Coexpression of microsomal prostaglandin E synthase with cyclooxygenase-2 in human rheumatoid synovial cells

Recently, microsomal prostaglandin (PG) E synthase (mPGES) was cloned as a terminal enzyme catalyzing PGH2 to PGE2. We investigated mPGES as well as cyclooxygenase (COX)-2, catalyzing arachidonic acid to PGH2, in synovial cells from patients with rheumatoid arthritis (RA). The effect of dexamethasone on mPGES expression was also studied.

Synovial cells were treated with interleukin 1beta (IL-1beta) and dexamethasone under various conditions, and expression of mPGES mRNA and protein was analyzed by Northern blot and Western blot, respectively. Conversions of arachidonic acid or PGH2 to PGE2 were measured by ELISA. Subcellular localization of mPGES and COX-2 was determined by immunofluorescent microscopic analysis.

mPGES mRNA and protein expression were significantly upregulated by IL-1beta in synovial cells. COX-2 mRNA and protein were also upregulated by IL-1beta, but with a different time course from that of mPGES. Conversion of PGH2 to PGE2 increased by IL-1beta and was correlated with mPGES expression. Increased conversion of arachidonic acid to PGE2 was maintained when mPGES and COX-2 were coexpressed. Subcellular localization of mPGES and COX-2 overlapped in the perinuclear region in IL-1beta stimulated synovial cells. Dexamethasone inhibited mRNA and protein expression for mPGES and increased conversion of arachidonic acid to PGE2, but inhibition of mPGES was weaker compared with that of COX-2 in IL-1beta stimulated cells.

The results suggest that abundant PGE2 production at inflammation sites such as rheumatoid synovia is caused by the coordinated upregulation of mPGES and COX-2. Thus mPGES might be a potential new target for therapeutic strategies to control PGE2 synthesis specifically in patients with RA and other inflammatory diseases.