Recent studies indicate that NF-E2 related factor 2 (Nrf2) is a substrate for the
ubiquitin-
proteasome pathway. The present study is aimed to determine whether increased protein stability is a mechanism by which
quinone compounds, like
tert-butylhydroquinone (
tBHQ), may enhance Nrf2-mediated transcriptional activation and subsequent
antioxidant protection. H2O2-induced necrotic cell death, evidenced by transmission electronic microscope (TEM) imaging with no
caspase 3 activation and PARP cleavage, was significantly attenuated by pretreatment with
tBHQ or overexpression of Nrf2 through advenovirus-mediated
infection in human neural stem cells (hNSCs). Microarray analysis showed that those identified
antioxidant genes, responsible for antiapoptotic action in IMR-32 cells (J. Li et al., 2002, J. Biol. Chem. 277, 388-394), were also coordinately upregulated through Nrf2-dependent
antioxidant responsive
element (ARE) activation in hNSC. The stabilization of Nrf2 by
tBHQ in IMR-32 cells was evidenced by a pulse-chase assay showing no significant increase in Nrf2
protein synthesis after
tBHQ treatment, and by
ubiquitin immunoprecipitation showing that
tBHQ stabilized ubiquitinated Nrf2. An in vitro proteasomal activity assay showed that
tBHQ did not act as a 20S/
26S proteasome inhibitor. Nrf2 stabilization by
tBHQ also was observed in hNSCs. Taken together, this study suggests that identified
antioxidant genes, which were upregulated through
tBHQ induced Nrf2 stabilization, confer protection on target cells against H2O2-induced apoptotic cell death in
neuroblastoma cells as well as the necrotic cell death in the hNSC. Nrf2 stabilization by pharmacological modulation or adenovirus-mediated Nrf2 overexpression, therefore, might be viable strategies to prevent a wide-spectrum of oxidative stress-related neuronal cell
injuries.