SummaryDuring the last years, several reports described an apoptosis-like programmed cell death process in yeast in response to different environmental aggressions. Here, evidence is presented that hyperosmotic stress caused by high glucose or sorbitol concentrations in culture medium induces in Saccharomyces cerevisiae a cell death process accompanied by morphological and biochemical indicators of apoptotic programmed cell death, namely chromatin condensation along the nuclear envelope, mitochondrial swelling and reduction of cristae number, production of reactive oxygen species and DNA strand breaks, with maintenance of plasma membrane integrity. Disruption of AIF1 had no effect on cell survival, but lack of Yca1p drastically reduced metacaspase activation and decreased cell death indicating that this death process was associated to activation of this protease. Supporting the involvement of mitochondria and cytochrome c in caspase activation, the mutant strains cyc1 Δ Δ Δ Δ cyc7 Δ Δ Δ Δ and cyc3 Δ Δ Δ Δ , both lacking mature cytochrome c , displayed a decrease in caspase activation associated to increased cell survival when exposed to hyperosmotic stress. These findings indicate that hyperosmotic stress triggers S. cerevisiae into an apoptosis-like programmed cell death that is mediated by a caspase-dependent mitochondrial pathway partially dependent on cytochrome c .

The inositolphosphosphingolipid phospholipase C (Isc1p) of Saccharomyces cerevisiae belongs to the family of neutral sphingomyelinases that generates the bioactive sphingolipid ceramide. In this work the role of Isc1p in oxidative stress resistance and chronological lifespan was investigated. Loss of Isc1p resulted in a higher sensitivity to hydrogen peroxide that was associated with an increase in oxidative stress markers, namely intracellular oxidation, protein carbonylation, and lipid peroxidation. Microarray analysis showed that Isc1p deficiency up-regulated the iron regulon leading to increased levels of iron, which is known to catalyze the production of the highly reactive hydroxyl radicals via the Fenton reaction. In agreement, iron chelation suppressed hydrogen peroxide sensitivity of isc1⌬ mutants. Cells lacking Isc1p also displayed a shortened chronological lifespan associated with oxidative stress markers and aging of parental cells was correlated with a decrease in Isc1p activity. The analysis of DNA fragmentation and caspase-like activity showed that Isc1p deficiency increased apoptotic cell death associated with oxidative stress and aging. Furthermore, deletion of Yca1p metacaspase suppressed the oxidative stress sensitivity and premature aging phenotypes of isc1⌬ mutants. These results indicate that Isc1p plays an important role in the regulation of cellular redox homeostasis, through modulation of iron levels, and of apoptosis.

Mitochondrial involvement in yeast apoptosis is probably the most unifying feature in the field. Reports proposing a role for mitochondria in yeast apoptosis present evidence ranging from the simple observation of ROS accumulation in the cell to the identification of mitochondrial proteins mediating cell death. Although yeast is unarguably a simple model it reveals an elaborate regulation of the death process involving distinct proteins and most likely different pathways, depending on the insult, growth conditions and cell metabolism. This complexity may be due to the interplay between the death pathways and the major signalling routes in the cell, contributing to a whole integrated response. The elucidation of these pathways in yeast has been a valuable help in understanding the intricate mechanisms of cell death in higher eukaryotes, and of severe human diseases associated with mitochondria-dependent apoptosis. In addition, the absence of obvious orthologues of mammalian apoptotic regulators, namely of the Bcl-2 family, favours the use of yeast to assess the function of such proteins. In conclusion, yeast with its distinctive ability to survive without respiration-competent mitochondria is a powerful model to study the involvement of mitochondria and mitochondria interacting proteins in cell death.

Acetic acid is the main component of the volatile acidity of grape musts and wines. It can be formed as a by-product of alcoholic fermentation or as a product of the metabolism of acetic and lactic acid bacteria, which can metabolize residual sugars to increase volatile acidity. Acetic acid has a negative impact on yeast fermentative performance and affects the quality of certain types of wine when present above a given concentration. In this mini-review, we present an overview of fermentation conditions and grape-must composition favoring acetic acid formation, as well the metabolic pathways leading to its formation and degradation by yeast. The negative effect of acetic acid on the fermentative performance of Saccharomyces cerevisiae will also be covered, including its role as a physiological inducer of apoptosis. Finally, currently available wine deacidification processes and new proposed solutions based on zymological deacidification by select S. cerevisiae strains will be discussed.

Mammalian protein kinase C (PKC) isoforms have been subject of particular attention because of their ability to modulate apoptotic proteins. However, the roles played by each PKC isoform in apoptosis are still unclear. Here, expression of individual mammalian PKC isoforms in Saccharomyces cerevisiae is used as a new approach to study the role of each isoform in apoptosis. The four isoforms tested, excepting PKC-δ, stimulate S. cerevisiae acetic-acid-induced apoptosis essentially through a mitochondrial ROS-dependent pathway. However, their co-expression with Bcl-xL reveals a PKC-isoform-dependent modulation of Bcl-xL anti-apoptotic activity. A yeast pathway homologue to the mammalian SAPK/JNK is responsible for acetic-acid-induced Bcl-xL phosphorylation that is differently modulated by PKC isoforms. The data obtained suggest conservation of an ancient mechanism of apoptosis regulation in yeast and mammals and offer new insights into mammalian apoptosis modulation by PKC isoforms.