REGULATORY ROLE OF PROSTAGLANDIN E-2 IN INDUCTION OF CYCLO-OXYGENASE-2 BY A THROMBOXANE A(2) ANALOG (U46619) AND BASIC FIBROBLAST GROWTH-FACTOR IN PORCINE AORTIC SMOOTH-MUSCLE CELLS

U46619, a thromboxane A(2) analogue, and basic fibroblast growth facto r (FGF-2) both induced the expression of the inducible cyclo-oxygenase (Cox)-2 in porcine aortic smooth-muscle cells. This induction was dos e-dependent (submaximal at 300 nM for U46619 and 1 ng/ml for FGF-2) an d time-dependent, with similar intensity and maximal expression at 2 h . Under these conditions, both inducers stimulated rapid activation of extracellular signal-regulated kinase (ERK2) at 5-10 min, a transient and lower intensity being induced by U46619 whereas that induced by F GF-2 was sustained (> 1 h). PD98059, an inhibitor of the ERK pathway, inhibited the expression of Cox-2. In contrast, activation of Jun-N-te rminal kinase (JNK1) was sustained with U46619 but poorly induced by F GF-2. Cox-2 expression induced by U46619 or FGF-2 was similarly reduce d by prostaglandin (PGE(2)), forskolin or dibutyryl-cAMP, suggesting a regulatory effect of adenylate cyclase on Cox-2 expression. However, activation of ERK2 by FGF-was not affected by PGE(2) whereas that of J NK1 by U46619 was inhibited, suggesting that inhibition of COX-2 expre ssion by cAMP may be downstream of ERK2. The effects of PGE(2) and for skolin on Cox-2 and phosphorylation of JNK1 were reversed with the pro tein kinase A inhibitor H89. In addition, endogenous PGE(2) downregula ted the expression of Cox-2 by the two inducers, as stimulation of the cells in the presence of different Cox inhibitors increased the expre ssion of the protein. Overall, these results suggest that exogenous an d endogenous PGE(2) exert negative inhibitory effects on Cox-2 express ion mediated by stimulation of protein kinase A.