RAPID AND TRANSIENT INDUCTION OF CYCLOOXYGENASE-2 BY EPIDERMAL GROWTH-FACTOR IN HUMAN AMNION-DERIVED WISH CELLS

The central enzyme in the prostaglandin (PG) biosynthetic cascade is P GH(2) synthase or cyclo-oxygenase (COX). At present, two distinct isof orms of PGH(2) synthase/COX have been identified: COX-1 and COX-2. In many systems, COX-1 is a constitutively expressed isoform that is resp onsible for normal physiological production of PGs, whereas COX-2 is a n inducible isoform that responds to cytokines, endotoxin and growth f actors by producing high levels of PGs. The regulation of COX-2 mRNA a nd protein, and the subsequent production of PGE(2), were therefore ex amined in amnion-derived WISH cells stimulated with epidermal growth f actor (EGF). Treatment of WISH cells with EGF (0.01-100 ng/ml) elicite d dose-dependent synthesis. of COX-2 mRNA and protein de novo. In addi tion, stimulation of WISH cells with EGF (10 ng/ml) induced steady-sta te levels of COX-2 mRNA and protein that appeared within 30 min and th en declined rapidly to near baseline levels within 2-4 h. In contrast, COX-1 protein was unchanged in response to treatment with EGF. PGE(2) production was also rapid and transient. Preincubation of cells with the novel COX-2 enzymic inhibitor NS-398 (10(-5)-10(-10) M) completely prevented PGE(2) formation in a dose-dependent manner. Preincubation of cells in dexamethasone (Dex; 0.1 mu M), however, resulted in only a 31% decrease in PGE(2) formation in response to EGF (10 ng/ml) while completely attenuating PGE(2) biosynthesis in tumour necrosis factor a lpha (TNF-alpha)-stimulated cells. In addition, Dex (0.1 mu M) was onl y partly effective at preventing EGF-induced COX-2 mRNA and protein ex pression de novo, whereas Dex completely inhibited TNF-alpha-promoted COX-2 mRNA and protein expression. Thus the results presented here dem onstrate that EGF induces the rapid but transient expression of COX-2 mRNA and protein and the subsequent production of PGE(2) in WISH cells .