Involvement of double-stranded RNA-dependent protein kinase and phosphorylation of eukaryotic initiation factor-2α in neuronal degeneration

Inhibition of protein translation plays an important role in apoptosis. While double-stranded RNA-dependent protein kinase (PKR) is named as it is activated by double-stranded RNA produced by virus, its activation induces an inhibition of protein translation and apoptosis via the phosphorylation of the eukaryotic initiation factor 2α (elF2cα). PKR is also a stress kinase and its levels increase during ageing. Here we show that PKR activation and elF2α phosphorylation play a significant role in apoptosis of neuroblastoma cells and primary neuronal cultures induced by the β-amyloid (Aβ) peptides, the calcium ionophore A23187 and flavonoids. The phosphorylation of elF2α and the number of apoptotic cells were enhanced in over-expressed wild-type PKR neuroblastoma cells exposed to Aβ peptide, while dominant-negative PKR reduced elF2α phosphorylation and apoptosis induced by Aβ peptide. Primary cultured neurons from PKR knockout mice were also less sensitive to Aβ peptide toxicity. Activation of PKR and elF2α pathway by Aβ peptide are triggered by an increase in intracellular calcium because the intracellular calcium chelator BAPTA-AM significantly reduced PKR phosphorylation. Taken together, these results reveal that PKR and elF2α phosphorylation could be involved in the molecular signalling events leading to neuronal apoptosis and death and could be a new target in neuroprotection.