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

Calcineurin promotes adaptation to chronic stress through two distinct mechanisms

Adaptation to environmental stress requires coordination between stress-defense programs and cell cycle progression. The immediate response to many stressors has been well characterized, but how cells survive in challenging environments long-term is unknown. Here, we investigate the role of the stress-activated phosphatase calcineurin (CN) in adaptation to chronic CaCl2 stress in Saccharomyces cerevisiae. We find that prolonged exposure to CaCl2 impairs mitochondrial function and demonstrate that cells respond to this stressor using two CN-dependent mechanisms - one that requires the downstream transcription factor Crz1 and another that is Crz1-independent. Our data indicate that CN maintains cellular fitness by promoting cell cycle progression and preventing CaCl2-induced cell death. When Crz1 is present, transient CN activation suppresses cell death and promotes adaptation despite high levels of mitochondrial loss. However, in the absence of Crz1, prolonged activation of CN prevents mitochondrial loss and further cell death by upregulating glutathione (GSH) biosynthesis genes thereby mitigating damage from reactive oxygen species. These findings illustrate how cells maintain long-term fitness during chronic stress and suggest that CN promotes adaptation in challenging environments by multiple mechanisms.

Amino acid metabolism and MAP kinase signaling pathway play opposite roles in the regulation of ethanol production during fermentation of sugarcane molasses in budding yeast

Sugarcane molasses is one of the main raw materials for bioethanol production, and Saccharomyces cerevisiae is the major biofuel-producing organism. In this study, a batch fermentation model has been used to examine ethanol titers of deletion mutants for all yeast nonessential genes in this yeast genome. A total of 42 genes are identified to be involved in ethanol production during fermentation of sugarcane molasses. Deletion mutants of seventeen genes show increased ethanol titers, while deletion mutants for twenty-five genes exhibit reduced ethanol titers. Two MAP kinases Hog1 and Kss1 controlling the high osmolarity and glycerol (HOG) signaling and the filamentous growth, respectively, are negatively involved in the regulation of ethanol production. In addition, twelve genes involved in amino acid metabolism are crucial for ethanol production during fermentation. Our findings provide novel targets and strategies for genetically engineering industrial yeast strains to improve ethanol titer during fermentation of sugarcane molasses.

Identification of the Beta Subunit Fas1p of Fatty Acid Synthetase as an Interacting Partner of Yeast Calcium/Calmodulin-Dependent Protein Kinase Cmk2p Through Mass Spectrometry Analysis

The calcium/calmodulin-dependent protein kinase II (CaMKII) is a mediator of calcium signals and regulates fatty acid metabolism in mammalian cells. Cmk2p is a yeast homolog of CaMKII and functions as a negative regulator of calcium signaling. However, its substrates remain to be identified. Combination of immunoprecipitation (IP) and mass spectrometry has been proven to be very useful for identification of interacting partner proteins and interactome. In this study, through these approaches, we have identified 65 and 110 potential Cmk2p-interacting proteins in yeast cells in the absence or presence of calcium stress, respectively. In yeast cells expressing both CMK2-HA and FAS1-GFP fusion proteins, in the absence or presence of calcium stress, less amounts of FAS1-GFP proteins are present in cell lysates after IP with anti-HA antibody than cell lysates before IP, while FAS1-GFP proteins are detected on both types of IP beads. However, as an internal control, similar amounts of Pgk1p proteins were detected in both after-IP and before-IP cell lysates but not on the IP beads. Therefore, our biochemical analysis demonstrates that the β subunit Fas1p of fatty acid synthetase interacts with Cmk2p in yeast cells independent of calcium stress. It is also interesting to note that, in addition to the expected 52-kDa CMK2-HA band, a faster-moving 48-kDa CMK2-HA band is present in the calcium-stressed cell lysate but not in the cell lysate without calcium stress. Our data would provide important clues for understanding the functions of CaMKII in the regulation of fatty acid metabolism as well as related diseases such as cancers, diabetes, and obesity.

Transcriptional expression of PHR2 is positively controlled by the calcium signaling transcription factor Crz1 through its binding motif in the promoter

IMPORTANCE

The fungal cell wall consists of glucans, mannoproteins, and chitin and is essential for cell viability, morphogenesis, and pathogenesis. The enzymes of the GH72 family are responsible for ß-(1,3)-glucan elongation and branching, which is crucial for the formation of the glucan-chitin polymer at the bud neck of yeast cells. In the human fungal pathogen Candida albicans, there are five GH72 enzyme-encoding genes: PHR1, PHR2, PHR3, PGA4, and PGA5. It is known that expression of PHR1 and PHR2 is controlled by the pH-responsive Rim101 pathway through the transcription factor Rim101. In this study, we have demonstrated that the transcription expression of PHR2 is also controlled by the transcription factor Crz1 through its binding motif in the promoter. Therefore, we have uncovered a dual-control mechanism by which PHR2 expression is negatively regulated via CaRim101 through the pH-responsive pathway and positively modulated by CaCrz1 through the calcium/calcineurin signaling pathway.

Dynamic calcium-mediated stress response and recovery signatures in the fungal pathogen, Candida albicans

IMPORTANCE

Intracellular calcium signaling plays an important role in the resistance and adaptation to stresses encountered by fungal pathogens within the host. This study reports the optimization of the GCaMP fluorescent calcium reporter for live-cell imaging of dynamic calcium responses in single cells of the pathogen, Candida albicans, for the first time. Exposure to membrane, osmotic or oxidative stress generated both specific changes in single cell intracellular calcium spiking and longer calcium transients across the population. Repeated treatments showed that calcium dynamics become unaffected by some stresses but not others, consistent with known cell adaptation mechanisms. By expressing GCaMP in mutant strains and tracking the viability of individual cells over time, the relative contributions of key signaling pathways to calcium flux, stress adaptation, and cell death were demonstrated. This reporter, therefore, permits the study of calcium dynamics, homeostasis, and signaling in C. albicans at a previously unattainable level of detail.

Calcineurin stimulation by Cnb1p overproduction mitigates protein aggregation and α-synuclein toxicity in a yeast model of synucleinopathy

The calcium-responsive phosphatase, calcineurin, senses changes in Ca2+ concentrations in a calmodulin-dependent manner. Here we report that under non-stress conditions, inactivation of calcineurin signaling or deleting the calcineurin-dependent transcription factor CRZ1 triggered the formation of chaperone Hsp100p (Hsp104p)-associated protein aggregates in Saccharomyces cerevisiae. Furthermore, calcineurin inactivation aggravated α-Synuclein-related cytotoxicity. Conversely, elevated production of the calcineurin activator, Cnb1p, suppressed protein aggregation and cytotoxicity associated with the familial Parkinson's disease-related mutant α-Synuclein A53T in a partly CRZ1-dependent manner. Activation of calcineurin boosted normal localization of both wild type and mutant α-synuclein to the plasma membrane, an intervention previously shown to mitigate α-synuclein toxicity in Parkinson's disease models. The findings demonstrate that calcineurin signaling, and Ca2+ influx to the vacuole, limit protein quality control in non-stressed cells and may have implications for elucidating to which extent aberrant calcineurin signaling contributes to the progression of Parkinson's disease(s) and other synucleinopathies. Video Abstract.

AaCaMKs Positively Regulate Development, Infection Structure Differentiation and Pathogenicity in Alternaria alternata, Causal Agent of Pear Black Spot

Calcium/calmodulin-dependent protein kinase (CaMK), a key downstream target protein in the Ca²⁺ signaling pathway of eukaryotes, plays an important regulatory role in the growth, development and pathogenicity of plant fungi. Three AaCaMKs (AaCaMK1, AaCaMK2 and AaCaMK3) with conserved PKC_like superfamily domains, ATP binding sites and ACT sites have been cloned from Alternaria alternata, However, their regulatory mechanism in A. alternata remains unclear. In this study, the function of the AaCaMKs in the development, infection structure differentiation and pathogenicity of A. alternata was elucidated through targeted gene disruption. The single disruption of AaCaMKs had no impact on the vegetative growth and spore morphology but significantly influenced hyphae growth, sporulation, biomass accumulation and melanin biosynthesis. Further expression analysis revealed that the AaCaMKs were up-regulated during the infection structure differentiation of A. alternata on hydrophobic and pear wax substrates. In vitro and in vivo analysis further revealed that the deletion of a single AaCaMKs gene significantly reduced the A. alternata conidial germination, appressorium formation and infection hyphae formation. In addition, pharmacological analysis confirmed that the CaMK specific inhibitor, KN93, inhibited conidial germination and appressorium formation in A. alternata. Meanwhile, the AaCaMKs genes deficiency significantly reduced the A. alternata pathogenicity. These results demonstrate that AaCaMKs regulate the development, infection structure differentiation and pathogenicity of A. alternata and provide potential targets for new effective fungicides.

Investigation the global effect of rare earth gadolinium on the budding Saccharomyces cerevisiae by genome-scale screening

Introduction

The rare earth gadolinium (Gd) is widely used in industry and medicine, which has been treated as an emerging pollutant in environment. The increasing pollution of Gd has potential hazards to living organisms. Thus it is essential to investigate the toxicity and action mechanism of Gd in biological system.

Methods

In this study, the global effect and activation mechanism of Gd on yeast were investigated by genome-scale screening.

Results and discussion

Our results show that 45 gene deletion strains are sensitive to Gd and 10 gene deletion strains are Gd resistant from the diploid gene deletion strain library of Saccharomyces cerevisiae. The result of localization analysis shows that most of these genes are involved in cell metabolism, cell cycle, transcription, translation, protein synthesis, protein folding, and cell transport. The result of functional analysis shows that four genes (CNB1, CRZ1, VCX1, and GDT1) are involved in the calcium signaling pathway, and four genes (PHO84, PHO86, PHO2, and PHO4) are involved in phosphorus metabolism. For Gd3+ has the similar ion radius with Ca2+ and easily binds to the phosphate radical, it affects Ca2+ signaling pathway and phosphorus metabolism. The genes ARF1, ARL1, ARL3, SYS1, COG5, COG6, YPT6, VPS9, SSO2, MRL1, AKL1, and TRS85 participate in vesicle transport and protein sorting. Thus, Gd accumulation affects the function of proteins related to vesicle transport, which may result in the failure of Gd transport out of cells. In addition, the intracellular Gd content in the 45 sensitive deletion strains is higher than that in the wild type yeast under Gd stress. It suggests that the sensitivity of yeast deletion strains is related to the excessive intracellular Gd accumulation.

The feedback loop between calcineurin, calmodulin-dependent protein kinase II, and nuclear factor of activated T-cells regulates the number of GABAergic neurons during planarian head regeneration

Disturbances in the excitatory/inhibitory balance of brain neural circuits are the main source of encephalopathy during neurodevelopment. Changes in the function of neural circuits can lead to depolarization or repeat rhythmic firing of neurons in a manner similar to epilepsy. GABAergic neurons are inhibitory neurons found in all the main domains of the CNS. Previous studies suggested that DjCamkII and DjCaln play a crucial role in the regulation of GABAergic neurons during planarian regeneration. However, the mechanisms behind the regeneration of GABAergic neurons have not been fully explained. Herein, we demonstrated that DjCamkII and DjCaln were mutual negative regulation during planarian head regeneration. DjNFAT exerted feedback positive regulation on both DjCaln and DjCamkII. Whole-mount in situ hybridization (WISH) and fluorescence in situ hybridization (FISH) revealed that DjNFAT was predominantly expressed in the pharynx and parenchymal cells in intact planarian. Interestingly, during planarian head regeneration, DjNFAT was predominantly located in the newborn brain. Down-regulation of DjNFAT led to regeneration defects in the brain including regenerative brain became small and the lateral nerves cannot be regenerated completely, and a decreasein the number of GABAergic neurons during planarian head regeneration. These findings suggest that the feedback loop between DjCaln, DjCamkII, and DjNFAT is crucial for the formation of GABAergic neurons during planarian head regeneration.

Characterization and Functional Analysis of a New Calcium/Calmodulin-Dependent Protein Kinase (CaMK1) in the Citrus Pathogenic Fungus Penicillium italicum

Calcium (Ca2+)/calmodulin-dependent protein kinases (CaMKs) act as a class of crucial elements in Ca2+-signal transduction pathways that regulate fungal growth, sporulation, virulence, and environmental stress tolerance. However, little is known about the function of such protein kinase in phytopathogenic Penicillium species. In the present study, a new CaMK gene from the citrus pathogenic fungus P. italicum, designated PiCaMK1, was cloned and functionally characterized by gene knockout and transcriptome analysis. The open reading frame of PiCaMK1 is 1209 bp in full length, which encodes 402 amino acid residues (putative molecular weight ~45.2 KD) with the highest homologous (~96.3%) to the P. expansum CaMK. The knockout mutant ΔPiCaMK1 showed a significant reduction in vegetative growth, conidiation, and virulence (i.e., to induce blue mold decay on citrus fruit). ΔPiCaMK1 was less sensitive to NaCl- or KCl-induced salinity stress and less resistant to mannitol-induced osmotic stress, indicating the functional involvement of PiCaMK1 in such environmental stress tolerance. In contrast, the PiCaMK1-complemented strain ΔPiCaMK1COM can restore all the defective phenotypes. Transcriptome analysis revealed that knockout of PiCaMK1 down-regulated expression of the genes involved in DNA replication and repair, cell cycle, meiosis, pyrimidine and purine metabolisms, and MAPK signaling pathway. Our results suggested the critical role of PiCaMK1 in regulating multiple physical and cellular processes of citrus postharvest pathogen P. italicum, including growth, conidiation, virulence, and environmental stress tolerance.

Substrates of the MAPK Slt2: Shaping Yeast Cell Integrity

The cell wall integrity (CWI) MAPK pathway of budding yeast Saccharomyces cerevisiae is specialized in responding to cell wall damage, but ongoing research shows that it participates in many other stressful conditions, suggesting that it has functional diversity. The output of this pathway is mainly driven by the activity of the MAPK Slt2, which regulates important processes for yeast physiology such as fine-tuning of signaling through the CWI and other pathways, transcriptional activation in response to cell wall damage, cell cycle, or determination of the fate of some organelles. To this end, Slt2 precisely phosphorylates protein substrates, modulating their activity, stability, protein interaction, and subcellular localization. Here, after recapitulating the methods that have been employed in the discovery of proteins phosphorylated by Slt2, we review the bona fide substrates of this MAPK and the growing set of candidates still to be confirmed. In the context of the complexity of MAPK signaling regulation, we discuss how Slt2 determines yeast cell integrity through phosphorylation of these substrates. Increasing data from large-scale analyses and the available methodological approaches pave the road to early identification of new Slt2 substrates and functions.

The Transient Receptor Potential Channel Yvc1 Deletion Recovers the Growth Defect of Calcineurin Mutant Under Endoplasmic Reticulum Stress in Candida albicans

Transient receptor potential (TRP) channel Yvc1 was related with hyphal growth, oxidative stress response, and pathogenicity. Calcineurin subunit Cnb1 was activated immediately in yeasts when exposed to severe stimulation. However, the relationship between Yvc1 and Cnb1-governed calcium ions and endoplasmic reticulum (ER) stress response remains unrevealed. In this study, we found that the mutant cnb1Δ/Δ was sensitive to TN, which was related with the overexpression of membrane calcium ion channels that could increase the cytosol calcium concentration. However, the growth of the cnb1Δ/Δyvc1Δ/Δ mutant was recovered and its cell vitality was better than the cnb1Δ/Δ strain. Meanwhile, the cellular calcium concentration was decreased and its fluctuation was weakened under ER stress in the cnb1Δ/Δyvc1Δ/Δ strain. To verify the regulation role of Yvc1 in the calcium concentration, we found that the addition of CaCl₂ led to the worse viability, while the growth state was relieved under the treatment of EGTA in the cnb1Δ/Δ strain. In conclusion, the deletion of YVC1 could reduce the cellular calcium and relieve the ER stress sensitivity of the cnb1Δ/Δ strain. Thereby, our findings shed a novel light on the relationship between the Yvc1-governed cellular calcium concentration and ER stress response in C. albicans.

A novel protoapigenone analog RY10-4 induces apoptosis of breast cancer cells by exacerbating mitochondrial Ca2+ influx through mitochondrial calcium uniporter

RY10-4, a novel protoapigenone analog with a specific nonaromatic B-ring, displayed enhanced cytotoxicity in various tumor cells, especially for breast cancer cells, but the underlying mechanism remains unclear. In the present study, we confirmed the pro-apoptotic effect of RY10-4 on breast cancer cells. Furthermore, mitochondrial calcium uniporter (MCU) was proved to be up-regulated in RY10-4-treated MDA-MB-231 cells, which resulted in the overload of mitochondrial calcium ([Ca2+]m) and subsequently disrupted mitochondrial functions (characterized by mitochondrial reactive oxygen species (mtROS) accumulation, membrane potential (ΔΨm) depolarization and permeability transition pore (mPTP) opening). And finally, the mitochondrial apoptosis was activated by the release of cytochrome C. Interestingly, knockdown of MCU attenuated the overload of [Ca2+]m and blocked the apoptosis of MDA-MB-231 cells induced by RY10-4, which was consistent with the in vivo results. Taken together, this study proved that RY10-4 could induce apoptosis of breast cancer cells by elevating [Ca2+]m through MCU. Our work contributed previously unknown insights into the mechanisms involving in the clinical efficacy of RY10-4 on breast cancer cells, which also advanced calcium homeostasis as a potential target for chemotherapeutic drugs.

The V-ATPase regulates localization of the TRP Ca2+ channel Yvc1 in response to oxidative stress in Candida albicans

The vacuolar-type H⁺-ATPase (V-ATPase) is a highly conserved protein complex among the eukaryotic cells. We previously revealed that both the V-ATPase and the transient receptor potential (TRP) channel Yvc1 are involved in oxidative stress response (OSR). However, the relationship between V-ATPase and Yvc1 during OSR remains unknown. In this study, disruption of the V-ATPase-encoding genes VPH2 and TFP1, similar with disruption of YVC1, caused H₂O₂ hypersensitivity and enhancement of vacuolar membrane permeability (VMP) under oxidative stress. Further investigations showed that unlike the wild type strain with vacuole membrane-localized Yvc1, both vph2Δ/Δ and tfp1Δ/Δ had Yvc1 localization in the vacuole cavity, indicating that disruption of VPH2 or TFP1 impaired normal vacuolar membrane-localization of Yvc1. Interestingly, addition of CaCl₂ alleviated the growth defect of vph2Δ/Δ and tfp1Δ/Δ under oxidative stress, leading to prevention of VMP, decrease in ROS levels and activation of OSR. In contrast, addition of the Ca²⁺ chelating agent glycol-bis-(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) aggravated H₂O₂ hypersensitivity of the mutants. These results showed that the V-ATPase plays an important role in maintenance of normal Yvc1 localization, which contributes to Ca²⁺ transport from the vacuoles to the cytosol for activation of OSR. This work sheds a novel light on the interaction between V-ATPase and Ca²⁺ transport for regulation of OSR in C. albicans.

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.

Calcium-Handling Defects and Neurodegenerative Disease

Calcium signaling is critical to neuronal function and regulates highly diverse processes such as gene transcription, energy production, protein handling, and synaptic structure and function. Because there are many common underlying calcium-mediated pathological features observed across several neurological conditions, it has been proposed that neurodegenerative diseases have an upstream underlying calcium basis in their pathogenesis. With certain diseases such as Alzheimer's, Parkinson's, and Huntington's, specific sources of calcium dysregulation originating from distinct neuronal compartments or channels have been shown to have defined roles in initiating or sustaining disease mechanisms. Herein, we will review the major hallmarks of these diseases, and how they relate to calcium dysregulation. We will then discuss neuronal calcium handling throughout the neuron, with special emphasis on channels involved in neurodegeneration.

CgCmk1 Activates CgRds2 To Resist Low-pH Stress in Candida glabrata

In Candida glabrata, the transcription factor CgRds2 has been previously characterized as a regulator of glycerophospholipid metabolism, playing a crucial role in the response to osmotic stress. Here, we report that CgRds2 is also involved in the response to pH 2.0 stress. At pH 2.0, the deletion of CgRDS2 led to reduced cell growth and survival, by 33% and 57%, respectively, compared with those of the wild-type strain. These adverse phenotypes resulted from the downregulation of genes related to energy metabolism in the Cgrds2Δ strain at pH 2.0, which led to a 34% reduction of the intracellular ATP content and a 24% decrease in membrane permeability. In contrast, the overexpression of CgRDS2 rescued the growth defect of the Cgrds2Δ strain and increased cell survival at pH 2.0 by 17% compared with that of the wild-type strain, and this effect was accompanied by significant increases in ATP content and membrane permeability, by 42% and 19%, respectively. Furthermore, we found that the calcium/calmodulin-dependent protein kinase (CaMK) CgCmk1 physically interacts with the PAS domain of CgRds2, and CgCmk1 is required for CgRds2 activation and translocation from the cytoplasm to the nucleus under pH 2.0 stress. Moreover, CgCmk1 is critical for CgRds2 function in resistance to pH 2.0 stress, because cells of the Cgrds2-pas strain with a disrupted CgCmk1-CgRds2 interaction exhibited impaired energy metabolism and membrane permeability at pH 2.0. Therefore, our results indicate that CgCmk1 positively regulates CgRds2 and suggest that they promote resistance to low-pH stress by enhancing energy metabolism and membrane permeability in C. glabrata IMPORTANCE An acidic environment is the main problem in the production of organic acids in C. glabrata The present study reports that the calcium/calmodulin-dependent protein kinase CgCmk1 positively regulates CgRds2 to increase intracellular ATP content, membrane permeability, and resistance to low-pH stress. Hence, the transcription factor CgRds2 may be a potential target for improving the acid stress tolerance of C. glabrata during the fermentation of organic acids. The present study also establishes a new link between the calcium signaling pathway and energy metabolism.