Choowong Auesukaree

The Greatwall-family protein kinase Rim15 is associated with the nutrient starvation response, whereas its role in oxidative stress responses remains unclear. Here, acetic acid and peroxide were used as two oxidative stress elicitors. The antioxidant indicator assay under acetic acid stress revealed the impaired growth in rim15Δ related to the regulation of antioxidant systems. Comparative transcriptome analysis revealed that differentially expressed genes (DEGs) are predicted to be mostly regulated by oxidative stress-responsive transcriptional factor Yap1. Among the DEGs, acetic acid stress-induced genes were found, and YAP1 disruption also inhibited their induction. The deletion of Rim15 or the Rim15 kinase domain in yap1Δ did not further decrease the gene expression, suggesting that Rim15 functions together with Yap1 in regulating acetic acid stress-induced genes, which requires Rim15 kinase activity. Additionally, Rim15 regulated H₂O₂ stress tolerance through partially similar but special mechanisms in that Rim15 kinase activity impacted acetic acid and H₂O₂ stress tolerance in different degrees, indicating the different mechanisms underlying Rim15-mediated redox regulation against different stressors. These results benefit the better understanding of stress signaling pathways related to Rim15. Given that Rim15 and some of its target genes are conserved across eukaryotes, these results also provide a basis for studies of oxidative stress-related processes in other organisms.

Summary: Cadmium is a highly toxic heavy metal that causes many harmful effects on human health and ecosystems. Metal chelation‐based techniques have become a common approach for the treatment of metal poisoning and also for the remediation of metal contamination. Phosphate, an essential nutrient required for key cellular functions, has been supposed to be effective in reducing cadmium bioavailability, possibly through its chelating potential. In this study, we explored the effects of phosphate on cadmium toxicity and cellular response to cadmium stress in the eukaryotic model Saccharomyces cerevisiae . Our results reveal that cadmium toxicity is unexpectedly enhanced during phosphate repletion and optimal phosphate levels for yeast growth under cadmium stress conditions decline with increasing cadmium concentrations. The profound cadmium toxicity during phosphate repletion is unlikely to result from either elevated cadmium accumulation or dysregulated homeostasis of essential metals, but rather due to increased production of intracellular reactive oxygen species. We show that, under phosphate‐depleted conditions, the activities of antioxidant enzymes, especially Mn‐superoxide dismutase and catalase, are significantly promoted through transcriptional upregulation. Our findings highlight the important role of cellular response to phosphate limitation in mitigating cadmium toxicity and endogenous oxidative stress through the enhancement of antioxidant enzyme activity.

Contamination of soil and water with heavy metals and metalloids is one of serious environmental problems. Cadmium and arsenic are major environmental contaminants that pose a serious threat to human health. Although toxicities of cadmium and arsenic to living organisms have been extensively studied, molecular mechanisms of cellular response to cadmium and arsenic remain poorly understood. In this study, we demonstrate that the cell wall integrity (CWI) pathway is involved in coping with cell wall stresses induced by cadmium and arsenate through its role in the regulation of cell wall modification. Interestingly, the Rlm1p and SBF (Swi4p-Swi6p) transcription factors of the CWI pathway were specifically required for tolerances to cadmium and arsenate, respectively. Furthermore, we found that PIR2 gene encoding cell wall O-mannosylated heat shock protein, whose expression is under the control of the CWI pathway, is important for maintaining cell wall integrity during cadmium and arsenate stresses. In addition, our results revealed that the CWI pathway is involved in modulating the expression of genes involved in cell wall biosynthesis and cell cycle control in response to cadmium and arsenate via distinct sets of transcriptional regulators. IMPORTANCE Environmental pollution by metal/metalloid such as cadmium and arsenic has become a serious problem in many countries, especially in developing countries. This study shows that, in yeast S. cerevisiae, the CWI pathway plays a protective role against cadmium and arsenate through the upregulation of genes involved in cell wall biosynthesis and cell cycle control, possibly in order to modulate cell wall reconstruction and cell cycle phase transition, respectively. These data provide insights into molecular mechanisms underlying adaptive response to cadmium and arsenate.

Summary: In Saccharomyces cerevisiae , vacuolar H ⁺ ‐ATPase (V‐ATPase) involved in the regulation of intracellular pH homeostasis has been shown to be important for tolerances to cadmium, cobalt and nickel. However, the molecular mechanism underlying the protective role of V‐ATPase against these metals remains unclear. In this study, we show that cadmium, cobalt and nickel disturbed intracellular pH balance by triggering cytosolic acidification and vacuolar alkalinization, likely via their membrane permeabilizing effects. Since V‐ATPase plays a crucial role in pumping excessive cytosolic protons into the vacuole, the metal‐sensitive phenotypes of the Δvma2 and Δvma3 mutants lacking V‐ATPase activity were supposed to result from highly acidified cytosol. However, we found that the metal‐sensitive phenotypes of these mutants were caused by increased production of reactive oxygen species, likely as a result of decreased expression and activities of manganese superoxide dismutase and catalase. In addition, the loss of V‐ATPase function led to aberrant vacuolar morphology and defective endocytic trafficking. Furthermore, the sensitivities of the Δvma mutants to other chemical compounds (i.e. acetic acid, H ₂ O ₂ , menadione, tunicamycin and cycloheximide) were a consequence of increased endogenous oxidative stress. These findings, therefore, suggest the important role of V‐ATPase in preventing endogenous oxidative stress induced by metals and other chemical compounds.