Membrane-associated prostaglandin E synthase (mPGES) is a recently identified terminal enzyme of the arachidonic acid cascade, which converts PGH(2) to PGE(2) in rheumatoid arthritis synovial fibroblasts (RASFs). This study was undertaken to investigate factors regulating the expression of mPGES.
RASFs were treated with interleukin-1beta (IL-1beta), indomethacin, NS-398, rofecoxib, or meloxicam. The effects of PGE(2) and selective agonists for PGE(2) receptor subtypes (EP1, EP2, EP3, and EP4) were also studied. Expression of mPGES messenger RNA (mRNA) and protein was measured by Northern and Western blot analysis, respectively. EP receptor mRNA expression in RASFs was determined by reverse transcriptase-polymerase chain reaction. Production of PGE(2) and cAMP was measured by enzyme-linked immunosorbent assay.
The enhanced expression of mPGES mRNA and protein in IL-1beta-stimulated RASFs was attenuated by the addition of indomethacin, NS-398, rofecoxib, or meloxicam. This reduction of expression was reversed by PGE(2). IL-1beta-induced PGES activity, measured by conversion of PGH(2) to PGE(2), was decreased by rofecoxib. EP2 and EP4 receptor mRNA was detected in RASFs. EP2 and EP4 agonists, as well as PGE(2), restored the inhibitory effect of rofecoxib on mPGES expression. The effect of PGE(2) was mimicked by forskolin, a direct activator of adenylate cyclase. Intracellular cAMP was increased by IL-1beta and was inhibited by rofecoxib.
Enhancement of mPGES expression by PGE(2) via the EP2/EP4 receptors with an increase in cAMP may play an important role in articular inflammation in patients with RA. It also seems that cyclooxygenase 2 (COX-2) inhibitors decrease PGE(2) production not only by direct inhibition of COX-2, but also by reducing mPGES expression in activated RASFs.