Expression of nitric oxide synthase by cytokines in vascular smooth muscle cells

Abstract

In cultured vascular smooth muscle cells, the baseline mRNA and protein levels of an inducible type of nitric oxide synthase were barely detectable. Interferon gamma, tumor necrosis factor-α, and interleukin-1β each markedly increased mRNA and protein levels of this enzyme in parallel with the production of nitrite, a stable oxidative metabolite of nitric oxide. Actinomycin D abolished the cytokine-induced increases in mRNA levels and nitrite production. Cycloheximide, which abolished the cytokine-induced increase in nitrite production, had no effect on the interferon-gamma-induced increase in mRNA levels but partially inhibited that induced by interleukin- 1β and markedly inhibited that induced by tumor necrosis factor-α. Transforming growth factor-β1, which inhibited the interferon gamma-, interleukin-1β-, and tumor necrosis factora-α-induced nitrite production, did not affect the increases in mRNA levels caused by these cytokines. Transforming growth factor-β1, however, significantly inhibited the increase in protein levels caused by these cytokines. These findings suggest that interferon gamma directly induces the expression of the inducible nitric oxide synthase gene, whereas tumor necrosis factor-α and interleukin-1β induce it, at least in part, via the induction of intermediary protein(s), and that transforming growth factor-β1 inhibits cytokine-induced nitric oxide production by blocking the posttranscriptional synthesis of inducible nitric oxide synthase. © 1994 American Heart Association, Inc.