Selenite-induced cell death in Saccharomyces cerevisiae: protective role of glutaredoxins

Abstract

Unlike in higher organisms, selenium is not essential for growth in Saccharomyces cerevisiae. In this species, it causes toxic effects at high concentrations. In the present study, we show that when supplied as selenite to yeast cultures growing under fermentative metabolism, its effects can be dissected into two death phases. From the time of initial treatment, it causes loss of membrane integrity and genotoxicity. Both effects occur at higher levels in mutants lacking Grx1p and Grx2p than in wild-type cells, and are reversed by expression of a cytosolic version of the membrane-associated Grx7p glutaredoxin. Grx7p can also rescue the high levels of protein carbonylation damage that occur in selenite-treated cultures of the grx1 grx2 mutant. After longer incubation times, selenite causes abnormal nuclear morphology and the appearance of TUNELpositive cells, which are considered apoptotic markers in yeast cells. This effect is independent of Grx1p and Grx2p. Therefore, the protective role of the two glutaredoxins is restricted to the initial stages of selenite treatment. Lack of Yca1p metacaspase or of a functional mitochondrial electron transport chain only moderately diminishes apoptotic-like death by selenite. In contrast, seleniteinduced apoptosis is dependent on the apoptosis-inducing factor Aif1p. In the absence of the latter, intracellular protein carbonylation is reduced after prolonged selenite treatment, supporting the supposition that part of the oxidative damage is contributed by apoptotic cells. INTRODUCTIONSelenium (Se) is a trace element which may have anticarcinogenic action at low concentrations (Letavayová et al., 2006). The essential character of Se in the mammalian diet is related to its presence as selenocysteine in a number of selenoproteins, such as thioredoxin reductases and glutathione peroxidases (Lu & Holmgren, 2009). These enzymes act in the defence against oxidative stress. In contrast, at high concentrations, Se is toxic because it generates oxidative stress and provokes DNA damage (Hatfield et al., 2006;Letavayová et al., 2006). Among the Se compounds that may come into contact with cells, selenite is a prooxidant because it undergoes glutathionemediated reduction to hydrogen selenide with the subsequent formation of superoxide radicals, which can undergo conversion into other reactive oxygen species (ROS) Spallholz, 1997;Tarze et al., 2007). Saccharomyces cerevisiae is a suitable organism to study the toxic properties of Se and the cellular mechanisms which prevent or repair its effects, without the interference due to an Se requirement for selenoproteins. In fact, S. cerevisiae, and fungi in general, do not contain selenoproteins and therefore Se is not essential for these organisms (Lu & Holmgren, 2009). High concentrations of Se cause DNA double-strand breaks in exponentially growing S. cerevisiae cells (Letavayová et al., 2008) and RAD9-dependent cell cycle arrest (Pinson et al., 2000). Accordingly, yeast mutants defective in the RAD9-mediated DNA repair pathway or the RAD6/RAD...

Production of Selenium-Enriched Yeast (Kluyveromyces marxianus) Biomass in a whey-based Culture Medium

“…It has been reported that yeasts are hypersensitive to sodium selenite; high concentrations of Se lead to DNA damage when the cells are growing in the exponential phase (Izquierdo et al, 2010). Studying different sodium selenite concentration, we did not observe an inhibition of K. marxianus growth.…”

Expulsion of selenium/protein nanoparticles through vesicle-like structures by Saccharomyces cerevisiae under microaerophilic environment

“…GSH) to reduce selenite to elemental selenium by an intrinsic detoxification mechanism (Izquierdo et al 2010). Elemental selenium can be generated by the Painter-type reactions of selenite with reduced glutathione (Zannoni et al 2008).…”

Redox regulation of the yeast voltage-gated Ca2+ channel homolog Cch1p by glutathionylation of specific cysteine residues

“…Global glutathionylation patterns have interestingly revealed that S. cerevisiae mutants lacking Grx1p and Grx2p do not have high levels of protein glutathionylation, while a mutant lacking the cytosolic TRXs, Trx1p and Trx2p constitutively display protein hyperglutathionylation (Greetham et al, 2010). One possible explanation for the higher Ca 2+ signals and increased glutathionylation in the grx1Δ strain is the high oxidizing conditions in the cells, since Grx1p has been shown to play a role in protection against oxidative stress (Izquierdo et al, 2010;Luikenhuis et al, 1998). Ca 2+ flux into the cytoplasm of the yeast S. cerevisiae is tightly controlled by the opening and closing of two channels: the vacuolar channel Yvc1p and the plasma membrane channel whose principal subunit is Cch1p.…”