The expression of prostaglandin E receptors EP2 and EP4 and their different regulation by lipopolysaccharide in C3H/HeN peritoneal macrophages

The expression and regulation of the PGE receptors, EP2 and EP4, both of wh ich are coupled to the stimulation of adenylate cyclase, were examined in p eritoneal resident macrophages from C3H/HeN mice. mRNA expression of EP4 bu t not EP2 was found in nonstimulated. cells, but the latter was induced by medium change alone, and this induction was augmented by LPS. mRNA expressi on of EP4 was down-regulated by LPS but not by medium change. PGE(2) increa sed the cAMP content of both LPS-treated and nontreated cells. ONO-604, an EP4 agonist, also increased cAMP content in nonstimulated cells and in cell s treated with LPS for 3 h, but not for 6 h. Butaprost, an EP2 agonist, was effective only in the cells treated with LPS for 6 h. The inhibitory effec ts of ONO-604 on TNF-alpha and IL-12 production were equipotent with PGE(2) at any time point, but the inhibitory effects of butaprost were only seen from 14 h after stimulation. PGE(2) or dibutyryl cAMP alone, but not butapr ost, reduced EP4 expression, and indomethacin reversed the LPS-induced down -regulation of EP4, indicating that the down-regulation of EP4 is mediated by LPS-induced PG synthesis and EP4 activation. Indeed, when we used C3H/He J (LPS-hyporesponsive) macrophages, such reduction in EP4 expression was fo und in the cells treated with PGE(2) alone, but not in LPS-treated cells. I n contrast, up-regulation of EP2 expression was again observed in LPS-treat ed C3H/HeJ macrophages. These results suggest that EP4 is involved mainly i n the inhibition of cytokine release, and that the gene expression of EP2 a nd EP4 is differentially regulated during macrophage activation.