Reactive oxygen species and yeast apoptosis

Silymarin exerts antifungal effects via membrane-targeted mode of action by increasing permeability and inducing oxidative stress

Silymarin, which is derived from the seeds of Silybum marianum, has been widely used to prevent and treat liver disorders. It is also consumed as a dietary supplement to improve liver function, as it does not exhibit any toxic effects in humans. Recently, silymarin has been reported to show antimicrobial effects against various pathogenic microorganisms, but the mode of action remains unknown. Thus, we investigated the antifungal activity of silymarin and aimed to determine the underlying mechanism. Initially, a propidium iodide assay was carried out; the results indicated that silymarin induced injury to the fungal plasma membrane. Subsequently, large unilamellar vesicles encapsulating calcein and fluorescein isothiocyanate-labeled dextrans (FDs) 4, 10, and 20 were prepared to analyze whether silymarin affects an artificial membrane model. The results indicated that silymarin increased membrane permeability by disturbing the membrane structure, thereby allowing free access to molecules smaller than FD20 (approximately 3.3nm). The accumulation of reactive oxygen species (ROS) results in deleterious effects to various cellular components. In particular, ROS easily react with the membrane lipids and induce lipid peroxidation, which increases membrane permeability and disturbs hydrophobic phospholipids. Using 2',7'-dichlorodihydrofluorescein diacetate and thiobarbituric acid, we confirmed that silymarin induced harmful effects on the plasma membrane. Membrane depolarization and K+ leakage, which were associated with an increase in membrane permeability, were also observed in Candida albicans cells. An assay using 1,6-diphenyl-1,3,5-hexatriene showed that silymarin decreased membrane fluidity. Taken together, we suggest that silymarin exerts its antifungal activity by targeting the C. albicans plasma membrane.

Scolopendin, an antimicrobial peptide from centipede, attenuates mitochondrial functions and triggers apoptosis in Candida albicans

Centipedes, a type of arthropod, reportedly produce antimicrobial peptides as part of an innate immune response. Scolopendin (SPSEKAGLQPVGRIGRMLKK) is a novel antimicrobial peptide derived from Scolopendra subspinipes mutilans Many antifungal agents have more than one type of cell death mechanism. Although scolopendin is involved in membrane perturbation, the corresponding intracellular changes require further investigation. Therefore, we assessed the cell morphology and calcium ion concentration of the cytosol and mitochondria of scolopendin-treated cells. The treated cells were shrunken, and calcium ion homeostasis was disrupted in both the cytosol and mitochondria. These conditions attenuated mitochondrial homeostasis, disrupting mitochondrial membrane potential and cytochrome c levels. Fungal cells treated with scolopendin exhibited various apoptotic phenotypes such as reactive oxygen species accumulation, phosphatidylserine exposure, chromatin condensation, and nuclear fragmentation. Scolopendin-induced cell death also triggered metacaspase activation. In conclusion, treatment of Candida albicans with scolopendin induced the apoptotic response, which in turn led to mitochondrial dysfunction, metacaspase activation, and cell death. The antimicrobial peptide scolopendin from the centipede S.s. mutilans demonstrated a novel apoptotic mechanism as an antifungal agent.

Influence of Oxidative Stress on Biocontrol Activity of Cryptococcus laurentii against Blue Mold on Peach Fruit

The limitations of chemical fungicides for the control of postharvest diseases have recently become more apparent. The utilization of antagonistic microorganisms is a promising alternative to that of fungicides to control postharvest decay. In previous studies, the antagonistic yeast Cryptococcus laurentii has shown excellent effects of biocontrol and great potential for practical application. Adverse conditions, such as oxidative stress, limit the practical application of antagonistic yeast. In this study, we investigated the oxidative stress tolerance of C. laurentii and the associated mechanisms. The results indicated that exogenous oxidative stress has a significant effect on the viability and biocontrol efficiency of C. laurentii. H2O2-induced oxidative stress led to the accumulation of reactive oxygen species. The results of flow cytometric analysis suggested that apoptosis is responsible for the reduced survival rate of C. laurentii under oxidative stress. Using tests of antioxidant activity, we found that C. laurentii could employ enzymatic systems to resist exogenous oxidative stress. The addition of exogenous glutathione, a non-enzymatic antioxidant, to the media can significantly enhance oxidative tolerance and biocontrol efficiency of C. laurentii.

Physical interaction between the MAPK Slt2 of the PKC1-MAPK pathway and Grx3/Grx4 glutaredoxins is required for the oxidative stress response in budding yeast

This study demonstrates that both monothiol glutaredoxins Grx3 and Grx4 physically interact with the MAPK Slt2 forming a complex involved in the cellular response to oxidative stress. The simultaneous absence of Grx3 and Grx4 provokes a serious impairment in cell viability, Slt2 activation and Rlm1 transcription in response to oxidative stress. Both in vivo and in vitro results clearly show that Slt2 can independently bind either Grx3 or Grx4 proteins. Our results suggest that Slt2 form iron/sulphur bridged clusters with Grx3 and Grx4. For the assembly of this complex, cysteines of the active site of each Grx3/4 glutaredoxins, glutathione and specific cysteine residues from Slt2 provide the ligands. One of the ligands of Slt2 is required for its dimerisation upon oxidative treatment and iron repletion. These interactions are relevant for the oxidative response, given that mutants in the cysteine ligands identified in the complex show a severe impairment of both cell viability and Slt2 phosphorylation upon oxidative stress. Grx4 is the relevant glutaredoxin that regulates Slt2 phosphorylation under oxidative conditions precluding cell survival. Our studies contribute to extend the functions of both monothiol glutaredoxins to the regulation of a MAPK in the context of the oxidative stress response.

Using an artificial tryptophan “wire” in cytochrome c peroxidase for oxidation of organic substrates

Addition of tryptophan residues between heme and the protein surface in cytochrome c peroxidase gives rise to new redox reactivity, in analogy to lignolytic peroxidases.

Fungicide Bac8c triggers attenuation of mitochondrial homeostasis and caspase-dependent apoptotic death

Bac8c (RIWVIWRR-NH₂), an 8-mer peptide modified from amino acids 4-11 of Bac2a, shows broad-spectrum activity against pathogenic bacteria and yeast, and it has been the focus of attention owing to its low cost of synthesis. Although Bac8c is effective against Candida albicans, its mode of action needs to be investigated further. Bac8c causes yeast cell death in a dose-dependent manner by eliciting the production of reactive oxygen species, thereby attenuating the antioxidant defense system. It is also involved in Ca²⁺ signaling, and produces apoptotic features, such as phosphatidylserine externalization and DNA fragmentation. Bac8c induces cell death by oxidative stress-dependent apoptotic death via disruption of mitochondrial homeostasis and metacaspase activation. This suggests that the concentration of Bac8c is important for the induction of apoptotic death, which is not necessarily accompanied by cell cycle arrest in C. albicans.

Role of cell death in the progression of heart failure

All multicellular organisms develop during evolution the highly regulated and interconnected pathways of cell death. This complex network contributes to the pathogenesis of various cardiovascular disorders including ischemia/reperfusion injury, myocardial infarction, heart failure, dysrhythmias and atherosclerosis. Chronic cardiac remodeling response and transition to overt HF have been associated with modestly increased apoptosis, although the actual burden of chronic cell loss attributable to apoptosis is not clear. Central mediators of cardiomyocyte survival and death are the mitochondrial organelles. Based on its morphological characteristics, cell death can be classified into three major types: apoptosis, necrosis and autophagy. Recently, a new pathway of regulated necrosis, necroptosis, has also been reported in the failing heart. The mitochondrial (intrinsic) and the death-receptor-mediated (extrinsic) converge at mitochondria inducing release of mitochondrial apoptogens to initiate the caspase cascade and eventually degradation of the doomed cardiomyocyte. Activation of death receptors can initiate not only extrinsic apoptotic pathway, but also necrosis. On the other hand, autophagy, which is characterized by the massive formation of lysosomal-derived vesicles, containing degenerating cytoplasmic contents, is primarily a survival response to nutrient deprivation, and a selective form of autophagy, mitophagy, is also a protective mechanism that allows to eliminate damaged mitochondria and thereby to attenuate mitochondria-mediated apoptosis and necrosis in the myocardium. Further insight into the molecular mechanisms underlying cell death will increase the efficiency and repertoire of therapeutic interventions available in cardiovascular disease.

Silibinin triggers yeast apoptosis related to mitochondrial Ca2+ influx in Candida albicans

Candida albicans is a common yeast that resides in the human body, but can occasionally cause systemic fungal infection, namely candidiasis. As this infection rate is gradually increasing, it is becoming a major problem to public health. Accordingly, we for the first time investigated the antifungal activity and mode of action of silibinin, a natural product extracted from Silybum marianum (milk thistle), against C. albicans. On treatment with 100μM silibinin, generation of reactive oxygen species (ROS) from mitochondria, which can cause yeast apoptosis via oxidative stress, was increased by 24.17% compared to that in untreated cells. Subsequently, we found disturbances in ion homeostasis such as release of intracellular K+ and accumulation of cytoplasmic and mitochondrial Ca2+. Among these phenomena, mitochondrial Ca2+ overload particularly plays a crucial role in the process of apoptosis, promoting the activation of pro-apoptotic factors. Therefore, we investigated the significance of mitochondrial Ca2+ in apoptosis by employing 20mM ruthenium red (RR). Additional apoptosis hallmarks such as mitochondrial membrane depolarization, cytochrome c release, caspase activation, phosphatidylserine (PS) exposure, and DNA damage were observed in response to silibinin treatment, whereas RR pre-treatment seemed to block these responses. In summary, our results suggest that silibinin induces yeast apoptosis mediated by mitochondrial Ca2+ signaling in C. albicans.

Mechanism of apoptosis induction in human breast cancer MCF-7 cell by Ruviprase, a small peptide from Daboia russelii russelii venom

Ruviprase, a 4.4 kDa peptide isolated from Daboia russelii russelii venom demonstrated antiproliferative activity against EMT6/AR1, U-87MG, HeLa and MCF-7 cancer cells with an IC50 value of 23.0, 8.8, 5.8 and 4.0 μg ml(-1), respectively. However, it was nontoxic to non-cancerous human embryonic kidney cell and human peripheral blood lymphocytes. Flow-cytometric analysis confirmed the apoptosis induction in MCF-7 cells by Ruviprase where it induced DNA condensation but did not cause mitotic blockage or chromosomal aberration in treated-cells. Immunofluorescence microscopic analysis indicated Ruviprase induced apoptosis in MCF-7 cells through p53 and p21-mediated pathways. Ruviprase generated reactive oxygen species (ROS), altered the mitochondrial transmembrane potential, and significantly decreased the cellular glutathione (GSH) content of MCF-7 cells. Immunoblotting and quantitative real-time PCR (qRT-PCR) analyses suggested that Ruviprase down-regulated the expression of anti-apoptotic protein Bcl-2, increased cleavage of poly (ADP-ribose) polymerase (PARP) protein, and up-regulated the expression of pro-apoptotic protein Bax, as well as executer protein caspase-7 to induced apoptosis in MCF-7 cells via intrinsic pathway. This is the first report on the characterization of the anticancer potential of a small, non-toxic and anticoagulant peptide purified from Russell's viper venom.

An integrative analysis of transcriptomic response of ethanol tolerant strains to ethanol in Saccharomyces cerevisiae

The accumulation of ethanol is one of the main environmental stresses that Saccharomyces cerevisiae cells are exposed to in industrial alcoholic beverage and bioethanol production processes. Despite the known impacts of ethanol, the molecular mechanisms underlying ethanol tolerance are still not fully understood. Novel gene targets leading to ethanol tolerance were previously identified via a network approach and the investigations of the deletions of these genes resulted in the improved ethanol tolerance of pmt7Δ/pmt7Δ and yhl042wΔ/yhl042wΔ strains. In the present study, an integrative system based approach was used to investigate the global transcriptional changes in these two ethanol tolerant strains in response to ethanol and hence to elucidate the mechanisms leading to the observed tolerant phenotypes. In addition to strain specific biological processes, a number of common and already reported biological processes were found to be affected in the reference and both ethanol tolerant strains. However, the integrative analysis of the transcriptome with the transcriptional regulatory network and the ethanol tolerance network revealed that each ethanol tolerant strain had a specific organization of the transcriptomic response. Transcription factors around which most important changes occur were determined and active subnetworks in response to ethanol and functional clusters were identified in all strains.

Overexpression of PMA1 enhances tolerance to various types of stress and constitutively activates the SAPK pathways in Saccharomyces cerevisiae

PMA1 encodes a transmembrane polypeptide that functions to pump protons out of the cell. Ectopic PMA1 overexpression in Saccharomyces cerevisiae enhances tolerance to weak acids, reactive oxygen species (ROS) and ethanol, and changes the following physiological properties: better proton efflux, lower membrane permeability, and lessened internal hydrogen peroxide production. The enhanced stress tolerance was dependent on the mitogen-activated protein kinase (MAPK) Hog1 of the high osmolarity glycerol (HOG) pathway, but not the MAPK Slt2 of the cell wall integrity (CWI) pathway; however, a PMA1 overexpression constitutively activated both Hog1 and Slt2. The constitutive Hog1 activation required the MAPK kinase kinase (MAP3K) Ssk2 of the HOG pathway, but not Ste11 and Ssk22, two other MAP3Ks of the same pathway. The constitutive Slt2 activation did not require Rom2 and the membrane sensors of the CWI pathway, whereas Bck1 was indispensable. The PMA1 overexpression activated the stress response element but not the cyclic AMP response element and the Rlm1 transcription factor. PMA1 overexpression may facilitate the construction of industrial strains with simultaneous tolerance to weak acids, ROS, and ethanol.

Reactive oxygen species and Ca2+ are involved in cadmium-induced cell killing in yeast cells

Cadmium (Cd) is one of the most toxic heavy metals. It is of great environmental concern and its toxicity has been investigated in a variety of cells. In this study, we elucidated the toxic effects of Cd in cells of yeast (Saccharomyces cerevisiae). Our results showed that Cd²⁺ (0.05-5.0 mmol·L^-1) significantly inhibited yeast cell growth, and the inhibitory effect was positively correlated with Cd²⁺ concentrations. Cd²⁺ caused loss of yeast cell viability in a concentration- and duration-dependent manner. Intracellular reactive oxygen species (ROS) and Ca²⁺ levels increased in yeast cells after exposure to 5.0 mmol·L^-1 Cd for 6 h. Cd²⁺-caused cell viability loss was blocked by antioxidants (0.5 mmol·L^-1 ascorbic acid or 500 U·mL^-1 catalase) or Ca²⁺ antagonists (0.5 mmol·L^-1 ethylene glycol tetraacetic acid or 0.5 mmol·L^-1 LaCl₃). Moreover, a collapse of mitochondrial membrane potential (ΔΨ_m) was observed in Cd²⁺-treated yeast cells. These results indicate that Cd-induced yeast cell killing was associated with the elevation of intracellular ROS and Ca²⁺ levels and also the loss of ΔΨ_m.

A novel fungal killing mechanism of propionic acid

Propionic acid (PPA) is a weak acid that has been used in food products as a preservative because of its inhibitory effect on microorganisms. In the present study, we investigated the PPA fungal killing mechanism, which showed apoptotic features. First, reactive oxygen species (ROS) accumulation and metacaspase activation were detected by 2',7'-dichlorodihydrofluorescein diacetate and CaspACE FITC-VAD-FMK staining, respectively. Increased fluorescence intensities were observed following exposure to PPA, indicating that PPA produced an oxidative environment through the generation of ROS and activation of metacaspase, which can promote apoptosis signaling. We also examined phosphatidylserine externalization (an early apoptosis marker) and DNA and nuclear fragmentation (late apoptosis markers) after exposure to PPA. Based on the results, we determined that PPA exerts its antifungal effect by inducing apoptotic cell death. Moreover, three additional mitochondrial experiments showed mitochondrial membrane depolarization, calcium accumulation and cytochrome c release after cells were exposed to PPA, indicating that the PPA-induced apoptosis pathway is mediated by mitochondria. In conclusion, PPA induces fungal cell death through mitochondria-mediated apoptosis. Results of this study contribute to a deeper understanding of the preservative effects of PPA.

25-Hydroxycholesterol impairs endothelial function and vasodilation by uncoupling and inhibiting endothelial nitric oxide synthase

Endothelial dysfunction is a key early step in atherosclerosis. 25-Hydroxycholesterol (25-OHC) is found in atherosclerotic lesions. However, whether 25-OHC promotes atherosclerosis is unclear. Here, we hypothesized that 25-OHC, a proinflammatory lipid, can impair endothelial function, which may play an important role in atherosclerosis. Bovine aortic endothelial cells were incubated with 25-OHC. Endothelial cell proliferation, migration, and tube formation were measured. Nitric oxide (NO) production and superoxide anion generation were determined. The expression and phosphorylation of endothelial NO synthase (eNOS) and Akt as well as the association of eNOS and heat shock protein (HSP)90 were detected by immunoblot analysis and immunoprecipitation. Endothelial cell apoptosis was monitored by TUNEL staining and caspase-3 activity, and expression of Bcl-2, Bax, cleaved caspase-9, and cleaved caspase-3 were detected by immunoblot analysis. Finally, aortic rings from Sprague-Dawley rats were isolated and treated with 25-OHC, and endothelium-dependent vasodilation was evaluated. 25-OHC significantly inhibited endothelial cell proliferation, migration, and tube formation. 25-OHC markedly decreased NO production and increased superoxide anion generation. 25-OHC reduced the phosphorylation of Akt and eNOS and the association of eNOS and HSP90. 25-OHC also enhanced endothelial cell apoptosis by decreasing Bcl-2 expression and increasing cleaved caspase-9 and cleaved caspase-3 expressions as well as caspase-3 activity. 25-OHC impaired endothelium-dependent vasodilation. These data demonstrated that 25-OHC could impair endothelial function by uncoupling and inhibiting eNOS activity as well as by inducing endothelial cell apoptosis. Our findings indicate that 25-OHC may play an important role in regulating atherosclerosis.

External and internal triggers of cell death in yeast

In recent years, yeast was confirmed as a useful eukaryotic model system to decipher the complex mechanisms and networks occurring in higher eukaryotes, particularly in mammalian cells, in physiological as well in pathological conditions. This article focuses attention on the contribution of yeast in the study of a very complex scenario, because of the number and interconnection of pathways, represented by cell death. Yeast, although it is a unicellular organism, possesses the basal machinery of different kinds of cell death occurring in higher eukaryotes, i.e., apoptosis, regulated necrosis and autophagy. Here we report the current knowledge concerning the yeast orthologs of main mammalian cell death regulators and executors, the role of organelles and compartments, and the cellular phenotypes observed in the different forms of cell death in response to external and internal triggers. Thanks to the ease of genetic manipulation of this microorganism, yeast strains expressing human genes that promote or counteract cell death, onset of tumors and neurodegenerative diseases have been constructed. The effects on yeast cells of some of these genes are also presented.

Programmed Cell Death Initiation and Execution in Budding Yeast

Apoptosis or programmed cell death (PCD) was initially described in metazoans as a genetically controlled process leading to intracellular breakdown and engulfment by a neighboring cell . This process was distinguished from other forms of cell death like necrosis by maintenance of plasma membrane integrity prior to engulfment and the well-defined genetic system controlling this process. Apoptosis was originally described as a mechanism to reshape tissues during development. Given this context, the assumption was made that this process would not be found in simpler eukaryotes such as budding yeast. Although basic components of the apoptotic pathway were identified in yeast, initial observations suggested that it was devoid of prosurvival and prodeath regulatory proteins identified in mammalian cells. However, as apoptosis became extensively linked to the elimination of damaged cells, key PCD regulatory proteins were identified in yeast that play similar roles in mammals. This review highlights recent discoveries that have permitted information regarding PCD regulation in yeast to now inform experiments in animals.

Function of Lipid Storage Droplet 1 (Lsd1) in Wing Development of Drosophila melanogaster

Perilipins are evolutionarily conserved from Drosophila to humans, the lipid storage droplet 1 (Lsd1) is a Drosophila homolog of human perilipin 1. The function of Lsd1 as a regulator of lipolysis in Drosophila has been demonstrated, as the Lsd1 mutant causes an increase of lipid droplet size. However, the functions of this gene during development are still under investigation. In order to determine the function of Lsd1 during development, Lsd1 was knocked down in Drosophila using the GAL4-UAS system. Selective knockdown of Lsd1 in the dorsal wing disc caused an atrophied wing phenotype. The generation of reactive oxygen species in the wing pouch compartment of the Lsd1-knockdown flies was significantly higher than in the control. Immunostaining with caspase-3 antibody revealed a greater number of apoptotic cells in Lsd1-knockdown wing discs than in the control. Cell death by autophagy was also induced in the knockdown flies. Moreover, cells deprived of Lsd1 showed mitochondrial expansion and decreased ATP levels. These results strongly suggest that knockdown of Lsd1 induces mitochondrial stress and the production of reactive oxygen species that result in cell death, via apoptosis and the autophagy pathway. These results highlight the roles of DrosophilaLsd1 during wing development.

Antibacterial activity of curcumin via apoptosis-like response in Escherichia coli

Curcumin, a naturally occurring phenolic compound, has been shown to exhibit antimicrobial activity against Candida albicans, Escherichia coli, Pseudomonas aeruginosa, etc., but the mechanism remains unclear. The present study was designed to investigate the novel antibacterial mechanism of curcumin that shows an apoptosis-like response in E. coli. We found that curcumin induces membrane damage at relatively high concentrations, but there was no effect at the minimum inhibitory concentration (MIC). At the MIC, curcumin-treated cells displayed various apoptotic markers such as reactive oxygen species (ROS) accumulation, membrane depolarization, and Ca(2+) influx. Expression of RecA protein, which mediates a bacterial apoptosis-like response, was also increased by curcumin. In order to evaluate the influence of RecA on the appearance of other apoptotic markers, phosphatidylserine (PS) exposure and DNA fragmentation were examined and compared with a RecA deletion strain (ΔRecA). These markers were detected in E. coli wild-type cells, but not in ΔRecA cells. In conclusion, our data demonstrate that curcumin induces an apoptosis-like response in E. coli that involves RecA.

The trade-off of availability and growth inhibition through copper for the production of copper-dependent enzymes by Pichia pastoris

Background

Copper is an essential chemical element for life as it is a part of prosthetic groups of enzymes including super oxide dismutase and cytochrome c oxidase; however, it is also toxic at high concentrations. Here, we present the trade-off of copper availability and growth inhibition of a common host used for copper-dependent protein production, Pichia pastoris.

Results

At copper concentrations ranging from 0.1 mM (6.35 mg/L) to 2 mM (127 mg/L), growth rates of 0.25 h⁻¹ to 0.16 h⁻¹ were observed with copper uptake of as high as 20 mg_copper/g_CDW. The intracellular copper content was estimated by subtracting the copper adsorbed on the cell wall from the total copper concentration in the biomass. Higher copper concentrations led to stronger cell growth retardation and, at 10 mM (635 mg/L) and above, to growth inhibition. To test the determined copper concentration range for optimal recombinant protein production, a laccase gene from Aspergillus clavatus [EMBL: EAW07265.1] was cloned under the control of the constitutive glyceraldehyde-3-phosphate (GAP) dehydrogenase promoter for expression in P. pastoris. Notably, in the presence of copper, laccase expression improved the specific growth rate of P. pastoris. Although copper concentrations of 0.1 mM and 0.2 mM augmented laccase expression 4 times up to 3 U/mL compared to the control (0.75 U/mL), while higher copper concentrations resulted in reduced laccase production. An intracellular copper content between 1 and 2 mg_copper/g_CDW was sufficient for increased laccase activity. The physiology of the yeast could be excluded as a reason for the stop of laccase production at moderate copper concentrations as no flux redistribution could be observed by ¹³C-metabolic flux analysis.

Conclusion

Copper and its pivotal role to sustain cellular functions is noteworthy. However, knowledge on its cellular accumulation, availability and distribution for recombinant protein production is limited. This study attempts to address one such challenge, which revealed the fact that intracellular copper accumulation influenced laccase production and should be considered for high protein expression of copper-dependent enzymes when using P. pastoris. The results are discussed in the context of P. pastoris as a general host for copper -dependent enzyme production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0251-3) contains supplementary material, which is available to authorized users.

Genetic engineering of AtAOX1a in Saccharomyces cerevisiae prevents oxidative damage and maintains redox homeostasis

This study aimed to validate the physiological importance of Arabidopsis thaliana alternative oxidase 1a (AtAOX1a) in alleviating oxidative stress using Saccharomyces cerevisiae as a model organism. The AOX1a transformant (pYES2AtAOX1a) showed cyanide resistant and salicylhydroxamic acid (SHAM)‐sensitive respiration, indicating functional expression of AtAOX1a in S. cerevisiae. After exposure to oxidative stress, pYES2AtAOX1a showed better survival and a decrease in reactive oxygen species (ROS) when compared to S. cerevisiae with empty vector (pYES2). Furthermore, pYES2AtAOX1a sustained growth by regulating GPX2 and/or TSA2, and cellular NAD⁺/NADH ratio. Thus, the expression of AtAOX1a in S. cerevisiae enhances its respiratory tolerance which, in turn, maintains cellular redox homeostasis and protects from oxidative damage.

Comparative study of preparation, characterization and anticandidal activities of a chitosan silver nanocomposite (CAgNC) compared with low molecular weight chitosan (LMW-chitosan)

A chitosan-silver nanocomposite (CAgNC) was synthesized in a green manner using low molecular weight chitosan (LMW-chitosan) and silver nitrate without applying external chemical reducing agents.

Impact of Phenylpropanoid Compounds on Heat Stress Tolerance in Carrot Cell Cultures

The phenylpropanoid and flavonoid families include thousands of specialized metabolites that influence a wide range of processes in plants, including seed dispersal, auxin transport, photoprotection, mechanical support and protection against insect herbivory. Such metabolites play a key role in the protection of plants against abiotic stress, in many cases through their well-known ability to inhibit the formation of reactive oxygen species (ROS). However, the precise role of specific phenylpropanoid and flavonoid molecules is unclear. We therefore investigated the role of specific anthocyanins (ACs) and other phenylpropanoids that accumulate in carrot cells cultivated in vitro, focusing on their supposed ability to protect cells from heat stress. First we characterized the effects of heat stress to identify quantifiable morphological traits as markers of heat stress susceptibility. We then fed the cultures with precursors to induce the targeted accumulation of specific compounds, and compared the impact of heat stress in these cultures and unfed controls. Data modeling based on projection to latent structures (PLS) regression revealed that metabolites containing coumaric or caffeic acid, including ACs, correlate with less heat damage. Further experiments suggested that one of the cellular targets damaged by heat stress and protected by these metabolites is the actin microfilament cytoskeleton.

Re-engineering of PIP3-antagonist triazole PITENIN's chemical scaffold: development of novel antifungal leads

A novel 4-(1-phenyl-1-hydroxyethyl)-1-(o-hydroxyphenyl)-1H-1,2,3-triazole was designed by integrating the structural features of triazole PITENIN anticancer agents and the azole class of antifungal drugs.

Quantification of oxidative stress phenotypes based on high-throughput growth profiling of protein kinase and phosphatase knockouts

Cellular responses to oxidative stress are important for restoring redox balance and ensuring cell survival. Genetic defects in response factors can lead to impaired response to oxidative damage and contribute to disease and aging. In single cell organisms, such as yeasts, the integrity of the oxidative stress response can be observed through its influences on growth characteristics. In this study, we investigated the time-dependent batch growth effects as a function of oxidative stress levels in protein kinase and phosphatase deletion backgrounds of Saccharomyces cerevisiae. In total, 41 different protein kinases and phosphatase mutants were selected for their known activities in oxidative stress or other stress response pathways and were investigated for their dosage-dependent response to hydrogen peroxide. Detailed growth profiles were analyzed after the induction of stress for growth rate, lag time duration and growth efficiency, and by a novel method to identify stress-induced diauxic shift delay. This approach extracts more phenotypic information than traditional plate-based methods due to the assessment of time dynamics in the time scale of minutes. With this approach, we were able to identify surprisingly diverse sensitivity and resistance patterns as a function of gene knockout.

Oxygen availability strongly affects chronological lifespan and thermotolerance in batch cultures of Saccharomyces cerevisiae

Stationary-phase (SP) batch cultures of Saccharomyces cerevisiae, in which growth has been arrested by carbon-source depletion, are widely applied to study chronological lifespan, quiescence and SP-associated robustness. Based on this type of experiments, typically performed under aerobic conditions, several roles of oxygen in aging have been proposed. However, SP in anaerobic yeast cultures has not been investigated in detail. Here, we use the unique capability of S. cerevisiae to grow in the complete absence of oxygen to directly compare SP in aerobic and anaerobic bioreactor cultures. This comparison revealed strong positive effects of oxygen availability on adenylate energy charge, longevity and thermotolerance during SP. A low thermotolerance of anaerobic batch cultures was already evident during the exponential growth phase and, in contrast to the situation in aerobic cultures, was not substantially increased during transition into SP. A combination of physiological and transcriptome analysis showed that the slow post-diauxic growth phase on ethanol, which precedes SP in aerobic, but not in anaerobic cultures, endowed cells with the time and resources needed for inducing longevity and thermotolerance. When combined with literature data on acquisition of longevity and thermotolerance in retentostat cultures, the present study indicates that the fast transition from glucose excess to SP in anaerobic cultures precludes acquisition of longevity and thermotolerance. Moreover, this study demonstrates the importance of a preceding, calorie-restricted conditioning phase in the acquisition of longevity and stress tolerance in SP yeast cultures, irrespective of oxygen availability.

Depletion of yeast PDK1 orthologs triggers a stress-like transcriptional response

BACKGROUND

Pkh proteins are the PDK1 orthologs in S. cerevisiae. They have redundant and essential activity and are responsible for the phosphorylation of several members of the AGC family of protein kinases. Pkh proteins have been involved in several cellular functions, including cell wall integrity and endocytosis. However the global expression changes caused by their depletion are still unknown.

RESULTS

A doxycycline-repressible tetO7 promoter driving the expression of PKH2 in cells carrying deletions of the PKH1 and PKH3 genes allowed us to progressively deplete cells from Pkh proteins when treated with doxycycline. Global gene expression analysis indicate that depletion of Pkh results in the up-regulation of genes involved in the accumulation of glycogen and also of those related to stress responses. Moreover, genes involved in the ion transport were quickly down-regulated when the levels of Pkh decreased. The reduction in the mRNA levels required for protein translation, however, was only observed after longer doxycycline treatment (24 h). We uncovered that Pkh is important for the proper transcriptional response to heat shock, and is mostly required for the effects driven by the transcription factors Hsf1 and Msn2/Msn4, but is not required for down-regulation of the mRNA coding for ribosomal proteins.

CONCLUSIONS

By using the tetO7 promoter we elucidated for the first time the transcriptomic changes directly or indirectly caused by progressive depletion of Pkh. Furthermore, this system enabled the characterization of the transcriptional response triggered by heat shock in wild-type and Pkh-depleted cells, showing that about 40 % of the observed expression changes were, to some degree, dependent on Pkh.

The Impact of Non-Enzymatic Reactions and Enzyme Promiscuity on Cellular Metabolism during (Oxidative) Stress Conditions

Cellular metabolism assembles in a structurally highly conserved, but functionally dynamic system, known as the metabolic network. This network involves highly active, enzyme-catalyzed metabolic pathways that provide the building blocks for cell growth. In parallel, however, chemical reactivity of metabolites and unspecific enzyme function give rise to a number of side products that are not part of canonical metabolic pathways. It is increasingly acknowledged that these molecules are important for the evolution of metabolism, affect metabolic efficiency, and that they play a potential role in human disease—age-related disorders and cancer in particular. In this review we discuss the impact of oxidative and other cellular stressors on the formation of metabolic side products, which originate as a consequence of: (i) chemical reactivity or modification of regular metabolites; (ii) through modifications in substrate specificity of damaged enzymes; and (iii) through altered metabolic flux that protects cells in stress conditions. In particular, oxidative and heat stress conditions are causative of metabolite and enzymatic damage and thus promote the non-canonical metabolic activity of the cells through an increased repertoire of side products. On the basis of selected examples, we discuss the consequences of non-canonical metabolic reactivity on evolution, function and repair of the metabolic network.

Transcription factors Asg1p and Hal9p regulate pH homeostasis in Candida glabrata

Candida glabrata is an important microorganism used in commercial fermentation to produce pyruvate, but very little is known about its mechanisms for surviving acid stress in culture. In this study, it was shown that transcription factors Asg1p and Hal9p play essential roles in C. glabrata in the tolerance of acid stress, as the deletion of CgASG1 or CgHAL9 resulted in the inability to survive in an acidic environment. Cgasg1Δ and Cghal9Δ mutant strains are unable to maintain pH homeostasis, as evidenced by a decrease in intracellular pH and an increase in reactive oxygen species production, which results in metabolic disorders. The results showed that intracellular acidification was partly due to the diminished activity of the plasma membrane proton pump, CgPma1p. In addition, transcriptome sequencing revealed that Cgasg1Δ and Cghal9Δ mutant strains displayed a variety of changes in gene expression under acidic conditions, including genes in the MAPK signaling pathway, plasma membrane, or cell wall organization, trehalose accumulation, and the RIM101 signaling pathway. Lastly, quantitative reverse-transcribed PCR and cellular localization showed that CgAsg1p and CgHal9p played independent roles in response to acid stress.

In vitro antifungal activity of baicalin against Candida albicans biofilms via apoptotic induction

The aim of this study was to investigate the antifungal activity of baicalin and its potential mechanism of action against Candida albicans biofilms. The standard techniques including microdilution method and checkerboard assay were employed to evaluate the susceptibilities of baicalin alone and in combination with fluconazole against planktonic and biofilm cells of C. albicans. Transmission electron microscope (TEM), scanning electron microscope (SEM), fluorescent microscope and flow cytometry were used to assess the apoptotic incidences induced by baicalin in biofilm cells. The expressions of four genes (RAS1, CAP1, PDE2 and TPK1) related to Ras-cAMP-PKA pathway were also analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The results showed that minimum inhibitory concentration (MIC) and sessile minimum inhibitory concentration (SMIC50) of baicalin were 500 and 2000 μg/mL with fractional inhibitory concentration indexs (FICIs) ranging from 0.28 to 0.75. A series of events related to apoptosis were observed in baicalin-treated C. albicans biofilms, including extensive chromatin condensation along the nuclear envelope, ROS accumulation, MMP reduction, PS externalization, nuclear fragmentation, chromatin condensation, metacaspase activation and Cyt C release. Additionally, the expressions of RAS1 and TPK1 were up-regulated by 3.2 and 2.9 folds respectively, while those of CAP1 and PDE2 were down-regulated by 3.3 and 6.6 folds respectively after exposure to baicalin in biofilm cells. In conclusion, baicalin can suppress the development of C. albicans biofilms most likely due to inducing cell death via apoptosis.

Involvement of an alternative oxidase in the regulation of hyphal growth and microsclerotial formation in Nomuraea rileyi CQNr01

Mitochondria of Nomuraea rileyi contain an alternative oxidase (Aox), which reduces oxygen to water by accepting electrons directly from ubiquinol. Furthermore, through a transcriptional analysis, we found that an alternative oxidase (Nraox) was up-regulated during microsclerotial formation. To study the function of NrAox, Nraox was cloned from N. rileyi CQNr01. The full-length cDNA was 1266 bp with an open reading frame of 1068 bp encoding 355 amino acids. A phylogenetic analysis revealed that the NrAox of N. rileyi was closely related to Metarhizium acridum Aox. The relative expression level of the Nraox was up-regulated during microsclerotial (MS) initiation. A salicylhydroxamic acid, a specific alternative oxidase inhibitor, application to the culture media severely decreased MS yields, changed the hyphae morphology and slowed the H2O2 removal. Nraox silencing caused mycelial deformations, reduced the MS yields by 97.3 % and increased MS size compared with those of the control. MS virulence was decreased to 26.2 % after Nraox was silenced. However, the Nraox-silenced strain was sensitive to environmental stress, and the growth rate was reduced under stress conditions. The results obtained suggested that Nraox is required for MS differentiation by regulating the intracellular H2O2 concentration and hypha growth. Additionally, Nraox had a great impact on the virulence of N. rileyi.

Identification of Azole Resistance Markers in Clinical Isolates of Candida tropicalis Using cDNA-AFLP Method

BACKGROUND

Global reports have highlighted the increasing prevalence of Candida tropicalis infections as well as organism(') s drug resistance. This study aimed at identifying azole resistance markers in clinical isolates of C. tropicalis, which will be a great resource for developing new drugs.

METHODS

Two susceptible and resistant isolates of C. tropicalis were recovered from an epidemiological investigation of candidiasis in immunocompromised patients. C. tropicalis ATCC 750 was used as reference strain. Antifungal susceptibility to fluconazole and itraconazole was determined using Clinical and Laboratory Standards Institute (CLSI) method. Complementary DNA-amplified fragment length polymorphism (cDNA-AFLP) technology and real-time reverse-transcriptase (RT) PCR were used for identification of potential genes involved in azole resistance of C. tropicalis clinical isolates.

RESULTS

Five genes encoding the following enzymes were identified as superoxide dismutase (SOD) implicated in antioxidant defense, ornithine aminotransferase (OAT), acetyl ornithine aminotransferase (ACOAT), adenosylmethionine-8-amino-7-oxononanoate aminotransferase (DAPA AT), and 4-aminobutyrate aminotransferase (ABAT)-belonging to pyridoxal phosphate (PLP) dependent enzymes and acting in an important physiological role in many fungal-cell cycles. Real-time RT-PCR confirmed mRNA level of the aforementioned genes.

CONCLUSION

Our findings showed that factors such as PLP-dependent enzymes and SOD might be implicated in drug resistance in C. tropicalis clinical isolate. Therefore, further studies are required to explore the accurate biological functions of the mentioned genes that would be helpful for effective drug development.

Calnexin is essential for survival under nitrogen starvation and stationary phase in Schizosaccharomyces pombe

Cell fate is determined by the balance of conserved molecular mechanisms regulating death (apoptosis) and survival (autophagy). Autophagy is a process by which cells recycle their organelles and macromolecules through degradation within the vacuole in yeast and plants, and lysosome in metazoa. In the yeast Schizosaccharomyces pombe, autophagy is strongly induced under nitrogen starvation and in aging cells. Previously, we demonstrated that calnexin (Cnx1p), a highly conserved transmembrane chaperone of the endoplasmic reticulum (ER), regulates apoptosis under ER stress or inositol starvation. Moreover, we showed that in stationary phase, Cnx1p is cleaved into two moieties, L_Cnx1p and S_Cnx1p. Here, we show that the processing of Cnx1p is regulated by autophagy, induced by nitrogen starvation or cell aging. The cleavage of Cnx1p involves two vacuolar proteases: Isp6, which is essential for autophagy, and its paralogue Psp3. Blocking autophagy through the knockout of autophagy-related genes (atg) results in inhibition of both, the cleavage and the trafficking of Cnx1p from the ER to the vacuole. We demonstrate that Cnx1p is required for cell survival under nitrogen-starvation and in chronological aging cultures. The death of the mini_cnx1 mutant (overlapping S_cnx1p) cells is accompanied by accumulation of high levels of reactive-oxygen species (ROS), a slowdown in endocytosis and severe cell-wall defects. Moreover, mutant cells expressing only S_Cnx1p showed cell wall defects. Co-expressing mutant overlapping the L_Cnx1p and S_Cnx1p cleavage products reverses the death, ROS phenotype and cell wall defect to wild-type levels. As it is involved in both apoptosis and autophagy, Cnx1p could be a nexus for the crosstalk between these pro-death and pro-survival mechanisms. Ours, and observations in mammalian systems, suggest that the multiple roles of calnexin depend on its sub-cellular localization and on its cleavage. The use of S. pombe should assist in further shedding light on the multiple roles of calnexin.

Different effects of sodium chloride preincubation on cadmium tolerance of Pichia kudriavzevii and Saccharomyces cerevisiae

Application of growing microorganisms for cadmium removal is restricted by high cadmium toxicity. The effects of sodium chloride (NaCl) preincubation on the cadmium tolerance and removal ability of Pichia kudriavzevii and Saccharomyces cerevisiae were investigated in this study. NaCl preincubation improved the biomass of P. kudriavzevii under cadmium stress, while no obvious effect was observed in S. cerevisiae. The improved activities of peroxidase (POD) and catalase (CAT) after NaCl preincubation might be an important reason for the decrease of the reactive oxygen species (ROS) accumulation, cell death, and oxidative damage of proteins and lipids induced by cadmium, contributing to the improvement of the yeast growth. The cadmium bioaccumulation capacity of P. kudriavzevii decreased significantly after NaCl preincubation, which played an important role in mitigating the cadmium toxicity to the yeast. The cadmium removal rate of P. kudriavzevii was obviously higher than S. cerevisiae and was significantly enhanced after NaCl preincubation. The results suggested that NaCl preincubation improved the cadmium tolerance and removal ability of P. kudriavzevii.

Respiration triggers heme transfer from cytochrome c peroxidase to catalase in yeast mitochondria

In exponentially growing yeast, the heme enzyme, cytochrome c peroxidase (Ccp1) is targeted to the mitochondrial intermembrane space. When the fermentable source (glucose) is depleted, cells switch to respiration and mitochondrial H2O2 levels rise. It has long been assumed that CCP activity detoxifies mitochondrial H2O2 because of the efficiency of this activity in vitro. However, we find that a large pool of Ccp1 exits the mitochondria of respiring cells. We detect no extramitochondrial CCP activity because Ccp1 crosses the outer mitochondrial membrane as the heme-free protein. In parallel with apoCcp1 export, cells exhibit increased activity of catalase A (Cta1), the mitochondrial and peroxisomal catalase isoform in yeast. This identifies Cta1 as a likely recipient of Ccp1 heme, which is supported by low Cta1 activity in ccp1Δ cells and the accumulation of holoCcp1 in cta1Δ mitochondria. We hypothesized that Ccp1's heme is labilized by hyperoxidation of the protein during the burst in H2O2 production as cells begin to respire. To test this hypothesis, recombinant Ccp1 was hyperoxidized with excess H2O2 in vitro, which accelerated heme transfer to apomyoglobin added as a surrogate heme acceptor. Furthermore, the proximal heme Fe ligand, His175, was found to be ∼ 85% oxidized to oxo-histidine in extramitochondrial Ccp1 isolated from 7-d cells, indicating that heme labilization results from oxidation of this ligand. We conclude that Ccp1 responds to respiration-derived H2O2 via a previously unidentified mechanism involving H2O2-activated heme transfer to apoCta1. Subsequently, the catalase activity of Cta1, not CCP activity, contributes to mitochondrial H2O2 detoxification.

Anti-oxidant effects of pomegranate juice on Saccharomyces cerevisiae cell growth

BACKGROUND

Pomegranate juice has a number of positive effects on both human and animal subjects.

MATERIAL AND METHODS

Four groups were used in this study. i: Control group, ii: H2O2 group, iii: Pomegranate juice (PJ) group and iv: PJ + H2O2 group. Following the sterilization method for pomegranate juice (10%) and H2O2 (6% v/v), Saccharomyces cerevisiae cultures were added and the cultivation incubated at 35°C for 72 hours. Fatty acids and vitamin concentrations were measured using HPLC and GC and the total protein bands profile were determined by SDS-PAGE.

RESULTS

According to our results statistically significant differences have been determined among the study groups in terms of fatty acids and vitamin (p<0,05). Fatty acid synthesis, vitamin control and cell density increased in groups to which PJ was given in comparison with the control group (p<0,05). Pomegranate juice increased vitamins, fatty acids and total protein expression in Saccharomyces cerevisiae in comparison with the control.

CONCLUSION

Pomegranate juice has a positive effect on fatty acid, vitamin and protein synthesis by Saccharomyces cerevisiae. Accordingly, we believe that it has significantly decreased oxidative damage thereby making a positive impact on yeast development.

Detection of in vivo protein tyrosine nitration in petite mutant of Saccharomyces cerevisiae: consequence of its formation and significance

Protein tyrosine nitration (PTN) is a selective post-translational modification often associated with physiological and pathophysiological conditions. Tyrosine is modified in the 3-position of the phenolic ring through the addition of a nitro group. In our previous study we first time showed that PTN occurs in vivo in Saccharomyces cerevisiae. In the present study we observed occurrence of PTN in petite mutant of S. cerevisiae which indicated that PTN is not absolutely dependent on functional mitochondria. Nitration of proteins in S. cerevisiae was also first time confirmed in immunohistochemical study using spheroplasts. Using proteosomal mutants Rpn10Δ, Pre9Δ, we first time showed that the fate of protein nitration in S. cerevisiae was not dependent on proteosomal clearing and probably played vital role in modulating signaling cascades. From our study it is evident that protein tyrosine nitration is a normal physiological event of S. cerevisiae.

Atmospheric-pressure plasma jet induces DNA double-strand breaks that require a Rad51-mediated homologous recombination for repair in Saccharomyces cerevisiae

Non-thermal plasma generated under atmospheric pressure produces a mixture of chemically reactive molecules and has been developed for a number of biomedical applications. Recently, plasma jet has been proposed as novel cancer therapies based on the observation that free radicals generated by plasma jet induce mitochondria-mediated apoptotic cell death. We show here that air plasma jet induces DNA double-strand breaks (DSBs) in yeast chromosomes leading to genomic instability and loss of viability, which are alleviated by Rad51, the yeast homolog of Escherichiacoli RecA recombinase, through DNA damage repair by a homologous recombination (HR) process. Hypersensitivity of rad51 mutant to air plasma was not restored by antioxidant treatment unlike sod1 mutant that was highly sensitive to reactive oxygen species (ROS) challenge, suggesting that plasma jet induces DSB-mediated cell death independent of ROS generation. These results may provide a new insight into the mechanism of air plasma jet-induced cell death.