Differential regulation of cyclooxygenase isozymes by cAMP-elevating agents

Bovine aortic endothelial cells produce prostacyclin as their major arachid onic acid metabolite. cAMP, in turn, is the second messenger for prostacycl in. In the present study, we investigated the effects of cAMP-elevating age nts on prostacyclin production by bovine aortic endothelial cells. Treatmen t of resting bovine aortic endothelial cells with cAMP-elevating agents inh ibited prostacyclin production and cyclooxygenase activity, without affecti ng arachidonic acid release. No change was detected in cyclooxygenase-l pro tein expression. The specific inhibitor of protein kinase A, Rp-cAMPS (aden osine 3',5'-cyclic monophosphorothioate, Rp-isomer, triethylammonium salt), and the phosphatase inhibitor, okadaic acid, both suppressed cAMP-induced inhibition, suggesting that this inhibition is mediated by a phosphorylatio n-dephosphorylation cascade, which is possibly protein kinase A-dependent. In lipopolysaccharide-treated cyclooxygenase-2 expressing bovine aortic end othelial cells, where cydooxygenase-1 activity was selectively inhibited, d ibutyryl cAMP failed to inhibit cyclooxygenase-2 activity. Cyclooxygenase-2 protein was induced upon treatment with dibutyryl cAMP and further inducti on of cyclooxygenase-2 protein was effected by IBMX (3-isobutyl-1-methyl-xa nthine) and dibutyryl cAMP in bacterial lipopolysaccharide-stimulated cells . These results suggest that increased cellular cAMP selectively inhibits c yclooxygenase-1 activity without altering cyclooxygenase-1 protein expressi on, and at the same time, up-regulates cyclooxygenase-2 protein. This compl ex regulation of cyclooxygenase activity and protein expression by cAMP may represent a prostacyclin-induced autoregulatory mechanism in bovine aortic endothelial cells. (C) 1999 Elsevier Science B.V. All rights reserved.