The Transcription Factor Sfp1 Regulates the Oxidative Stress Response in Candida albicans

Transcriptional profiling reveals the role of Candida albicans Rap1 in oxidative stress response

Candida albicans is a member of the human commensal microbiota but can also cause opportunistic infections, including life-threatening invasive candidiasis, particularly in immunocompromised patients. One of the important features of C. albicans commensalism and virulence is its ability to adapt to diverse environmental stress conditions within the host. Rap1 is a DNA-binding protein identified in yeasts, protozoa, and mammalian cells, and it plays multiple functions, including telomere regulation. Intriguingly, our previous study showed that Rap1 is also involved in cell wall integrity, biofilm formation, and virulence in C. albicans. In this work, using RNA-seq analysis and other approaches, the role of C. albicans Rap1 in oxidative stress response was further revealed. The RAP1-deletion mutant exhibited greater resistance to the superoxide generator menadione, a lower level of intracellular reactive oxygen species (ROS) upon menadione treatment, and higher expression levels of superoxide dismutase genes, all in response to oxidative stress. Moreover, the association between Rap1-mediated oxidative stress response and the mitogen-activated protein kinase (MAPK) Hog1, the transcription factor Cap1 and the TOR signalling was also determined. Together, these findings expand our understanding of the complex signalling and transcriptional mechanisms regulating stress responses in C. albicans.

Systematic identification and characterization of five transcription factors mediating the oxidative stress response in Candida albicans

Candida albicans is an opportunistic human fungal pathogen that causes superficial and systemic infections, particularly in immunocompromised individuals. In response to C. albicans infection, innate immune cells of the host produce and accumulate reactive oxygen species (ROS), which can lead to irreversible damage and apoptosis of fungal cells. Several transcription factors involved in this oxidative stress response have been identified; however, a systematic study to identify the transcription factors that mediate the oxidative stress response has not yet been conducted. Here, we screened a comprehensive transcription factor mutant library consisting of 211 transcription factor deletion mutant strains in the presence and absence of hydrogen peroxide (H2O2), a potent ROS inducer, and identified five transcription factors (Skn7, Dpb4, Cap1, Dal81, and Stp2) that are sensitive to H2O2. Genome-wide transcriptional profiling revealed that H2O2 induces a discrete set of differentially regulated genes among the five identified transcription factor mutant strains. Functional enrichment analysis identified KEGG pathways pertaining to glycolysis/gluconeogenesis, amino sugar and nucleotide sugar metabolism, and ribosome synthesis as the most enriched pathways. GO term analysis of the top common differentially expressed genes among the transcription factor mutant strains identified hexose catabolism and iron transport as the most enriched GO terms upon exposure to H2O2. This study is the first to systematically identify and characterise the transcription factors involved in the response to H2O2. Based on our transcriptional profiling results, we found that exposure to H2O2 modulates several downstream genes involved in fungal virulence. Overall, this study sheds new light on the metabolism, physiological functions, and cellular processes involved in the H2O2-induced oxidative stress response in C. albicans.

Antifungal Activity of Chitosan against Histoplasma capsulatum in Planktonic and Biofilm Forms: A Therapeutic Strategy in the Future?

Histoplasmosis is a respiratory disease caused by Histoplasma capsulatum, a dimorphic fungus, with high mortality and morbidity rates, especially in immunocompromised patients. Considering the small existing therapeutic arsenal, new treatment approaches are still required. Chitosan, a linear polysaccharide obtained from partial chitin deacetylation, has anti-inflammatory, antimicrobial, biocompatibility, biodegradability, and non-toxicity properties. Chitosan with different deacetylation degrees and molecular weights has been explored as a potential agent against fungal pathogens. In this study, the chitosan antifungal activity against H. capsulatum was evaluated using the broth microdilution assay, obtaining minimum inhibitory concentrations (MIC) ranging from 32 to 128 µg/mL in the filamentous phase and 8 to 64 µg/mL in the yeast phase. Chitosan combined with classical antifungal drugs showed a synergic effect, reducing chitosan's MICs by 32 times, demonstrating that there were no antagonistic interactions relating to any of the strains tested. A synergism between chitosan and amphotericin B or itraconazole was detected in the yeast-like form for all strains tested. For H. capsulatum biofilms, chitosan reduced biomass and metabolic activity by about 40% at 512 µg/mL. In conclusion, studying chitosan as a therapeutic strategy against Histoplasma capsulatum is promising, mainly considering its numerous possible applications, including its combination with other compounds.

The Role of Sfp1 in Candida albicans Cell Wall Maintenance

The cell wall is the first interface for Candida albicans interaction with the surrounding environment and the host cells. Therefore, maintenance of cell wall integrity (CWI) is crucial for C. albicans survival and host-pathogen interaction. In response to environmental stresses, C. albicans undergoes cell wall remodeling controlled by multiple signaling pathways and transcription regulators. Here, we explored the role of the transcription factor Sfp1 in CWI. A deletion of the SFP1 gene not only caused changes in cell wall properties, cell wall composition and structure but also modulated expression of cell wall biosynthesis and remodeling genes. In addition, Cas5 is a known transcription regulator for C. albicans CWI and cell wall stress response. Interestingly, our results indicated that Sfp1 negatively controls the CAS5 gene expression by binding to its promoter element. Together, this study provides new insights into the regulation of C. albicans CWI and stress response.

Photosensitizer to the rescue: in planta and field application of photodynamic inactivation against plant pathogenic bacteria

Control of plant pathogens using chemical and synthetic pesticides raises a major safety concern for humans and the environment. Despite the ongoing exploration of sustainable alternative methods, management practices for pathogens, especially bacteria, have remained almost unchanged over decades, whereby long-term uses of copper and antibiotics has led to widespread bacterial resistance in the field. Antimicrobial photodynamic inactivation (aPDI) of bacteria is emerging as an alternative strategy to combat resistant plant pathogens. aPDI utilizes light-sensitive molecules (photosensitizers) that upon illumination produce reactive oxygen species able to kill pathogens. Here we explore the potential of an anionic semisynthetic water-soluble derivative of chlorophyl (Sodium Magnesium Chlorophyllin: Mg-chl), as an antibacterial agent in planta, by simulating processes naturally occurring in the field. Mg-chl in combination with Na2EDTA (cell wall permeabilizing agent) was able to effectively inhibit Pseudomonas syringae pv. tomato DC3000 in vitro and in planta in both tomato and N. benthamiana. Notably, Mg-chl in combination with Na2EDTA and the common surfactant Morwet D-400 significantly reduced Xanthomonas hortorum pv. gardneri and Xanthomonas fragarie, respectively, in a commercial greenhouse trial against bacterial spot disease in tomato and in field experiments against angular leaf spot disease in strawberries.

The high osmolarity glycerol (HOG) pathway in fungi†

While fungi are widely occupying nature, many species are responsible for devastating mycosis in humans. Such niche diversity explains how quick fungal adaptation is necessary to endow the capacity of withstanding fluctuating environments and to cope with host-imposed conditions. Among all the molecular mechanisms evolved by fungi, the most studied one is the activation of the phosphorelay signalling pathways, of which the high osmolarity glycerol (HOG) pathway constitutes one of the key molecular apparatus underpinning fungal adaptation and virulence. In this review, we summarize the seminal knowledge of the HOG pathway with its more recent developments. We specifically described the HOG-mediated stress adaptation, with a particular focus on osmotic and oxidative stress, and point out some lags in our understanding of its involvement in the virulence of pathogenic species including, the medically important fungi Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus, compared to the model yeast Saccharomyces cerevisiae. Finally, we also highlighted some possible applications of the HOG pathway modifications to improve the fungal-based production of natural products in the industry.

Candida albicans Sfp1 Is Involved in the Cell Wall and Endoplasmic Reticulum Stress Responses Induced by Human Antimicrobial Peptide LL-37

Candida albicans is a commensal fungus of humans but can cause infections, particularly in immunocompromised individuals, ranging from superficial to life-threatening systemic infections. The cell wall is the outermost layer of C. albicans that interacts with the host environment. Moreover, antimicrobial peptides (AMPs) are important components in innate immunity and play crucial roles in host defense. Our previous studies showed that the human AMP LL-37 binds to the cell wall of C. albicans, alters the cell wall integrity (CWI) and affects cell adhesion of this pathogen. In this study, we aimed to further investigate the molecular mechanisms underlying the C. albicans response to LL-37. We found that LL-37 causes cell wall stress, activates unfolded protein response (UPR) signaling related to the endoplasmic reticulum (ER), induces ER-derived reactive oxygen species and affects protein secretion. Interestingly, the deletion of the SFP1 gene encoding a transcription factor reduced C. albicans susceptibility to LL-37, which is cell wall-associated. Moreover, in the presence of LL-37, deletion of SFP1 attenuated the UPR pathway, upregulated oxidative stress responsive (OSR) genes and affected bovine serum albumin (BSA) degradation by secreted proteases. Therefore, these findings suggested that Sfp1 positively regulates cell wall integrity and ER homeostasis upon treatment with LL-37 and shed light on pathogen-host interactions.

Comprehensive genomic survey, structural classification and expression analysis of C2H2-type zinc finger factor in wheat (Triticum aestivum L.)

BACKGROUND

The C2H2-type zinc finger proteins (C2H2-ZFPs) are one of major classes of transcription factors that play important roles in plant growth, development and stress responses. Limit information about the C2H2-ZF genes hinders the molecular breeding in bread wheat (Triticum aestivum).

RESULTS

In this study, 457 C2H2-ZFP proteins (including 253 splice variants), which contain four types of conserved domain (named Q, M, Z, and D), could be further classified into ten subsets. They were identified to be distributed in 21 chromosomes in T. aestivum. Subset-specific motifs, like NPL-, SFP1-, DL- (EAR-like-motif), R-, PL-, L- and EK-, might make C2H2-ZFP diverse multifunction. Interestingly, NPL- and SFP1-box were firstly found to be located in C2H2-ZFP proteins. Synteny analyses showed that only 4 pairs of C2H2 family genes in T. aestivum, 65 genes in B. distachyon, 66 genes in A. tauschii, 68 genes in rice, 9 genes in Arabidopsis, were syntenic relationships respectively. It indicated that TaZFPs were closely related to genes in Poaceae. From the published transcriptome data, totally 198 of 204 TaC2H2-ZF genes have expression data. Among them, 25 TaC2H2-ZF genes were certificated to be significantly differentially expressed in 5 different organs and 15 different development stages by quantitative RT-PCR. The 18 TaC2H2-ZF genes were verified in response to heat, drought, and heat & drought stresses. According to expression pattern analysis, several TaZFPs, like Traes_5BL_D53A846BE.1, were not only highly expressed in L2DAAs, RTLS, RMS, but also endowed tolerance to drought and heat stresses, making them good candidates for molecular breeding.

CONCLUSIONS

This study systematically characterized the TaC2H2-ZFPs and their potential roles in T. aestivum. Our findings provide new insights into the C2H2-ZF genes in T. aestivum as well as a foundation for further studies on the roles of TaC2H2-ZF genes in T. aestivum molecular breeding.

Phytogenic Fabrication of Ag-Fe Bimetallic Nanoparticles for Cell Cycle Arrest and Apoptosis Signaling Pathways in Candida auris by Generating Oxidative Stress

Novel green synthetic nanomedicines have been recognized as alternative therapies with the potential to be antifungal agents. Apoptosis induction, cell cycle arrest and activation of the antioxidant defense system in fungal cells have also gained attention as emerging drug targets. In this study, a facile and biodegradable synthetic route was developed to prepare Ag-Fe bimetallic nanoparticles using aqueous extract of Beta vulgaris L. Surface plasmon resonance of Beta vulgaris-assisted AgNPs nanoparticles was not observed in the UV-visible region of Ag-Fe bimetallic NPs, which confirms the formation of Ag-Fe nanoparticles. Beta vulgaris-assisted Ag-Fe NPs were characterized by FTIR spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and TGA-DTG analysis for their structural and morphological properties. The as-prepared Ag-Fe NPs were well dispersed and spherical with the average particle size of 15 nm. The antifungal activity of these Ag-Fe NPs against clinical isolates of Candida auris was determined by broth microdilution and cell viability assays. For insights into mechanisms, induction of apoptosis and triggering cell cycle arrest were studied following standard protocols. Furthermore, analysis of antioxidant defense enzymes was determined spectrophotometrically. Antifungal susceptibility results revealed high antifungal activity with MIC values ranging from 0.19 to 0.39 µg/mL. Further studies showed that Ag-Fe NPs were able to induce apoptosis, cell cycle arrest in G2/M phase and disturbances in primary and secondary antioxidant enzymes. This study presents the potential of Ag-Fe NPs to inhibit and potentially eradicate C. auris by inducing apoptosis, cell cycle arrest and increased levels of oxidative stress.

Modulation of antioxidant defence system in response to berberine in Candida albicans

Emergence of multidrug resistant species of Candida is evolving, which advocates an urgent need for the development of new therapeutic strategies and antifungal drugs. Activation of antioxidant defence system in Candida albicans is known as forefront mechanism to escape drug toxicity. This study evaluated the role of antioxidant defence genes in the susceptibility to fluconazole in C. albicans and also determined the effect of berberine on growth, antioxidant enzymes and the expression of their genes in C. albicans isolates. Expression of major antioxidant genes was significantly increased in fluconazole-resistant isolates in comparison with the susceptible group. Antifungal susceptibility against berberine showed MIC values ranging from 125 to 500 μg/ml. Berberine treatment caused upregulation of mRNA expression and enzymatic activities of the targeted major antioxidants. Interestingly, C. albicans exhibited efficient antioxidant response at lower concentrations but could not sufficiently alleviate berberine-induced oxidative stress occurring at concentrations greater than 250 μg/ml. Therefore, berberine could serve as a potent Reactive Oxygen Species (ROS)-inducing agent, disrupting the antioxidant system especially in fluconazole-resistant C. albicans to overcome antifungal drug resistance. TAKE AWAYS: Evaluated the role of antioxidant enzymes in FLC resistance in C. albicans Studied the effect of berberine on growth of different C. albicans isolates Investigated the modulation of antioxidant enzymes by berberine in C. albicans Studied the effect of berberine on antioxidant gene expression in C. albicans.

Identification of Genomewide Alternative Splicing Events in Sequential, Isogenic Clinical Isolates of Candida albicans Reveals a Novel Mechanism of Drug Resistance and Tolerance to Cellular Stresses

The emergence of resistance in Candida albicans, an opportunistic pathogen, against the commonly used antifungals is becoming a major obstacle in its treatment. The necessity to identify new drug targets demands fundamental insights into the mechanisms used by this organism to develop drug resistance. C. albicans has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Using the RNA-sequencing data from isogenic pairs of azole-sensitive and -resistant isolates of C. albicans, here, we show how C. albicans uses modulations in mRNA splicing to overcome antifungal drug stress.

Alternative splicing (AS)—a process by which a single gene gives rise to different protein isoforms in eukaryotes—has been implicated in many basic cellular processes, but little is known about its role in drug resistance and fungal pathogenesis. The most common human fungal pathogen, Candida albicans, has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Here, we report AS regulating drug resistance in C. albicans. Comparative RNA-sequencing of two different sets of sequential, isogenic azole-sensitive and -resistant isolates of C. albicans revealed differential expression of splice isoforms of 14 genes. One of these was the superoxide dismutase gene SOD3, which contains a single intron. The sod3Δ/Δ mutant was susceptible to the antifungals amphotericin B (AMB) and menadione (MND). While AMB susceptibility was rescued by overexpression of both the spliced and unspliced SOD3 isoforms, only the spliced isoform could overcome MND susceptibility, demonstrating the functional relevance of this splicing in developing drug resistance. Furthermore, unlike AMB, MND inhibits SOD3 splicing and acts as a splicing inhibitor. Consistent with these observations, MND exposure resulted in increased levels of unspliced SOD3 isoform that are unable to scavenge reactive oxygen species (ROS), resulting in increased drug susceptibility. Collectively, these observations suggest that AS is a novel mechanism for stress adaptation and overcoming drug susceptibility in C. albicans.

IMPORTANCE The emergence of resistance in Candida albicans, an opportunistic pathogen, against the commonly used antifungals is becoming a major obstacle in its treatment. The necessity to identify new drug targets demands fundamental insights into the mechanisms used by this organism to develop drug resistance. C. albicans has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Using the RNA-sequencing data from isogenic pairs of azole-sensitive and -resistant isolates of C. albicans, here, we show how C. albicans uses modulations in mRNA splicing to overcome antifungal drug stress.

The Role of Secretory Pathways in Candida albicans Pathogenesis

Candida albicans is a fungus that is a commensal organism and a member of the normal human microbiota. It has the ability to transition into an opportunistic invasive pathogen. Attributes that support pathogenesis include secretion of virulence-associated proteins, hyphal formation, and biofilm formation. These processes are supported by secretion, as defined in the broad context of membrane trafficking. In this review, we examine the role of secretory pathways in Candida virulence, with a focus on the model opportunistic fungal pathogen, Candida albicans.

Mitogen activated protein kinase-1 and cell division control protein-42 are putative targets for the binding of novel natural lead molecules: a therapeutic intervention against Candida albicans

Candida albicans, fungal yeast causes several lethal infections in immune-suppressed patients and recently emerged as drug-resistant pathogens worldwide. The present study aimed to screen putative drug targets of Candia albicans and to study the binding potential of novel natural lead compounds towards these targets by computational virtual screening and molecular dynamic (MD) simulation. Through extensive analysis of mitogen-activated protein kinase (MAPK) signalling pathways, mitogen-activated protein kinase-1 (HOG1) and cell division control protein-42 (CDC42) genes were prioritized as putative targets based on their virulent functions. The three-dimensional structures of these genes, not available in their native forms, were computationally modeled and validated. 76 lead molecules from various natural sources were screened and their drug likeliness and pharmacokinetic features were predicted. Among these ligands, two lead molecules that demonstrated ideal drug-likeliness and pharmacokinetic features were docked against HOG1 and CDC42 and their binding potential was compared with the binding of conventional drug Fluconazole with their usual target. The prediction was computationally validated by MD simulation. The current study revealed that Cudraxanthone-S present in Cudrania cochinchinensis and Scutifoliamide-B present in Piper scutifolium exhibited ideal drug likeliness, pharmacokinetics and binding potential to the prioritized targets in comparison with the binding of Fluconazole and their usual target. MD simulation showed that CDC42-Cudraxanthone-S and HOG1-Scutifoliamide-B complexes were exhibited stability throughout MD simulation. Thus, the study provides significant insight into employing HOG1 and CDC42 of MAPK as putative drug targets of C. albicans and Cudraxanthone-S and Scutifoliamide-B as potential inhibitors for drug discovery.Communicated by Ramaswamy H. Sarma.