Glutathione protects cells against arsenite-induced toxicity

To understand the role of glutathione (GSH) in the protection of cells from arsenite toxicity, we studied the mechanism of apoptotic cell death in cells genetically unable to synthesize GSH (GCS-2 cells). Arsenite stimulated an increase in protein ubiquitination in GCS-2 cells while the wild-type cells were unaffected. Arsenite treatment increased lipid peroxidation and induced ubiquitination of molecular chaperone Hsp90 and impaired its ability to bind cochaperone p50^Cdc-37 and client proteins Plk-1 and Cdk-4 in GCS-2 cells. Treatment with arsenite also partially inhibited proteasome activity in GCS-2 cells. In these cells stably transfected with GFP^u (a reporter consisting of a short degron fused to the COOH-terminus of GFP), intracellular fluorescence increased, suggesting the accumulation of GFP aggregates. GCS-2 cells underwent apoptosis accompanied by release of cytochrome c into the cytoplasm. Taken together, these data suggest that a possible mechanism of arsenite-induced apoptosis is the accumulation of ubiquitinated proteins and impairment of the protein degradative pathway. Further, protection from arsenite-induced ubiquitination is mediated by GSH and to a lesser extent by available reducing equivalents in the cells.