Hydrogen peroxide‐mediated phosphorylation of ERK1/2, Akt/PKB and JNK in cortical neurones: dependence on Ca2+ and PI3‐kinase

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Abstract
Primary cortical neurones exposed to an oxidative insult in the form of hydrogen peroxide (H2O2) for 30 min showed a concentration‐dependent increase in oxidative stress followed by␣a␣delayed NMDA receptor‐dependent cell death measured␣24 h later. Extracellular signal‐regulated protein kinase (ERK1/2), c‐jun N‐terminal kinase (JNK) and the kinase Akt/PKB may regulate neuronal viability in response to oxidative insults. Using phospho‐specific antibodies, a 15‐min stimulation of neurones with H2O2 (100 µm−1 mm) produced a concentration‐dependent phosphorylation of ERK1/2 and Akt/PKB that was partly dependent on extracellular Ca2+ and phosphatidylinositol 3‐kinase (PI3‐K). Higher concentrations of H2O2 (1 mm) also stimulated a phosphorylation of JNK which was totally dependent on extracellular Ca2+ but not PI3‐K. H2O2‐induced phosphorylation of ERK1/2, Akt/PKB or JNK were unaffected by the NMDA channel blocker MK801. Blocking ERK1/2 activation with the upstream inhibitor U0126 (10 µm) enhanced H2O2‐induced (100–300 µm range) neurotoxicity and inhibited H2O2‐mediated phosphorylation of the cyclic AMP regulatory binding protein (CREB), suggesting that ERK1/2 signals to survival under these conditions. At higher concentrations (mm), H2O2‐stimulated a phosphorylation of c‐jun. It is likely, therefore, that subjecting neurones to moderate oxidative‐stress recruits pro‐survival signals to CREB but during severe oxidative stress pro‐death signals through JNK and c‐jun are dominant.

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