Cathepsin D–Bax death pathway in oxidative stressed neuroblastoma cells

Hydrogen peroxide, the major oxidoradical species in the central nervous system, has been involved in neuronal cell death and associated neurodegenerative diseases. In this study, we have investigated the involvement of the lysosomal pathway in the cytotoxic mechanism of hydrogen peroxide in human neuroblastoma cells. Alteration of lysosomal and mitochondrial membrane integrity was shown to be an early event in the lethal cascade triggered by oxidative stress. Desferrioxamine (DFO), an iron chelator that abolishes the formation of reactive oxygen species within lysosomes, prevented lysosome leakage, mitochondrial permeabilization and caspase-dependent apoptosis in hydrogen peroxide-treated cells. Inhibition of cathepsin D, not of cathepsin B, as well as small-interference RNA-mediated silencing of the cathepsin D gene prevented hydrogen peroxide-induced injury of mitochondria, caspase activation, and TUNEL-positive cell death. Cathepsin D activity was shown indispensable for translocation of Bax onto mitochondrial membrane associated with oxidative stress. DFO abolished both the cytosolic relocation of Cathepsin D and the mitochondrial relocation of Bax in hydrogen peroxide-treated cells. siRNA-mediated down-regulation of Bax expression protected the cells from oxidoradical injury. The present study identifies the lysosome as the primary target and the axis cathepsin D-Bax as the effective pathway of hydrogen peroxide lethal activity in neuroblastoma cells.