title: Opposing roles for ERK1/2 in neuronal oxidative toxicity: distinct mechanisms of ERK1/2 action at early versus late phases of oxidative stress.
abstract: Glutamate-induced oxidative toxicity is mediated by glutathione depletion in the HT22 mouse hippocampal cell line. Previous results with pharmacological agents implicated the extracellular signal-regulated kinases-1/2 (ERK1/2) in glutamate toxicity in HT22 cells and immature embryonic rat cortical neurons. In this report, we definitively establish a role for ERK1/2 in oxidative toxicity using dominant negative MEK1 expression in transiently transfected HT22 cells to block glutamate-induced cell death. In contrast, chronic activation of ERK (i.e. brought about by transfection of constitutively active ERK2 chimera) is not sufficient to trigger HT22 cell death demonstrating that ERK1/2 activation is not sufficient for toxicity. Activation of ERK1/2 in HT22 cells has a distinct kinetic profile with an initial peak occurring between 30 min and 1 h of glutamate treatment and a second peak typically emerging after 6 h. We demonstrate here that the initial phase of ERK1/2 induction is because of activation of metabotropic glutamate receptor type I (mGluRI). ERK1/2 activation by mGluRI contributes to an HT22 cell adaptive response to oxidative stress as glutamate-induced toxicity is enhanced upon pharmacological inhibition of mGluRI. The protective effect of ERK1/2 activation at early times after glutamate treatment is mediated by a restoration of glutathione (GSH) levels that are reduced because of depletion of intracellular cysteine pools. Thus, ERK1/2 appears to play dual roles in HT22 cells acting as part of a cellular adaptive response during the initial phases of glutamate-induced oxidative stress and contributing to toxicity during later stages of stress.
authors.affiliation: Center for Neuroscience and Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Luo
authors.forename: Donald B
authors.initials: DB
authors.lastname: DeFranco
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism
chemical_list: D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D018698:Glutamic Acid; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D010100:Oxygen