title: Compromised proteasome degradation elevates neuronal nitric oxide synthase levels and induces apoptotic cell death.
abstract: The significance of impairment of proteasome activity in PC12 cells was examined in connection with nitrative/nitrosative stress and apoptotic cell death. Treatment of differentiated PC12 cells with MG132, a proteasome inhibitor, elicited a dose- and time-dependent increase in neuronal nitric oxide synthase (nNOS) protein levels, decreased cell viability, and increased cytotoxicity. Viability and cytotoxicity were ameliorated by L-NAME (a broad NOS inhibitor). Nitric oxide/peroxynitrite formation was increased upon treatment of PC12 cells with MG132 and decreased upon treatment with the combination of MG132 and 7-NI (a specific inhibitor of nNOS). The decreases in cell viability appeared to be effected by an activation of JNK and its effect on mitochondrial Bcl-x(L) phosphorylation. These effects are strengthened by the activation of caspase-9 along with increased caspase-3 activity upon treatment of PC12 cells with MG132. These results suggest that impairment of proteasome activity and consequent increases in nNOS levels lead to a nitrative stress that involves the coordinated response of JNK cytosolic signaling and mitochondrion-driven apoptotic pathways.
authors.affiliation: Department of Pharmacology & Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90089, USA.
authors.forename: Philip Y
authors.initials: PY
authors.lastname: Lam
authors.forename: Enrique
authors.initials: E
authors.lastname: Cadenas
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D007191:Indazoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D016716:PC12 Cells; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D051381:Rats; D026361:Reactive Nitrogen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007191:Indazoles; D007976:Leupeptins; D061988:Proteasome Inhibitors; D026361:Reactive Nitrogen Species; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D048031:JNK Mitogen-Activated Protein Kinases; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; C080122:7-nitroindazole