REPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE AND CYCLOOXYGENASE-2 BYPROSTAGLANDIN E(2) AND OTHER CYCLIC-AMP STIMULANTS IN J774 MACROPHAGES

The enhanced nitric oxide (NO) and prostaglandin (PG) generation of ac tivated macrophages is controlled by glucocorticoid-sensitive inducibl e nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), respectiv ely. Negative feedback regulation of iNOS expression by the products o f both pathways has been suggested, but their effects on COX-2 express ion have not been examined. We have investigated the effect of E- and I-series prostaglandins that activate adenylate cyclase (AC), forskoli n (a direct activator of AC), and other agents that influence the cycl ic AMP/cyclicGMP systems on the ability of E. coli endotoxin (lipopoly saccharide, LPS) to induce iNOS and COX-2 in the murine macrophage cel l line J774. After a 2-hr pretreatment before adding endotoxin, PGE(2) , PGI(2), forskolin, IBMX (isobutylmethylxanthine, a cyclicAMP/cyclicG MP phosphodiesterase inhibitor), 8-bromo cyclicAMP, and arachidonic ac id itself all inhibited the expression of both iNOS and COX-2 (as show n by Western blotting), and reduced NO release and COX activity, where as PGF(2 alpha) and 8-bromo cyclic GMP were only weakly effective. The effects of PGE(2), PGI(2), and forskolin were enhanced by cotreatment with IBMX. The suppression of LPS-induced iNOS induction by PGE(2) wa s functionally significant, in that it protected against the mild cyto toxicity of the NO generated in response to endotoxin. These results p rovide the first direct evidence for the feedback regulatory suppressi on of COX-2 induction by a PG-driven cAMP-mediated process, and show t hat the modulation of iNOS and COX-2 induction shares common features. They also suggest that such modulation is normally held in check by h igh phosphodiesterase activity with these cells. (C) 1997 Elsevier Sci ence Inc.