Expression of NYV1 encoding the negative regulator of Pmc1 is repressed by two transcriptional repressors, Nrg1 and Mig1

The pH-sensing Rim101 pathway positively regulates the transcriptional expression of the calcium pump gene PMR1 to affect calcium sensitivity in budding yeast

In Saccharomyces cerevisiae, the Rim101 pathway senses extracellular pH changes through a complex consisted of Rim8, Rim9 and Rim21 at the plasma membrane. Activation of this sensor complex induces a proteolytical complex composed of Rim13 and Rim20 and leads to the C-terminal processing and activation of the transcription factor Rim101. Deletion mutants for RIM8, RIM9, RIM13, RIM20, RIM21 and RIM101 causes yeast cells to be sensitive to calcium stress, but how they regulate calcium sensitivity remain unknown. Here we show that deletion mutations of these six Rim101 pathway components elevate the activation level of the calcium/calcineurin signaling and the transcriptional expression level of the vacuolar calcium pump gene PMC1, but lead to a reduction in transcriptional expression level of the ER/Golgi calcium pump gene PMR1 in yeast cells. Deletion of NRG1, encoding one of the repression targets of Rim101, rescues the transcriptional expression of PMR1 in all these mutants. Furthermore, ectopic expression of a constitutively active form of Rim101 or further deletion of NRG1 suppresses the calcium sensitivity of these six deletion mutants. Therefore, the pH-sensing Rim101 pathway positively regulates the transcriptional expression of PMR through its downstream target Nrg1 to affect the calcium sensitivity of yeast cells.

The Hog1 positive regulated YCT1 gene expression under cadmium tolerance of budding yeast

Cadmium (Cd) is a heavy metal that is the cause of irreversible hazards to living organisms. Cadmium ions can induce the phosphorylation of MAPKs pathway molecules such as Hog1 and Slt2, but downstream effectors and potential activation pathways are still unclear. In this study, the RNA-seq data analysis in Cd-stressed yeast was performed to predict and screen the signal transduction pathway and the potential effect molecules regulated by MAPKs. Based on differentially expressed genes and Venn diagrams, 31 genes regulated by Hog1p and two genes induced by Slt2p, which related to carbohydrate metabolism, oxidative damage, DNA replication stress and detoxification, were characterized under Cd exposure to yeast. A cysteine-specific transporter (Yct1) modulated by Hog1 was confirmed via RNA-seq results. Meanwhile, we tested the Cd-sensitivity, intracellular Cd concentrations and β-galactosidase assay, and results indicated that the hypersensitivity of the hog1 mutant to Cd was partly abrogated in YCT1 gene deletion, induction of YCT1 was dependent on Hog1 and its transcription factors, and Yct1p would be epistatic to the Hog1p in Cd-tolerance. The investigation of the transcriptome of MAPKs under Cd stress provided valuable information for future molecular studies of Cd-tolerance.

The protein kinase Cmk2 negatively regulates the calcium/calcineurin signalling pathway and expression of calcium pump genes PMR1 and PMC1 in budding yeast

Through a genome-wide screen we have identified calcium-tolerant deletion mutants for five genes in the budding yeast Saccharomyces cerevisiae. In addition to CNB1 and RCN1 that are known to play a role in the calcium signalling pathway, the protein kinase gene CMK2, the sphingolipid homeostasis-related gene ORM2 and the gene SIF2 encoding the WD40 repeat-containing subunit of Set3C histone deacetylase complex are involved in the calcium sensitivity of yeast cells to extracellular calcium. Cmk2 and the transcription factor Crz1 have opposite functions in the response of yeast cells to calcium stress. Deletion of CMK2 elevates the level of calcium/calcineurin signalling and increases the expression level of PMR1 and PMC1, which is dependent on Crz1. Effects of Cmk2 on calcium sensitivity and calcium/calcineurin signalling are dependent on its kinase activity. Therefore, Cmk2 is a negative feedback controller of the calcium/calcineurin signalling pathway. Furthermore, the cmk2 crz1 double deletion mutant is more resistant than the crz1 deletion mutant, suggesting that Cmk2 has an additional Crz1-independent role in promoting calcium tolerance.

Cadmium induces the activation of cell wall integrity pathway in budding yeast

MAP kinases are important signaling molecules regulating cell survival, proliferation and differentiation, and can be activated by cadmium stress. In this study, we demonstrate that cadmium induces phosphorylation of the yeast cell wall integrity (CWI) pathway_MAP kinase Slt2, and this cadmium-induced CWI activation is mediated by the cell surface sensor Mid2 through the GEF Rom1, the central regulator Rho1 and Bck1. Nevertheless, cadmium stress does not affect the subcellular localization of Slt2 proteins. In addition, this cadmium-induced CWI activation is independent on the calcium/calcineurin signaling and the high osmolarity glycerol (HOG) signaling pathways in yeast cells. Furthermore, we tested the cadmium sensitivity of 42 paired double-gene deletion mutants between six CWI components and seven components of the HOG pathway. Our results indicate that the CWI pathway is epistatic to the HOG pathway in cadmium sensitivity. However, gene deletion mutations for the Swi4/Swi6 transcription factor complex show synergistic effects with mutations of HOG components in cadmium sensitivity.