation of eosinophils derived from the cPLA2-deficient mouse corroborated that hVPLA2 mediates the release of AA and leukotriene in a cPLA2-independent manner. As such, this study represents a unique example in which a secretory phospholipase induces the eicosanoid formation in inflammatory cells, completely independent of cPLA2 activation.

Highlights

Phospholipase A2 (PLA2)1 catalyzes the hydrolysis of the sn-2 ester bond of membrane phospholipids, the products of which can be transformed into potent inflammatory lipid mediators, including eicosanoids and platelet-activating factor
Release of arachidonic acid (AA) and leukotriene C4 (LTC4) by Exogenous human group V PLA2 (hVPLA2) in Eosinophils—It has been shown that human eosinophils contain cytosolic phospholipase A2 (cPLA2) [29] and hIIaPLA2 [30]
We previously reported that the lipolytic action of hVPLA2 on the outer plasma membrane of human neutrophils resulted in an increase in [Ca2ϩ]i and cPLA2 phosphorylation, both of which led to cPLA2 activation [14]

Summary

Introduction

Phospholipase A2 (PLA2)1 catalyzes the hydrolysis of the sn-2 ester bond of membrane phospholipids, the products of which can be transformed into potent inflammatory lipid mediators, including eicosanoids (i.e. prostaglandins, leukotrienes, and thromboxanes) and platelet-activating factor. Release of AA and LTC4 by Exogenous hVPLA2 in Eosinophils—It has been shown that human eosinophils contain cPLA2 [29] and hIIaPLA2 [30].

Results

Conclusion