Further, emerging evidence shows that OGT may be regulated by the interaction with its target, such as p38 mitogen-activated protein kinase or a proteasome regulatory complex. An increase in the association of OGT with Rpt2 was detected when NO was present, in parallel with an increase in Rpt2 OGlcNAcylation. Alternatively, the increased levels of intracellular UDP-GlcNAc have been found to enhance OGT activity leading to upregulated O-GlcNAcylation of the SCH727965 779353-01-4 target proteins. In line with these observations, our study demonstrated that incubation with exogenous glucosamine mimicked the NO-mediated effects in endothelial cells, while NO donors increased the expression of O-GlcNAcylated proteins. It warrants further investigation to determine how eNOS and eNOS-derived NO through their mediator regulate OGT and O-GlcNAc levels in vascular endothelial cells. In conclusion, the present study provides the first evidence that NO functions as a physiological suppressor of the 26S proteasome in vascular endothelial cells, a mechanism that may bridge an essential endothelial regulator with the metabolic sensors and the protein quality control machinery. Although it has yet to establish that 26S proteasome functionality mediates the vascular protective effects of eNOSderived NO, mechanisms identified in the present study could advance our understanding of 26S proteasome regulation and may facilitate the identification of new therapeutic targets for proteasome associated diseases. The MYC family members c-MYC, MYCN and L-MYC are transcription factors crucial for the regulation of normal cellular functions including proliferation, cell growth, differentiation, metabolism and apoptosis. However, the genes encoding these proteins are also the most frequently deregulated oncogenes in several types of human cancers. c-MYC and MYCN, exert their functions mainly through transcriptional modulation of their target genes. The C-terminal domain of MYC comprises a basic helix-loop-helix leucine zipper domain, necessary for the dimerization with its partner MAX and for sequence-specific binding to DNA, while the Nterminal transactivation domain interacts with co-factors to regulate transcription. There is a large overlap between the downstream targets of c-MYC and MYCN and insertion of the mycn gene into the c-myc locus can fully rescue the embryonic lethal phenotype of a c-myc knockout mouse. However, in normal tissue the expression pattern of these two proteins differ significantly. In the developing embryo, MYCN is expressed in certain tissues including the central and peripheral nervous systems, lung and spleen, whereas in adults its expression is very low or absent. In contrast, c-MYC is expressed in all proliferating cells in adults. In human tumors, oncogenic alterations in MYC are common and include point mutations that increase protein stability, gene amplification, gene translocation, and enhanced translation. MYCN is amplified in cancers such as neuroblastoma, medulloblastoma, lung cancer and glioma. In NB, a pediatric cancer of the sympathetic nervous system, MYCNamplification is strongly correlated with poor prognosis and advanced tumor stage, and these tumors are often resistant to multimodal therapy. MYC is therefore an attractive target for cancer therapy. It has been shown that downregulation of MYC leads to cancer cell growth arrest, senescence, enhanced apoptosis, differentiation and/or tumor regression in mouse models of human cancer. Importantly, even transient downregulation of MYC has been reported sufficient to diminish the tumor burden in animal models, and the effects of MYC inhibition on normal tissue has been shown to be well tolerated and Enzalutamide side effects reversible in adult mice.