Selenium Toxicity toward Yeast as Assessed by Microarray Analysis and Deletion Mutant Library Screen: A Role for DNA Repair Dominika Ma ́ nikova ́ , † Danus ̌ a Vlasa ́ kova ́ , † Lucia Letavayova ́ , † Vlasta Klobuc ̌ nikova ́ , ‡ Peter Griac ̌ , ‡ and Miroslav Chovanec* ,† † Laboratory of Molecular Genetics, Cancer Research Institute, Vla ́ rska 7, 833 91 Bratislava, Slovak Republic ‡ Institute of Animal Biochemistry and Genetics, Moyzesova 61, 900 28 Ivanka pri Dunaji, Slovak Republic * S Supporting Information ABSTRACT: Selenium (Se) is a trace element that is essential for human health as it takes part in many cellular processes. The cellular response to this compound elicits very diverse processes including DNA damage response and repair. Because an inorganic form of Se, sodium selenite (SeL), has often been a part of numerous studies and because this form of Se is used as a dietary supplement by the public, here, we elucidated mechanisms of SeL-induced toxicity in yeast Saccharomyces cerevisiae using a combination of systematic genetic and transcriptome analysis. First, we screened the yeast haploid deletion mutant library for growth in the presence of this Se compound. We identified 39 highly SeL sensitive mutants. The corresponding deleted genes encoded mostly proteins involved in DNA damage response and repair, vacuole function, glutathione (GSH) metabolism, transcription, and chromatin metabolism. DNA damage response and repair mutants were examined in more detail: a synergistic interaction between postreplication (PRR) and homologous recombination (HRR) repair pathways was revealed. In addition, the effect of combined defects in HRR and GSH metabolism was analyzed, and again, the synergistic interaction was found. Second, microarray analysis was used to reveal expression profile changes after SeL exposure. The gene process categories “amino acid metabolism” and “generation of precursor metabolites and energy” comprised the greatest number of induced and repressed genes, respectively. We propose that SeL-induced toxicity markedly results from DNA injury, thereby highlighting the importance of DNA damage response and repair pathways in protecting cells against toxic effects of this Se compound. In addition, we suggest that SeL toxicity also originates from damage to cellular proteins, including those acting in DNA damage response and repair. ■ INTRODUCTION Selenium (Se) is an essential trace element that is indispensable for human health. This compound is required for numerous cellular processes, and both chemical form and dose determine its bioactivity in living systems. As to dose, an intake of about 55 μg/day optimally fulfills the dietary need for humans. Higher doses of about 200-300 μg/day have been proposed to be required for chemopreventing activities of Se against cancer. Up to doses of 750-800 μg/day, no adverse effects of Se intake have been observed. However, an intake above this level may cause adverse effects that vary from being moderate at doses of 1540-1600 μg/day to the occurrence of selenosis and DNA damage and cell death induction at doses of 3200-5000 μg/ day. In contrast, intake of 40 μg/day represents the minimum dietary requirement, and levels below 11 μg/day can lead to deficiency problems in humans. 1-5 Se exists in different forms, and these are generally classified as inorganic and organic. Sodium selenite (Na 2 SeO 3 ; SeL), an inorganic form of Se, was the first Se compound used in chemopreventing studies. In nature, this Se compound is, however, relatively rare, and its concentrations are quite low. SeL gets converted into hydrogen selenide (H 2 Se) and/or elementary Se in the presence of glutathione (GSH) via seleno- diglutathione (GSSeSG), generating reactive oxygen species (ROS) as a byproduct. 1,2 Notably, oxidative stress as a consequence of ROS production was proposed to be responsible for the SeL-induced toxic effects, 6-9 which are, at least in part, thought to be caused by direct DNA injury. Indeed, SeL has been demonstrated to cause DNA single- strand (SSBs) and double-strand (DSBs) breaks in murine leukemia cells and other murine mammary carcinoma cell lines. 10,11 SeL exposure also leads to chromosomal damage in Swiss albino mice and in human peripheral lymphocytes. 12,13 In addition to DNA strand breaks, SeL was reported to induce oxidative DNA base damage, 8-oxo-7,8-dihydroguanine, in mouse keratinocytes 14 and in rat liver cells. 15 Expectedly, the induction of DNA damage was accompanied with a loss of cell Received: February 14, 2012 Published: June 28, 2012 Article pubs.acs.org/crt © 2012 American Chemical Society 1598 dx.doi.org/10.1021/tx300061n | Chem. Res. Toxicol. 2012, 25, 1598-1608