We have recently demonstrated that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) increases endothelial nitric oxide synthase (eNOS) phosphorylation, NOS activity, and nitric oxide (NO) synthesis in cultured human umbilical vein endothelial cells (HUVEC), without inducing apoptotic cell death. Although an important factor that regulates eNOS activity is its localization within the cells, little is known about the role of TRAIL in the regulation of eNOS trafficking among cellular compartments and the cytoskeleton involvement in this machinery. Then, we did both quantitative and semi-quantitative evaluations with biochemical assays and immune fluorescence microscopy in the presence of specific inhibitors of NOS activity as well as of cytoskeletal microtubule structures. In our cellular model, TRAIL treatment not only increased NO levels but also caused a time-dependent NO migration of fluorescent spots from the plasma membrane to the inner part of the cells. In unstimulated cells, most of the eNOS was localized at the cell membranes. However, within 10 min following addition of TRAIL, nearly all the cells showed an increased cytoplasm localization of eNOS which appeared co-localized with the Golgi apparatus at a higher extent than in unstimulated cells. These effects were associated to an increased formation of trans-cytoplasm stress fibers with no significant changes of the microtubule network. Conversely, microtubule disruption and Golgi scattering induced with Nocodazole treatment inhibited TRAIL-increased NOS activity, indicating that, on cultured HUVEC, TRAIL ability to affect NO production by regulating eNOS sub-cellular distribution is mediated by cytoskeleton and Golgi complex modification
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