Endoplasmic reticulum (ER)-stress is known to induce neuronal cell death and to play roles in
neurodegenerative diseases. Phosphorylation of
double stranded RNA-dependent
protein kinase (PKR) has been demonstrated in brain tissues in patients with Alzheimer's, Parkinson's, and Huntington's diseases. Here, we examined the effect of a PKR inhibitor (an imidazolo-
oxindole derivative that acts as an
ATP-binding site-directed inhibitor of PKR) on the neuronal cell death induced by ER-stress in cultured human
neuroblastoma cells (SH-SY5Y). Cell damage was induced by
tunicamycin (an ER-stress inducer), and cell viability was measured by
Hoechst 33342 and
YO-PRO-1 double staining and by the
resazurin-reduction test (to evaluate metabolic activity). Treatment with
tunicamycin at 2 microg/ml for 24 h induced apoptotic cell death accompanied by nuclear condensation and/or fragmentation, and these cells were positive for
YO-PRO-1 (early-phase apoptosis and
necrosis indicator). Treatment with the PKR inhibitor at 0.1 or 0.3 microM led to a decrease in the number of apoptotic cells induced by
tunicamycin. In the
resazurin-reduction test, the PKR inhibitor (at 0.1 and 0.3 microM) concentration-dependently inhibited the
tunicamycin-induced decrease in metabolic activity. On the other hand, treatment with the PKR inhibitor alone (at 0.3 microM) had no effect on cell morphology or viability (versus in normal control cells). These results indicate that inhibition of PKR activation may be neuroprotective against ER stress-induced cell damage.