Nitric Oxide Synthase Trafficking Inducer is a pleiotropic regulator of endothelial cell function and signaling [Signal Transduction]

Endothelial nitric oxide synthase (eNOS) and its bioactive product nitric oxide (NO) mediate many endothelial cell functions, including angiogenesis and vascular permeability. For example, vascular endothelial growth factor (VEGF)-mediated angiogenesis is inhibited upon reduction of NO bioactivity both in vitro and in vivo. Moreover, genetic disruption or pharmacological inhibition of eNOS attenuates angiogenesis during tissue repair, resulting in delayed wound closure. These observations emphasize that eNOS-derived NO can promote angiogenesis. Intriguingly, eNOS activity is regulated by nitric oxide synthase trafficking inducer (NOSTRIN), which sequesters eNOS, thereby attenuating NO production. This has prompted significant interest in NOSTRINs function in endothelial cells. We show here that NOSTRIN affects the functional-transcriptome of endothelial cells by down-regulating several genes, important for invasion and angiogenesis. Interestingly, NOSTRINs effects on endothelial gene expression were independent of eNOS activity. NOSTRIN also affected the expression of secreted cytokines involved in inflammatory responses, and ectopic NOSTRIN over-expression functionally restricted endothelial cell proliferation, invasion, adhesion, and VEGF-induced capillary tube formation. Furthermore, NOSTRIN directly interacted with TNF receptor associated factor 6 (TRAF6), leading to suppression of NFkB activity and inhibition of Akt activation via phosphorylation. Interestingly, TNF-α-induced NFkB pathway activation was reversed by NOSTRIN. We found that the SH3 domain of NOSTRIN is involved in the NOSTRIN-TRAF6 interaction and is required for NOSTRIN-induced down-regulation of endothelial cell proteins. These results have broad biological implications, as aberrant NOSTRIN expression leading to the deactivation of NFkB pathway and, in turn, triggering an anti-angiogenic cascade, might inhibit tumorigenesis and cancer progression.

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