Exclusive expression of the Gs‐linked prostaglandin E2 receptor subtype 4 mRNA in human mononuclear Jurkat and KM‐3 cells and coexpression of subtype 4 and 2 mRNA in U‐937 cells

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Abstract
Prostaglandin E2 (PGE2) is regarded as a potent regulator of the immune system. It can regulate apoptosis in monunuclear cells and modulate the cytokine secretion pattern from T-helper cell subpopulations via an increase in cyclic AMP (cAMP). Of the 4 PGE2 receptor subtypes (EP1–EP4) that are defined pharmacologically by their affinity to subtype-specific ligands and their coupling to G proteins, EP2 and EP4 receptors couple to Gs. It is as yet unknown which of these two receptor subtypes mediates the immunomodulatory effects. By quantitative RT-PCR, the mRNA for EP4 receptors was demonstrated and quantified in the human mononuclear cell lines Jurkat, KM-3 and U-937. However, EP2 receptor mRNA was only present in U-937 cells and was 100-fold less abundant than EP4 receptor mRNA. PGE2 increased cAMP formation with an ED50 of 50–100 nM in all cell lines. cAMP formation was inhibited by the EP4R-specific antagonist AH23848. Since AH23848 inhibited PGE2-induced cAMP formation in U-937 cells to a similar extent as in Jurkat and KM-3, EP2 receptors seem to play, if any, only a secondary role for the PGE2-mediated cAMP formation in U-937 cells.