scholarly journals Regulation of the Hypoxic Response in Candida albicans

2010 ◽  
Vol 9 (11) ◽  
pp. 1734-1746 ◽  
Author(s):  
John M. Synnott ◽  
Alessandro Guida ◽  
Siobhan Mulhern-Haughey ◽  
Desmond G. Higgins ◽  
Geraldine Butler

ABSTRACT The regulation of the response of Candida albicans to hypoxic (low-oxygen) conditions is poorly understood. We used microarray and other transcriptional analyses to investigate the role of the Upc2 and Bcr1 transcription factors in controlling expression of genes involved in cell wall metabolism, ergosterol synthesis, and glycolysis during adaptation to hypoxia. Hypoxic induction of the ergosterol pathway is mimicked by treatment with sterol-lowering drugs (ketoconazole) and requires UPC2. Expression of three members of the family CFEM (common in several fungal extracellular membranes) of cell wall genes (RBT5, PGA7, and PGA10) is also induced by hypoxia and ketoconazole and requires both UPC2 and BCR1. Expression of glycolytic genes is induced by hypoxia but not by treatment with sterol-lowering drugs, whereas expression of respiratory pathway genes is repressed. However, Upc2 does not play a major role in regulating expression of genes required for central carbon metabolism. Our results indicate that regulation of gene expression in response to hypoxia in C. albicans is complex and is signaled both via lowered sterol levels and other unstudied mechanisms. We also show that induction of filamentation under hypoxic conditions requires the Ras1- and Cdc35-dependent pathway.

mBio ◽  
2018 ◽  
Vol 9 (6) ◽  
Author(s):  
Arnab Pradhan ◽  
Gabriela M. Avelar ◽  
Judith M. Bain ◽  
Delma S. Childers ◽  
Daniel E. Larcombe ◽  
...  

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.


2013 ◽  
Vol 57 (9) ◽  
pp. 4470-4480 ◽  
Author(s):  
Min Jung Kwun ◽  
Gabriela Novotna ◽  
Andrew R. Hesketh ◽  
Lionel Hill ◽  
Hee-Jeon Hong

ABSTRACTVanRS two-component regulatory systems are key elements required for the transcriptional activation of inducible vancomycin resistance genes in bacteria, but the precise nature of the ligand signal that activates these systems has remained undefined. Using the resistance system inStreptomyces coelicoloras a model, we have undertaken a series ofin vivostudies which indicate that the VanS sensor kinase in VanB-type resistance systems is activated by vancomycin in complex with thed-alanyl-d-alanine (d-Ala-d-Ala) termini of cell wall peptidoglycan (PG) precursors. Complementation of an essentiald-Ala-d-Ala ligase activity by constitutive expression ofvanAencoding a bifunctionald-Ala-d-Ala andd-alanyl-d-lactate (d-Ala-d-Lac) ligase activity allowed construction of strains that synthesized variable amounts of PG precursors containingd-Ala-d-Ala. Assays quantifying the expression of genes under VanRS control showed that the response to vancomycin in these strains correlated with the abundance ofd-Ala-d-Ala-containing PG precursors; strains producing a lower proportion of PG precursors terminating ind-Ala-d-Ala consistently exhibited a lower response to vancomycin. Pretreatment of wild-type cells with vancomycin or teicoplanin to saturate and mask thed-Ala-d-Ala binding sites in nascent PG also blocked the transcriptional response to subsequent vancomycin exposure, and desleucyl vancomycin, a vancomycin analogue incapable of interacting withd-Ala-d-Ala residues, failed to inducevangene expression. Activation of resistance by a vancomycin–d-Ala-d-Ala PG complex predicts a limit to the proportion of PG that can be derived from precursors terminating ind-Ala-d-Lac, a restriction also enforced by the bifunctional activity of the VanA ligase.


2014 ◽  
Vol 82 (10) ◽  
pp. 4405-4413 ◽  
Author(s):  
Sarah E. Davis ◽  
Alex Hopke ◽  
Steven C. Minkin ◽  
Anthony E. Montedonico ◽  
Robert T. Wheeler ◽  
...  

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.


2013 ◽  
Vol 13 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Frans M. Klis ◽  
Chris G. de Koster ◽  
Stanley Brul

ABSTRACTBionumbers and bioestimates are valuable tools in biological research. Here we focus on cell wall-related bionumbers and bioestimates of the budding yeastSaccharomyces cerevisiaeand the polymorphic, pathogenic fungusCandida albicans. We discuss the linear relationship between cell size and cell ploidy, the correlation between cell size and specific growth rate, the effect of turgor pressure on cell size, and the reason why using fixed cells for measuring cellular dimensions can result in serious underestimation ofin vivovalues. We further consider the evidence that individual buds and hyphae grow linearly and that exponential growth of the population results from regular formation of new daughter cells and regular hyphal branching. Our calculations show that hyphal growth allowsC. albicansto cover much larger distances per unit of time than the yeast mode of growth and that this is accompanied by strongly increased surface expansion rates. We therefore predict that the transcript levels of genes involved in wall formation increase during hyphal growth. Interestingly, wall proteins and polysaccharides seem barely, if at all, subject to turnover and replacement. A general lesson is how strongly most bionumbers and bioestimates depend on environmental conditions and genetic background, thus reemphasizing the importance of well-defined and carefully chosen culture conditions and experimental approaches. Finally, we propose that the numbers and estimates described here offer a solid starting point for similar studies of other cell compartments and other yeast species.


2010 ◽  
Vol 9 (9) ◽  
pp. 1329-1342 ◽  
Author(s):  
Claire A. Walker ◽  
Beatriz L. Gómez ◽  
Héctor M. Mora-Montes ◽  
Kevin S. Mackenzie ◽  
Carol A. Munro ◽  
...  

ABSTRACT The fungal pathogen Candida albicans produces dark-pigmented melanin after 3 to 4 days of incubation in medium containing l-3,4-dihydroxyphenylalanine (l-DOPA) as a substrate. Expression profiling of C. albicans revealed very few genes significantly up- or downregulated by growth in l-DOPA. We were unable to determine a possible role for melanin in the virulence of C. albicans. However, we showed that melanin was externalized from the fungal cells in the form of electron-dense melanosomes that were free or often loosely bound to the cell wall exterior. Melanin production was boosted by the addition of N-acetylglucosamine to the medium, indicating a possible association between melanin production and chitin synthesis. Melanin externalization was blocked in a mutant specifically disrupted in the chitin synthase-encoding gene CHS2. Melanosomes remained within the outermost cell wall layers in chs3Δ and chs2Δ chs3Δ mutants but were fully externalized in chs8Δ and chs2Δ chs8Δ mutants. All the CHS mutants synthesized dark pigment at equivalent rates from mixed membrane fractions in vitro, suggesting it was the form of chitin structure produced by the enzymes, not the enzymes themselves, that was involved in the melanin externalization process. Mutants with single and double disruptions of the chitinase genes CHT2 and CHT3 and the chitin pathway regulator ECM33 also showed impaired melanin externalization. We hypothesize that the chitin product of Chs3 forms a scaffold essential for normal externalization of melanosomes, while the Chs8 chitin product, probably produced in cell walls in greater quantity in the absence of CHS2, impedes externalization.


mSphere ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Anaïs Burgain ◽  
Faiza Tebbji ◽  
Inès Khemiri ◽  
Adnane Sellam

ABSTRACT Hypoxia is the predominant condition that the human opportunistic fungus Candida albicans encounters in the majority of the colonized niches within the host. So far, the impact of such a condition on the overall metabolism of this important human-pathogenic yeast has not been investigated. Here, we have undertaken a time-resolved metabolomics analysis to uncover the metabolic landscape of fungal cells experiencing hypoxia. Our data showed a dynamic reprogramming of many fundamental metabolic pathways, such as glycolysis, the pentose phosphate pathway, and different metabolic routes related to fungal cell wall biogenesis. The C. albicans lipidome was highly affected by oxygen depletion, with an increased level of free fatty acids and biochemical intermediates of membrane lipids, including phospholipids, lysophospholipids, sphingolipids, and mevalonate. The depletion of oxygen-dependent lipids such as ergosterol or phosphatidylcholine with longer and polyunsaturated lateral fatty acid chains was observed only at the later hypoxic time point (180 min). Transcriptomics data supported the main metabolic response to hypoxia when matched to our metabolomic profiles. The hypoxic metabolome reflected different physiological alterations of the cell wall and plasma membrane of C. albicans under an oxygen-limiting environment that were confirmed by different approaches. This study provided a framework for future in vivo investigations to examine relevant hypoxic metabolic trajectories in fungal virulence and fitness within the host. IMPORTANCE A critical aspect of cell fitness is the ability to sense and adapt to variations in oxygen levels in their local environment. Candida albicans is an opportunistic yeast that is the most prevalent human fungal pathogen. While hypoxia is the predominant condition that C. albicans encounters in most of its niches, its impact on fungal metabolism remains unexplored so far. Here, we provided a detailed landscape of the C. albicans metabolome that emphasized the importance of many metabolic routes for the adaptation of this yeast to oxygen depletion. The fungal hypoxic metabolome identified in this work provides a framework for future investigations to assess the contribution of relevant metabolic pathways in the fitness of C. albicans and other human eukaryotic pathogens with similar colonized human niches. As hypoxia is present at most of the fungal infection foci in the host, hypoxic metabolic pathways are thus an attractive target for antifungal therapy.


2010 ◽  
Vol 9 (3) ◽  
pp. 352-359 ◽  
Author(s):  
Clara M. Bien ◽  
Peter J. Espenshade

ABSTRACT Sterol regulatory element binding proteins (SREBPs) are membrane-bound transcription factors whose proteolytic activation is controlled by the cellular sterol concentration. Mammalian SREBPs are activated in cholesterol-depleted cells and serve to regulate cellular lipid homeostasis. Recent work demonstrates that SREBP is functionally conserved in fungi. While the ability to respond to sterols is conserved, fungal SREBPs are hypoxic transcription factors required for adaptation to a low-oxygen environment. In the fission yeast Schizosaccharomyces pombe, oxygen regulates the SREBP homolog Sre1 by independently controlling both its proteolytic activation and its degradation. SREBP is also required for adaptation to hypoxia in the human pathogens Cryptococcus neoformans and Aspergillus fumigatus. In these organisms, SREBP is required for virulence and resistance to antifungal drugs, making the SREBP pathway a potential target for antifungal therapy.


mBio ◽  
2019 ◽  
Vol 10 (5) ◽  
Author(s):  
Fabien Cottier ◽  
Sarah Sherrington ◽  
Sarah Cockerill ◽  
Valentina del Olmo Toledo ◽  
Stephen Kissane ◽  
...  

ABSTRACT Candida albicans is a commensal yeast of the human gut which is tolerated by the immune system but has the potential to become an opportunistic pathogen. One way in which C. albicans achieves this duality is through concealing or exposing cell wall pathogen-associated molecular patterns (PAMPs) in response to host-derived environment cues (pH, hypoxia, and lactate). This cell wall remodeling allows C. albicans to evade or hyperactivate the host’s innate immune responses, leading to disease. Previously, we showed that adaptation of C. albicans to acidic environments, conditions encountered during colonization of the female reproductive tract, induces significant cell wall remodeling resulting in the exposure of two key fungal PAMPs (β-glucan and chitin). Here, we report that this pH-dependent cell wall remodeling is time dependent, with the initial change in pH driving cell wall unmasking, which is then remasked at later time points. Remasking of β-glucan was mediated via the cell density-dependent fungal quorum sensing molecule farnesol, while chitin remasking was mediated via a small, heat-stable, nonproteinaceous secreted molecule(s). Transcript profiling identified a core set of 42 genes significantly regulated by pH over time and identified the transcription factor Efg1 as a regulator of chitin exposure through regulation of CHT2. This dynamic cell wall remodeling influenced innate immune recognition of C. albicans, suggesting that during infection, C. albicans can manipulate the host innate immune responses. IMPORTANCE Candida albicans is part of the microbiota of the skin and gastrointestinal and reproductive tracts of humans and has coevolved with us for millennia. During that period, C. albicans has developed strategies to modulate the host’s innate immune responses, by regulating the exposure of key epitopes on the fungal cell surface. Here, we report that exposing C. albicans to an acidic environment, similar to the one of the stomach or vagina, increases the detection of the yeast by macrophages. However, this effect is transitory, as C. albicans is able to remask these epitopes (glucan and chitin). We found that glucan remasking is controlled by the production of farnesol, a molecule secreted by C. albicans in response to high cell densities. However, chitin-remasking mechanisms remain to be identified. By understanding the relationship between environmental sensing and modulation of the host-pathogen interaction, new opportunities for the development of innovative antifungal strategies are possible.


mBio ◽  
2012 ◽  
Vol 3 (4) ◽  
Author(s):  
Matthew J. Reichlen ◽  
Venkata R. Vepachedu ◽  
Katsuhiko S. Murakami ◽  
James G. Ferry

ABSTRACT Results are presented supporting a regulatory role for the product of the MA3302 gene locus (designated MreA) previously annotated as a hypothetical protein in the methanogenic species Methanosarcina acetivorans of the domain Archaea. Sequence analysis of MreA revealed identity to the TrmB family of transcription factors, albeit the sequence is lacking the sensor domain analogous to TrmBL2, abundant in nonmethanogenic species of the domain Archaea. Transcription of mreA was highly upregulated during growth on acetate versus methylotrophic substrates, and an mreA deletion (ΔmreA) strain was impaired for growth with acetate in contrast to normal growth with methylotrophic substrates. Transcriptional profiling of acetate-grown cells identified 280 genes with altered expression in the ΔmreA strain versus the wild-type strain. Expression of genes unique to the acetate pathway decreased whereas expression of genes unique to methylotrophic metabolism increased in the ΔmreA strain relative to the wild type, results indicative of a dual role for MreA in either the direct or indirect activation of acetate-specific genes and repression of methylotrophic-specific genes. Gel shift experiments revealed specific binding of MreA to promoter regions of regulated genes. Homologs of MreA were identified in M. acetivorans and other Methanosarcina species for which expression patterns indicate roles in regulating methylotrophic pathways. IMPORTANCE Species in the domain Archaea utilize basal transcription machinery resembling that of the domain Eukarya, raising questions addressing the role of numerous putative transcription factors identified in sequenced archaeal genomes. Species in the genus Methanosarcina are ideally suited for investigating principles of archaeal transcription through analysis of the capacity to utilize a diversity of substrates for growth and methanogenesis. Methanosarcina species switch pathways in response to the most energetically favorable substrate, metabolizing methylotrophic substrates in preference to acetate marked by substantial regulation of gene expression. Although conversion of the methyl group of acetate accounts for most of the methane produced in Earth’s biosphere, no proteins involved in the regulation of genes in the acetate pathway have been reported. The results presented here establish that MreA participates in the global regulation of diverse methanogenic pathways in the genus Methanosarcina. Finally, the results contribute to a broader understanding of transcriptional regulation in the domain Archaea.


2015 ◽  
Vol 14 (6) ◽  
pp. 578-587 ◽  
Author(s):  
Zhiyun Guan ◽  
Haoping Liu

ABSTRACTNucleosome destabilization by histone variants and modifications has been implicated in the epigenetic regulation of gene expression, with the histone variant H2A.Z and acetylation of H3K56 (H3K56ac) being two examples. Here we find that deletion ofSWR1, the major subunit of the SWR1 complex depositing H2A.Z into chromatin in exchange for H2A, promotes epigenetic white-opaque switching inCandida albicans. We demonstrate through nucleosome mapping that SWR1 is required for proper nucleosome positioning on the promoter ofWOR1, the master regulator of switching, and that its effects differ in white and opaque cells. Furthermore, we find that H2A.Z is enriched adjacent to nucleosome-free regions at theWOR1promoter in white cells, suggesting a role in the stabilization of a repressive chromatin state. Deletion ofYNG2, a subunit of the NuA4 H4 histone acetyltransferase (HAT) that targets SWR1 activity through histone acetylation, produces a switching phenotype similar to that ofswr1, and both may act downstream of the GlcNAc signaling pathway. We further uncovered a genetic interaction betweenswr1and elevated H3K56ac with the discovery that theswr1deletion mutant is highly sensitive to nicotinamide. Our results suggest that the interaction of H2A.Z and H3K56ac regulates epigenetic switching at the nucleosome level, as well as having global effects.


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