Tetramethylthiuram disulfide or dimethyldithiocarbamate induces the synthesis of cadystins, heavy metal chelating peptides, in Schizosaccharomyces pombe

Effects of four oxidants, menadione, 1-chloro-2,4-dinitrobenzene, hydrogen peroxide and cumene hydroperoxide, on fission yeast Schizosaccharmoyces pombe

Several chemical agents have been used to exert oxidative stress in the study of stress response, but differences in the effects of different reagents have received little attention. To elucidate whether such differences exist, the response of Schizosaccharomyces pombe to menadione (MD), 1-chloro-2,4-dinitrobenzene (CDNB), hydrogen peroxide and cumene hydroperoxide (CHP), which are frequently used to exert oxidative stress, was investigated. Sensitivity to these reagents differed among mutants deficient in genes involved in oxidative stress resistance. N-Acetylcysteine restored resistance to MD, CHP and hydrogen peroxide but did not change sensitivity to CDNB. The induction kinetics of genes induced by oxidative stress differed for each reagent. MD, CDNB and hydrogen peroxide caused a transient induction of genes, but the peak times of induction differed among the reagents. CHP gave quite different kinetics in that the induction continued for up to 2 h. The ctt1(+) gene was not induced by CHP. GSH rapidly decreased in the cells treated with high concentrations of these reagents, but at a low concentration only CDNB decreased GSH. These results indicated that S. pombe responded differently to the oxidative stress exerted by these different reagents.

Combined cadmium and thiuram show synergistic toxicity and induce mitochondrial petite mutants

A bioassay is a system for monitoring toxicity of chemicals in the environment via the biological responses of experimental organisms. These responses can be detected by analysis of genome-wide changes in mRNA expression levels using DNA microarrays. We applied this system for evaluation of synergistic toxicity by cadmium and thiuram, as this combination showed mutual growth inhibition in yeast. Hierarchical cluster analysis using mRNA expression profiles suggested the response of yeast to this combination is similar to that seen with cadmium treatment alone. Functional characterization of genes induced by this combinational treatment also suggests that the toxicity of cadmium was enhanced. This toxicity was observed as the damage to mitochondrial functions, which were not observed with either cadmium or thiuram treatments alone. The potential toxicity to mitochondria by this combinational treatment was confirmed as the result of deletion of mitochondria with petite colony formation frequency. We could evaluate synergistic toxicity by cadmium and thiuram and show the possible use of transcriptome bioassay for synergistic toxicity.

Pro-oxidant action of phloxine B on fission yeastSchizosaccharomyces pombe

A Schizosaccharomyces pombe mutant deficient in Cu,Zn-superoxide dismutase (sod1 mutant) was hypersensitive to phloxine B, which is used as a food-colouring agent and also to distinguish diploid strains of Sz. pombe from haploid strains, under illumination with light. The pro-oxidant nature of phloxine B was confirmed biochemically. The carbonyl content of proteins (which represents protein oxidation) increased, and the reduced form of glutathione was transiently decreased by phloxine B treatment under illumination with light. When cells were treated with phloxine B under light, carbonyl content of proteins in the sod1 mutant was greater than that in the wild-type and amount of glutathione was much decreased in the sod1 mutant compared with the wild-type. Genes induced by oxidative stress were induced by phloxine B under illumination with light and some were induced by phloxine B without light.

The synthesis of cadystins, heavy metal chelating peptides, is induced in the fission yeast by wounds of the cell wall or by incubation with chitosan

It has been shown that heavy metal administration induced the synthesis of cadystins, the small metal chelating peptide with the general structure of (gamma-glu-cys)n-gly, in the fission yeast and in plants. Besides heavy metals, wounds to the cell surface or the incubation with chitosan induced the cadystin synthesis in the fission yeast. Under these induction conditions, the membrane permeability of the fission yeast significantly increased suggesting the structural alteration of the membrane. In these induction, the synthesized cadystins formed complexes with the cellular zinc ions together with or without glutathione.