A moderate decline in U937 cell GSH levels triggers PI3 kinase/Akt-dependent Bad phosphorylation, thereby preventing an otherwise prompt apoptotic response

We report that a moderate decline in GSH levels causes remarkable changes in Bad sub-cellular localization. An about 30% reduction of the GSH pool, regardless of whether mediated by diamide or DL-buthionine-[S,R]-sulfoximine, indeed promoted loss of the fraction of Bad normally associated with the mitochondria of untreated U937 cells via a phosphatidylinositol 3-kinase (PI3K)-dependent mechanism. Interestingly, inhibition of this pathway was associated with an unexpected delayed lethal response, preceded by the translocation and enforced accumulation of Bad and Bax in the mitochondrial compartment, prevented by inhibitors of mitochondrial permeability transition and characterized by morphological and biochemical features of apoptosis. Collectively, the results herein presented demonstrate that mild redox imbalance associated with a slight reduction of the GSH pool commits U937 cells to apoptosis, however prevented by events leading to PI3K/Akt-dependent mitochondrial loss of Bad.