Upregulation of immunoproteasomes by nitric oxide: Potential antioxidative mechanism in endothelial cells

Nitric oxide ((NO)-N-center dot) was shown to stimulate the proteasomal function and the ubiquitin-proteasome pathway and to ameliorate endothelial apoptotic signaling induced by oxidants. Understanding the regulatory mechanisms by which (NO)-N-center dot stimulates proteasomes and affords cytoprotection in endothelial cells has therapeutic implications, as many vascular diseases are characterized by a deficiency in (NO)-N-center dot. Here we report that (NO)-N-center dot/cGMP/cAMP-induced immunoproteasome subunit expression is responsible for the increased proteasomal activities. Cells pretreated with protein kinase G and protein kinase A inhibitors markedly attenuated (NO)-N-center dot-dependent proteasome activation. Results show that the signaling mechanism enhanced the phosphorylation of the transcription factor cAMP-response element-binding protein, elevated the cAMP-response element-promoter activity and induced the expression of immunoproteasomal subunits (LMP2 and LMP7). (NO)-N-center dot-dependent proteasomal activity was abrogated in cells transfected with antisense LMP2 and LMP7 oligonucleotides. Lower levels of LMP2 and LMP7 were detected in aorta of iNOS(-/-) mice compared to wild-type controls, Suggesting that endogenous production of (NO)-N-center dot is important in the basal regulation Of immunoproteasome. The (NO)-N-center dot/cGMP/cAMP signaling pathway mitigates transferrin-iron-mediated oxidative stress and apoptosis through induction of immunoproteasomes. These results provide new insights on the regulatory mechanisms by which the (NO)-N-center dot-mediated immunoproteasome signaling pathway affords cytoprotection in endothelial cells. (C) 2005 Elsevier Inc. All rights reserved.