ABSTRACT
The elevation of Hsp104 (heat shock protein) content under heat shock plays a key role in yeast (Saccharomyces cerevisiae) cells. Hsp104 synthesis is increased under heat stress in the stationary growth phase. As shown, the loss of mitochondrial DNA (petite mutation) inhibited the induction of the Hsp104 synthesis under heat stress (39 degrees C) during the transition to the stationary growth phase. Also, the petite mutation suppressed the activity of antioxidant enzymes in the same phase, which led to lower thermotolerance. At the same time, the mutation inhibited production of the reactive oxygen species and prevented cell death under heat shock in the logarithmic growth phase. The results of this study suggest that disruption of the mitochondrial functional state suppresses the expression level of yeast nuclear genes upon transitioning to the stationary growth phase.
Subject(s)
DNA, Mitochondrial/genetics , Heat-Shock Proteins/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Gene Deletion , Heat-Shock Proteins/biosynthesis , Heat-Shock Proteins/genetics , Heat-Shock Response , Reactive Oxygen Species/metabolism , S Phase , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/physiology , Saccharomyces cerevisiae Proteins/biosynthesis , Saccharomyces cerevisiae Proteins/geneticsABSTRACT
The mechanism of yeast cell death induced by heat shock was found to be dependent on the intensity of heat exposure. Moderate (45°C) heat shock strongly increased the generation of reactive oxygen species (ROS) and cell death. Pretreatment with cycloheximide (at 30°C) suppressed cell death, but produced no effect on ROS production. The protective effect was absent if cycloheximide was added immediately before heat exposure and the cells were incubated with the drug during the heat treatment and recovery period. The rate of ROS production and protective effect of cycloheximide on viability were significantly decreased in the case of severe (50°C) heat shock. Treatment with cycloheximide at 39°C inhibited the induction of Hsp104 synthesis and suppressed the development of induced thermotolerance to severe shock (50°C), but it had no effect on induced thermotolerance to moderate (45°C) heat shock. At the same time, Hsp104 effectively protected cells from death independently of the intensity of heat exposure. These data indicate that moderate heat shock induced programmed cell death in the yeast cells, and cycloheximide suppressed this process by inhibiting general synthesis of proteins.
Subject(s)
Cycloheximide/pharmacology , Protein Synthesis Inhibitors/pharmacology , Saccharomyces cerevisiae/drug effects , Cycloheximide/chemistry , Heat-Shock Proteins/chemistry , Heat-Shock Proteins/metabolism , Protein Synthesis Inhibitors/chemistry , Reactive Oxygen Species/metabolism , Saccharomyces cerevisiae/metabolism , Saccharomyces cerevisiae Proteins/chemistry , Saccharomyces cerevisiae Proteins/metabolism , TemperatureABSTRACT
Amiodarone (AMD) is known to induce a transient increase in cytosolic Ca2+ level in cells of the yeast Saccharomyces cerevisiae. In the present study the effect of AMD on the thermotolerance and Hsp104p synthesis of the yeast was studied. AMD induced Hsp104p synthesis and increased survival of the yeast after a severe heat shock (50°C). The development of thermotolerance to a considerable extent depended on the presence of Hsp104p. The same effect was achieved by treatment with the classical uncoupler CCCP, which is also known to increase the cytosolic Ca2+ level. It is supposed that the change in intracellular Ca2+ concentration plays an important role in activation of the HSP104 gene expression and in increasing the thermotolerance of the yeast. The possible link between mitochondrial activity and calcium homeostasis is discussed.
