Proteasome inhibition: an early or late event in nitric oxide-induced neuronal death?
Nitric oxide (NO), ubiquitously expressed in the central nervous system, has been perceived to be a potential neuromodulator. Employing cultured murine primary cortical neurons, NO resulted in an inhibition of the ubiquitin-proteasome system (UPS) with a dose- and time-dependent decrease in cell viability. This is consistent with a previous study that reported a dysfunction of UPS with consequential apoptotic death in macrophage cell with NO treatment. However, it cannot be unclear if the drop in UPS efficiency is directly imposed on by NO. Therefore by using microarray analysis, our study revealed an early down-regulation or non-significant differential expression of genes encoding UPS proteins in NOC-18 (NO donor)-treated neurons as compared to an observed elevation of corresponding gene expression genes in lactacystin (classical proteasome inhibitor)-treated neurons (conducted earlier). Furthermore, time-course analysis of proteasome activity in NOC-18-treated neurons demonstrated a late onset of reduction. This is intriguing as it is well established that in an exclusive proteasome dysfunction-induced cell death, a compensatory feedback mechanism will be activated with an initial and concerted up-regulation of genes encoding proteins involved in UPS as seen when neurons were treated with lactacystin. Thus, it is highly suggestive that NO-triggered neuronal death takes on a different signaling cascade from that of a classical proteasome inhibitor, and that the late reduction of proteasome activity is a downstream event following the activation of apoptotic cellular signaling cascade. In intracellular condition, the proteasome is not NO preferred primary target responsible for the trigger of the cell death machinery. In conclusion, we presented novel findings that shed light into NO-induced cell death signaling cascade, which would be important in understanding the pathogenesis of neurodegenerative disorders such as Parkinson's disease.
Peng
Zhao Feng
ZF
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore.
Chen
Minghui Jessica
MJ
Yap
Yann Wan
YW
Manikandan
Jayapal
J
Melendez
Alirio J
AJ
Choy
Meng Shyan
MS
Moore
Philip K
PK
Cheung
Nam Sang
NS
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D005456:Fluorescent Dyes; D051379:Mice; D019579:Neocortex / Q000166:cytology / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects*; D009569:Nitric Oxide / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D061988:Proteasome Inhibitors; D013050:Spectrometry, Fluorescence
D015853:Cysteine Proteinase Inhibitors; D005456:Fluorescent Dyes; D061988:Proteasome Inhibitors; D009569:Nitric Oxide