Occupancy of adenosine A2a receptors promotes fMLP-induced cyclic AMP accumulation in human neutrophils: impact on phospholipase D activity and recruitment of small GTPases to membranes

Abstract

The aim of this study was to assess in human neutrophils theimplication of an adenosine 3′,5′-cyclic monophosphate (cAMP)-dependentpathway in the inhibitory effects of A2a receptor engagement. We foundthat Ro20-1724, a cAMP phosphodiesterase inhibitor, in the presence ofadenosine deaminase (ADA) or A2a receptor antagonists renderedtransient the fMLP-induced sustained increases in cAMP levels. The roleof A2a receptor stimulation was demonstrated by the ability of the A2areceptor agonist, CGS21680, to prevent ADA-mediated reduction of thepersistent cAMP elevation induced by fMLP. Persistent cAMP elevationcorrelated with inhibition of fMLP-induced PLD activation andrecruitment of Arf, RhoA, and PKC to membranes. The suppressive effectof CGS21680 or isoproterenol, a β-adrenergic receptor agonist, wasincreased by Ro20-1724 or by the adenylyl cyclase activator, forskolin, and reversed, at least in part, by the inhibitor of adenylyl cyclase,2′,5′-dideoxyadenosine. The activator of protein kinase A (PKA),Sp-cAMP inhibited fMLP-induced PLD activation and translocation of Arfand RhoA to membranes. In contrast, the suppression by A2a receptorstimulation of fMLP-induced PLD activation and cofactor recruitment wasantagonized by PKA inhibitors, Rp-cAMP and H89. In conclusion, A2areceptor occupancy by extracellular adenosine inhibits fMLP-inducedneutrophil activation via cAMP and PKA-regulated events.