NOS regulation

Protein tyrosine kinase-dependent protein activation

Huang, K.T., Kuo, L. and J.C. Liao (1998) Lipopolysaccharide activates endothelial nitric oxide synthase through protein tyrosine kinase, Biochem. Biophys. Res. Comm. 245, 33-37.

Vascular endothelial cell injury or activation by lipopolysaccharide (LPS) plays an important role in the pathogenesis of endotoxin shock. However, the effect of LPS on NO production from vascular endothelial cells (ECs) is incompletely understood. In this study, bovine coronary venular ECs were treated with LPS and the release of NO and expression of the endothelial NO synthase (ecNOS) were examined. We found that the ecNOS activity is transiently enhanced by LPS within the time scale of about 10 h due to the interplay between two LPS-induced mechanisms. Within the first 10 h of LPS treatment, the specific activity of ecNOS is increased by a post-translational modification mediated through a protein tyrosine kinase cascade. After about 10 h of treatment, however, LPS destabilizes the transcript of ecNOS and thus decreased the expression level and total activity. 

Transcript Degradation

Lu, J-T. Schmiege, L.M. III. Kuo, L. and J.C Liao (1996) Downregulation of Endothelial Constitutive Nitric Oxide Synthase Expression by Lipopolysaccharide , Biochem. Biophys. Res. Comm. 225, 1-5.

Lipopolysaccharide (LPS), a causal agent of sepsis, has been shown to induce systemic nitric oxide (NO) synthesis through complex mechanisms. However, the effect of LPS on endothelial cells is incompletely understood. To investigate the mechanism by which LPS influences the release of NO from endothelial cells, the effect of this compound on endothelial constitutive nitric oxide synthase (ecNOS) was studied in cultured bovine coronary venular endothelial cells. Western and Northern analyses showed that LPS decreased ecNOS expression at the protein and mRNA levels in a time-dependent and dose-responsive manner. Concurrent treatment of the endothelial cells with LPS and a transcription inhibitor, actinomycin D, resulted in decreased ecNOS mRNA within 8 hours. In contrast, treatment with actinomycin D had only a relatively insignificant effect on the ecNOS transcript level. This result suggests that the reduction of ecNOS by LPS resulted from an increased degradation rate of its transcript.