Inhibition of Prostaglandin Endoperoxide Synthase-2 Expression in Stimulated Human Monocytes by Inhibitors of P38 Mitogen-activated Protein Kinase

Prostaglandin endoperoxide synthase (PGHS; cyclooxygenase), the rate-limiting enzyme in the conversion of arachidonic acid to prostanoids, has two isoforms. PGHS-1 is constitutively expressed and involved in homeostasis, whereas PGHS-2 is inducible in monocytes in response to proinflammatory agents. Using freshly elutriated human monocytes, we examined the effect on PGHS-2 expression of certain cytokine-suppressive anti-inflammatory drugs such as SK&F 86002. Incubation with serum-treated zymosan (STZ) stimulated the expression of PGHS-2 in a time- and dose-dependent manner. SK&F 86002 dose-dependently inhibited this STZ-induced expression of PGHS-2 protein, which correlated with a decrease in prostaglandin E2 and thromboxane A2 production. However, suppression of PGHS-2 expression is not the result of suppressed cytokine production, because SK&F 86002 suppressed PGHS-2 expression initiated by IL-1beta and TNF-alpha, in addition to other stimuli. Moreover, this effect was selective in that the protein expression of two other important enzymes involved in the metabolism of arachidonic acid, cytosolic phospholipase A2 and 5-lipoxygenase, was not affected. Stimulation with STZ caused a time-dependent increase in levels of PGHS-2 mRNA; incubation with cytokine-suppressive agents caused a decrease of these levels, suggesting the involvement of transcription and/or mRNA stability events in the inhibition of PGHS-2. These results indicate a new and potentially important anti-inflammatory property of SK&F 86002, namely the specific suppression of PGHS-2 induction.