EGFR-dependent ERK activation triggers hydrogen peroxide-induced apoptosis in OK renal epithelial cells

Oxidative stress induces activation of extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase families. However, it is unclear in renal epithelial cells whether the ERK activation is involved in cell survival or cell death in H₂O₂-treated cells. The present study was undertaken to determine the role of the ERK activation in H₂O₂-induced apoptosis of renal epithelial cells using opossum kidney (OK) cells, an established proximal tubular epithelial cell line. H₂O₂ resulted in a time- and dose-dependent apoptosis of OK cells. H₂O₂ treatment caused marked sustained activation of ERK. The ERK activation was prevented by PD98059 and U0126, inhibitors of ERK1/2 upstream kinase MEK1/2. Apoptosis caused by H₂O₂ was prevented by U0126. Transient transfection with constitutive active MEK1 increased the H₂O₂-induced apoptosis, whereas transfection with dominant-negative mutants of MEK1 decreased the apoptosis. H₂O₂ produced hyperpolarization of mitochondrial membrane potential and activation of caspases-3. H₂O₂-induced ERK activation was inhibited by the Src family selective inhibitor PP2 and the epidermal growth factor receptor inhibitor AG1478. The presence of AG1478, but not PP2, prevented H₂O₂-induced cell death. Taken together, our findings suggest that the ERK activation mediated by epidermal growth factor receptor plays an active role in inducing H₂O₂-induced apoptosis of OK cells and functions upstream of mitochondria-dependent pathway to initiate the apoptotic signal.