Faculty Opinions recommendation of Multiple Alternative Carbon Pathways Combine To Promote Candida albicans Stress Resistance, Immune Interactions, and Virulence.

ABSTRACT The phagocytic cells of the innate immune system are an essential first line of antimicrobial defense, and yet Candida albicans, one of the most problematic fungal pathogens, is capable of resisting the stresses imposed by the macrophage phagosome, eventually resulting in the destruction of the phagocyte. C. albicans rapidly adapts to the phagosome by upregulating multiple alternative carbon utilization pathways, particularly those for amino acids, carboxylic acids, and N-acetylglucosamine (GlcNAc). Here, we report that C. albicans recognizes these carbon sources both as crucial nutrients and as independent signals in its environment. Even in the presence of glucose, each carbon source promotes increased resistance to a unique profile of stressors; lactate promotes increased resistance to osmotic and cell wall stresses, amino acids increased resistance to oxidative and nitrosative stresses, and GlcNAc increased resistance to oxidative stress and caspofungin, while all three alternative carbon sources have been shown to induce resistance to fluconazole. Moreover, we show mutants incapable of utilizing these carbon sources, in particular, strains engineered to be defective in all three pathways, are significantly attenuated in both macrophage and mouse models, with additive effects observed as multiple carbon pathways are eliminated, suggesting that C. albicans simultaneously utilizes multiple carbon sources within the macrophage phagosome and during disseminated candidiasis. Taking the data together, we propose that, in addition to providing energy to the pathogen within host environments, alternative carbon sources serve as niche-specific priming signals that allow C. albicans to recognize microenvironments within the host and to prepare for stresses associated with that niche, thus promoting host adaptation and virulence. IMPORTANCE Candida albicans is a fungal pathogen and a significant cause of morbidity and mortality, particularly in people with defects, sometimes minor ones, in innate immunity. The phagocytes of the innate immune system, particularly macrophages and neutrophils, generally restrict this organism to its normal commensal niches, but C. albicans shows a robust and multifaceted response to these cell types. Inside macrophages, a key component of this response is the activation of multiple pathways for the utilization of alternative carbon sources, particularly amino acids, carboxylic acids, and N-acetylglucosamine. These carbon sources are key sources of energy and biomass but also independently promote stress resistance, induce cell wall alterations, and affect C. albicans interactions with macrophages. Engineered strains incapable of utilizing these alternative carbon pathways are attenuated in infection models. These data suggest that C. albicans recognizes nutrient composition as an indicator of specific host environments and tailors its responses accordingly.

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Role of Retrograde Trafficking in Stress Response, Host Cell Interactions, and Virulence of Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00295-13 ◽

2013 ◽

Vol 13 (2) ◽

pp. 279-287 ◽

Cited By ~ 19

Author(s):

Yaoping Liu ◽

Norma V. Solis ◽

Clemens J. Heilmann ◽

Quynh T. Phan ◽

Aaron P. Mitchell ◽

...

Keyword(s):

Candida Albicans ◽

Host Cell ◽

Signaling Pathway ◽

Stress Resistance ◽

Cell Interactions ◽

Content Type ◽

Retrograde Trafficking ◽

Host Cell Interactions ◽

Vacuolar Protein ◽

Calcineurin Signaling

ABSTRACTInSaccharomyces cerevisiae, the vacuolar protein sorting complexes Vps51/52/53/54 and Vps15/30/34/38 are essential for efficient endosome-to-Golgi complex retrograde transport. Here we investigated the function of Vps15 and Vps51, representative members of these complexes, in the stress resistance, host cell interactions, and virulence ofCandida albicans. We found thatC. albicansvps15Δ/Δ andvps51Δ/Δ mutants had abnormal vacuolar morphology, impaired retrograde protein trafficking, and dramatically increased susceptibility to a variety of stressors. These mutants also had reduced capacity to invade and damage oral epithelial cellsin vitroand attenuated virulence in the mouse model of oropharyngeal candidiasis. Proteomic analysis of the cell wall of thevps51Δ/Δ mutant revealed increased levels of the Crh11 and Utr2 transglycosylases, which are targets of the calcineurin signaling pathway. The transcript levels of the calcineurin pathway membersCHR11,UTR2,CRZ1,CNA1, andCNA2were elevated in thevps15Δ/Δ andvps51Δ/Δ mutants. Furthermore, these strains were highly sensitive to the calcineurin-specific inhibitor FK506. Also, deletion ofCHR11andUTR2further increased the stress susceptibility of these mutants. In contrast, overexpression ofCRH11andUTR2partially rescued their defects in stress resistance, but not host cell interactions. Therefore, intact retrograde trafficking inC. albicansis essential for stress resistance, host cell interactions, and virulence. Aberrant retrograde trafficking stimulates the calcineurin signaling pathway, leading to the increased expression of Chr11 and Utr2, which enablesC. albicansto withstand environmental stress.

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Role for Endosomal and Vacuolar GTPases in Candida albicans Pathogenesis

Infection and Immunity ◽

10.1128/iai.01458-08 ◽

2009 ◽

Vol 77 (6) ◽

pp. 2343-2355 ◽

Cited By ~ 26

Author(s):

Douglas A. Johnston ◽

Karen E. Eberle ◽

Joy E. Sturtevant ◽

Glen E. Palmer

Keyword(s):

Candida Albicans ◽

Stress Resistance ◽

Double Mutant ◽

Hyphal Growth ◽

Filamentous Growth ◽

Rab Gtpases ◽

Fungal Cell ◽

Cellular Stresses ◽

Vacuole Biogenesis

ABSTRACT The vacuole has crucial roles in stress resistance and adaptation of the fungal cell. Furthermore, in Candida albicans it has been observed to undergo dramatic expansion during the initiation of hyphal growth, to produce highly “vacuolated” subapical compartments. We hypothesized that these functions may be crucial for survival within the host and tissue-invasive hyphal growth. We also considered the role of the late endosome or prevacuole compartment (PVC), a distinct organelle involved in vacuolar and endocytic trafficking. We identified two Rab GTPases, encoded by VPS21 and YPT72, required for trafficking through the PVC and vacuole biogenesis, respectively. Deletion of VPS21 or YPT72 led to mild sensitivities to some cellular stresses. However, deletion of both genes resulted in a synthetic phenotype with severe sensitivity to cellular stress and impaired growth. Both the vps21Δ and ypt72Δ mutants had defects in filamentous growth, while the double mutant was completely deficient in polarized growth. The defects in hyphal growth were not suppressed by an “active” RIM101 allele or loss of the hyphal repressor encoded by TUP1. In addition, both single mutants had significant attenuation in a mouse model of hematogenously disseminated candidiasis, while the double mutant was rapidly cleared. Histological examination confirmed that the vps21Δ and ypt72Δ mutants are deficient in hyphal growth in vivo. We suggest that the PVC and vacuole are required on two levels during C. albicans infection: (i) stress resistance functions required for survival within tissue and (ii) a role in filamentous growth which may aid host tissue invasion.

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Farnesol Induces Hydrogen Peroxide Resistance in Candida albicans Yeast by Inhibiting the Ras-Cyclic AMP Signaling Pathway

Eukaryotic Cell ◽

10.1128/ec.00321-09 ◽

2010 ◽

Vol 9 (4) ◽

pp. 569-577 ◽

Cited By ~ 66

Author(s):

Aurélie Deveau ◽

Amy E. Piispanen ◽

Angelyca A. Jackson ◽

Deborah A. Hogan

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Candida Albicans ◽

Adenylate Cyclase ◽

Signaling Pathway ◽

Stress Resistance ◽

Ros Generation ◽

Signaling Molecule ◽

Content Type ◽

Oxidative Stress Resistance

ABSTRACT Farnesol, a Candida albicans cell-cell signaling molecule that participates in the control of morphology, has an additional role in protection of the fungus against oxidative stress. In this report, we show that although farnesol induces the accumulation of intracellular reactive oxygen species (ROS), ROS generation is not necessary for the induction of catalase (Cat1)-mediated oxidative-stress resistance. Two antioxidants, α-tocopherol and, to a lesser extent, ascorbic acid effectively reduced intracellular ROS generation by farnesol but did not alter farnesol-induced oxidative-stress resistance. Farnesol inhibits the Ras1-adenylate cyclase (Cyr1) signaling pathway to achieve its effects on morphology under hypha-inducing conditions, and we demonstrate that farnesol induces oxidative-stress resistance by a similar mechanism. Strains lacking either Ras1 or Cyr1 no longer exhibited increased protection against hydrogen peroxide upon preincubation with farnesol. While we also observed the previously reported increase in the phosphorylation level of Hog1, a known regulator of oxidative-stress resistance, in the presence of farnesol, the hog1/hog1 mutant did not differ from wild-type strains in terms of farnesol-induced oxidative-stress resistance. Analysis of Hog1 levels and its phosphorylation states in different mutant backgrounds indicated that mutation of the components of the Ras1-adenylate cyclase pathway was sufficient to cause an increase of Hog1 phosphorylation even in the absence of farnesol or other exogenous sources of oxidative stress. This finding indicates the presence of unknown links between these signaling pathways. Our results suggest that farnesol effects on the Ras-adenylate cyclase cascade are responsible for many of the observed activities of this fungal signaling molecule.

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Phosphoric Metabolites Link Phosphate Import and Polysaccharide Biosynthesis for Candida albicans Cell Wall Maintenance

mBio ◽

10.1128/mbio.03225-19 ◽

2020 ◽

Vol 11 (2) ◽

Cited By ~ 3

Author(s):

Ning-Ning Liu ◽

Maikel Acosta-Zaldívar ◽

Wanjun Qi ◽

Joann Diray-Arce ◽

Louise A. Walker ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Stress Resistance ◽

Wall Stress ◽

Phosphate Starvation ◽

Nucleotide Sugar ◽

Content Type ◽

Cell Wall Stress ◽

Chitin Synthases ◽

Nucleotide Sugars

ABSTRACT The Candida albicans high-affinity phosphate transporter Pho84 is required for normal Target of Rapamycin (TOR) signaling, oxidative stress resistance, and virulence of this fungal pathogen. It also contributes to C. albicans’ tolerance of two antifungal drug classes, polyenes and echinocandins. Echinocandins inhibit biosynthesis of a major cell wall component, beta-1,3-glucan. Cells lacking Pho84 were hypersensitive to other forms of cell wall stress beyond echinocandin exposure, while their cell wall integrity signaling response was weak. Metabolomics experiments showed that levels of phosphoric intermediates, including nucleotides like ATP and nucleotide sugars, were low in pho84 mutant compared to wild-type cells recovering from phosphate starvation. Nonphosphoric precursors like nucleobases and nucleosides were elevated. Outer cell wall phosphomannan biosynthesis requires a nucleotide sugar, GDP-mannose. The nucleotide sugar UDP-glucose is the substrate of enzymes that synthesize two major structural cell wall polysaccharides, beta-1,3- and beta-1,6-glucan. Another nucleotide sugar, UDP-N-acetylglucosamine, is the substrate of chitin synthases which produce a stabilizing component of the intercellular septum and of lateral cell walls. Lack of Pho84 activity, and phosphate starvation, potentiated pharmacological or genetic perturbation of these enzymes. We posit that low substrate concentrations of beta-d-glucan- and chitin synthases, together with pharmacologic inhibition of their activity, diminish enzymatic reaction rates as well as the yield of their cell wall-stabilizing products. Phosphate import is not conserved between fungal and human cells, and humans do not synthesize beta-d-glucans or chitin. Hence, inhibiting these processes simultaneously could yield potent antifungal effects with low toxicity to humans. IMPORTANCE Candida species cause hundreds of thousands of invasive infections with high mortality each year. Developing novel antifungal agents is challenging due to the many similarities between fungal and human cells. Maintaining phosphate balance is essential for all organisms but is achieved completely differently by fungi and humans. A protein that imports phosphate into fungal cells, Pho84, is not present in humans and is required for normal cell wall stress resistance and cell wall integrity signaling in C. albicans. Nucleotide sugars, which are phosphate-containing building block molecules for construction of the cell wall, are diminished in cells lacking Pho84. Cell wall-constructing enzymes may be slowed by lack of these building blocks, in addition to being inhibited by drugs. Combined targeting of Pho84 and cell wall-constructing enzymes may provide a strategy for antifungal therapy by which two sequential steps of cell wall maintenance are blocked for greater potency.

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Effects of Disruption of PMC1 in the tfp1∆/∆ Mutant on Calcium Homeostasis, Oxidative and Osmotic Stress Resistance in Candida albicans

Mycopathologia ◽

10.1007/s11046-017-0216-7 ◽

2017 ◽

Vol 183 (2) ◽

pp. 315-327 ◽

Cited By ~ 3

Author(s):

Chang Jia ◽

Kai Zhang ◽

Dan Zhang ◽

Qilin Yu ◽

Chenpeng Xiao ◽

...

Keyword(s):

Candida Albicans ◽

Osmotic Stress ◽

Calcium Homeostasis ◽

Stress Resistance ◽

Osmotic Stress Resistance

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Redox Regulation, Rather than Stress-Induced Phosphorylation, of a Hog1 Mitogen-Activated Protein Kinase Modulates Its Nitrosative-Stress-Specific Outputs

mBio ◽

10.1128/mbio.02229-17 ◽

2018 ◽

Vol 9 (2) ◽

pp. e02229-17 ◽

Cited By ~ 15

Author(s):

Carmen Herrero-de-Dios ◽

Alison M. Day ◽

Anna T. Tillmann ◽

Stavroula L. Kastora ◽

David Stead ◽

...

Keyword(s):

Candida Albicans ◽

Map Kinase ◽

Protein Kinases ◽

Stress Resistance ◽

Map Kinases ◽

Nitrosative Stress ◽

Nuclear Accumulation ◽

Cysteine Residues ◽

Mitogen Activated Protein Kinases ◽

Mitogen Activated Protein

ABSTRACTIn all eukaryotic kingdoms, mitogen-activated protein kinases (MAPKs) play critical roles in cellular responses to environmental cues. These MAPKs are activated by phosphorylation at highly conserved threonine and tyrosine residues in response to specific inputs, leading to their accumulation in the nucleus and the activation of their downstream targets. A specific MAP kinase can regulate different downstream targets depending on the nature of the input signal, thereby raising a key question: what defines the stress-specific outputs of MAP kinases? We find that the Hog1 MAPK contributes to nitrosative-stress resistance inCandida albicanseven though it displays minimal stress-induced phosphorylation under these conditions. We show that Hog1 becomes oxidized in response to nitrosative stress, accumulates in the nucleus, and regulates the nitrosative stress-induced transcriptome. Mutation of specific cysteine residues revealed that C156 and C161 function together to promote stress resistance, Hog1-mediated nitrosative-stress-induced gene expression, resistance to phagocytic killing, andC. albicansvirulence. We propose that the oxidation of Hog1, rather than its phosphorylation, contributes to the nitrosative-stress-specific responses of this MAP kinase.IMPORTANCEMitogen-activated protein kinases play key roles in the responses of eukaryotic cells to extracellular signals and are critical for environmental-stress resistance. The widely accepted paradigm is that MAP kinases are activated by phosphorylation, which then triggers their nuclear accumulation and the activation of target proteins and genes that promote cellular adaptation. Our data suggest that alternative forms of posttranslational modification can modulate MAP kinase functionality inCandida albicans. We demonstrate that Hog1 is not significantly phosphorylated in response to nitrosative stress, yet it displays nuclear accumulation and contributes to the global transcriptional response to this stress, as well as promoting nitrosative-stress resistance. Instead, nitrosative stress triggers changes in the redox status of Hog1. We also show that specific Hog1 cysteine residues influence its activation of stress genes. Therefore, alternative posttranslational modifications appear to regulate the stress-specific outputs of MAP kinases.

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