Compensatory activation of ERK1/2 in Atg5-deficient mouse embryo fibroblasts suppresses oxidative stress-induced cell death

Despite of the increasing evidence that oxidative stress may induce non-apoptotic cell death or autophagic cell death, the mechanism of this process is unclear. Here, we report a role and a down-stream molecular event of Atg5 during oxidative stress-induced cell death. Compared to wild type (WT) cells, Atg5-deficient mouse embryo fibroblasts (Atg5^-/- MEFs) and Atg5 knockdown HT22 neuronal cells were more resistant to cell death induced by H₂O₂. On the contrary, Atg5^-/- MEFs were as sensitive to tumor necrosis factor (TNF)-α and cycloheximide as WT cells, and were more sensitive to cell death triggered by amino acid-deprivation than WT MEFs. Treatment with H₂O₂ induced the recruitment of a GFP-LC3 fusion protein and conversion of LC3 I to LC3 II, correlated with the extent of autophagosome formation in WT cells, but much less in Atg5-deficient cells. Among stress kinases, ERK1/2 was markedly activated in Atg5^-/- MEFs and Atg5 knockdown HT22 and SH-SY5Y neuronal cells. The inhibition of ERK1/2 by MEK1 inhibitor (PD98059) or dominant negative ERK2 enhanced the susceptibility of Atg5^-/- MEFs to H₂O₂-induced cell death. Further, reconstitution of Atg5 sensitized Atg5^-/- MEFs to H₂O₂ and suppressed the activation of ERK1/2. These results suggest that the inhibitory effect of Atg5 deficiency on cell death is attributable by the compensatory activation of ERK1/2 in Atg5^-/- MEFs during oxidative stress-induced cell death.