Organisms growing in aerobic environments must cope with
Reactive Oxygen Species (ROS). Although ROS damage all the cellular macromolecules, they play a central role in a range of biological processes requiring a tight control of redox homeostasis. It is achieved by
antioxidant systems involving a large collection of
enzymes that scavenge or degrade the ROS produced endogenously during cell growth. In addition to this enzymatic protection against ROS, cells also contain small
antioxidant molecules, such as
glutathione (GSH). With an intracellular concentration between 1 and 10mM, GSH is the most abundant non-
protein thiol in the cell and is considered as the major redox
buffer of the cell. To better characterize its essential function during oxidative stress conditions, we studied the physiological response of H2O2-treated yeast cells containing different amounts of GSH. We showed that the transcriptional response of GSH-depleted cells is severely impaired, despite an efficient nuclear accumulation of the
transcription factor Yap1. Moreover, oxidative stress generates high
genome instability in GSH-depleted cells, but does not activate the checkpoint
kinase Rad53. Surprisingly, scarce amounts of intracellular GSH are sufficient to preserve cell viability under H2O2 treatment. In these cells, oxidative stress still causes the accumulation of oxidized
proteins and the inactivation of the translational activity, but nuclear
DNA and nuclear functions are protected against oxidative injury, as exemplified by low mutation frequency, moderate
histone carbonylation, activation of the checkpoint
kinase Rad53 and of the H2O2 transcriptional response. We conclude that the essential role of GSH is to preserve nuclear function, allowing cell survival and growth resumption after oxidative stress release. We propose that cytosolic
proteins are part of a protective machinery that shields the nucleus by scavenging
reactive oxygen species before they can cross the nuclear membrane.