Sensors of endoplasmic reticulum (ER) stress function in a co-ordinated manner. In the present study we investigated
the relationship between IRE1α and PERK pathways and survival of ER stressed U937 cells and BC3 cells. To this end,
we investigated the effects of a subcytotoxic concentration of Tunicamycin in IRE1α-proficient and in IRE1α-deficient
cells, by pharmacological inhibition with 4μ8 C or down-regulation by specific siRNA. We show that either type of
IRE1α deficiency affects eIF2α expression and causes cell death increase. GSK2606414, a PERK inhibitor, and PERK
specific siRNA prevent eIF2α down-regulation and restore cell survival. Degradation of this protein is due to
autophagy, as it is prevented by bafilomycin and not by proteasome inhibition. Furthermore, activation of the
autophagy flux is PERK dependent. Also the Cathepsin B inhibitor CA074 prevents eIF2α from degradation and reduces
cell death. Altogether, these results show that IRE1α deficiency in ER stressed cells leads to an unexpected decrease of
eIF2α, an important molecule for protein translation, through PERK dependent autophagy. Thus, IRE1/XBP1 inhibitors
may represent a feasible strategy for tumor therapy, while PERK inhibitors may vanish the goal
