Inhibition of Respiration of Candida albicans by Small Molecules Increases Phagocytosis Efficacy by Macrophages

ABSTRACT Candida albicans adapts to various conditions in different body niches by regulating gene expression, protein synthesis, and metabolic pathways. These adaptive reactions not only allow survival but also influence the interaction with host cells, which is governed by the composition and structure of the fungal cell wall. Numerous studies had shown linkages between mitochondrial functionality, cell wall integrity and structure, and pathogenicity. Thus, we decided to inhibit single complexes of the respiratory chain of C. albicans and to analyze the resultant interaction with macrophages via their phagocytic activity. Remarkably, inhibition of the fungal bc1 complex by antimycin A increased phagocytosis, which correlated with an increased accessibility of β-glucans. To contribute to mechanistic insights, we performed metabolic studies, which highlighted significant changes in the abundance of constituents of the plasma membrane. Collectively, our results reinforce the strong linkage between fungal energy metabolism and other components of fungal physiology, which also determine the vulnerability to immune defense reactions. IMPORTANCE The yeast Candida albicans is one of the major fungal human pathogens, for which new therapeutic approaches are required. We aimed at enhancements of the phagocytosis efficacy of macrophages by targeting the cell wall structure of C. albicans, as the coverage of the β-glucan layer by mannans is one of the immune escape mechanisms of the fungus. We unambiguously show that inhibition of the fungal bc1 complex correlates with increased accessibilities of β-glucans and improved phagocytosis efficiency. Metabolic studies proved not only the known direct effects on reactive oxygen species (ROS) production and fermentative pathways but also the clear downregulation of the ergosterol pathway and upregulation of unsaturated fatty acids. The changed composition of the plasma membrane could also influence the interaction with the overlying cell wall. Thus, our work highlights the far-reaching relevance of energy metabolism, indirectly also for host-pathogen interactions, without affecting viability.

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The Candida albicans Sur7 Protein Is Needed for Proper Synthesis of the Fibrillar Component of the Cell Wall That Confers Strength

Eukaryotic Cell ◽

10.1128/ec.00167-10 ◽

2010 ◽

Vol 10 (1) ◽

pp. 72-80 ◽

Cited By ~ 30

Author(s):

Hong X. Wang ◽

Lois M. Douglas ◽

Vishukumar Aimanianda ◽

Jean-Paul Latgé ◽

James B. Konopka

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Plasma Membrane ◽

Wall Structure ◽

Cell Wall Synthesis ◽

Calcofluor White ◽

Content Type ◽

Membrane Compartment ◽

Fibrillar Component ◽

And Function

ABSTRACTTheCandida albicansplasma membrane plays important roles in interfacing with the environment, morphogenesis, and cell wall synthesis. The role of the Sur7 protein in cell wall structure and function was analyzed, since previous studies showed that this plasma membrane protein is needed to prevent abnormal intracellular growth of the cell wall. Sur7 localizes to stable patches in the plasma membrane, known as MCC (membrane compartment occupied by Can1), that are associated with eisosome proteins. Thesur7Δ mutant cells displayed increased sensitivity to factors that exacerbate cell wall defects, such as detergent (SDS) and the chitin-binding agents calcofluor white and Congo red. Thesur7Δ cells were also slightly more sensitive to inhibitors that block the synthesis of cell wall chitin (nikkomycin Z) and β-1,3-glucan (caspofungin). In contrast, Fmp45, a paralog of Sur7 that also localizes to punctate plasma membrane patches, did not have a detectable role in cell wall synthesis. Chemical analysis of cell wall composition demonstrated thatsur7Δ cells contain decreased levels of β-glucan, a glucose polymer that confers rigidity on the cell wall. Consistent with this,sur7Δ cells were more sensitive to lysis, which could be partially rescued by increasing the osmolarity of the medium. Interestingly, Sur7 is present in static patches, whereas β-1,3-glucan synthase is mobile in the plasma membrane and is often associated with actin patches. Thus, Sur7 may influence β-glucan synthesis indirectly, perhaps by altering the functions of the cell signaling components that localize to the MCC and eisosome domains.

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Mitochondrial Sorting and Assembly Machinery Subunit Sam37 in Candida albicans: Insight into the Roles of Mitochondria in Fitness, Cell Wall Integrity, and Virulence

Eukaryotic Cell ◽

10.1128/ec.05292-11 ◽

2012 ◽

Vol 11 (4) ◽

pp. 532-544 ◽

Cited By ~ 38

Author(s):

Yue Qu ◽

Branka Jelicic ◽

Filomena Pettolino ◽

Andrew Perry ◽

Tricia L. Lo ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Mitochondrial Function ◽

Drug Tolerance ◽

Cell Wall Integrity ◽

Mitochondrial Outer Membrane ◽

Wall Structure ◽

Content Type ◽

Mitochondrial Functions ◽

Insight Into

ABSTRACT Recent studies indicate that mitochondrial functions impinge on cell wall integrity, drug tolerance, and virulence of human fungal pathogens. However, the mechanistic aspects of these processes are poorly understood. We focused on the mitochondrial outer membrane SAM ( S orting and A ssembly M achinery) complex subunit Sam37 in Candida albicans . Inactivation of SAM37 in C. albicans leads to a large reduction in fitness, a phenotype not conserved with the model yeast Saccharomyces cerevisiae . Our data indicate that slow growth of the sam37ΔΔ mutant results from mitochondrial DNA loss, a new function for Sam37 in C. albicans , and from reduced activity of the essential SAM complex subunit Sam35. The sam37ΔΔ mutant was hypersensitive to drugs that target the cell wall and displayed altered cell wall structure, supporting a role for Sam37 in cell wall integrity in C. albicans . The sensitivity of the mutant to membrane-targeting antifungals was not significantly altered. The sam37ΔΔ mutant was avirulent in the mouse model, and bioinformatics showed that the fungal Sam37 proteins are distant from their animal counterparts and could thus represent potential drug targets. Our study provides the first direct evidence for a link between mitochondrial function and cell wall integrity in C. albicans and is further relevant for understanding mitochondrial function in fitness, antifungal drug tolerance, and virulence of this major pathogen. Beyond the relevance to fungal pathogenesis, this work also provides new insight into the mitochondrial and cellular roles of the SAM complex in fungi.

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Hypoxia Promotes Immune Evasion by Triggering β-Glucan Masking on theCandida albicansCell Surface via Mitochondrial and cAMP-Protein Kinase A Signaling

mBio ◽

10.1128/mbio.01318-18 ◽

2018 ◽

Vol 9 (6) ◽

Cited By ~ 38

Author(s):

Arnab Pradhan ◽

Gabriela M. Avelar ◽

Judith M. Bain ◽

Delma S. Childers ◽

Daniel E. Larcombe ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Protein Kinase ◽

Immune Evasion ◽

Fungal Pathogen ◽

Wall Structure ◽

Adaptation To Hypoxia ◽

Low Oxygen ◽

Content Type ◽

Kinase A

ABSTRACTOrganisms must adapt to changes in oxygen tension if they are to exploit the energetic benefits of reducing oxygen while minimizing the potentially damaging effects of oxidation. Consequently, organisms in all eukaryotic kingdoms display robust adaptation to hypoxia (low oxygen levels). This is particularly important for fungal pathogens that colonize hypoxic niches in the host. We show that adaptation to hypoxia in the major fungal pathogen of humansCandida albicansincludes changes in cell wall structure and reduced exposure, at the cell surface, of β-glucan, a key pathogen-associated molecular pattern (PAMP). This leads to reduced phagocytosis by murine bone marrow-derived macrophages and decreased production of IL-10, RANTES, and TNF-α by peripheral blood mononuclear cells, suggesting that hypoxia-induced β-glucan masking has a significant effect uponC. albicans-host interactions. We show that hypoxia-induced β-glucan masking is dependent upon both mitochondrial and cAMP-protein kinase A (PKA) signaling. The decrease in β-glucan exposure is blocked by mutations that affect mitochondrial functionality (goa1Δ andupc2Δ) or that decrease production of hydrogen peroxide in the inner membrane space (sod1Δ). Furthermore, β-glucan masking is enhanced by mutations that elevate mitochondrial reactive oxygen species (aox1Δ). The β-glucan masking defects displayed bygoa1Δ andupc2Δ cells are suppressed by exogenous dibutyryl-cAMP. Also, mutations that inactivate cAMP synthesis (cyr1Δ) or PKA (tpk1Δtpk2Δ) block the masking phenotype. Our data suggest thatC. albicansresponds to hypoxic niches by inducing β-glucan masking via a mitochondrial cAMP-PKA signaling pathway, thereby modulating local immune responses and promoting fungal colonization.IMPORTANCEAnimal, plant, and fungal cells occupy environments that impose changes in oxygen tension. Consequently, many species have evolved mechanisms that permit robust adaptation to these changes. The fungal pathogenCandida albicanscan colonize hypoxic (low oxygen) niches in its human host, such as the lower gastrointestinal tract and inflamed tissues, but to colonize its host, the fungus must also evade local immune defenses. We reveal, for the first time, a defined link between hypoxic adaptation and immune evasion inC. albicans. As this pathogen adapts to hypoxia, it undergoes changes in cell wall structure that include masking of β-glucan at its cell surface, and it becomes better able to evade phagocytosis by innate immune cells. We also define the signaling mechanisms that mediate hypoxia-induced β-glucan masking, showing that they are dependent on mitochondrial signaling and the cAMP-protein kinase pathway. Therefore, hypoxia appears to trigger immune evasion in this fungal pathogen.

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The MARVEL Domain Protein Nce102 Regulates Actin Organization and Invasive Growth of Candida albicans

mBio ◽

10.1128/mbio.00723-13 ◽

2013 ◽

Vol 4 (6) ◽

Cited By ~ 19

Author(s):

Lois M. Douglas ◽

Hong X. Wang ◽

James B. Konopka

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Plasma Membrane ◽

Virulence Factors ◽

Fungal Pathogen ◽

Invasive Growth ◽

Cell Wall Synthesis ◽

Content Type ◽

Actin Organization ◽

Domain Protein

ABSTRACTInvasive growth of the fungal pathogenCandida albicansinto tissues promotes disseminated infections in humans. The plasma membrane is essential for pathogenesis because this important barrier mediates morphogenesis and invasive growth, as well as secretion of virulence factors, cell wall synthesis, nutrient import, and other processes. Previous studies showed that the Sur7 tetraspan protein that localizes to MCC (membrane compartment occupied by Can1)/eisosome subdomains of the plasma membrane regulates a broad range of key functions, including cell wall synthesis, morphogenesis, and resistance to copper. Therefore, a distinct tetraspan protein found in MCC/eisosomes, Nce102, was investigated. Nce102 belongs to the MARVEL domain protein family, which is implicated in regulating membrane structure and function. Deletion ofNCE102did not cause the broad defects seen insur7Δcells. Instead, thence102Δmutant displayed a unique phenotype in that it was defective in forming hyphae and invading low concentrations of agar but could invade well in higher agar concentrations. This phenotype was likely due to a defect in actin organization that was observed by phalloidin staining. In support of this, the invasive growth defect of abni1Δmutant that mislocalizes actin due to lack of the Bni1 formin was also reversed at high agar concentrations. This suggests that a denser matrix provides a signal that compensates for the actin defects. Thence102Δmutant displayed decreased virulence and formed abnormal hyphae in mice. These studies identify novel ways that Nce102 and the physical environment surroundingC. albicansregulate morphogenesis and pathogenesis.IMPORTANCEThe plasma membrane promotes virulence of the human fungal pathogenCandida albicansby acting as a protective barrier around the cell and mediating dynamic activities, such as morphogenesis, cell wall synthesis, secretion of virulence factors, and nutrient uptake. To better understand how the plasma membrane contributes to virulence, we analyzed a set of eight genes encoding MARVEL family proteins that are predicted to function in membrane organization. Interestingly, deletion of one gene,NCE102, caused a strong defect in formation of invasive hyphal growthin vitroand decreased virulence in mice. Thence102Δmutant cells showed defects in actin organization that underlie the morphogenesis defect, since mutation of a known regulator of actin organization caused a similar defect. These studies identify a novel way in which the plasma membrane regulates the actin cytoskeleton and contributes to pathogenesis.

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Transcription Factor Efg1 Shows a Haploinsufficiency Phenotype in Modulating the Cell Wall Architecture and Immunogenicity of Candida albicans

Eukaryotic Cell ◽

10.1128/ec.05206-11 ◽

2011 ◽

Vol 11 (2) ◽

pp. 129-140 ◽

Cited By ~ 15

Author(s):

Martin Zavrel ◽

Olivia Majer ◽

Karl Kuchler ◽

Steffen Rupp

Keyword(s):

Cell Wall ◽

Transcription Factor ◽

Candida Albicans ◽

Structural Changes ◽

Protein Composition ◽

Surface Proteins ◽

Wall Structure ◽

Content Type ◽

Cell Wall Biogenesis ◽

General Metabolism

ABSTRACTTheCandida albicanstranscription factor Efg1 is known to be involved in many different cellular processes, including morphogenesis, general metabolism, and virulence. Here we show that besides its manifold roles, Efg1 also has a prominent effect on cell wall structure and composition, strongly affecting the structural glucan part. Deletion of only one allele ofEFG1already results in severe phenotypes for cell wall biogenesis, comparable to those with deletion of both alleles, indicative of a severe haploinsufficiency forEFG1. The observed defects in structural setup of the cell wall, together with previously reported alterations in expression of cell surface proteins, result in altered immunogenic properties of strains with compromised Efg1 function. This is shown by interaction studies with macrophages and primary dendritic cells. The structural changes in the cell wall carbohydrate meshwork presented here, together with the manifold changes in cell wall protein composition and metabolism reported in other studies, contribute to the altered immune response mounted by innate immune cells and to the altered virulence phenotypes observed for strains lackingEFG1.

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Sur7 Promotes Plasma Membrane Organization and Is Needed for Resistance to Stressful Conditions and to the Invasive Growth and Virulence of Candida albicans

mBio ◽

10.1128/mbio.00254-11 ◽

2011 ◽

Vol 3 (1) ◽

Cited By ~ 32

Author(s):

Lois M. Douglas ◽

Hong X. Wang ◽

Sabine Keppler-Ross ◽

Neta Dean ◽

James B. Konopka

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Plasma Membrane ◽

Fungal Pathogen ◽

Antifungal Drugs ◽

Membrane Organization ◽

Content Type ◽

Human Fungal Pathogen ◽

Membrane Compartment ◽

Systemic Infections

ABSTRACTThe human fungal pathogenCandida albicanscauses lethal systemic infections because of its ability to grow and disseminate in a host. TheC. albicansplasma membrane is essential for virulence by acting as a protective barrier and through its key roles in interfacing with the environment, secretion of virulence factors, morphogenesis, and cell wall synthesis. Difficulties in studying hydrophobic membranes have limited the understanding of how plasma membrane organization contributes to its function and to the actions of antifungal drugs. Therefore, the role of the recently discovered plasma membrane subdomains termed the membrane compartment containing Can1 (MCC) was analyzed by assessing the virulence of asur7Δ mutant. Sur7 is an integral membrane protein component of the MCC that is needed for proper localization of actin, morphogenesis, cell wall synthesis, and responding to cell wall stress. MCC domains are stable 300-nm-sized punctate patches that associate with a complex of cytoplasmic proteins known as an eisosome. Analysis of virulence-related properties of asur7Δ mutant revealed defects in intraphagosomal growth in macrophages that correlate with increased sensitivity to oxidation and copper. Thesur7Δ mutant was also strongly defective in pathogenesis in a mouse model of systemic candidiasis. The mutant cells showed a decreased ability to initiate an infection and greatly diminished invasive growth into kidney tissues. These studies on Sur7 demonstrate that the plasma membrane MCC domains are critical for virulence and represent an important new target for the development of novel therapeutic strategies.IMPORTANCECandida albicans, the most common human fungal pathogen, causes lethal systemic infections by growing and disseminating in a host. The plasma membrane plays key roles in enablingC. albicansto growin vivo, and it is also the target of the most commonly used antifungal drugs. However, plasma membrane organization is poorly understood because of the experimental difficulties in studying hydrophobic components. Interestingly, recent studies have identified a novel type of plasma membrane subdomain in fungi known as the membrane compartment containing Can1 (MCC). Cells lacking the MCC-localized protein Sur7 display broad defects in cellular organization and response to stressin vitro. Consistent with this,C. albicanscells lacking theSUR7gene were more susceptible to attack by macrophages than cells with the gene and showed greatly reduced virulence in a mouse model of systemic infection. Thus, Sur7 and other MCC components represent novel targets for antifungal therapy.

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Attachment of Enterohemorrhagic Escherichia coli to Host Cells Reduces O Antigen Chain Length at the Infection Site That Promotes Infection

mBio ◽

10.1128/mbio.02692-21 ◽

2021 ◽

Author(s):

Bin Liu ◽

Chengqian Qian ◽

Pan Wu ◽

Xiaodan Li ◽

Yutao Liu ◽

...

Keyword(s):

Escherichia Coli ◽

Cell Wall ◽

Infection Process ◽

Enterohemorrhagic Escherichia Coli ◽

Cell Wall Structure ◽

Host Cells ◽

Intestinal Lumen ◽

Wall Structure ◽

Content Type ◽

Enteropathogenic Bacteria

Little is known about the regulation of cell wall structure of enteropathogenic bacteria within the host. Here, we report that enterohemorrhagic Escherichia coli regulates its cell wall structure during the infection process, which balances its survival in the intestinal lumen and infection of intestinal epithelial cells.

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Faculty Opinions recommendation of Wood cell-wall structure requires local 2D-microtubule disassembly by a novel plasma membrane-anchored protein.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.4116957.3896055 ◽

2010 ◽

Author(s):

Clive Lloyd

Keyword(s):

Cell Wall ◽

Plasma Membrane ◽

Wood Cell Wall ◽

Cell Wall Structure ◽

Wall Structure

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Masking of β(1-3)-Glucan in the Cell Wall of Candida albicans from Detection by Innate Immune Cells Depends on Phosphatidylserine

Infection and Immunity ◽

10.1128/iai.01612-14 ◽

2014 ◽

Vol 82 (10) ◽

pp. 4405-4413 ◽

Cited By ~ 32

Author(s):

Sarah E. Davis ◽

Alex Hopke ◽

Steven C. Minkin ◽

Anthony E. Montedonico ◽

Robert T. Wheeler ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

De Novo ◽

Invasive Disease ◽

Innate Immune ◽

Dependent Manner ◽

Content Type ◽

Immune Effector ◽

Host Interactions ◽

Innate Immune Effector

ABSTRACTThe virulence ofCandida albicansin a mouse model of invasive candidiasis is dependent on the phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE). Disruption of the PS synthase geneCHO1(i.e.,cho1Δ/Δ) eliminates PS and blocks thede novopathway for PE biosynthesis. In addition, thecho1Δ/Δ mutant's ability to cause invasive disease is severely compromised. Thecho1Δ/Δ mutant also exhibits cell wall defects, and in this study, it was determined that loss of PS results in decreased masking of cell wall β(1-3)-glucan from the immune system. In wild-typeC. albicans, the outer mannan layer of the wall masks the inner layer of β(1-3)-glucan from exposure and detection by innate immune effector molecules like the C-type signaling lectin Dectin-1, which is found on macrophages, neutrophils, and dendritic cells. Thecho1Δ/Δ mutant exhibits increases in exposure of β(1-3)-glucan, which leads to greater binding by Dectin-1 in both yeast and hyphal forms. The unmasking of β(1-3)-glucan also results in increased elicitation of TNF-α from macrophages in a Dectin-1-dependent manner. The role of phospholipids in fungal pathogenesis is an emerging field, and this is the first study showing that loss of PS inC. albicansresults in decreased masking of β(1-3)-glucan, which may contribute to our understanding of fungus-host interactions.

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