U46619, a thromboxane A2 analogue, and basic fibroblast growth factor (FGF-2) both induced the expression of the inducible cyclo-oxygenase (Cox)-2 in porcine aortic smooth-muscle cells. This induction was dose-dependent (submaximal at 300 nM for U46619 and 1 ng/ml for FGF-2) and 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 FGF-2 was sustained (>1 h). PD98059, an inhibitor of the ERK pathway, inhibited the expression of Cox-2. In contrast, activation of Jun-N-terminal kinase (JNK1) was sustained with U46619 but poorly induced by FGF-2. Cox-2 expression induced by U46619 or FGF-2 was similarly reduced by prostaglandin (PGE2), forskolin or dibutyryl-cAMP, suggesting a regulatory effect of adenylate cyclase on Cox-2 expression. However, activation of ERK2 by FGF-2 was not affected by PGE2 whereas that of JNK1 by U46619 was inhibited, suggesting that inhibition of COX-2 expression by cAMP may be downstream of ERK2. The effects of PGE2 and forskolin on Cox-2 and phosphorylation of JNK1 were reversed with the protein kinase A inhibitor H89. In addition, endogenous PGE2 down-regulated the expression of Cox-2 by the two inducers, as stimulation of the cells in the presence of different Cox inhibitors increased the expression of the protein. Overall, these results suggest that exogenous and endogenous PGE2 exert negative inhibitory effects on Cox-2 expression mediated by stimulation of protein kinase A.