Survival and cell death in cells constitutively unable to synthesize glutathione

Abstract

We examined the role of GSH in survival and cell death using GCS-2 cells that are deficient in glutamate cysteine ligase (γ-glutamyl cysteine synthetase, γGCS), an enzyme essential for GSH synthesis. Cells maintained in 2.5 mM GSH have GSH levels that are ∼2% of wild type and grow indefinitely; however, they express both pro- and anti-apoptotic Bcl-2 family members and have detectable levels of cytoplasmic cytochrome C. Withdrawal of GSH from the medium results in a fall in intracellular GSH to undetectable levels, decreased mitochondrial dehydrogenase activity, decreased anti-apoptotic factor RNAs, increased pro-apoptoic factor RNAs, additional cytochrome C release, and a fall in ATP levels; however, cells continue to grow for another 24 h. At 48 h, these trends continue with the exception that mitochondrial membrane potential and ATP levels rise; DNA fragmentation begins at 48 h. Thus, severe reduction of GSH to 2% of wild type produces a metastable state compatible with survival, but complete absence of GSH triggers apoptosis.