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Phosphorylation of Cytosolic Phospholipase A₂ and the Release of Arachidonic Acid in Human Neutrophils¹

Department of Physiology, University of Connecticut Health Center, Farmington, CT 06030

Kinases mediating phosphorylation and activation of cytosolic phospholipase A₂ (cPLA₂) in intact cells remain to be fully characterized. Platelet-activating factor stimulation of human neutrophils increases cPLA₂ phosphorylation. This increase is inhibited by PD 98059, a mitogen-activated protein (MAP)/extracellular signal-regulating kinase (erk) 1 inhibitor, but not by SB 203580, a p38 MAP kinase inhibitor, indicating that this action is mediated through activation of the p42 MAP kinase (erk2). However, platelet-activating factor-induced arachidonic acid release is inhibited by both PD 98059 and SB 203580. Stimulation by TNF- increases cPLA₂ phosphorylation, which is inhibited by SB 203580, but not PD 98059, suggesting a role for p38 MAP kinase. LPS increases cPLA₂ phosphorylation and arachidonic acid release. However, neither of these actions is inhibited by either PD 98059 or SB 203580. PMA increases cPLA₂ phosphorylation. This action is inhibited by PD 98059 but not SB 203580. Finally, FMLP increases cPLA₂ phosphorylation and arachidonic acid release. Interestingly, while the FMLP-induced phosphorylation of cPLA₂ is not affected by the inhibitors of the p38 MAP kinase or erk cascades, both inhibitors significantly decrease arachidonic acid release stimulated by FMLP. SB 203580 or PD 98059 has no inhibitory effects on the activity of coenzyme A-independent transacylase.