Regulation of Purinergic Signaling by Prostaglandin E₂ in Murine Macrophages

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Extracellular nucleotides are primary signals for tissue injury, acting together with various chemical mediators such as prostanoids at the inflammatory site. We investigated whether prostaglandin E₂ (PGE₂) affects purinergic signaling in murine J774 macrophages. J774 cells expressed four different purinoceptor mRNAs: the ionotropic P2X₄ and P2X₇ receptors and G-protein–coupled P2Y₂ and P2Y₆ receptors. Functional responses mediated by these purinoceptor subtypes were confirmed by measurement of intracellular Ca²⁺ concentration ([Ca²⁺]_i) in fura-2–loaded cells. Thus, low concentrations (10 μM) of ATP (P2Y₂ agonist) and UDP (P2Y₆ agonist) evoked Ca²⁺ transient in a phospholipase C (PLC)-dependent manner, whereas the P2X₇ agonist benzoylbenzoyl-ATP (BzATP, 500 μM) caused a sustained rise in [Ca²⁺]_i. Furthermore, ivermectin, an activator of the P2X₄-receptor channel, enhanced the ATP-induced [Ca²⁺]_i elevation. PGE₂ inhibited ATP- and UDP-induced [Ca²⁺]_i elevation, without affecting the BzATP-induced sustained [Ca²⁺]_i elevation. Stimulation of J774 cells by UDP or BzATP increased the production of macrophage inflammatory peptide-α (MIP-α). PGE₂ abolished the UDP-induced MIP-α production, but not the BzATP-induced one. These results demonstrate that purinergic signalings in macrophages were regulated by PGE₂ in a subtype-specific manner. The different inhibitory effects on distinct purinoceptor functions may be related to the anti-inflammatory property of PGE₂.