Group V phospholipase A2 induces leukotriene biosynthesis in human neutrophils through the activation of group IVA phospholipase A2

We reported previously that exogenously added human group V phospholipase A(2) (hVPLA(2)) could elicit leukotriene B-4 (LTB4) biosynthesis in human neutrophils (Han, S. K., Kim, K. P., Koduri, R., Bittova, L., Munoz, N. M., Leff, A. R., Wilton, D. C., Gelb, M. H., and Cho, W. (1999) J. Biol. Chem. 274, 11881-11888). To determine the mechanism of the hVPLA(2)-induced LTB4 biosynthesis in neutrophils, we thoroughly examined the effects of hVPLA(2) and their lipid products on the activity of group IVA cytosolic PLA(2) (cPLA(2)) and LTB4 biosynthesis under different conditions. As low as 1 nm exogenous hVPLA(2) was able to induce the release of arachidonic acid (AA) and LTB4. Typically, AA and LTB4 were released in two phases, which were synchronized with a rise in intracellular calcium concentration ([Ca2+](i)) near the perinuclear region and cPLA(2) phosphorylation. A cellular PLA(2) assay showed that hVPLA(2) acted primarily on the outer plasma membrane, liberating fatty acids and lysophosphatidylcholine (lyso-PC), whereas cPLA(2) acted on the perinuclear membrane. Lyso-PC and polyunsaturated fatty acids including AA activated cPLA(2) and 5-lipoxygenase by increasing [Ca2+](i) and inducing cPLA(2) phosphorylation, which then led to LTB4 biosynthesis. The delayed phase was triggered by the binding of secreted LTB4 to the cell surface LTB4 receptor, which resulted in a rise in [Ca2+](i) and cPLA(2) phosphorylation through the activation of mitogen-activated protein kinase, extracellular signal-regulated kinase 1/2. These results indicate that a main role of exogenous hVPLA(2) in neutrophil activation and LTB4 biosynthesis is to activate cPLA(2) and 5-lipoxygenase primarily by liberating from the outer plasma membrane lyso-PC that induces [Ca2+](i) increase and cPLA(2) phosphorylation and that hVPLA(2)-induced LTB4 production is augmented by the positive feedback activation of cPLA, by LTB4.