title: Proteasome inhibition down-regulates endothelial nitric-oxide synthase phosphorylation and function.
abstract: Endothelial nitric-oxide synthase (eNOS) function is fundamentally modulated by protein phosphorylation. In particular, phosphorylation of serine 1179 (bovine)/1177 (human) by Akt has been shown to be the central mechanism of eNOS regulation. Here we revealed a novel role of proteasome in controlling eNOS serine 1179 phosphorylation and function. Rather than affecting eNOS turnover, proteasomal inhibition specifically dephosphorylated eNOS serine 1179, leading to decreased enzymatic activity. Blocking protein phosphatase 2A (PP2A) by okadaic acid or PP2A knockdown restored eNOS serine 1179 phosphorylation and activity in proteasome-inhibited cells. Although total PP2A expression and activity in cells were not affected by proteasome inhibitors, proteasomal inhibition induced PP2A ubiquitination and ubiquitinated PP2A translocated from cytosol to membrane. Further biochemical analyses demonstrated that eNOS associated with PP2A on cell membranes. Proteasomal inhibition markedly enhanced PP2A association to eNOS, and this increase of PP2A dephosphorylated eNOS and its upstream kinase Akt. Taken together, these studies identified a novel pathway in which proteasome modulates eNOS phosphorylation by inducing intracellular PP2A translocation.
authors.affiliation: Davis Heart and Lung Research Institute, Division of Cardiovascular Medicine, Department of Molecular and Cellular Biochemistry, Ohio State University Medical Center, Columbus, Ohio 43210.
authors.forename: Qin
authors.initials: Q
authors.lastname: Wei
authors.affiliation: Davis Heart and Lung Research Institute, Division of Cardiovascular Medicine, Department of Molecular and Cellular Biochemistry, Ohio State University Medical Center, Columbus, Ohio 43210. Electronic address: yong.xia@osumc.edu.
authors.forename: Yong
authors.initials: Y
authors.lastname: Xia
mesh_terms: D000818:Animals; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism* / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D061988:Proteasome Inhibitors; D054648:Protein Phosphatase 2; D021381:Protein Transport; D012694:Serine / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: C432785:PPP2R1B protein, human; D061988:Proteasome Inhibitors; D025801:Ubiquitin; D012694:Serine; D052250:Nitric Oxide Synthase Type III; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2