Antifungal activity of amiodarone is mediated by disruption of calcium homeostasis

Effect of Ca2+ signal on the activity of key enzymes of carbon metabolism and related gene expression in yeast under high sugar fermentation

BACKGROUND

Saccharomyces cerevisiae is a fungus widely used in the food industry and biofuel industry, whereas it is usually exposed to high sugar stress during the fermentation process. Ca2+ is a key second messenger of the cell, it can regulate cell metabolism. The present study investigated the effect of the Ca2+ signal on the activity of key enzymes of carbon metabolism and related gene expression in yeast under high sugar fermentation.

RESULTS

The expression of genes encoding hexokinase was up-regulated in the high sugar environment, the activity of hexokinase was increased, glucose transmembrane transport capacity was enhanced, the ability of glucose to enter into glycolytic metabolism was increased, and the expression of genes related to pentose phosphate metabolism, glycerol metabolism and trehalose metabolism was up-regulated in the high glucose with Ca2+ group.

CONCLUSION

Ca2+ signal regulates the cellular metabolism of glycerol and trehalose and optimizes the allocation of carbon flow by regulating the key enzymes and related gene expression to enhance the resistance of yeast to high sugar stress. © 2024 Society of Chemical Industry.

Erg251 has complex and pleiotropic effects on sterol composition, azole susceptibility, filamentation, and stress response phenotypes

Ergosterol is essential for fungal cell membrane integrity and growth, and numerous antifungal drugs target ergosterol. Inactivation or modification of ergosterol biosynthetic genes can lead to changes in antifungal drug susceptibility, filamentation and stress response. Here, we found that the ergosterol biosynthesis gene ERG251 is a hotspot for point mutations during adaptation to antifungal drug stress within two distinct genetic backgrounds of Candida albicans. Heterozygous point mutations led to single allele dysfunction of ERG251 and resulted in azole tolerance in both genetic backgrounds. This is the first known example of point mutations causing azole tolerance in C. albicans. Importantly, single allele dysfunction of ERG251 in combination with recurrent chromosome aneuploidies resulted in bona fide azole resistance. Homozygous deletions of ERG251 caused increased fitness in low concentrations of fluconazole and decreased fitness in rich medium, especially at low initial cell density. Homozygous deletions of ERG251 resulted in accumulation of ergosterol intermediates consistent with the fitness defect in rich medium. Dysfunction of ERG251, together with FLC exposure, resulted in decreased accumulation of the toxic sterol (14-ɑ-methylergosta-8,24(28)-dien-3β,6α-diol) and increased accumulation of non-toxic alternative sterols. The altered sterol composition of the ERG251 mutants had pleiotropic effects on transcription, filamentation, and stress responses including cell membrane, osmotic and oxidative stress. Interestingly, while dysfunction of ERG251 resulted in azole tolerance, it also led to transcriptional upregulation of ZRT2, a membrane-bound Zinc transporter, in the presence of FLC, and overexpression of ZRT2 is sufficient to increase azole tolerance in wild-type C. albicans. Finally, in a murine model of systemic infection, homozygous deletion of ERG251 resulted in decreased virulence while the heterozygous deletion mutants maintain their pathogenicity. Overall, this study demonstrates that single allele dysfunction of ERG251 is a recurrent and effective mechanism of acquired azole tolerance. We propose that altered sterol composition resulting from ERG251 dysfunction mediates azole tolerance as well as pleiotropic effects on stress response, filamentation and virulence.

Marine-Derived Metabolites Act as Promising Antifungal Agents

The incidence of invasive fungal diseases (IFDs) is on the rise globally, particularly among immunocompromised patients, leading to significant morbidity and mortality. Current clinical antifungal agents, such as polyenes, azoles, and echinocandins, face increasing resistance from pathogenic fungi. Therefore, there is a pressing need for the development of novel antifungal drugs. Marine-derived secondary metabolites represent valuable resources that are characterized by varied chemical structures and pharmacological activities. While numerous compounds exhibiting promising antifungal activity have been identified, a comprehensive review elucidating their specific underlying mechanisms remains lacking. In this review, we have compiled a summary of antifungal compounds derived from marine organisms, highlighting their diverse mechanisms of action targeting various fungal cellular components, including the cell wall, cell membrane, mitochondria, chromosomes, drug efflux pumps, and several biological processes, including vesicular trafficking and the growth of hyphae and biofilms. This review is helpful for the subsequent development of antifungal drugs due to its summary of the antifungal mechanisms of secondary metabolites from marine organisms.

Erg251 has complex and pleiotropic effects on azole susceptibility, filamentation, and stress response phenotypes

Ergosterol is essential for fungal cell membrane integrity and growth, and numerous antifungal drugs target ergosterol. Inactivation or modification of ergosterol biosynthetic genes can lead to changes in antifungal drug susceptibility, filamentation and stress response. Here, we found that the ergosterol biosynthesis gene ERG251 is a hotspot for point mutations during adaptation to antifungal drug stress within two distinct genetic backgrounds of Candida albicans. Heterozygous point mutations led to single allele dysfunction of ERG251 and resulted in azole tolerance in both genetic backgrounds. This is the first known example of point mutations causing azole tolerance in C. albicans. Importantly, single allele dysfunction of ERG251 in combination with recurrent chromosome aneuploidies resulted in bona fide azole resistance. Homozygous deletions of ERG251 caused increased fitness in low concentrations of fluconazole and decreased fitness in rich medium, especially at low initial cell density. Dysfunction of ERG251 resulted in transcriptional upregulation of the alternate sterol biosynthesis pathway and ZRT2, a Zinc transporter. Notably, we determined that overexpression of ZRT2 is sufficient to increase azole tolerance in C. albicans. Our combined transcriptional and phenotypic analyses revealed the pleiotropic effects of ERG251 on stress responses including cell wall, osmotic and oxidative stress. Interestingly, while loss of either allele of ERG251 resulted in similar antifungal drug responses, we observed functional divergence in filamentation regulation between the two alleles of ERG251 (ERG251-A and ERG251-B) with ERG251-A exhibiting a dominant role in the SC5314 genetic background. Finally, in a murine model of systemic infection, homozygous deletion of ERG251 resulted in decreased virulence while the heterozygous deletion mutants maintain their pathogenicity. Overall, this study provides extensive genetic, transcriptional and phenotypic analysis for the effects of ERG251 on drug susceptibility, fitness, filamentation and stress responses.

Lipopeptides from Bacillus velezensis induced apoptosis-like cell death in the pathogenic fungus Fusarium concentricum

AIMS

Stem rot caused by Fusarium concentricum is a new disease of Paris polyphylla reported by our research group. The present study investigates the growth inhibitory and apoptotic effects of Bacillus velezensis FJAT-54560 lipopeptide against F. concentricum.

METHODS AND RESULTS

HPLC preparation and LC-MS analysis results show that the crude lipopeptides secreted by Bacillus velezensis FJAT-54560 isolated from Jasminum sambac consist of C14-17 iturin A, C14 fengycin B, C16 fengycin A/A2, C18 fengycin A, C20 fengycin B2, C21 fengycin A2, C22-23 fengycin A, C12-16 surfactin A, and C15 surfactin A derivatives. The mass ratios (g/g) of iturin, fengycin, and surfactin in lipopeptides are 2.40, 67.51, and 30.08%, respectively. Through inhibition zone and inhibition rate experiments, we found that crude lipopeptides and purified fengycin exhibit strong antifungal activity against F. concentricum, including accumulation of reactive oxygen species, loss of mitochondrial membrane potential, DNA fragmentation, Ca2+ accumulation, chromatin condensation, and phosphatidylserine externalization. Transcriptomic analysis indicates that crude lipopeptide-induced apoptosis in F. concentricum cells may be mediated by apoptosis-inducing factors and apoptosis mediators and can serve as a metacaspase-independent model.

CONCLUSION

Lipopeptides from Bacillus velezensis FJAT-54560 can control the pathogenic fungus F. concentricum by inducing apoptosis.

Understanding fluconazole tolerance in Candida albicans: implications for effective treatment of candidiasis and combating invasive fungal infections

OBJECTIVES

Fluconazole (FLC) tolerant phenotypes in Candida species contribute to persistent candidemia and the emergence of FLC resistance. Therefore, making FLC fungicidal and eliminating FLC tolerance are important for treating invasive fungal diseases (IFDs) caused by Candida species. However, the mechanisms of FLC tolerance in Candida species remain to be fully explored.

METHODS

This review discusses the high incidence of FLC tolerance in Candida species and the importance of successfully clearing FLC tolerance in treating candidiasis. We further define and characterize FLC tolerance in C. albicans.

RESULTS

This review identifies global factors affecting FLC tolerance and suggest that FLC tolerance is a strategy of C. albicans response to FLC damage whose mechanism differs from FLC resistance.

CONCLUSIONS

This review highlights the significance of the cell membrane and cell wall integrity in FLC tolerance, guiding approaches to combat IFDs caused by Candida species..

Enantiomeric pairs of copper(II) complexes with tridentate Schiff bases derived from R- and S-methionine: the role of decorating organic groups of the ligand in crystal packing and biological activity

Three enantiomeric pairs consisting of copper(II) complexes with tridentate Schiff bases have been synthesized for employing in biological assessments: 1∞[Cu₂(R/S-salmet)₂(H₂O)] (1-R/S·H2O), 1∞[Cu(R/S-3-HOMe-5-Me-salmet)] (2-R/S), and 1∞[Cu(R/S-3-MeO-salmet)] (3-R/S) (where R/S-salmetH₂, R/S-3-HOMe-5-Me-salmetH₂, and R/S-3-MeO-salmetH₂ result from the condensation of R/S-methionine with salicylaldehyde, 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde, and 3-methoxy-salicylaldehyde, respectively, in a 1 : 1 molar ratio). The crystal structures of 1-R·H2O and 2-R/S are reported. Moreover, the 1-R/S·H2O enantiomers have been subjected to a single-crystal-to-single-crystal (SC-SC) transformation by heating at 160 °C to afford their dehydrated forms, 1∞[Cu₂(R/S-salmet)₂] (1-R/S), whose structures have also been crystallographically determined. The coordination polyhedra of the metal centers, the binding modes of the ligands, and the 1-D double chain assemblies generated by the chiral mononuclear units are comparatively described. The diffuse reflectance UV-Vis and circular dichroism (CD) spectra of compounds 1-R/S·H2O, 1-R/S, and 2-R/S are analysed with respect to their structural peculiarities and compared to those of 3-R/S. The UV-Vis and CD spectra of solutions of 1-R/S, 2-R/S, and 3-R/S point to the collapse of the double chains via dissolution. Biological tests performed on the model eukaryote Saccharomyces cerevisiae indicated low toxicity for 1-R/S, 2-R/S, and 3-R, and moderate toxicity for 3-S. The S-type complexes were accumulated by cells in higher quantity compared to their R-type counterparts due to selective transport via the high-affinity S-methionine transporter, Mup1. A chemogenomic analysis of 3-S toxicity performed on a collection of yeast knockout mutants revealed that most of the deleted genes identified in the screen were involved in the cell response to oxidative stress, calcium-mediated response, or metal homeostasis. Altogether, it was concluded that 3-S accumulation may perturb the redox state of the cell, also interfering with the calcium-mediated response to oxidative stress or metal-related oxidative stress.

Interaction of Amiodarone with Azoles Against Aspergillus Planktonic Cells and Biofilms in vitro

Aspergillus spp. is the most common clinical pathogen of invasive fungal infection with high mortality. Existing treatments for Aspergillus spp. infection are still inefficient and accompanied by drug resistance, so it is still urgent to find new treatment approaches. The antiarrhythmic drug amiodarone (AMD) has demonstrated antifungal activity against a range of fungi. This study evaluated the efficacy of AMD in combination with triazoles for Aspergillus spp. infection. We tested the combined effect of AMD and three triazole drugs, namely, itraconazole (ITR), voriconazole (VRC), and posaconazole (POS), on the planktonic cells and biofilms of 20 strains of Aspergillus spp. via a checkerboard microdilution assay derived from 96-well plate-based method. Our results reveal that the combination of AMD with ITR or POS against Aspergillus biofilms has synergistic fungicidal effects. By contrast, the combination of AMD with VRC exhibits no antagonistic and synergistic effects. In this way, the use of AMD in combination with ITR or POS could be an effective adjunctive treatment for Aspergillus spp. infection.

A dual action small molecule enhances azoles and overcomes resistance through co-targeting Pdr5 and Vma1

Fungal infection threatens human health worldwide due to the limited arsenal of antifungals and the rapid emergence of resistance. Epidermal growth factor receptor (EGFR) is demonstrated to mediate epithelial cell endocytosis of the leading human fungal pathogen, Candida albicans. However, whether EGFR inhibitors act on fungal cells remains unknown. Here, we discovered that the specific EGFR inhibitor osimertinib mesylate (OSI) potentiates azole efficacy against diverse fungal pathogens and overcomes azole resistance. Mechanistic investigation revealed a conserved activity of OSI by promoting intracellular fluconazole accumulation via inhibiting Pdr5 and disrupting V-ATPase function via targeting Vma1 at serine 274, eventually leading to inactivation of the global regulator TOR. Evaluation of the in vivo efficacy and toxicity of OSI demonstrated its potential clinical application in impeding fluconazole resistance. Thus, the identification of OSI as a dual action antifungal with co-targeting activity proposes a potentially effective therapeutic strategy to treat life-threatening fungal infection and overcome antifungal resistance.

Dose-dependent interaction of two heavy metals with amiodarone toxicity in Saccharomyces cerevisiae

Amiodarone (AMD) is an antiarrhythmic drug that induces idiosyncratic toxicity. Environmental pollutants, including heavy metals, could interact with its toxicity by affecting pharmacokinetics and pharmacodynamics. Other levels of interaction could exist in yeast, such as oxidative stress and the general stress response. In this study, we investigated the interaction of mercury chloride (HgCl₂) and cadmium chloride (CdCl₂) with AMD toxicity on Saccharomyces cerevisiae. Interaction type - synergistic, additive, or antagonistic - was determined by median drug effect analysis using "CompuSyn". HgCl₂ potentiated AMD toxicity at high doses (≥ 71.4 μm, which yielded more than 60% inhibition). CdCl₂ acted similarly at high doses (≥ 57.9 μm). An antagonistic effect appeared at lower doses with both heavy metals (≤ 49.4 μm for HgCl₂ and AMD; ≤ 18.9 μm for CdCl₂ and AMD). The threshold concentrations (HgCl₂ or CdCl₂ combined with AMD) that switched the interaction from antagonistic to additive, and then to synergistic, were decreased in the yeast strain mutant in catalase (CTT1), suggesting an important role for this enzyme. Moreover, mutation of the nutrient sensing receptor gene GPR1 caused the synergistic interaction of CdCl₂, but not HgCl₂, with AMD to occur at the lowest tested concentrations (1.2 μm). The reverse was obtained with the mutant strain in calcium-manganese transporter gene PMR1, where the synergistic interaction of HgCl₂ with AMD occurred at concentrations (20.7 μm) lower than that of the wild type (71.4 μm). These results demonstrated a dose-dependent interaction between the two heavy metals with AMD toxicity, and the involvement of oxidative stress, calcium homeostasis, and nutrient sensing in the observed interaction.

D319 induced antifungal effects through ROS-mediated apoptosis and inhibited isocitrate lyase in Candida albicans

BACKGROUND

Candida albicans (C. albicans) is an opportunistic pathogen that can cause superficial and life-threatening systemic infections in immunocompromised patients. However, the available clinically antifungals are limited. Therefore, the development of effective antifungal agents and therapies is urgently needed. Quinoline type of compounds were reported to possess potent anti-fungal effect. A series of quinoline derivatives were synthesized. Moreover their inhibitory activities and mechanisms on C. albicans were evaluated in this study.

METHODS

The structure of D319 was identified by extensive spectroscopic analysis. The antifungal activity of D319 on C. albicans was evaluated using conventional methods, including the inhibition zone diameters with filter paper, Clinical Laboratory Standard Institute (CLSI) broth microdilution method in vitro, and in a murine model in vivo. Flow cytometry, fluorescence microscopy, western blot, knockout mutant and revertant strain techniques, and molecular modeling were applied to explore the mechanism of action of D319 in anti-Candida.

RESULTS

D319 exhibited potent anti-Candida activity with Minimum Inhibitory Concentration value of 2.5 μg/mL in vitro. D319 significantly improved survival rate and reduced fungal burden compared to vehicle control in a murine model in vivo. The treatment of C. albicans with D319 resulted in fungal apoptosis through reactive oxygen species (ROS) accumulation in C. albicans. Furthermore, D319 inhibited the glyoxylate enzyme isocitrate lyase (ICL) of C. albicans, which was also confirmed by docking analysis.

CONCLUSIONS

Quinoline compound D319 exhibited strong anti-Candida activities in vitro and in vivo models through inhibiting ICL activity and ROS accumulation in C. albicans.

GENERAL SIGNIFICANCE

This study showed that compound D319 as a novel isocitrate lyase inhibitor, would be a promising anti-Candida lead compound, which provided a potential application of this type of compounds in fighting clinical fungal infections. Furthermore, this study also supported ICL as a potential target for anti-Candida drug discovery.

Effect of molecular weight on the antibacterial activity of polysaccharides produced by Chaetomium globosum CGMCC 6882

This study investigated the effect of molecular weight on antibacterial activity of polysaccharides. Results showed that low molecular weight (3.105 × 10⁴ Da) polysaccharide (GCP-2) had higher inhibitory effects against Escherichia coli and Staphylococcus aureus than high molecular weight (5.340 × 10⁴ Da) polysaccharide (GCP-1). Meanwhile, antibacterial activities of GCP-2 and GCP-1 against S. aureus were higher than those of E. coli. Minimum inhibitory concentrations (MICs) of GCP-1 against E. coli and S. aureus were 2.0 mg/mL and 1.2 mg/mL, and MICs of GCP-2 against E. coli and S. aureus were 1.75 mg/mL and 0.85 mg/mL, respectively. Antibacterial mechanisms investigation revealed that GCP-2 and GCP-1 influenced cell membrane integrity, Ca²⁺-Mg²⁺-ATPase activity on cell membrane and calcium ions in cytoplasm of E. coli and S. aureus, but not cell wall. Present work provided important implications for future studies on development of antibacterial polysaccharides based on molecular weight feature.

New nanotechnological formulation based on amiodarone-loaded lipid core nanocapsules displays anticryptococcal effect

Cryptococcus neoformans is the etiological agent of cryptococcal meningoencephalitis. The recommended available treatment has low efficiency, with high toxicity and resistance as recurrent problems. In the search of new treatment protocols, the proposal of new pharmacological approaches is considered an innovative strategy, mainly nanotechnological systems considering fungal diseases. The antiarrhythmic drug amiodarone has demonstrated antifungal activity against a range of fungi, including C. neoformans. Here, considering the importance of calcium storage mediated by transporters on cryptococcal virulence, we evaluated the use of the calcium channel blocker amiodarone as an alternative therapy for cryptococcosis. C. neoformans displayed high sensitivity to amiodarone, which was also synergistic with fluconazole. Amiodarone treatment influenced some virulence factors, interrupting the calcium-calcineurin signaling pathway. Experiments with murine cryptococcosis models revealed that amiodarone treatment increased the fungal burden in the lungs, while its combination with fluconazole did not improve treatment compared to fluconazole alone. In addition, we have developed different innovative nanotechnological formulations, one of which combining two drugs with different mechanisms of action. Lipid-core nanocapsules (LNC) loaded with amiodarone (LNC_AMD), fluconazole (LNC_FLU) and both (LNC_AMD+FLU) were produced to achieve a better efficacy in vivo. In an intranasal model of treatment, all the LNC formulations had an antifungal effect. In an intraperitoneal treatment, LNC_AMD showed an enhanced anticryptococcal effect compared to the free drug, whereas LNC_FLU or LNC_AMD+FLU displayed no differences from the free drugs. In this way, nanotechnology using amiodarone formulations could be an effective therapy for cryptococcal infections.

Drug repurposing strategies in the development of potential antifungal agents

Abstract

The morbidity and mortality caused by invasive fungal infections are increasing across the globe due to developments in transplant surgery, the use of immunosuppressive agents, and the emergence of drug-resistant fungal strains, which has led to a challenge in terms of treatment due to the limitations of three classes of drugs. Hence, it is imperative to establish effective strategies to identify and design new antifungal drugs. Drug repurposing is a potential way of expanding the application of existing drugs. Recently, various existing drugs have been shown to be useful in the prevention and treatment of invasive fungi. In this review, we summarize the currently used antifungal agents. In addition, the most up-to-date information on the effectiveness of existing drugs with antifungal activity is discussed. Moreover, the antifungal mechanisms of existing drugs are highlighted. These data will provide valuable knowledge to stimulate further investigation and clinical application in this field.

Key points

• Conventional antifungal agents have limitations due to the occurrence of drug-resistant strains.

• Non-antifungal drugs act as antifungal agents in various ways toward different targets.

• Non-antifungal drugs with antifungal activity are demonstrated as effective antifungal strategies.

Activity and Mechanism of Action of Antifungal Peptides from Microorganisms: A Review

Harmful fungi in nature not only cause diseases in plants, but also fungal infection and poisoning when people and animals eat food derived from crops contaminated with them. Unfortunately, such fungi are becoming increasingly more resistant to traditional synthetic antifungal drugs, which can make prevention and control work increasingly more difficult to achieve. This means they are potentially very harmful to human health and lifestyle. Antifungal peptides are natural substances produced by organisms to defend themselves against harmful fungi. As a result, they have become an important research object to help deal with harmful fungi and overcome their drug resistance. Moreover, they are expected to be developed into new therapeutic drugs against drug-resistant fungi in clinical application. This review focuses on antifungal peptides that have been isolated from bacteria, fungi, and other microorganisms to date. Their antifungal activity and factors affecting it are outlined in terms of their antibacterial spectra and effects. The toxic effects of the antifungal peptides and their common solutions are mentioned. The mechanisms of action of the antifungal peptides are described according to their action pathways. The work provides a useful reference for further clinical research and the development of safe antifungal drugs that have high efficiencies and broad application spectra.

The Effect of Honokiol on Ergosterol Biosynthesis and Vacuole Function in Candida albicans

Ergosterol, an essential constituent of membrane lipids of yeast, is distributed in both the cell membrane and intracellular endomembrane components such as vacuoles. Honokiol, a major polyphenol isolated from Magnolia officinalis, has been shown to inhibit the growth of Candida albicans. Here, we assessed the effect of honokiol on ergosterol biosynthesis and vacuole function in C. albicans. Honokiol could decrease the ergosterol content and upregulate the expression of genes related with the ergosterol biosynthesis pathway. The exogenous supply of ergosterol attenuated the toxicity of honokiol against C. albicans. Honokiol treatment could induce cytosolic acidification by blocking the activity of the plasma membrane Pma1p H⁺-ATPase. Furthermore, honokiol caused abnormalities in vacuole morphology and function. Concomitant ergosterol feeding to some extent restored the vacuolar morphology and the function of acidification in cells treated by honokiol. Honokiol also disrupted the intracellular calcium homeostasis. Amiodarone attenuated the antifungal effects of honokiol against C. albicans, probably due to the activation of the calcineurin signaling pathway which is involved in honokiol tolerance. In conclusion, this study demonstrated that honokiol could inhibit ergosterol biosynthesis and decrease Pma 1p H⁺-ATPase activity, which resulted in the abnormal pH in vacuole and cytosol.

Calcium homeostasis plays important roles in the internalization and activities of the small synthetic antifungal peptide PAF26

Fungal diseases are responsible for the deaths of over 1.5 million people worldwide annually. Antifungal peptides represent a useful source of antifungals with novel mechanisms-of-action, and potentially provide new methods of overcoming resistance. Here we investigate the mode-of-action of the small, rationally designed synthetic antifungal peptide PAF26 using the model fungus Neurospora crassa. Here we show that the cell killing activity of PAF26 is dependent on extracellular Ca²⁺ and the presence of fully functioning fungal Ca²⁺ homeostatic/signaling machinery. In a screen of mutants with deletions in Ca²⁺ -signaling machinery, we identified three mutants more tolerant to PAF26. The Ca²⁺ ATPase NCA-2 was found to be involved in the initial interaction of PAF26 with the cell envelope. The vacuolar Ca²⁺ channel YVC-1 was shown to be essential for its accumulation and concentration within the vacuolar system. The Ca²⁺ channel CCH-1 was found to be required to prevent the translocation of PAF26 across the plasma membrane. In the wild type, Ca²⁺ removal from the medium resulted in the peptide remaining trapped in small vesicles as in the Δyvc-1 mutant. It is, therefore, apparent that cell killing by PAF26 is complex and unusually dependent on extracellular Ca²⁺ and components of the Ca²⁺ -regulatory machinery.

Amiodarone that has antibacterial effect against human pathogens may represent a novel catheter lock

Infection is one of the most feared hospital-acquired complications. Infusion therapy is frequently administered through a central line. Infusions facilitating bacterial growth may be a source of central line-associated bloodstream infections. On the other hand, medications that kill bacteria may protect against this kind of infection and may be used as a catheter lock.In this study, we examined the impact of amiodarone on bacterial growth. Amiodarone is used for controlling cardiac arrhythmias and can be administered as an infusion for weeks. Standard microbiological methods have been used to study the growth of laboratory strains and clinical isolates of Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and multidrug-resistant Acinetobacter baumannii in amiodarone. The minimum inhibitory concentration (MIC) of amiodarone was determined. Bacterial growth from in use amiodarone syringes and giving sets was also investigated.Most examined strains were killed within 1 min in amiodarone. The other strains were killed within 1 h. The MICs of amiodarone were <0.5-32 μg/mL.Amiodarone infusion is unlikely to be responsible for bloodstream infections as contaminating bacteria are killed within 1 h. Amiodarone may also protect against central line infections if used as a catheter lock.

Deletion of the Golgi Ca2+-ATPase PMR1 gene potentiates antifungal effects of dodecanol that depend on intracellular Ca2+ accumulation in budding yeast

One strategy for overcoming infectious diseases caused by drug-resistant fungi involves combining drugs rendered inactive by resistance with agents targeting the drug resistance mechanism. The antifungal activity of n-dodecanol disappears as incubation time passes. In Saccharomyces cerevisiae, anethole, a principal component of anise oil, prolongs the transient antifungal effect of dodecanol by downregulating genes of multidrug efflux pumps, mainly PDR5. However, the detailed mechanisms of dodecanol's antifungal action and the anethole-induced prolonged antifungal action of dodecanol are unknown. Screening of S. cerevisiae strains lacking genes related to Ca2+ homeostasis and signaling identified a pmr1Δ strain lacking Golgi Ca2+-ATPase as more sensitive to dodecanol than the parental strain. Dodecanol and the dodecanol + anethole combination significantly increased intracellular Ca2+ levels in both strains, but the mutant failed to clear intracellular Ca2+ accumulation. Further, dodecanol and the drug combination reduced PMR1 expression and did not lead to specific localization of Pmr1p in the parental strain after 4-h treatment. By contrast with the parental strain, dodecanol did not stimulate PDR5 expression in pmr1Δ. Based on these observations, we propose that the antifungal activity of dodecanol is related to intracellular Ca2+ accumulation, possibly dependent on PMR1 function, with anethole enabling Ca2+ accumulation by restricting dodecanol efflux.

Functional Coupling between the Unfolded Protein Response and Endoplasmic Reticulum/Golgi Ca2+-ATPases Promotes Stress Tolerance, Cell Wall Biosynthesis, and Virulence of Aspergillus fumigatus

Many species of pathogenic fungi deploy the unfolded protein response (UPR) to expand the folding capacity of the endoplasmic reticulum (ER) in proportion to the demand for virulence-related proteins that traffic through the secretory pathway. Although Ca²⁺ plays a pivotal role in ER function, the mechanism by which transcriptional upregulation of the protein folding machinery is coordinated with Ca²⁺ homeostasis is incompletely understood. In this study, we investigated the link between the UPR and genes encoding P-type Ca²⁺-ATPases in the human-pathogenic mold Aspergillus fumigatus We demonstrate that acute ER stress increases transcription of the srcA gene, encoding a member of the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) family, as well as that of pmrA, encoding a secretory pathway Ca²⁺-ATPase (SPCA) in the Golgi membrane. Loss of the UPR transcription factor HacA prevented the induction of srcA and pmrA transcription during ER stress, defining these ER/Golgi Ca²⁺ pumps as novel downstream targets of this pathway. While deletion of srcA alone caused no major deficiencies, a ΔsrcA/ΔpmrA mutant displayed a severe polarity defect, was hypersensitive to ER stress, and showed attenuated virulence. In addition, cell wall analyses revealed a striking reduction in mannose levels in the absence of both Ca²⁺ pumps. The ΔhacA mutant was hypersensitive to agents that block calcineurin-dependent signaling, consistent with a functional coupling between the UPR and Ca²⁺ homeostasis. Together, these findings demonstrate that the UPR integrates the need for increased levels of chaperone and folding enzymes with an influx of Ca²⁺ into the secretory pathway to support fungal growth, stress adaptation, and pathogenicity.IMPORTANCE The UPR is an intracellular signal transduction pathway that maintains homeostasis of the ER. The pathway is also tightly linked to the expression of virulence-related traits in diverse species of human-pathogenic and plant-pathogenic fungal species, including the predominant mold pathogen infecting humans, Aspergillus fumigatus Despite advances in the understanding of UPR signaling, the linkages and networks that are governed by this pathway are not well defined. In this study, we revealed that the UPR is a major driving force for stimulating Ca²⁺ influx at the ER and Golgi membranes and that the coupling between the UPR and Ca²⁺ import is important for virulence, cell wall biosynthesis, and resistance to antifungal compounds that inhibit Ca²⁺ signaling.

Antibacterial mechanism of the polysaccharide produced by Chaetomium globosum CGMCC 6882 against Staphylococcus aureus

GCP, a polysaccharide produced by endophytic fungus Chaetomium globosum CGMCC 6882, was found to be antibacterial against Staphylococcus aureus via disrupting cell permeability. However, the antibacterial mechanism of GCP has not been studied before. In present work, results showed that GCP could retard the growth of S. aureus by inducing the depolarization of cell membrane, decreasing the activity of Ca²⁺-Mg²⁺-ATPase on cell membrane, and increasing the accumulation of calcium ions in cytoplasm. Moreover, we found that GCP could also inhibit the synthesis of whole cell proteins of S. aureus. Overall, this study proved that the antibacterial mechanism of GCP could be diversified and more studies are needed in the investigation of the antibacterial mechanisms of various polysaccharides.

The Role of LAM Genes in the Pheromone-Induced Cell Death of S. cerevisiae Yeast

Lam1-4 proteins perform non-vesicular transport of sterols from the plasma membrane to the endoplasmic reticulum. Disruption of their function leads to an increase in the content of sterols in the plasma membrane. In mammals, homologs of Lam proteins are responsible for the internalization of plasma cholesterol. The biological role of Lam proteins in yeast remains unclear, since the strains lacking individual LAM genes do not display any pronounced phenotype. Deletion of LAM1 (YSP1) gene inhibits the regulated death of Saccharomyces cerevisiae yeast cells induced by the mating pheromone. Here, we investigated whether LAM2 also plays a role in the cell death induced by the excess of mating pheromone and assessed genetic interactions between LAM2 and genes responsible for ergosterol biosynthesis. We have shown that LAM2 deletion partially prevents pheromone-induced death of yeast cells of the laboratory strain W303, while deletions of three other LAM genes - LAM1, LAM3, and LAM4 - does not provide any additional rescuing effect. The UPC2-1 mutation in the transcription factor UPC2 gene, which leads to the excessive accumulation of sterols in the cell, promotes cell survival in the presence of the pheromone and shows additivity with the LAM2 deletion. On the contrary, LAM2 deletion stimulates pheromone-induced cell death in the laboratory strain BY4741. We have found that the deletion of ergosterol biosynthesis genes ERG2 and ERG6 reduces the effect of LAM2 deletion. Deletion of LAM2 in the Δerg4 strain lacking the gene of the last step of ergosterol biosynthesis, significantly increased the proportion of dead cells and decreased the growth rate of the yeast suspension culture even in the absence of the pheromone. We suggest that the absence of the effect of LAM2 deletion in the Δerg6 and Δerg2 strains indicates the inability of Lam2p to transport some ergosterol biosynthesis intermediates, such as lanosterol. Taken together, our data suggest that the role of Lam proteins in the regulated death of yeast cells caused by the mating pheromone is due to their effect on the plasma membrane sterol composition.

LAM Genes Contribute to Environmental Stress Tolerance but Sensibilize Yeast Cells to Azoles

Lam proteins transport sterols between the membranes of different cellular compartments. In Saccharomyces cerevisiae, the LAM gene family consists of three pairs of paralogs. Because the function of paralogous genes can be redundant, the phenotypes of only a small number of LAM gene deletions have been reported; thus, the role of these genes in yeast physiology is still unclear. Here, we surveyed the phenotypes of double and quadruple deletants of paralogous LAM2(YSP2)/LAM4 and LAM1(YSP1)/LAM3(SIP3) genes that encode proteins localized in the junctions of the plasma membrane and endoplasmic reticulum. The quadruple deletant showed increased sterol content and a strong decrease in ethanol, heat shock and high osmolarity resistance. Surprisingly, the quadruple deletant and LAM2/LAM4 double deletion strain showed increased tolerance to the azole antifungals clotrimazole and miconazole. This effect was not associated with an increased rate of ABC-transporter substrate efflux. Possibly, increased sterol pool in the LAM deletion strains postpones the effect of azoles on cell growth. Alternatively, LAM deletions might alleviate the toxic effect of sterols as Lam proteins can transport toxic sterol biosynthesis intermediates into membrane compartments that are sensitive to these compounds. Our findings reveal novel biological roles of LAM genes in stress tolerance and suggest that mutations in these genes may confer upregulation of a mechanism that provides resistance to azole antifungals in pathogenic fungi.

The chromogranin A-derived antifungal peptide CGA-N9 induces apoptosis in Candida tropicalis

CGA-N9, a peptide derived from human chromogranin A (CGA), was found to have antimicrobial activity in our previous investigation, but its mechanism of action remains unclear. Herein, the mechanism of action of CGA-N9 was investigated. We found that CGA-N9 induced the depolarization of the cell membrane and uptake of calcium ions into the cytosol and mitochondria. With the disruption of the mitochondrial membrane potential, the generation of intracellular reactive oxygen species (ROS) increased. Accordingly, we assessed apoptotic processes in Candida tropicalis cells post-treatment with CGA-N9 and found cytochrome c leakage, chromatin condensation and DNA degradation. The interaction of CGA-N9 with DNA in vitro showed that CGA-N9 did not degrade DNA but bound to DNA via an electrostatic interaction. In conclusion, CGA-N9 exhibits antifungal activity by inducing apoptosis in C. tropicalis.

Effectiveness of amiodarone in treatment of cutaneous leishmaniasis caused by Leishmania major

Development of new chemotherapeutic agents is an essential issue in the treatment and control of a disease. This study aimed to evaluate the anti-leishmanial activity of amiodarone, an antiarrhythmic class III drug, against Leishmania major, the most prevalent etiological agent of cutaneous leishmaniasis in the old world. The proliferation of promastigotes and intracellular amastigotes in the absence or presence of amiodarone was estimated, in an in vitro study. For in vivo study, five weeks after infection of BALB/c mice with L. major, when the lesions appeared at the injection site, the mice were divided into four groups (n = 6 each); treatment was conducted for 28 consecutive days with vehicle, amiodarone at 40 mg/kg orally and glucantime at 60 mg/kg intraperitoneally. Therapy with amiodarone reduced the size of lesions compared to the untreated group after 12 days. Amiodarone decreased the parasite load and inflammatory responses, particularly the macrophages containing amastigotes, and enhanced granulation tissue formation in the dermis and subcutaneous area. The Tumor necrosis factor-α and Interleukin-6 levels were significantly lower in the cell culture supernatants of the inguinal lymph node in the amiodarone treated group compared to the vehicle and untreated groups. Amiodarone significantly increased the activity of glutathione peroxidase in comparison to the vehicle and untreated groups but did not affect the plasma levels of superoxide dismutase, malondialdehyde, adiponectin, and ferric reducing ability of plasma. Therefore, the anti- L. major activity and immunomodulatory effects of amiodarone reduced the parasitic load and enhanced wound healing in cutaneous leishmaniasis in BALB/c mice. Amiodarone reduced the lesion surface area, but it did not cure it completely.

Manganese Suppresses the Haploinsufficiency of Heterozygous trpy1Δ/TRPY1 Saccharomyces cerevisiae Cells and Stimulates the TRPY1-Dependent Release of Vacuolar Ca2+ under H₂O₂ Stress

Transient potential receptor (TRP) channels are conserved cation channels found in most eukaryotes, known to sense a variety of chemical, thermal or mechanical stimuli. The Saccharomyces cerevisiae TRPY1 is a TRP channel with vacuolar localization involved in the cellular response to hyperosmotic shock and oxidative stress. In this study, we found that S. cerevisiae diploid cells with heterozygous deletion in TRPY1 gene are haploinsufficient when grown in synthetic media deficient in essential metal ions and that this growth defect is alleviated by non-toxic Mn²⁺ surplus. Using cells expressing the Ca²⁺-sensitive photoprotein aequorin we found that Mn²⁺ augmented the Ca²⁺ flux into the cytosol under oxidative stress, but not under hyperosmotic shock, a trait that was absent in the diploid cells with homozygous deletion of TRPY1 gene. TRPY1 activation under oxidative stress was diminished in cells devoid of Smf1 (the Mn²⁺-high-affinity plasma membrane transporter) but it was clearly augmented in cells lacking Pmr1 (the endoplasmic reticulum (ER)/Golgi located ATPase responsible for Mn²⁺ detoxification via excretory pathway). Taken together, these observations lead to the conclusion that increased levels of intracytosolic Mn²⁺ activate TRPY1 in the response to oxidative stress.

Promising Antifungal Targets Against Candida albicans Based on Ion Homeostasis

In recent decades, invasive fungal infections have been increasing significantly, contributing to high incidences and mortality in immunosuppressed patients. Candida albicans (C. albicans) is the most prevalent opportunistic fungal pathogen in humans that can cause severe and often fatal bloodstream infections. Current antifungal agents have several limitations, including that only a small number of classes of antifungals are available, certain of which have severe toxicity and high cost. Moreover, the emergence of drug resistance is a new limitation to successful patient outcomes. Therefore, the development of antifungals with novel targets is an essential strategy for the efficient management of C. albicans infections. It is widely recognized that ion homeostasis is crucial for all living cells. Many studies have identified that ion-signaling and transduction networks are central to fungal survival by regulating gene expression, morphological transition, host invasion, stress response, and drug resistance. Dysregulation of ion homeostasis rapidly mediates cell death, forming the mechanistic basis of a growing number of compounds that elicit antifungal activity. Most of the potent antifungals have been widely used in the clinic, and certain of them have low toxicity, meaning that they may be expected to be used as antifungal drugs in the future. Hence, we briefly summarize the homeostasis regulation of several important ions, potential antifungal targets based on these ion-signaling networks, and antifungal compounds based on the disruption of ion homeostasis. This summary will help in designing effective drugs and identifying new targets for combating fungal diseases.

Emerging role of amiodarone and dronedarone, as antiarrhythmic drugs, in treatment of leishmaniasis

Leishmaniasis is a group of human and animal diseases causing 20,000-40,000 annual deaths and its etiological agents belong to the Leishmania genus. The most current treatment against leishmaniasis is chemotherapy. Pentavalent antimonials such as glucantime and pentostam have been administrated as the first-line drugs in treatment of various forms of leishmaniasis. The second-line drugs such as amphotericin B, liposomal amphotericin B, miltefosine, pentamidine, azole drugs and paromomycin are used in resistant cases to pentavalent antimonials. Because of drawbacks of the first-line and second-line drugs including adverse side effects on different organs, increasing resistance, high cost, need to hospitalization and long-term treatment, it is necessary to find an alternative drug for leishmaniasis treatment. Several investigations have reported the effectiveness of amiodarone, the most commonly used antiarrhythmic drug, against fungi, Trypanosomes and Leishmania spp. in vitro, in vivo and clinical conditions. Moreover, the beneficial effects of dronedarone, amiodarone analogues, against Trypanosoma cruzi and Leishmania mexicana have recently been demonstrated and such treatment regimens resulted in lower side effects. The anti- leishmanial and anti- trypanosomal effectiveness of amiodarone and dronedarone has been attributed to destabilization of intracellular Ca²⁺ homeostasis, inhibition of sterol biosynthesis and collapse of mitochondrial membrane potential. Because of relative low cost, excellent pharmacokinetic properties, easy accessibility and beneficial effects of amiodarone and dronedarone on leishmaniasis, they are proper candidates to replace the current drugs used in leishmaniasis treatment.

The Sec1/Munc18 (SM) protein Vps45 is involved in iron uptake, mitochondrial function and virulence in the pathogenic fungus Cryptococcus neoformans

The battle for iron between invading microorganisms and mammalian hosts is a pivotal determinant of the outcome of infection. The pathogenic fungus, Cryptococcus neoformans, employs multiple mechanisms to compete for iron during cryptococcosis, a disease primarily of immunocompromised hosts. In this study, we examined the role of endocytic trafficking in iron uptake by characterizing a mutant defective in the Sec1/Munc18 (SM) protein Vps45. This protein is known to regulate the machinery for vesicle trafficking and fusion via interactions with SNARE proteins. As expected, a vps45 deletion mutant was impaired in endocytosis and showed sensitivity to trafficking inhibitors. The mutant also showed poor growth on iron-limited media and a defect in transporting the Cfo1 ferroxidase of the high-affinity iron uptake system from the plasma membrane to the vacuole. Remarkably, we made the novel observation that Vps45 also contributes to mitochondrial function in that a Vps45-Gfp fusion protein associated with mitotracker, and a vps45 mutant showed enhanced sensitivity to inhibitors of electron transport complexes as well as changes in mitochondrial membrane potential. Consistent with mitochondrial function, the vps45 mutant was impaired in calcium homeostasis. To assess the relevance of these defects for virulence, we examined cell surface properties of the vps45 mutant and found increased sensitivity to agents that challenge cell wall integrity and to antifungal drugs. A change in cell wall properties was consistent with our observation of altered capsule polysaccharide attachment, and with attenuated virulence in a mouse model of cryptococcosis. Overall, our studies reveal a novel role for Vps45-mediated trafficking for iron uptake, mitochondrial function and virulence.

Cryptococcus neoformans is a causative agent of cryptococcal meningitis, a disease that is estimated to cause ~ 15% of AIDS-related deaths. In this context, cryptococosis is one of the most common causes of mortality in people with HIV/AIDS, closely behind tuberculosis. Unfortunately, very few antifungal drugs are available to treat this disease. However, understanding mechanisms involved in the pathogenesis of C. neoformans can lead to new therapeutic avenues. In this study, we discovered a new role for a regulatory protein involved in vesicle transport. Specifically, we found that the Vps45 protein, which regulates vesicle fusion, participates in the trafficking of iron into fungal cells, supports mitochondria function, mediates antifungal resistance and is required for virulence. These discoveries shed light on the molecular mechanisms underlying the uptake and use of iron as an essential nutrient for the virulence of C. neoformans. Further investigations could lead to the development of drugs that target Vps45-mediated processes.

Overexpression or Deletion of Ergosterol Biosynthesis Genes Alters Doubling Time, Response to Stress Agents, and Drug Susceptibility in Saccharomyces cerevisiae

Ergosterol (ERG) is a critical sterol in the cell membranes of fungi, and its biosynthesis is tightly regulated by 25 known enzymes along the ERG production pathway. The effects of changes in expression of each ERG biosynthesis enzyme in Saccharomyces cerevisiae were analyzed by the use of gene deletion or plasmid-borne overexpression constructs. The strains overexpressing the ERG pathway genes were examined for changes in doubling time and responses to a variety of stress agents. In addition, ERG gene overexpression strains and ERG gene deletion strains were tested for alterations in antifungal drug susceptibility. The data show that disruptions in ergosterol biosynthesis regulation can affect a diverse set of cellular processes and can cause numerous phenotypic effects. Some of the phenotypes observed include dramatic increases in doubling times, respiratory deficiencies on glycerol media, cell wall insufficiencies on Congo red media, and disrupted ion homeostasis under iron or calcium starvation conditions. Overexpression or deletion of specific enzymes in the ERG pathway causes altered susceptibilities to a variety of classes of antifungal ergosterol inhibitors, including fluconazole, fenpropimorph, lovastatin, nystatin, amphotericin B, and terbinafine. This analysis of the effect of perturbations to the ERG pathway caused by systematic overexpression of each of the ERG pathway genes contributes significantly to the understanding of the ergosterol biosynthetic pathway and its relationship to stress response and basic biological processes. The data indicate that precise regulation of ERG genes is essential for cellular homeostasis and identify several ERG genes that could be exploited in future antifungal development efforts.IMPORTANCE A common target of antifungal drug treatment is the fungal ergosterol biosynthesis pathway. This report helps to identify ergosterol biosynthesis enzymes that have not previously been appreciated as drug targets. The effects of overexpression of each of the 25 ERG genes in S. cerevisiae were analyzed in the presence of six stress agents that target essential cellular processes (cell wall biosynthesis, protein translation, respiration, osmotic/ionic stress, and iron and calcium homeostasis), as well as six antifungal inhibitors that target ergosterol biosynthesis. The importance of identifying cell perturbations caused by gene overexpression or deletion is emphasized by the prevalence of gene expression alterations in many pathogenic and drug-resistant clinical isolates. Genes whose altered expression causes the most extensive phenotypic alterations in the presence of stressors or inhibitors have the potential to be drug targets.

TOR complex 2-regulated protein kinase Ypk1 controls sterol distribution by inhibiting StARkin domain-containing proteins located at plasma membrane-endoplasmic reticulum contact sites

In our proteome-wide screen, Ysp2 (also known as Lam2/Ltc4) was identified as a likely physiologically relevant target of the TOR complex 2 (TORC2)-dependent protein kinase Ypk1 in the yeast Saccharomyces cerevisiae. Ysp2 was subsequently shown to be one of a new family of sterol-binding proteins located at plasma membrane (PM)-endoplasmic reticulum (ER) contact sites. Here we document that Ysp2 and its paralogue Lam4/Ltc3 are authentic Ypk1 substrates in vivo and show using genetic and biochemical criteria that Ypk1-mediated phosphorylation inhibits the ability of these proteins to promote retrograde transport of sterols from the PM to the ER. Furthermore, we provide evidence that a change in PM sterol homeostasis promotes cell survival under membrane-perturbing conditions known to activate TORC2-Ypk1 signaling. These observations define the underlying molecular basis of a new regulatory mechanism for cellular response to plasma membrane stress.

Regulated Forms of Cell Death in Fungi

Cell death occurs in all domains of life. While some cells die in an uncontrolled way due to exposure to external cues, other cells die in a regulated manner as part of a genetically encoded developmental program. Like other eukaryotic species, fungi undergo programmed cell death (PCD) in response to various triggers. For example, exposure to external stress conditions can activate PCD pathways in fungi. Calcium redistribution between the extracellular space, the cytoplasm and intracellular storage organelles appears to be pivotal for this kind of cell death. PCD is also part of the fungal life cycle, in which it occurs during sexual and asexual reproduction, aging, and as part of development associated with infection in phytopathogenic fungi. Additionally, a fungal non-self-recognition mechanism termed heterokaryon incompatibility (HI) also involves PCD. Some of the molecular players mediating PCD during HI show remarkable similarities to major constituents involved in innate immunity in metazoans and plants. In this review we discuss recent research on fungal PCD mechanisms in comparison to more characterized mechanisms in metazoans. We highlight the role of PCD in fungi in response to exogenic compounds, fungal development and non-self-recognition processes and discuss identified intracellular signaling pathways and molecules that regulate fungal PCD.

Intracellular Calcium Mobilization in Response to Ion Channel Regulators via a Calcium-Induced Calcium Release Mechanism

Free intracellular calcium ([Ca²⁺]_i), in addition to being an important second messenger, is a key regulator of many cellular processes including cell membrane potential, proliferation, and apoptosis. In many cases, the mobilization of [Ca²⁺]_i is controlled by intracellular store activation and calcium influx. We have investigated the effect of several ion channel modulators, which have been used to treat a range of human diseases, on [Ca²⁺]_i release, by ratiometric calcium imaging. We show that six such modulators [amiodarone (Ami), dofetilide, furosemide (Fur), minoxidil (Min), loxapine (Lox), and Nicorandil] initiate release of [Ca²⁺]_i in prostate and breast cancer cell lines, PC3 and MCF7, respectively. Whole-cell currents in PC3 cells were inhibited by the compounds tested in patch-clamp experiments in a concentration-dependent manner. In all cases [Ca²⁺]_i was increased by modulator concentrations comparable to those used clinically. The increase in [Ca²⁺]_i in response to Ami, Fur, Lox, and Min was reduced significantly (P < 0.01) when the external calcium was reduced to nM concentration by chelation with EGTA. The data suggest that many ion channel regulators mobilize [Ca²⁺]_i. We suggest a mechanism whereby calcium-induced calcium release is implicated; such a mechanism may be important for understanding the action of these compounds.

Coupling of a voltage-gated Ca2+ channel homologue with a plasma membrane H+ -ATPase in yeast

Yeast has a homologue of mammalian voltage-gated Ca²⁺ channels (VGCCs), enabling the efficient uptake of Ca²⁺ . It comprises two indispensable subunits, Cch1 and Mid1, equivalent to the mammalian pore-forming α₁ and auxiliary α₂ /δ subunits, respectively. Unlike the physiological roles of Cch1/Mid1 channels, the regulatory mechanisms of the yeast VGCC homologue remain unclear. Therefore, we screened candidate proteins that interact with Mid1 by an unbiased proteomic approach and identified a plasma membrane H⁺ -ATPase, Pma1, as a candidate. Mid1 coimmunoprecipitated with Pma1, and Mid1-EGFP colocalized with Pma1-mCherry at the plasma membrane. The physiological relevance of their interaction was determined using the temperature-sensitive mutant, pma1-10. At the nonpermissive temperature, the membrane potential was less negative and Ca²⁺ uptake was lower in pma1-10 than in wild-type cells. Increased extracellular H⁺ increased the rate of Ca²⁺ uptake. Therefore, H⁺ extrusion by Pma1 may be important for Ca²⁺ influx through Cch1/Mid1. These results suggest that Pma1 interacts physically with Cch1/Mid1 Ca²⁺ channels to enhance their activity via its H⁺ -pumping activity.

Calcium channel regulator Mid1 links TORC2-mediated changes in mitochondrial respiration to autophagy

Rapamycin-insensitive TORC2 signaling promotes amino acid starvation–induced autophagy through inhibition of the calcium-dependent phosphatase calcineurin. Vlahakis et al. show that this regulation requires the ER calcium channel regulatory protein Mid1, which couples mitochondrial ROS accumulation in TORC2 mutants to calcineurin activation and autophagy repression.

Autophagy is a catabolic process that recycles cytoplasmic contents and is crucial for cell survival during stress. The target of rapamycin (TOR) kinase regulates autophagy as part of two distinct protein complexes, TORC1 and TORC2. TORC1 negatively regulates autophagy according to nitrogen availability. In contrast, TORC2 functions as a positive regulator of autophagy during amino acid starvation, via its target kinase Ypk1, by repressing the activity of the calcium-dependent phosphatase calcineurin and promoting the general amino acid control (GAAC) response. Precisely how TORC2-Ypk1 signaling regulates calcineurin within this pathway remains unknown. Here we demonstrate that activation of calcineurin requires Mid1, an endoplasmic reticulum–localized calcium channel regulatory protein implicated in the oxidative stress response. We find that normal mitochondrial respiration is perturbed in TORC2-Ypk1–deficient cells, which results in the accumulation of mitochondrial-derived reactive oxygen species that signal to Mid1 to activate calcineurin, thereby inhibiting the GAAC response and autophagy. These findings describe a novel pathway involving TORC2, mitochondrial oxidative stress, and calcium homeostasis for autophagy regulation.

Endosomal Trafficking Defects Can Induce Calcium-Dependent Azole Tolerance in Candida albicans

The azole antifungals arrest fungal growth through inhibition of ergosterol biosynthesis. We recently reported that a Candida albicans vps21Δ/Δ mutant, deficient in membrane trafficking through the late endosome/prevacuolar compartment (PVC), continues to grow in the presence of the azoles despite the depletion of cellular ergosterol. Here, we report that the vps21Δ/Δ mutant exhibits less plasma membrane damage upon azole treatment than the wild type, as measured by the release of a cytoplasmic luciferase reporter into the culture supernatant. Our results also reveal that the vps21Δ/Δ mutant has abnormal levels of intracellular Ca²⁺ and, in the presence of fluconazole, enhanced expression of a calcineurin-responsive RTA2-GFP reporter. Furthermore, the azole tolerance phenotype of the vps21Δ/Δ mutant is dependent upon both extracellular calcium levels and calcineurin activity. These findings underscore the importance of endosomal trafficking in determining the cellular consequences of azole treatment and indicate that this may occur through modulation of calcium- and calcineurin-dependent responses.

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.

Valproate inhibits MAP kinase signalling and cell cycle progression in S. cerevisiae

The mechanism of action of valproate (VPA), a widely prescribed short chain fatty acid with anticonvulsant and anticancer properties, remains poorly understood. Here, the yeast Saccharomyces cerevisiae was used as model to investigate the biological consequences of VPA exposure. We found that low pH strongly potentiates VPA-induced growth inhibition. Transcriptional profiling revealed that under these conditions, VPA modulates the expression of genes involved in diverse cellular processes including protein folding, cell wall organisation, sexual reproduction, and cell cycle progression. We further investigated the impact of VPA on selected processes and found that this drug: i) activates markers of the unfolded protein stress response such as Hac1 mRNA splicing; ii) modulates the cell wall integrity pathway by inhibiting the activation of the Slt2 MAP kinase, and synergizes with cell wall stressors such as micafungin and calcofluor white in preventing yeast growth; iii) prevents activation of the Kss1 and Fus3 MAP kinases of the mating pheromone pathway, which in turn abolishes cellular responses to alpha factor; and iv) blocks cell cycle progression and DNA replication. Overall, our data identify heretofore unknown biological responses to VPA in budding yeast, and highlight the broad spectrum of cellular pathways influenced by this chemical in eukaryotes.

Comparative proteomic analysis reveals intracellular targets for bacillomycin L to induce Rhizoctonia solani Kühn hyphal cell death

Bacillomycin L, a natural iturinic lipopeptide produced by Bacillus amyloliquefaciens, is characterized by strong antifungal activity against a variety of agronomically important filamentous fungi including Rhizoctonia solani Kühn. To further understand its antifungal actions, proteomes were comparatively studied within R. solani hyphal cells treated with or without bacillomycin L. The results show that 39 proteins were alternatively expressed within cells in response to this lipopeptide, which are involved in stress response, carbohydrate, amino acid and nucleotide metabolism, cellular component organization, calcium homeostasis, protein degradation, RNA processing, gene transcription, and others, suggesting that, in addition to inducing cell membrane permeabilization, iturin exhibits antibiotic activities by targeting intracellular molecules. Based on these results, a model of action of bacillomycin L against R. solani hyphal cells was proposed. Our study provides new insight into the antibiotic mechanisms of iturins.

Regulatory roles of phosphorylation in model and pathogenic fungi

Over the past 20 years, considerable advances have been made toward our understanding of how post-translational modifications affect a wide variety of biological processes, including morphology and virulence, in medically important fungi. Phosphorylation stands out as a key molecular switch and regulatory modification that plays a critical role in controlling these processes. In this article, we first provide a comprehensive and up-to-date overview of the regulatory roles that both Ser/Thr and non-Ser/Thr kinases and phosphatases play in model and pathogenic fungi. Next, we discuss the impact of current global approaches that are being used to define the complete set of phosphorylation targets (phosphoproteome) in medically important fungi. Finally, we provide new insights and perspectives into the potential use of key regulatory kinases and phosphatases as targets for the development of novel and more effective antifungal strategies.

Tfp1 is required for ion homeostasis, fluconazole resistance and N-Acetylglucosamine utilization in Candida albicans

The vacuolar-type H+-ATPase (V-ATPase) is crucial for the maintenance of ion homeostasis. Dysregulation of ion homeostasis affects various aspects of cellular processes. However, the importance of V-ATPase in Candida albicans is not totally clear. In this study, we demonstrated the essential roles of V-ATPase through Tfp1, a putative V-ATPase subunit. Deletion of TFP1 led to generation of an iron starvation signal and reduced total iron content, which was associated with mislocalization of Fet34p that was finally due to disorders in copper homeostasis. Furthermore, the tfp1∆/∆ mutant exhibited weaker growth and lower aconitase activity on nonfermentable carbon sources, and iron or copper addition partially rescued the growth defect. In addition, the tfp1∆/∆ mutant also showed elevated cytosolic calcium levels in normal or low calcium medium that were relevant to calcium release from vacuole. Kinetics of cytosolic calcium response to an alkaline pulse and VCX1 (VCX1 encodes a putative vacuolar Ca2+/H+ exchanger) overexpression assays indicated that the cytosolic calcium status was in relation to Vcx1 activity. Spot assay and concentration-kill curve demonstrated that the tfp1∆/∆ mutant was hypersensitive to fluconazole, which was attributed to reduced ergosterol biosynthesis and CDR1 efflux pump activity, and iron/calcium dysregulation. Interestingly, carbon source utilization tests found the tfp1∆/∆ mutant was defective for growth on N-Acetylglucosamine (GlcNAc) plate, which was associated with ATP depletion due to the decreased ability to catabolize GlcNAc. Taken together, our study gives new insights into functions of Tfp1, and provides the potential to better exploit V-ATPase as an antifungal target.

Ca(2+) homeostasis in the budding yeast Saccharomyces cerevisiae: Impact of ER/Golgi Ca(2+) storage

Yeast has proven to be a powerful tool to elucidate the molecular aspects of several biological processes in higher eukaryotes. As in mammalian cells, yeast intracellular Ca(2+) signalling is crucial for a myriad of biological processes. Yeast cells also bear homologs of the major components of the Ca(2+) signalling toolkit in mammalian cells, including channels, co-transporters and pumps. Using yeast single- and multiple-gene deletion strains of various plasma membrane and organellar Ca(2+) transporters, combined with manipulations to estimate intracellular Ca(2+) storage, we evaluated the contribution of individual transport systems to intracellular Ca(2+) homeostasis. Yeast strains lacking Pmr1 and/or Cod1, two ion pumps implicated in ER/Golgi Ca(2+) homeostasis, displayed a fragmented vacuolar phenotype and showed increased vacuolar Ca(2+) uptake and Ca(2+) influx across the plasma membrane. In the pmr1Δ strain, these effects were insensitive to calcineurin activity, independent of Cch1/Mid1 Ca(2+) channels and Pmc1 but required Vcx1. By contrast, in the cod1Δ strain increased vacuolar Ca(2+) uptake was not affected by Vcx1 deletion but was largely dependent on Pmc1 activity. Our analysis further corroborates the distinct roles of Vcx1 and Pmc1 in vacuolar Ca(2+) uptake and point to the existence of not-yet identified Ca(2+) influx pathways.

Components of the calcium-calcineurin signaling pathway in fungal cells and their potential as antifungal targets

In recent years, the emergence of fungal resistance has become frequent, partly due to the widespread clinical use of fluconazole, which is minimally toxic and effective in the prevention and treatment of Candida albicans infections. The limited selection of antifungal drugs for clinical fungal infection therapy has prompted us to search for new antifungal drug targets. Calcium, which acts as the second messenger in both mammals and fungi, plays a direct role in controlling the expression patterns of its signaling systems and has important roles in cell survival. In addition, calcium and some of the components, mainly calcineurin, in the fungal calcium signaling pathway mediate fungal resistance to antifungal drugs. Therefore, an overview of the components of the fungal calcium-calcineurin signaling network and their potential roles as antifungal targets is urgently needed. The calcium-calcineurin signaling pathway consists of various channels, transporters, pumps, and other proteins or enzymes. Many transcriptional profiles have indicated that mutant strains that lack some of these components are sensitized to fluconazole or other antifungal drugs. In addition, many researchers have identified efficient compounds that exhibit antifungal activity by themselves or in combination with antifungal drugs by targeting some of the components in the fungal calcium-calcineurin signaling pathway. This targeting disrupts Ca(2+) homeostasis, which suggests that this pathway contains potential targets for the development of new antifungal drugs.