Regulation of interleukin-1β-stimulated inducible nitric oxide synthase expression in cultured vascular smooth muscle cells by hemostatic proteins

Experiments were performed to examine the mechanism by which specific hemostatic proteins regulate the release of nitric oxide from interleukin-1β (IL-1β) stimulated cultured rat aortic smooth muscle cells. Treatment of smooth muscle cells with IL-β stimulated inducible nitric oxide synthase (iNOS) mRNA expression, which preceded the release of NO (as measured by the accumulation of nitrite in the culture media). The cytokine-stimulated production of nitrite was blocked by the protein synthesis inhibitor cycloheximide, the transcriptional inhibitor actinomycin D, and the competitive inhibitor of NOS nitro-L-arginine. However, only actinomycin D inhibited IL-1β-stimulated iNOS mRNA expression. Treatment of smooth muscle cells with IL-1β in the presence of platelet derived growth factor or thrombin resulted in the inhibition of cytokine-stimulated expression of iNOS mRNA and NO release. The inhibitory effect of thrombin was reversed by hirudin and was mimicked by a 14 amino acid thrombin receptor activating peptide. In contrast, the concomitant exposure of smooth muscle cells to IL-1β and plasmin resulted in the potentiation of both IL-1β-stimulated iNOS expression and NO generation. Finally, treatment of smooth muscle cells with IL-1β in the presence of the hemostatic proteins did not affect the half-life of iNOS mRNA. These results demonstrate that specific protein components of the hemostatic system regulate IL-1β-stimulated iNOS mRNA expression in vascular smooth muscle cells. The capacity of hemostatic proteins to modulate the induction of vascular iNOS activity may play an important role in governing the release of NO and regulating thrombogenesis in vivo.