Prostaglandin E2Inhibits the Phospholipase D Pathway Stimulated by Formyl-methionyl-leucyl-phenylalanine in Human Neutrophils. Involvement of EP2Receptors and Phosphatidylinositol 3-kinase γ

Abstract

Prostaglandin E₂ (PGE₂), originally discovered as a pro-inflammatory mediator, also inhibits several chemoattractant-elicited neutrophil functions, including adhesion, secretion of cytotoxic enzymes, production of superoxide anions, and chemotaxis. In this study, we have examined the effects of PGE₂ and prostaglandin E (EP) receptor-selective agonists/antagonists on several steps of the formyl-methionyl-leucyl-phenylalanine (fMLP)-induced phospholipase D (PLD) activation pathway in human neutrophils to elucidate the PGE₂ inhibitory mechanism. PGE₂ and EP₂ receptor agonists inhibited the stimulation of the activity of PLD induced by fMLP in a concentration-dependent manner. The fMLP-stimulated translocation to membranes of protein kinase C α, Rho, and Arf GTPases was diminished in the presence of PGE₂ or EP₂ agonists. Moreover, PGE₂ and EP₂ agonists decreased the activation of phosphatidylinositol 3-kinase γ (PI3Kγ) and Tec kinases as well as the tyrosine phosphorylation of proteins stimulated by fMLP. These data provide strong evidence that 1) the inhibitory effects of PGE₂ on the fMLP-induced PLD activation pathway were mediated via EP₂ receptors and that 2) the suppression of PI3Kγ activity was the crucial step in the EP₂-mediated inhibition of the fMLP-induced signaling cascade.