Differential Roles of a Family of Flavodoxin-Like Proteins That Promote Resistance to Quinone Mediated Oxidative Stress in Candida albicans

Infection and Immunity ◽

10.1128/iai.00670-20 ◽

2021 ◽

Author(s):

Jenna E. Foderaro ◽

James B. Konopka

Keyword(s):

Oxidative Stress ◽

Candida Albicans ◽

Fungal Pathogen ◽

Constitutive Expression ◽

Mammalian Host ◽

Protein Levels ◽

Antioxidant Mechanism ◽

Semiquinone Radicals ◽

Tert Butyl Hydroperoxide ◽

Electron Reduction

Survival of the fungal pathogen Candida albicans within a mammalian host relies on its ability to resist oxidative stress. The four flavodoxin-like proteins (PstI, PstII, Pst3, and Ycp4) that reside on the inner surface of the C. albicans plasma membrane represent a recently discovered antioxidant mechanism that is essential for virulence. Flavodoxin-like proteins combat oxidative stress by promoting a two-electron reduction of quinone molecules, which prevents formation of toxic semiquinone radicals. Previous studies indicated that Pst3 played a major role in promoting resistance to the small quinone molecules p-benzoquinone and menadione. Analysis of additional quinones confirmed this role for Pst3. To better define their function, antibodies were raised against each of the four flavodoxin-like proteins and used to quantify protein levels. Interestingly, the basal level of flavodoxin-like proteins differed, with Pst3 and Ycp4 being the most abundant. However, after induction with p-benzoquinone, PstI and Pst3 were the most highly induced, resulting in Pst3 becoming the most abundant. Constitutive expression of the flavodoxin-like protein genes from a TDH3 promoter resulted in similar protein levels and showed that PstI and Pst3 were better at protecting C. albicans against p-benzoquinone than PstII or Ycp4. In contrast, PstI and Ycp4 provided better protection against oxidative damage induced by tert-butyl hydroperoxide. Thus, both the functional properties and the relative abundance contribute to the distinct roles of the flavodoxin-like proteins in resisting oxidative stress. These results further define how C. albicans combats the host immune response and survives in an environment rich in oxidative stress.

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The Role of MAPK Signal Transduction Pathways in the Response to Oxidative Stress in the Fungal Pathogen Candida albicans: Implications in Virulence

Current Protein and Peptide Science ◽

10.2174/138920310794557655 ◽

2010 ◽

Vol 11 (8) ◽

pp. 693-703 ◽

Cited By ~ 29

Author(s):

Carmen Herrero de Dios ◽

Elvira Roman ◽

Rebeca Alonso Monge ◽

Jesus Pla

Keyword(s):

Oxidative Stress ◽

Signal Transduction ◽

Candida Albicans ◽

Fungal Pathogen ◽

Signal Transduction Pathways

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Oxidative Stress Responses in the Human Fungal Pathogen, Candida albicans

Biomolecules ◽

10.3390/biom5010142 ◽

2015 ◽

Vol 5 (1) ◽

pp. 142-165 ◽

Cited By ~ 97

Author(s):

Alessandra Dantas ◽

Alison Day ◽

Mélanie Ikeh ◽

Iaroslava Kos ◽

Beatrice Achan ◽

...

Keyword(s):

Oxidative Stress ◽

Candida Albicans ◽

Stress Responses ◽

Fungal Pathogen ◽

Human Fungal Pathogen ◽

Oxidative Stress Responses

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High Resistance to Oxidative Stress in the Fungal Pathogen Candida glabrata Is Mediated by a Single Catalase, Cta1p, and Is Controlled by the Transcription Factors Yap1p, Skn7p, Msn2p, and Msn4p

Eukaryotic Cell ◽

10.1128/ec.00011-08 ◽

2008 ◽

Vol 7 (5) ◽

pp. 814-825 ◽

Cited By ~ 104

Author(s):

Mayra Cuéllar-Cruz ◽

Marcela Briones-Martin-del-Campo ◽

Israel Cañas-Villamar ◽

Javier Montalvo-Arredondo ◽

Lina Riego-Ruiz ◽

...

Keyword(s):

Oxidative Stress ◽

Saccharomyces Cerevisiae ◽

Candida Albicans ◽

Transcription Factors ◽

Adaptive Response ◽

Fungal Pathogen ◽

Candida Glabrata ◽

Systemic Infection ◽

Oxidative Stress Response

ABSTRACT We characterized the oxidative stress response of Candida glabrata to better understand the virulence of this fungal pathogen. C. glabrata could withstand higher concentrations of H2O2 than Saccharomyces cerevisiae and even Candida albicans. Stationary-phase cells were extremely resistant to oxidative stress, and this resistance was dependent on the concerted roles of stress-related transcription factors Yap1p, Skn7p, and Msn4p. We showed that growing cells of C. glabrata were able to adapt to high levels of H2O2 and that this adaptive response was dependent on Yap1p and Skn7p and partially on the general stress transcription factors Msn2p and Msn4p. C. glabrata has a single catalase gene, CTA1, which was absolutely required for resistance to H2O2 in vitro. However, in a mouse model of systemic infection, a strain lacking CTA1 showed no effect on virulence.

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Expression of CaPTC7 is developmentally regulated during serum-induced morphogenesis in the human fungal pathogen Candida albicans

Canadian Journal of Microbiology ◽

10.1139/w06-125 ◽

2007 ◽

Vol 53 (2) ◽

pp. 237-244 ◽

Cited By ~ 19

Author(s):

Jihong Wang ◽

Zhihui Yan ◽

Shi-Hsiang Shen ◽

Malcolm Whiteway ◽

Linghuo Jiang

Keyword(s):

Candida Albicans ◽

Fungal Pathogen ◽

Potential Role ◽

Terminal Sequence ◽

Developmentally Regulated ◽

Core Domain ◽

Protein Levels ◽

Human Fungal Pathogen ◽

C Terminus ◽

Affect Cell Viability

Type 2C protein phosphatases (PP2C) represent a diversified protein phosphatase family and play various roles in cells. We previously identified and characterized a novel PP2C phosphatase encoded by the CaPTC7 gene in the human fungal pathogen Candida albicans . The CaPtc7p has 365 amino acids with a PP2C core domain at the C terminus and an additional 116-residue N-terminal sequence containing a mitochondrion-targeting sequence. Here, we show that CaPtc7p is indeed localized in the mitochondrion, the only eukaryotic PP2C phosphatase that has been directly shown to reside in the mitochondrion, suggesting its potential role in the regulation of mitochondrial physiology. Furthermore, we show that the expression of CaPTC7 at both transcriptional and protein levels is developmentally regulated during the serum-induced morphogenesis of C. albicans cells. However, disruption of the two alleles of CaPTC7 does not affect cell viability or filamentous development in C. albicans.

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Robust Extracellular pH Modulation byCandida albicansduring Growth in Carboxylic Acids

mBio ◽

10.1128/mbio.01646-16 ◽

2016 ◽

Vol 7 (6) ◽

Cited By ~ 29

Author(s):

Heather A. Danhof ◽

Slavena Vylkova ◽

Elisa M. Vesely ◽

Amy E. Ford ◽

Manuel Gonzalez-Garay ◽

...

Keyword(s):

Transcription Factor ◽

Candida Albicans ◽

Amino Acid ◽

Carboxylic Acids ◽

Fungal Pathogen ◽

Mammalian Host ◽

Phagocytic Cells ◽

Acidic Environments ◽

In Cells

ABSTRACTThe opportunistic fungal pathogenCandida albicansthrives within diverse niches in the mammalian host. Among the adaptations that underlie this fitness is an ability to utilize a wide array of nutrients, especially sources of carbon that are disfavored by many other fungi; this contributes to its ability to survive interactions with the phagocytes that serve as key barriers against disseminated infections. We have reported thatC. albicansgenerates ammonia as a byproduct of amino acid catabolism to neutralize the acidic phagolysosome and promote hyphal morphogenesis in a manner dependent on the Stp2 transcription factor. Here, we report that this species rapidly neutralizes acidic environments when utilizing carboxylic acids like pyruvate, α-ketoglutarate (αKG), or lactate as the primary carbon source. Unlike in cells growing in amino acid-rich medium, this does not result in ammonia release, does not induce hyphal differentiation, and is genetically distinct. While transcript profiling revealed significant similarities in gene expression in cells grown on either carboxylic or amino acids, genetic screens for mutants that fail to neutralize αKG medium identified a nonoverlapping set of genes, includingCWT1, encoding a transcription factor responsive to cell wall and nitrosative stresses. Strains lackingCWT1exhibit retarded αKG-mediated neutralizationin vitro, exist in a more acidic phagolysosome, and are more susceptible to macrophage killing, while doublecwt1Δ stp2Δmutants are more impaired than either single mutant. Together, our observations indicate thatC. albicanshas evolved multiple ways to modulate the pH of host-relevant environments to promote its fitness as a pathogen.IMPORTANCEThe fungal pathogenCandida albicansis a ubiquitous and usually benign constituent of the human microbial ecosystem. In individuals with weakened immune systems, this organism can cause potentially life-threatening infections and is one of the most common causes of hospital-acquired infections. Understanding the interactions betweenC. albicansand immune phagocytic cells, such as macrophages and neutrophils, will define the mechanisms of pathogenesis in this species. One such adaptation is an ability to make use of nonstandard nutrients that we predict are plentiful in certain niches within the host, including within these phagocytic cells. We show here that the metabolism of certain organic acids enablesC. albicansto neutralize acidic environments, such as those within macrophages. This phenomenon is distinct in several significant ways from previous reports of similar processes, indicating thatC. albicanshas evolved multiple mechanisms to combat the harmful acidity of phagocytic cells.

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Niche-Specific Activation of the Oxidative Stress Response by the Pathogenic Fungus Candida albicans

Infection and Immunity ◽

10.1128/iai.01680-06 ◽

2007 ◽

Vol 75 (5) ◽

pp. 2143-2151 ◽

Cited By ~ 107

Author(s):

Brice Enjalbert ◽

Donna M. MacCallum ◽

Frank C. Odds ◽

Alistair J. P. Brown

Keyword(s):

Oxidative Stress ◽

Candida Albicans ◽

Stress Response ◽

Fluorescent Protein ◽

Ex Vivo ◽

Pathogenic Fungus ◽

Systemic Infection ◽

Oxidative Stress Response ◽

Mammalian Host ◽

Phagocytic Cells

ABSTRACT Candida albicans is a major opportunistic pathogen of humans. The pathogenicity of this fungus depends upon its ability to deal effectively with the host defenses and, in particular, the oxidative burst of phagocytic cells. We have explored the activation of the oxidative stress response in C. albicans in ex vivo infection models and during systemic infection of a mammalian host. We have generated C. albicans strains that contain specific green fluorescent protein (GFP) promoter fusions and hence act as biosensors of environmental oxidative stress at the single-cell level. Having confirmed that CTA1-, TRX1-, and TTR1/GRX2-GFP reporters respond specifically to oxidative stress, and not to heat shock, nitrosative, or osmotic stresses, we used these reporters to show that individual C. albicans cells activate an oxidative stress response following phagocytosis by neutrophils, but not by macrophages. Significantly, only a small proportion of C. albicans cells (about 4%) activated an oxidative stress response during systemic infection of the mouse kidney. The response of these cells was generally equivalent to exposure to 0.4 mM hydrogen peroxide in vitro. We conclude that most C. albicans cells are exposed to an oxidative stress when they come into contact with neutrophils in the bloodstream of the host but that oxidative killing is no longer a significant threat once an infection has been established in the kidney.

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The Sho1 Adaptor Protein Links Oxidative Stress to Morphogenesis and Cell Wall Biosynthesis in the Fungal Pathogen Candida albicans

Molecular and Cellular Biology ◽

10.1128/mcb.25.23.10611-10627.2005 ◽

2005 ◽

Vol 25 (23) ◽

pp. 10611-10627 ◽

Cited By ~ 123

Author(s):

Elvira Román ◽

César Nombela ◽

Jesús Pla

Keyword(s):

Oxidative Stress ◽

Cell Wall ◽

Candida Albicans ◽

Map Kinase ◽

Congo Red ◽

Fungal Pathogen ◽

Adaptor Protein ◽

Hog Pathway ◽

Pathogenic Yeast ◽

High Osmolarity

ABSTRACT The Sho1 adaptor protein is an important element of one of the two upstream branches of the high-osmolarity glycerol (HOG) mitogen-activated protein (MAP) kinase pathway in Saccharomyces cerevisiae, a signal transduction cascade involved in adaptation to stress. In the present work, we describe its role in the pathogenic yeast Candida albicans by the construction of mutants altered in this gene. We report here that sho1 mutants are sensitive to oxidative stress but that Sho1 has a minor role in the transmission of the phosphorylation signal to the Hog1 MAP kinase in response to oxidative stress, which mainly occurs through a putative Sln1-Ssk1 branch of the HOG pathway. Genetic analysis revealed that double ssk1 sho1 mutants were still able to grow on high-osmolarity media and activate Hog1 in response to this stress, indicating the existence of alternative inputs of the pathway. We also demonstrate that the Cek1 MAP kinase is constitutively active in hog1 and ssk1 mutants, a phenotypic trait that correlates with their resistance to the cell wall inhibitor Congo red, and that Sho1 is essential for the activation of the Cek1 MAP kinase under different conditions that require active cell growth and/or cell wall remodeling, such as the resumption of growth upon exit from the stationary phase. sho1 mutants are also sensitive to certain cell wall interfering compounds (Congo red, calcofluor white), presenting an altered cell wall structure (as shown by the ability to aggregate), and are defective in morphogenesis on different media, such as SLAD and Spider, that stimulate hyphal growth. These results reveal a role for the Sho1 protein in linking oxidative stress, cell wall biogenesis, and morphogenesis in this important human fungal pathogen.

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Inhibition of Classical and Alternative Modes of Respiration in Candida albicans Leads to Cell Wall Remodeling and Increased Macrophage Recognition

mBio ◽

10.1128/mbio.02535-18 ◽

2019 ◽

Vol 10 (1) ◽

pp. e02535-18 ◽

Cited By ~ 18

Author(s):

Lucian Duvenage ◽

Louise A. Walker ◽

Aleksandra Bojarczuk ◽

Simon A. Johnston ◽

Donna M. MacCallum ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Electron Transport ◽

Fungal Pathogen ◽

Fungal Infections ◽

Nitric Oxide Donor ◽

Mammalian Host ◽

Content Type ◽

Human Fungal Pathogen ◽

Cell Wall Remodeling

ABSTRACT The human fungal pathogen Candida albicans requires respiratory function for normal growth, morphogenesis, and virulence. Mitochondria therefore represent an enticing target for the development of new antifungal strategies. This possibility is bolstered by the presence of characteristics specific to fungi. However, respiration in C. albicans, as in many fungal organisms, is facilitated by redundant electron transport mechanisms, making direct inhibition a challenge. In addition, many chemicals known to target the electron transport chain are highly toxic. Here we made use of chemicals with low toxicity to efficiently inhibit respiration in C. albicans. We found that use of the nitric oxide donor sodium nitroprusside (SNP) and of the alternative oxidase inhibitor salicylhydroxamic acid (SHAM) prevents respiration and leads to a loss of viability and to cell wall rearrangements that increase the rate of uptake by macrophages in vitro and in vivo. We propose that treatment with SNP plus SHAM (SNP+SHAM) leads to transcriptional changes that drive cell wall rearrangement but which also prime cells to activate the transition to hyphal growth. In line with this, we found that pretreatment of C. albicans with SNP+SHAM led to an increase in virulence. Our data reveal strong links between respiration, cell wall remodeling, and activation of virulence factors. Our findings demonstrate that respiration in C. albicans can be efficiently inhibited with chemicals that are not damaging to the mammalian host but that we need to develop a deeper understanding of the roles of mitochondria in cellular signaling if they are to be developed successfully as a target for new antifungals. IMPORTANCE Current approaches to tackling fungal infections are limited, and new targets must be identified to protect against the emergence of resistant strains. We investigated the potential of targeting mitochondria, which are organelles required for energy production, growth, and virulence, in the human fungal pathogen Candida albicans. Our findings suggest that mitochondria can be targeted using drugs that can be tolerated by humans and that this treatment enhances their recognition by immune cells. However, release of C. albicans cells from respiratory inhibition appears to activate a stress response that increases the levels of traits associated with virulence. Our results make it clear that mitochondria represent a valid target for the development of antifungal strategies but that we must determine the mechanisms by which they regulate stress signaling and virulence ahead of successful therapeutic advance.

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