Deletion of the Candida albicans histidine kinase gene CHK1 improves recognition by phagocytes through an increased exposure of cell wall β-1,3-glucans

The pathogenic fungus Candida albicans is able to cover its most potent proinflammatory cell wall molecules, the β-glucans, underneath a dense mannan layer, so that the pathogen becomes partly invisible for immune cells such as phagocytes. As the C. albicans histidine kinases Chk1p, Cos1p and CaSln1p had been reported to be involved in virulence and cell wall biosynthesis, we investigated whether deletion of the respective genes influences the activity of phagocytes against C. albicans. We found that among all histidine kinase genes, CHK1 plays a prominent role in phagocyte activation. Uptake of the deletion mutant Δchk1 as well as the acidification of Δchk1-carrying phagosomes was significantly increased compared with the parental strain. These improved activities could be correlated with an enhanced accessibility of the mutant β-1,3-glucans for immunolabelling. In addition, any inhibition of β-1,3-glucan-mediated phagocytosis resulted in a reduced uptake of Δchk1, while ingestion of the parental strain was hardly affected. Moreover, deletion of CHK1 caused an enhanced release of interleukins 6 and 10, indicating a stronger activation of the β-1,3-glucan receptor dectin-1. In conclusion, the Chk1p protein is likely to be involved in masking β-1,3-glucans from immune recognition. As there are no homologues of fungal histidine kinases in mammals, Chk1p has to be considered as a promising target for new antifungal agents.

Download Full-text

Cell Wall-Related Bionumbers and Bioestimates of Saccharomyces cerevisiae and Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00250-13 ◽

2013 ◽

Vol 13 (1) ◽

pp. 2-9 ◽

Cited By ~ 58

Author(s):

Frans M. Klis ◽

Chris G. de Koster ◽

Stanley Brul

Keyword(s):

Saccharomyces Cerevisiae ◽

Cell Wall ◽

Candida Albicans ◽

Cell Size ◽

Pathogenic Fungus ◽

Turgor Pressure ◽

Hyphal Growth ◽

Biological Research ◽

Content Type ◽

Starting Point

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.

Download Full-text

Isolation of CaSLN1 and CaNIK1, the genes for osmosensing histidine kinase homologues, from the pathogenic fungus Candida albicans

Microbiology ◽

10.1099/00221287-144-2-425 ◽

1998 ◽

Vol 144 (2) ◽

pp. 425-432 ◽

Cited By ~ 109

Author(s):

S. Nagahashi ◽

T. Mio ◽

N. Ono ◽

T. Yamada-Okabe ◽

M. Arisawa ◽

...

Keyword(s):

Candida Albicans ◽

Histidine Kinase ◽

Pathogenic Fungus

Download Full-text

The Role of Dimorphism Regulating Histidine Kinase (Drk1) in the Pathogenic Fungus Paracoccidioides brasiliensis Cell Wall

Journal of Fungi ◽

10.3390/jof7121014 ◽

2021 ◽

Vol 7 (12) ◽

pp. 1014

Author(s):

Marina Valente Navarro ◽

Yasmin Nascimento de Barros ◽

Wilson Dias Segura ◽

Alison Felipe Alencar Chaves ◽

Grasielle Pereira Jannuzzi ◽

...

Keyword(s):

Cell Wall ◽

Histidine Kinase ◽

Mammalian Cells ◽

Paracoccidioides Brasiliensis ◽

Pathogenic Fungus ◽

Fungal Resistance ◽

Phagocytic Index ◽

Mammalian Host ◽

Control Group

Dimorphic fungi of the Paracoccidioides genus are the causative agents of paracoccidioidomycosis (PCM), an endemic disease in Latin America with a high incidence in Brazil. This pathogen presents as infective mycelium at 25 °C in the soil, reverting to its pathogenic form when inhaled by the mammalian host (37 °C). Among these dimorphic fungal species, dimorphism regulating histidine kinase (Drk1) plays an essential role in the morphological transition. These kinases are present in bacteria and fungi but absent in mammalian cells and are important virulence and cellular survival regulators. Hence, the purpose of this study was to investigate the role of PbDrk1 in the cell wall modulation of P. brasiliensis. We observed that PbDrk1 participates in fungal resistance to different cell wall-disturbing agents by reducing viability after treatment with iDrk1. To verify the role of PbDRK1 in cell wall morphogenesis, qPCR results showed that samples previously exposed to iDrk1 presented higher expression levels of several genes related to cell wall modulation. One of them was FKS1, a β-glucan synthase that showed a 3.6-fold increase. Furthermore, confocal microscopy analysis and flow cytometry showed higher β-glucan exposure on the cell surface of P. brasiliensis after incubation with iDrk1. Accordingly, through phagocytosis assays, a significantly higher phagocytic index was observed in yeasts treated with iDrk1 than the control group, demonstrating the role of PbDrk1 in cell wall modulation, which then becomes a relevant target to be investigated. In parallel, the immune response profile showed increased levels of proinflammatory cytokines. Finally, our data strongly suggest that PbDrk1 modulates cell wall component expression, among which we can identify β-glucan. Understanding this signalling pathway may be of great value for identifying targets of antifungal molecular activity since HKs are not present in mammals.

Download Full-text

Remasking of Candida albicans β-Glucan in Response to Environmental pH Is Regulated by Quorum Sensing

mBio ◽

10.1128/mbio.02347-19 ◽

2019 ◽

Vol 10 (5) ◽

Cited By ~ 7

Author(s):

Fabien Cottier ◽

Sarah Sherrington ◽

Sarah Cockerill ◽

Valentina del Olmo Toledo ◽

Stephen Kissane ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Quorum Sensing ◽

Immune Responses ◽

Female Reproductive Tract ◽

Innate Immune ◽

Immune Recognition ◽

Innate Immune Responses ◽

Content Type ◽

Cell Wall Remodeling

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.

Download Full-text

The Candida albicans histidine kinase Chk1p: Signaling and cell wall mannan

Fungal Genetics and Biology ◽

10.1016/j.fgb.2009.06.008 ◽

2009 ◽

Vol 46 (10) ◽

pp. 731-741 ◽

Cited By ~ 27

Author(s):

Dongmei Li ◽

David Williams ◽

Douglas Lowman ◽

Mario A. Monteiro ◽

Xuan Tan ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Histidine Kinase ◽

Cell Wall Mannan

Download Full-text

Deletions of the Endocytic Components VPS28 and VPS32 in Candida albicans Lead to Echinocandin and Azole Hypersensitivity

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00391-06 ◽

2006 ◽

Vol 50 (10) ◽

pp. 3492-3495 ◽

Cited By ~ 21

Author(s):

Muriel Cornet ◽

Claude Gaillardin ◽

Mathias L. Richard

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Signaling Pathways ◽

Antifungal Agents ◽

Cell Wall Disruption

ABSTRACT Vps28p and Vps32p act in both the endocytic and the pH signaling pathways in yeasts and are required for Candida albicans virulence. Here, we show that deletions of VPS28 and VPS32 increase the susceptibility of C. albicans to cell wall disruption agents, echinocandin and azole antifungal agents.

Download Full-text

Nanoscopic cell-wall architecture of an immunogenic ligand in Candida albicans during antifungal drug treatment

Molecular Biology of the Cell ◽

10.1091/mbc.e15-06-0355 ◽

2016 ◽

Vol 27 (6) ◽

pp. 1002-1014 ◽

Cited By ~ 19

Author(s):

Jia Lin ◽

Michael J. Wester ◽

Matthew S. Graus ◽

Keith A. Lidke ◽

Aaron K. Neumann

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Cell Walls ◽

Innate Immune ◽

Immune Recognition ◽

Cell Wall Polysaccharide ◽

Stochastic Optical Reconstruction Microscopy ◽

Before And After ◽

Antifungal Chemotherapy ◽

Optical Reconstruction

The cell wall of Candida albicans is composed largely of polysaccharides. Here we focus on β-glucan, an immunogenic cell-wall polysaccharide whose surface exposure is often restricted, or “masked,” from immune recognition by Dectin-1 on dendritic cells (DCs) and other innate immune cells. Previous research suggested that the physical presentation geometry of β-glucan might determine whether it can be recognized by Dectin-1. We used direct stochastic optical reconstruction microscopy to explore the fine structure of β-glucan exposed on C. albicans cell walls before and after treatment with the antimycotic drug caspofungin, which alters glucan exposure. Most surface-accessible glucan on C. albicans yeast and hyphae is limited to isolated Dectin-1–binding sites. Caspofungin-induced unmasking caused approximately fourfold to sevenfold increase in total glucan exposure, accompanied by increased phagocytosis efficiency of DCs for unmasked yeasts. Nanoscopic imaging of caspofungin-unmasked C. albicans cell walls revealed that the increase in glucan exposure is due to increased density of glucan exposures and increased multiglucan exposure sizes. These findings reveal that glucan exhibits significant nanostructure, which is a previously unknown physical component of the host– Candida interaction that might change during antifungal chemotherapy and affect innate immune activation.

Download Full-text

A role for the MAP kinase gene MKC1 in cell wall construction and morphological transitions in Candida albicans

Microbiology ◽

10.1099/00221287-144-2-411 ◽

1998 ◽

Vol 144 (2) ◽

pp. 411-424 ◽

Cited By ~ 102

Author(s):

F. Navarro-Garcia ◽

R. Alonso-Monge ◽

H. Rico ◽

J. Pla ◽

R. Sentandreu ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Map Kinase ◽

Kinase Gene ◽

Morphological Transitions ◽

Wall Construction

Download Full-text

The Ess1 Prolyl Isomerase Is Required for Growth and Morphogenetic Switching in Candida albicans

Genetics ◽

10.1093/genetics/160.1.37 ◽

2002 ◽

Vol 160 (1) ◽

pp. 37-48

Author(s):

Gina Devasahayam ◽

Vishnu Chaturvedi ◽

Steven D Hanes

Keyword(s):

Saccharomyces Cerevisiae ◽

Candida Albicans ◽

Rna Polymerase ◽

Rna Polymerase Ii ◽

Antifungal Agents ◽

Pathogenic Fungus ◽

Prolyl Isomerase

Abstract Prolyl-isomerases (PPIases) are found in all organisms and are important for the folding and activity of many proteins. Of the 13 PPIases in Saccharomyces cerevisiae only Ess1, a parvulin-class PPIase, is essential for growth. Ess1 is required to complete mitosis, and Ess1 and its mammalian homolog, Pin1, interact directly with RNA polymerase II. Here, we isolate the ESS1 gene from the pathogenic fungus Candida albicans and show that it is functionally homologous to the S. cerevisiae ESS1. We generate conditional-lethal (ts) alleles of C. albicans ESS1 and use these mutations to demonstrate that ESS1 is essential for growth in C. albicans. We also show that reducing the dosage or activity of ESS1 blocks morphogenetic switching from the yeast to the hyphal and pseudohyphal forms under certain conditions. Analysis of double mutants of ESS1 and TUP1 or CPH1, two genes known to be involved in morphogenetic switching, suggests that ESS1 functions in the same pathway as CPH1 and upstream of or in parallel to TUP1. Given that switching is important for virulence of C. albicans, inhibitors of Ess1 might be useful as antifungal agents.

Download Full-text