Activation of mitogen-activated protein kinases is essential for hydrogen peroxide-induced apoptosis in retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells are constantly exposed to oxidative injury while clearing byproducts of photoreceptor turnover, a circumstance thought to be responsible for degenerative retinal diseases. The mechanisms of hydrogen peroxide (H2O2)-induced apoptosis in RPE cells are not fully understood. We studied signal transduction mechanisms of H2O2-induced apoptosis in the human RPE cell line ARPE-19. Activation of two stress kinases (JNK and p38) occurs during H2O2 stimulation, and H2O2-mediated cell death was significantly reduced by their specific inhibition. Exposure to a lethal dose of H2O2 elicited Bax translocation to the mitochondria and release of apoptosis-inducing factor (AIF) from the mitochondria, both of which were abolished by either JNK- or p38-specific inhibitors. Both H2O2-induced cell death and JNK/p38 phosphorylation were partially inhibited by C. difficile toxin B, inhibitor of Rho, Rac, and cdc42. Use of pull-down assays revealed that the small GTPase activated by H2O2 is Rac1. This study is the first to demonstrate that H2O2 induces a Rac1/JNK1/p38 signaling cascade, and that JNK and p38 activation is important for H2O2-induced apoptosis as well as AIF/Bax translocation of RPE cells.