Mechanisms for Sensitization to Tnf–Induced Apoptosis by Acute Glutathione Depletion in Murine Hepatocytes

We previously reported that depletion of glutathione in murine hepatocytes by diethylmaleate (DEM) or acetaminophen (APAP) leads to oxidative stress-dependent necrosis and sensitizes to tumor necrosis factor (TNF)-induced apoptosis in an oxidative stress-independent fashion, which could not be explained by interference with nuclear factor kappaB (NF-kappaB) nuclear translocation. The present report explores the mechanisms of these effects. We observed that DEM led to necrosis when both mitochondrial and cytosol glutathione were depleted profoundly but sensitized to TNF-induced apoptosis when cytosol glutathione was depleted selectively. DEM and APAP lead to a significant decrease in reduced glutathione (GSH)/glutathione disulfide (GSSG) ratio. Glutathione depletion by DEM or APAP was associated with inhibition of TNF-induced NF-kappaB transactivation of anti-apoptotic genes, including inducible nitric oxide synthase (i-NOS). Provision of exogenous NO partially abrogated the sensitization to TNF in response to glutathione depletion. Glutathione depletion alone led to sustained increase in phospho-jun levels and c-Jun-N-terminal kinase (JNK) activity. JNK inhibitor partially blocked the sensitization to TNF-induced apoptosis accompanying glutathione depletion. In conclusion, these findings suggest that extramitochondrial glutathione depletion alters the thiol-disulfide redox state, leading to inhibition of NF-kappaB transactivation of survival genes and to sustained activation of JNK, both of which contribute to the sensitization to TNF-induced apoptosis.