NITRIC-OXIDE INDUCES HEME OXYGENASE-1 GENE-EXPRESSION AND CARBON-MONOXIDE PRODUCTION IN VASCULAR SMOOTH-MUSCLE CELLS

Since recent studies demonstrate that vascular smooth muscle cells syn thesize two distinct guanylate cyclase-stimulatory gases, NO and CO, w e examined possible regulatory interactions between these two signalin g molecules. Treatment of rat aortic smooth muscle cells with the NO d onors, sodium nitroprusside, S-nitroso-N-acetyl-penicillamine, or 3-mo rpholinosydnonimine, increased heme oxygenase-1 (HO-1) mRNA and protei n levels in a concentration- and time-dependent manner. Both actinomyc in D and cycloheximide blocked NO-stimulated HO-1 mRNA and protein exp ression. Nuclear run-on experiments demonstrated that NO donors increa sed HO-1 gene transcription between 3- and 6-fold. In contrast, NO don ors had no effect on the stability of HO-1 mRNA. Incubation of vascula r smooth muscle cells with the membrane-permeable cGMP analogues, dibu tyryl cGMP and 8-bromo-cGMP, failed to induce HO-1 gene expression. Tr eatment of vascular smooth muscle cells with NO donors also stimulated the production and release of CO, as demonstrated by the CO-dependent increase in intracellular cGMP levels in coincubated platelets. Final ly, incubating vascular smooth muscle cells with interleukin-1 beta an d tumor necrosis factor-alpha induced NO synthesis and also significan tly increased the level of HO-1 protein. The cytokine-stimulated produ ction of both NO and HO-1 protein in smooth muscle cells was blocked b y the NO synthase inhibitor methyl-L-arginine. These results demonstra te that exogenously administered or endogenously released NO stimulate s HO-1 gene expression and CO production in vascular smooth muscle cel ls. The ability of NO to induce HO-catalyzed CO release from vascular smooth muscle cells provides a novel mechanism by which NO might modul ate soluble guanylate cyclase and, thereby, vascular smooth muscle cel l and platelet function.