scholarly journals Sterol-Response Pathways Mediate Alkaline Survival in Diverse Fungi

mBio ◽  
2020 ◽  
Vol 11 (3) ◽  
Author(s):  
Hannah E. Brown ◽  
Calla L. Telzrow ◽  
Joseph W. Saelens ◽  
Larissa Fernandes ◽  
J. Andrew Alspaugh
Keyword(s):  
Cryptococcus Neoformans ◽  
Fungal Pathogens ◽  
Fungal Infections ◽  
Membrane Integrity ◽  
Extracellular Ph ◽  
Alkaline Ph ◽  
Content Type ◽  
Alkaline Environment ◽  
Ph Response ◽  
The Impact

ABSTRACT The ability for cells to maintain homeostasis in the presence of extracellular stress is essential for their survival. Stress adaptations are especially important for microbial pathogens to respond to rapidly changing conditions, such as those encountered during the transition from the environment to the infected host. Many fungal pathogens have acquired the ability to quickly adapt to changes in extracellular pH to promote their survival in the various microenvironments encountered during a host infection. For example, the fungus-specific Rim/Pal alkaline response pathway has been well characterized in many fungal pathogens, including Cryptococcus neoformans. However, alternative mechanisms for sensing and responding to host pH have yet to be extensively studied. Recent observations from a genetic screen suggest that the C. neoformans sterol homeostasis pathway is required for growth at elevated pH. This work explores interactions among mechanisms of membrane homeostasis, alkaline pH tolerance, and Rim pathway activation. We find that the sterol homeostasis pathway is necessary for growth in an alkaline environment and that an elevated pH is sufficient to induce Sre1 activation. This pH-mediated activation of the Sre1 transcription factor is linked to the biosynthesis of ergosterol but is not dependent on Rim pathway signaling, suggesting that these two pathways are responding to alkaline pH independently. Furthermore, we discover that C. neoformans is more susceptible to membrane-targeting antifungals under alkaline conditions, highlighting the impact of microenvironmental pH on the treatment of invasive fungal infections. Together, these findings further connect membrane integrity and composition with the fungal pH response and pathogenesis. IMPORTANCE The work described here further elucidates how microorganisms sense and adapt to changes in their environment to establish infections in the human host. Specifically, we uncover a novel mechanism by which an opportunistic human fungal pathogen, Cryptococcus neoformans, responds to increases in extracellular pH in order to survive and thrive within the relatively alkaline environment of the human lung. This mechanism, which is intimately linked with fungal membrane sterol homeostasis, is independent of the previously well-studied alkaline response Rim pathway. Furthermore, this ergosterol-dependent alkaline pH response is present in Candida albicans, indicating that this mechanism spans diverse fungal species. These results are also relevant for novel antimicrobial drug development as we show that currently used ergosterol-targeting antifungals are more active in alkaline environments.

scholarly journals Sterol-response pathways mediate alkaline survival in diverse fungi

2020 ◽  
Author(s):  
Hannah E. Brown ◽  
Calla L. Telzrow ◽  
Joseph W. Saelens ◽  
Larissa Fernandes ◽  
J. Andrew Alspaugh
Keyword(s):  
Fungal Pathogens ◽  
Fungal Infections ◽  
Membrane Integrity ◽  
Microbial Pathogens ◽  
Alkaline Ph ◽  
Ph Response ◽  
Ph Tolerance ◽  
Alkaline Conditions ◽  
Host Infection ◽  
The Impact

AbstractThe ability for cells to maintain homeostasis in the presence of extracellular stress is essential for their survival. Stress adaptations are especially important for microbial pathogens to respond to rapidly changing conditions, such as those encountered during the transition from the environment to the infected host. Many fungal pathogens have acquired the ability to quickly adapt to changes in extracellular pH to promote their survival in the various micro-environments encountered during a host infection. For example, the fungal-specific Rim/Pal alkaline response pathway has been well characterized in many fungal pathogens, including Cryptococcus neoformans. However, alternative mechanisms for sensing and responding to host pH have yet to be extensively studied. Recent observations from a genetic screen suggest that the C. neoformans sterol homeostasis pathway is required for growth at elevated pH. This work explores interactions among mechanisms of membrane homeostasis, alkaline pH tolerance, and Rim pathway activation. We find that the sterol homeostasis pathway is necessary for growth in an alkaline environment, and that an elevated pH is sufficient to induce Sre1 activation. This pH-mediated activation of the Sre1 transcription factor is linked to the biosynthesis of ergosterol, but is not dependent on Rim pathway signaling, suggesting that these two pathways are responding to alkaline pH independently. Furthermore, we discover that C. neoformans is more susceptible to membrane-targeting antifungals in alkaline conditions highlighting the impact of micro-environmental pH on the treatment of invasive fungal infections. Together, these findings further connect membrane integrity and composition with the fungal pH response and pathogenesis.

scholarly journals Trends in Antifungal Drug Susceptibility of Cryptococcus neoformans Isolates Obtained through Population-Based Surveillance in South Africa in 2002-2003 and 2007-2008

2011 ◽  
Vol 55 (6) ◽  
pp. 2606-2611 ◽  
Author(s):  
Nelesh P. Govender ◽  
Jaymati Patel ◽  
Marelize van Wyk ◽  
Tom M. Chiller ◽  
Shawn R. Lockhart ◽  
...  
Keyword(s):  
South Africa ◽  
Cryptococcus Neoformans ◽  
Amphotericin B ◽  
Fungal Infections ◽  
Antifungal Susceptibility ◽  
Drug Susceptibility ◽  
Population Based ◽  
Content Type ◽  
Microdilution Method ◽  
Broth Microdilution Method

ABSTRACTCryptococcus neoformansis the most common cause of meningitis among adult South Africans with HIV infection/AIDS. Widespread use of fluconazole for treatment of cryptococcal meningitis and other HIV-associated opportunistic fungal infections in South Africa may lead to the emergence of isolates with reduced fluconazole susceptibility. MIC testing using a reference broth microdilution method was used to determine if isolates with reduced susceptibility to fluconazole or amphotericin B had emerged among cases of incident disease. Incident isolates were tested from two surveillance periods (2002-2003 and 2007-2008) when population-based surveillance was conducted in Gauteng Province, South Africa. These isolates were also tested for susceptibility to flucytosine, itraconazole, voriconazole, and posaconazole. Serially collected isolate pairs from cases at several large South African hospitals were also tested for susceptibility to fluconazole. Of the 487 incident isolates tested, only 3 (0.6%) demonstrated a fluconazole MIC of ≥16 μg/ml; all of these isolates were from 2002-2003. All incident isolates were inhibited by very low concentrations of amphotericin B and exhibited very low MICs to voriconazole and posaconazole. Of 67 cases with serially collected isolate pairs, only 1 case was detected where the isolate collected more than 30 days later had a fluconazole MIC value significantly higher than the MIC of the corresponding incident isolate. Although routine antifungal susceptibility testing of incident isolates is not currently recommended in clinical settings, it is still clearly important for public health to periodically monitor for the emergence of resistance.

scholarly journals Pleiotropic Roles of the Msi1-Like Protein Msl1 in Cryptococcus neoformans

2012 ◽  
Vol 11 (12) ◽  
pp. 1482-1495 ◽  
Author(s):  
Dong-Hoon Yang ◽  
Shinae Maeng ◽  
Anna K. Strain ◽  
Anna Floyd ◽  
Kirsten Nielsen ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Stress Responses ◽  
Fungal Pathogens ◽  
Independent Manner ◽  
Content Type ◽  
Antifungal Drug Resistance ◽  
Human Fungal Pathogen ◽  
Assembly Factor ◽  
Life Threatening ◽  
Stress Related Genes

ABSTRACT Msi1-like (MSIL) proteins contain WD40 motifs and have a pleiotropic cellular function as negative regulators of the Ras/cyclic AMP (cAMP) pathway and components of chromatin assembly factor 1 (CAF-1), yet they have not been studied in fungal pathogens. Here we identified and characterized an MSIL protein, Msl1, in Cryptococcus neoformans , which causes life-threatening meningoencephalitis in humans. Notably, Msl1 plays pleiotropic roles in C. neoformans in both cAMP-dependent and -independent manners largely independent of Ras. Msl1 negatively controls antioxidant melanin production and sexual differentiation, and this was repressed by the inhibition of the cAMP-signaling pathway. In contrast, Msl1 controls thermotolerance, diverse stress responses, and antifungal drug resistance in a Ras/cAMP-independent manner. Cac2, which is the second CAF-1 component, appears to play both redundant and distinct functions compared to the functions of Msl1. Msl1 is required for the full virulence of C. neoformans . Transcriptome analysis identified a group of Msl1-regulated genes, which include stress-related genes such as HSP12 and HSP78 . In conclusion, this study demonstrates pleiotropic roles of Msl1 in the human fungal pathogen C. neoformans , providing insight into a potential novel antifungal therapeutic target.

scholarly journals Lipids Affect the Cryptococcus neoformans-Macrophage Interaction and Promote Nonlytic Exocytosis

2017 ◽  
Vol 85 (12) ◽  
Author(s):  
Sabrina J. Nolan ◽  
Man Shun Fu ◽  
Isabelle Coppens ◽  
Arturo Casadevall
Keyword(s):  
Oleic Acid ◽  
Cryptococcus Neoformans ◽  
Lipid Droplets ◽  
Fungal Pathogens ◽  
Cellular Lipid ◽  
Content Type ◽  
Acid Supplementation

ABSTRACT Many microbes exploit host cellular lipid droplets during the host-microbe interaction, but this phenomenon has not been extensively studied for fungal pathogens. In this study, we analyzed the role of lipid droplets during the interaction of Cryptococcus neoformans with macrophages in the presence and the absence of exogenous lipids, in particular, oleate. The addition of oleic acid increased the frequency of lipid droplets in both C. neoformans and macrophages. C. neoformans responded to oleic acid supplementation by faster growth inside and outside macrophages. Fungal cells were able to harvest lipids from macrophage lipid droplets. Supplementation of C. neoformans and macrophages with oleic acid significantly increased the rate of nonlytic exocytosis while having no effect on lytic exocytosis. The process for lipid modulation of nonlytic exocytosis was associated with actin changes in macrophages. In summary, C. neoformans harvests lipids from macrophages, and the C. neoformans-macrophage interaction is modulated by exogenous lipids, providing a new tool for studying nonlytic exocytosis.

scholarly journals In Vitro Activity of a Novel Antifungal Compound, MYC-053, against Clinically Significant Antifungal-Resistant Strains of Candida glabrata, Candida auris, Cryptococcus neoformans, and Pneumocystis spp.

2019 ◽  
Vol 63 (4) ◽  
Author(s):  
G. Tetz ◽  
M. Collins ◽  
D. Vikina ◽  
V. Tetz
Keyword(s):  
Cryptococcus Neoformans ◽  
Candida Glabrata ◽  
Fungal Infections ◽  
Antifungal Compound ◽  
Candida Auris ◽  
Content Type ◽  
Treatment And Prevention ◽  
Resistant Strains ◽  
Clinically Significant

ABSTRACT An urgent need exists for new antifungal compounds to treat fungal infections in immunocompromised patients. The aim of the current study was to investigate the potency of a novel antifungal compound, MYC-053, against the emerging yeast and yeast-like pathogens Candida glabrata, Candida auris, Cryptococcus neoformans, and Pneumocystis species. MYC-053 was equally effective against the susceptible control strains, clinical isolates, and resistant strains, with MICs of 0.125 to 4.0 μg/ml. Notably, unlike other antifungals such as azoles, polyenes, and echinocandins, MYC-053 was effective against Pneumocystis isolates, therefore being the only synthetic antifungal that may potentially be used against Pneumocystis spp., Candida spp., and Cryptococcus spp. MYC-053 was highly effective against preformed 48-h-old C. glabrata and C. neoformans biofilms, with minimal biofilm eradication concentrations equal to 1 to 4 times the MIC. Together, these data indicated that MYC-053 may be developed into a promising antifungal agent for the treatment and prevention of invasive fungal infections caused by yeasts and yeast-like fungi.

scholarly journals Efficacy of Oral Encochleated Amphotericin B in a Mouse Model of Cryptococcal Meningoencephalitis

mBio ◽  
2019 ◽  
Vol 10 (3) ◽  
Author(s):  
R. Lu ◽  
C. Hollingsworth ◽  
J. Qiu ◽  
A. Wang ◽  
E. Hughes ◽  
...  
Keyword(s):  
Mouse Model ◽  
Cryptococcus Neoformans ◽  
Amphotericin B ◽  
Oral Absorption ◽  
Oral Formulation ◽  
Significant Saving ◽  
Content Type ◽  
Cryptococcal Meningoencephalitis ◽  
Cryptococcal Disease ◽  
The Impact

ABSTRACT Cryptococcus neoformans is an encapsulated yeast responsible for approximately a quarter of a million deaths worldwide annually despite therapy, and upwards of 11% of HIV/AIDS-related deaths, rivaling the impact of tuberculosis and malaria. However, the most effective antifungal agent, amphotericin B, requires intravenous delivery and has significant renal and hematopoietic toxicity, making it difficult to utilize, especially in resource-limited settings. The present studies describe a new nanoparticle crystal encapsulated formulation of amphotericin B known as encochleated amphotericin B (CAmB) that seeks to provide an oral formulation that is low in toxicity and cost. Using a 3-day delayed model of murine cryptococcal meningoencephalitis and a large inoculum of a highly virulent strain of serotype A C. neoformans, CAmB, in combination with flucytosine, was found to have efficacy equivalent to parental amphotericin B deoxycholate with flucytosine and superior to oral fluconazole without untoward toxicity. Transport of fluorescent CAmB particles to brain as well as significant brain levels of amphotericin drug was demonstrated in treated mice, and immunological profiles were similar to those of mice treated with conventional amphotericin B. Additional toxicity studies using a standardized rat model showed negligible toxicity after a 28-day treatment schedule. These studies thus offer the potential for an efficacious oral formulation of a known fungicidal drug against intrathecal cryptococcal disease. IMPORTANCE Cryptococcus neoformans is a significant global fungal pathogen that kills an estimated quarter of a million HIV-infected individuals yearly and has poor outcomes despite therapy. The most effective therapy, amphotericin B, is highly effective in killing the fungus but is available only in highly toxic, intravenous formulations that are unavailable in most of the developing world, where cryptococcal disease in most prevalent. For example, in Ethiopia, reliance on the orally available antifungal fluconazole results in high mortality, even when initiated as preemptive therapy at the time of HIV diagnosis. Thus, alternative agents could result in significant saving of lives. Toward this end, the present work describes the development of a new formulation of amphotericin B (CAmB) that encapsulates the drug as a crystal lipid nanoparticle that facilitates oral absorption and prevents toxicity. Successful oral absorption of the drug was demonstrated in a mouse model that, in combination with the antifungal flucytosine, provided efficacy equal to a parental preparation of amphotericin B plus flucytosine. These studies demonstrate the potential for CAmB in combination with flucytosine to provide an effective oral formulation of a well-known, potent fungicidal drug combination.

scholarly journals Structures of Pathogenic Fungal FKBP12s Reveal Possible Self-Catalysis Function

mBio ◽  
2016 ◽  
Vol 7 (2) ◽  
Author(s):  
Nam K. Tonthat ◽  
Praveen Rao Juvvadi ◽  
Hengshan Zhang ◽  
Soo Chan Lee ◽  
Ron Venters ◽  
...  
Keyword(s):  
Active Site ◽  
Fungal Pathogens ◽  
Active Sites ◽  
Fungal Infections ◽  
Cellular Protein ◽  
Prolyl Isomerase ◽  
Peptidyl Prolyl Isomerase ◽  
Deep Insertion ◽  
The Impact

ABSTRACT Invasive fungal infections remain difficult to treat and require novel targeting strategies. The 12-kDa FK506-binding protein (FKBP12) is a ubiquitously expressed peptidyl-prolyl isomerase with considerable homology between fungal pathogens and is thus a prime candidate for future targeting efforts to generate a panfungal strategy. Despite decades of research on FKBPs, their substrates and mechanisms of action remain unclear. Here we describe structural, biochemical, and in vivo analyses of FKBP12s from the pathogenic fungi Candida albicans , Candida glabrata , and Aspergillus fumigatus . Strikingly, multiple apo A. fumigatus and C. albicans FKBP12 crystal structures revealed a symmetric, intermolecular interaction involving the deep insertion of an active-site loop proline into the active-site pocket of an adjacent subunit. Such interactions have not been observed in previous FKBP structures. This finding indicates the possibility that this is a self-substrate interaction unique to the A. fumigatus and C. albicans fungal proteins that contain this central proline. Structures obtained with the proline in the cis and trans states provide more data in support of self-catalysis. Moreover, cysteine cross-linking experiments captured the interacting dimer, supporting the idea that it forms in solution. Finally, genetic studies exploring the impact of mutations altering the central proline and an adjacent residue provide evidence that any dimeric state formed in vivo , where FKBP12 concentrations are low, is transient. Taken together, these findings suggest a unique mechanism of self-substrate regulation by fungal FKBP12s, lending further novel understanding of this protein for future drug-targeting efforts. IMPORTANCE FKBP12 is a cis-trans peptidyl-prolyl isomerase that plays key roles in cellular protein homeostasis. FKBP12s also bind the immunosuppressive drug FK506 to inhibit the phosphatase calcineurin (CaN). CaN is required for virulence of A. fumigatus , C. albicans , C. glabrata , and other deadly fungal pathogens, marking FKBP12 and CaN as potential broad-spectrum drug targets. Here we describe structures of fungal FKBP12s. Multiple apo A. fumigatus and C. albicans FKBP12 structures reveal the insertion of a proline, conspicuously conserved in these proteins, into the active sites of adjacent molecules. This suggests that these proteins might serve as their own substrates. Cysteine disulfide trapping experiments provide support for this self-interaction and hence possible intermolecular catalysis by these enzymes.

scholarly journals The Mechanisms of Mating in Pathogenic Fungi—A Plastic Trait

Genes ◽  
2019 ◽  
Vol 10 (10) ◽  
pp. 831
Author(s):  
Jane Usher
Keyword(s):  
Fungal Pathogens ◽  
Crop Yields ◽  
Fungal Infections ◽  
Pathogenic Fungi ◽  
Yeast Saccharomyces Cerevisiae ◽  
Closely Related Species ◽  
Sexual And Asexual Reproduction ◽  
Target Dna ◽  
High Degree ◽  
The Impact

The impact of fungi on human and plant health is an ever-increasing issue. Recent studies have estimated that human fungal infections result in an excess of one million deaths per year and plant fungal infections resulting in the loss of crop yields worth approximately 200 million per annum. Sexual reproduction in these economically important fungi has evolved in response to the environmental stresses encountered by the pathogens as a method to target DNA damage. Meiosis is integral to this process, through increasing diversity through recombination. Mating and meiosis have been extensively studied in the model yeast Saccharomyces cerevisiae, highlighting that these mechanisms have diverged even between apparently closely related species. To further examine this, this review will inspect these mechanisms in emerging important fungal pathogens, such as Candida, Aspergillus, and Cryptococcus. It shows that both sexual and asexual reproduction in these fungi demonstrate a high degree of plasticity.

scholarly journals Peroxisomal and Mitochondrial β-Oxidation Pathways Influence the Virulence of the Pathogenic Fungus Cryptococcus neoformans

2012 ◽  
Vol 11 (8) ◽  
pp. 1042-1054 ◽  
Author(s):  
Matthias Kretschmer ◽  
Joyce Wang ◽  
James W. Kronstad
Keyword(s):  
Carbon Source ◽  
Cryptococcus Neoformans ◽  
Virulence Factor ◽  
Fungal Pathogens ◽  
Pathogenic Fungus ◽  
Subsequent Work ◽  
Content Type ◽  
Capsule Production ◽  
Human Pathogenic Fungus ◽  
Host Tissues

ABSTRACTAn understanding of the connections between metabolism and elaboration of virulence factors during host colonization by the human-pathogenic fungusCryptococcus neoformansis important for developing antifungal therapies. Lipids are abundant in host tissues, and fungal pathogens in the phylum basidiomycota possess both peroxisomal and mitochondrial β-oxidation pathways to utilize this potential carbon source. In addition, lipids are important signaling molecules in both fungi and mammals. In this report, we demonstrate that defects in the peroxisomal and mitochondrial β-oxidation pathways influence the growth ofC. neoformanson fatty acids as well as the virulence of the fungus in a mouse inhalation model of cryptococcosis. Disease attenuation may be due to the cumulative influence of altered carbon source acquisition or processing, interference with secretion, changes in cell wall integrity, and an observed defect in capsule production for the peroxisomal mutant. Altered capsule elaboration in the context of a β-oxidation defect was unexpected but is particularly important because this trait is a major virulence factor forC. neoformans. Additionally, analysis of mutants in the peroxisomal pathway revealed a growth-promoting activity forC. neoformans, and subsequent work identified oleic acid and biotin as candidates for such factors. Overall, this study reveals that β-oxidation influences virulence inC. neoformansby multiple mechanisms that likely include contributions to carbon source acquisition and virulence factor elaboration.

scholarly journals The F-Box Protein Fbp1 Regulates Sexual Reproduction and Virulence in Cryptococcus neoformans

2011 ◽  
Vol 10 (6) ◽  
pp. 791-802 ◽  
Author(s):  
Tong-Bao Liu ◽  
Yina Wang ◽  
Sabriya Stukes ◽  
Qing Chen ◽  
Arturo Casadevall ◽  
...  
Keyword(s):  
Sexual Reproduction ◽  
Cryptococcus Neoformans ◽  
Stress Responses ◽  
Membrane Integrity ◽  
Infection Model ◽  
Calcofluor White ◽  
Fungal Virulence ◽  
Content Type ◽  
F Box Protein

ABSTRACTCryptococcus neoformansis the leading cause of fungal meningitis in immunocomprised populations. Although extensive studies have been conducted on signal transduction pathways important for fungal sexual reproduction and virulence, how fungal virulence is regulated during infection is still not understood. In this study, we identified the F-box protein Fbp1, which contains a putative F-box domain and 12 leucine-rich repeats (LRR). Althoughfbp1mutants showed normal growth and produced normal major virulence factors, such as melanin and capsule, Fbp1 was found to be essential for fungal virulence, asfbp1mutants were avirulent in a murine systemic-infection model. Fbp1 is also important for fungal sexual reproduction. Basidiospore production was blocked in bilateral mating betweenfbp1mutants, even though normal dikaryotic hyphae were observed during mating.In vitroassays of stress responses revealed thatfbp1mutants are hypersensitive to SDS, but not calcofluor white (CFW) or Congo red, indicating that Fbp1 may regulate cell membrane integrity. Fbp1 physically interacts with Skp1 homologues in bothSaccharomyces cerevisiaeandC. neoformansvia its F-box domain, suggesting it may function as part of an SCF (Skp1, Cullins, F-box proteins) E3 ligase. Overall, our study revealed that the F-box protein Fbp1 is essential for fungal sporulation and virulence inC. neoformans, which likely represents a conserved novel virulence control mechanism that involves the SCF E3 ubiquitin ligase-mediated proteolysis pathway.

Sign in / Sign up

Export Citation Format

Share Document