Regulation of Cytosolic Prostaglandin E Synthase

Abstract

Biosynthesis of prostaglandin E2 (PGE2), the most common prostanoid with potent and various biological activities, is regulated by three sequential steps of cyclooxygenase (COX) pathway. We reported the molecular identification of cytosolic prostaglandin E synthase (cPGES), a terminal enzyme of the COX-mediated PGE2 biosynthetic pathway. Of interest, it is identical to the co-chaperone p23 that binds to heat shock protein 90 (Hsp90). Incubation of recombinant cPGES/p23 and Hsp90 resulted in a remarkable increase in PGES activity in vitro. Furthermore, A23187-induced PGE2 generation in 3Y1 cells was suppressed by Hsp90 inhibitors, which destabilized the cPGES/p23-Hsp90 complex, and reduced cPGES/p23 activity and PGE2 production to basal levels. Next, we found that cPGES/p23 underwent serine phosphorylation, which was accelerated transiently after cell activation. In activated cells, cPGES/p23 phosphorylation occurred in parallel with increased cPGES/p23 enzymic activity and PGE2 production from exogenous and endogenous arachidonic acid, and these processes were facilitated by Hsp90 that formed a tertiary complex with cPGES/p23 and protein kinase CK2. Treatment of cells with inhibitors of CK2 and Hsp90 and with a dominant-negative CK2 attenuated the formation of the cPGES/p23-CK2-Hsp90 complex and attendant cPGES/p23 phosphorylation and activation. Mutations of either of two predicted CK2 phosphorylation sites on cPGES/p23 (Ser113 and Ser118) abrogated its phosphorylation and activation both in vitro and in vivo. These results provide the first evidence that the cellular function of this eicosanoid-biosynthetic enzyme is under the control of a molecular chaperone and its client protein kinase.