scholarly journals Novel Biological Functions of the NsdC Transcription Factor in Aspergillus fumigatus

mBio ◽  
2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Patrícia Alves de Castro ◽  
Clara Valero ◽  
Jéssica Chiaratto ◽  
Ana Cristina Colabardini ◽  
Lakhansing Pardeshi ◽  
...  
Keyword(s):  
Cell Wall ◽  
Transcription Factor ◽  
Aspergillus Fumigatus ◽  
Sexual Reproduction ◽  
Rna Polymerase Ii ◽  
Vegetative Growth ◽  
Wall Structure ◽  
Immune Recognition ◽  
Biological Functions ◽  
Content Type

ABSTRACT The fungal zinc finger transcription factor NsdC is named after, and is best known for, its essential role in sexual reproduction (never in sexual development). In previous studies with Aspergillus nidulans, it was also shown to have roles in promotion of vegetative growth and suppression of asexual conidiation. In this study, the function of the nsdC homologue in the opportunistic human pathogen A. fumigatus was investigated. NsdC was again found to be essential for sexual development, with deletion of the nsdC gene in both MAT1-1 and MAT1-2 mating partners of a cross leading to complete loss of fertility. However, a functional copy of nsdC in one mating partner was sufficient to allow sexual reproduction. Deletion of nsdC also led to decreased vegetative growth and allowed conidiation in liquid cultures, again consistent with previous findings. However, NsdC in A. fumigatus was shown to have additional biological functions including response to calcium stress, correct organization of cell wall structure, and response to the cell wall stressors. Furthermore, virulence and host immune recognition were affected. Gene expression studies involving chromatin immunoprecipitation (ChIP) of RNA polymerase II (PolII) coupled to next-generation sequencing (Seq) revealed that deletion of nsdC resulted in changes in expression of over 620 genes under basal growth conditions. This demonstrated that this transcription factor mediates the activity of a wide variety of signaling and metabolic pathways and indicates that despite the naming of the gene, the promotion of sexual reproduction is just one among multiple roles of NsdC. IMPORTANCE Aspergillus fumigatus is an opportunistic human fungal pathogen and the main causal agent of invasive aspergillosis, a life-threatening infection especially in immunocompromised patients. A. fumigatus can undergo both asexual and sexual reproductive cycles, and the regulation of both cycles involves several genes and pathways. Here, we have characterized one of these genetic determinants, the NsdC transcription factor, which was initially identified in a screen of transcription factor null mutants showing sensitivity when exposed to high concentrations of calcium. In addition to its known essential roles in sexual reproduction and control of growth rate and asexual reproduction, we have shown in the present study that A. fumigatus NsdC transcription factor has additional previously unrecognized biological functions including calcium tolerance, cell wall stress response, and correct cell wall organization and functions in virulence and host immune recognition. Our results indicate that NsdC can play novel additional biological functions not directly related to its role played during sexual and asexual processes.

scholarly journals The Transcription Factor SomA Synchronously Regulates Biofilm Formation and Cell Wall Homeostasis in Aspergillus fumigatus

mBio ◽  
2020 ◽  
Vol 11 (6) ◽  
Author(s):  
Yuan Chen ◽  
Francois Le Mauff ◽  
Yan Wang ◽  
Ruiyang Lu ◽  
Donald C. Sheppard ◽  
...  
Keyword(s):  
Cell Wall ◽  
Transcription Factor ◽  
Aspergillus Fumigatus ◽  
Biofilm Formation ◽  
Wall Stress ◽  
Fungal Cell ◽  
Glucan Synthase ◽  
Content Type ◽  
Cell Wall Stress ◽  
Chitin Synthases

ABSTRACT Polysaccharides are key components of both the fungal cell wall and biofilm matrix. Despite having distinct assembly and regulation pathways, matrix exopolysaccharide and cell wall polysaccharides share common substrates and intermediates in their biosynthetic pathways. It is not clear, however, if the biosynthetic pathways governing the production of these polysaccharides are cooperatively regulated. Here, we demonstrate that cell wall stress promotes production of the exopolysaccharide galactosaminogalactan (GAG)-depend biofilm formation in the major fungal pathogen of humans Aspergillus fumigatus and that the transcription factor SomA plays a crucial role in mediating this process. A core set of SomA target genes were identified by transcriptome sequencing and chromatin immunoprecipitation coupled to sequencing (ChIP-Seq). We identified a novel SomA-binding site in the promoter regions of GAG biosynthetic genes agd3 and ega3, as well as its regulators medA and stuA. Strikingly, this SomA-binding site was also found in the upstream regions of genes encoding the cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Thus, SomA plays a direct regulation of both GAG and cell wall polysaccharide biosynthesis. Consistent with these findings, SomA is required for the maintenance of normal cell wall architecture and compositions in addition to its function in biofilm development. Moreover, SomA was found to globally regulate glucose uptake and utilization, as well as amino sugar and nucleotide sugar metabolism, which provides precursors for polysaccharide synthesis. Collectively, our work provides insight into fungal adaptive mechanisms in response to cell wall stress where biofilm formation and cell wall homeostasis were synchronously regulated. IMPORTANCE The cell wall is essential for fungal viability and is absent from human hosts; thus, drugs disrupting cell wall biosynthesis have gained more attention. Caspofungin is a member of a new class of clinically approved echinocandin drugs to treat invasive aspergillosis by blocking β-1,3-glucan synthase, thus damaging the fungal cell wall. Here, we demonstrate that caspofungin and other cell wall stressors can induce galactosaminogalactan (GAG)-dependent biofilm formation in the human pathogen Aspergillus fumigatus. We further identified SomA as a master transcription factor playing a dual role in both biofilm formation and cell wall homeostasis. SomA plays this dual role by direct binding to a conserved motif upstream of GAG biosynthetic genes and genes involved in cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Collectively, these findings reveal a transcriptional control pathway that integrates biofilm formation and cell wall homeostasis and suggest SomA as an attractive target for antifungal drug development.

scholarly journals Aspergillus fumigatus Transcription Factors Involved in the Caspofungin Paradoxical Effect

mBio ◽  
2020 ◽  
Vol 11 (3) ◽  
Author(s):  
Clara Valero ◽  
Ana Cristina Colabardini ◽  
Jéssica Chiaratto ◽  
Lakhansing Pardeshi ◽  
Patrícia Alves de Castro ◽  
...  
Keyword(s):  
Cell Wall ◽  
Transcription Factors ◽  
Invasive Aspergillosis ◽  
Aspergillus Fumigatus ◽  
Rna Polymerase Ii ◽  
Respiratory Function ◽  
Antifungal Agents ◽  
Fungal Species ◽  
Content Type ◽  
Cell Wall Remodeling

ABSTRACT Aspergillus fumigatus is the leading cause of pulmonary fungal diseases. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, in the last 10 years there have been several reports of azole resistance in A. fumigatus and new strategies are needed to combat invasive aspergillosis. Caspofungin is effective against other human-pathogenic fungal species, but it is fungistatic only against A. fumigatus. Resistance to caspofungin in A. fumigatus has been linked to mutations in the fksA gene that encodes the target enzyme of the drug β-1,3-glucan synthase. However, tolerance of high caspofungin concentrations, a phenomenon known as the caspofungin paradoxical effect (CPE), is also important for subsequent adaptation and drug resistance evolution. Here, we identified and characterized the transcription factors involved in the response to CPE by screening an A. fumigatus library of 484 null transcription factors (TFs) in CPE drug concentrations. We identified 11 TFs that had reduced CPE and that encoded proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism, and cell wall remodeling. One of these TFs, FhdA, was important for mitochondrial respiratory function and iron metabolism. The ΔfhdA mutant showed decreased growth when exposed to Congo red or to high temperature. Transcriptome sequencing (RNA-seq) analysis and further experimental validation indicated that the ΔfhdA mutant showed diminished respiratory capacity, probably affecting several pathways related to the caspofungin tolerance and resistance. Our results provide the foundation to understand signaling pathways that are important for caspofungin tolerance and resistance. IMPORTANCE Aspergillus fumigatus, one of the most important human-pathogenic fungal species, is able to cause aspergillosis, a heterogeneous group of diseases that presents a wide range of clinical manifestations. Invasive pulmonary aspergillosis is the most serious pathology in terms of patient outcome and treatment, with a high mortality rate ranging from 50% to 95% primarily affecting immunocompromised patients. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, there were several reports of evolution of clinical azole resistance in the last decade. Caspofungin, a noncompetitive β-1,3-glucan synthase inhibitor, has been used against A. fumigatus, but it is fungistatic and is recommended as second-line therapy for invasive aspergillosis. More information about caspofungin tolerance and resistance is necessary in order to refine antifungal strategies that target the fungal cell wall. Here, we screened a transcription factor (TF) deletion library for TFs that can mediate caspofungin tolerance and resistance. We have identified 11 TFs that are important for caspofungin sensitivity and/or for the caspofungin paradoxical effect (CPE). These TFs encode proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism or cell wall remodeling, and mitochondrial respiratory function. The study of those genes regulated by TFs identified in this work will provide a better understanding of the signaling pathways that are important for caspofungin tolerance and resistance.

scholarly journals Proteome Analysis Reveals the Conidial Surface Protein CcpA Essential for Virulence of the Pathogenic FungusAspergillus fumigatus

mBio ◽  
2018 ◽  
Vol 9 (5) ◽  
Author(s):  
Vera Voltersen ◽  
Matthew G. Blango ◽  
Sahra Herrmann ◽  
Franziska Schmidt ◽  
Thorsten Heinekamp ◽  
...  
Keyword(s):  
Cell Wall ◽  
Aspergillus Fumigatus ◽  
Surface Structure ◽  
Fungal Spores ◽  
Fungal Spore ◽  
Invasive Infection ◽  
Immune Recognition ◽  
Wild Type ◽  
Content Type ◽  
Conidial Surface

ABSTRACTAspergillus fumigatusis a common airborne fungal pathogen of humans and a significant source of mortality in immunocompromised individuals. Here, we provide the most extensive cell wall proteome profiling to date ofA. fumigatusresting conidia, the fungal morphotype pertinent to first contact with the host. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified proteins within the conidial cell wall by hydrogen-fluoride (HF)–pyridine extraction and proteins exposed on the surface using a trypsin-shaving approach. One protein, designatedconidialcell wallproteinA(CcpA), was identified by both methods and was found to be nearly as abundant as hydrophobic rodlet layer-forming protein RodA. CcpA, an amphiphilic protein, like RodA, peaks in expression during sporulation on resting conidia. Despite high cell wall abundance, the cell surface structure of ΔccpAresting conidia appeared normal. However, trypsin shaving of ΔccpAconidia revealed novel surface-exposed proteins not detected on conidia of the wild-type strain. Interestingly, the presence of swollen ΔccpAconidia led to higher activation of neutrophils and dendritic cells than was seen with wild-type conidia and caused significantly less damage to epithelial cellsin vitro. In addition, virulence was highly attenuated when cortisone-treated, immunosuppressed mice were infected with ΔccpAconidia. CcpA-specific memory T cell responses were detectable in healthy human donors naturally exposed toA. fumigatusconidia, suggesting a role for CcpA as a structural protein impacting conidial immunogenicity rather than possessing a protein-intrinsic immunosuppressive effect. Together, these data suggest that CcpA serves as a conidial stealth protein by altering the conidial surface structure to minimize innate immune recognition.IMPORTANCEThe mammalian immune system relies on recognition of pathogen surface antigens for targeting and clearance. In the absence of immune evasion strategies, pathogen clearance is rapid. In the case ofAspergillus fumigatus, the successful fungus must avoid phagocytosis in the lung to establish invasive infection. In healthy individuals, fungal spores are cleared by immune cells; however, in immunocompromised patients, clearance mechanisms are impaired. Here, using proteome analyses, we identified CcpA as an important fungal spore protein involved in pathogenesis.A. fumigatuslacking CcpA was more susceptible to immune recognition and prompt eradication and, consequently, exhibited drastically attenuated virulence. In infection studies, CcpA was required for virulence in infected immunocompromised mice, suggesting that it could be used as a possible immunotherapeutic or diagnostic target in the future. In summary, our report adds a protein to the list of those known to be critical to the complex fungal spore surface environment and, more importantly, identifies a protein important for conidial immunogenicity during infection.

scholarly journals Reducing Aspergillus fumigatus Virulence through Targeted Dysregulation of the Conidiation Pathway

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
James I. P. Stewart ◽  
Vinicius M. Fava ◽  
Joshua D. Kerkaert ◽  
Adithya S. Subramanian ◽  
Fabrice N. Gravelat ◽  
...  
Keyword(s):  
Mouse Model ◽  
Aspergillus Fumigatus ◽  
Vegetative Growth ◽  
Wall Structure ◽  
Invasive Infection ◽  
Phenotypic Analysis ◽  
Airborne Spores ◽  
Content Type

ABSTRACT Inhalation of conidia of the opportunistic mold Aspergillus fumigatus by immunocompromised hosts can lead to invasive pulmonary disease. Inhaled conidia that escape immune defenses germinate to form filamentous hyphae that invade lung tissues. Conidiation rarely occurs during invasive infection of the human host, allowing the bulk of fungal energy to be directed toward vegetative growth. We hypothesized that forced induction of conidiation during infection can suppress A. fumigatus vegetative growth, impairing the ability of this organism to cause disease. To study the effects of conidiation pathway dysregulation on A. fumigatus virulence, a key transcriptional regulator of conidiation (brlA) was expressed under the control of a doxycycline-inducible promoter. Time- and dose-dependent brlA overexpression was observed in response to doxycycline both in vitro and in vivo. Exposure of the inducible brlA overexpression strain to low doses of doxycycline under vegetative growth conditions in vitro induced conidiation, whereas high doses arrested growth. Overexpression of brlA attenuated A. fumigatus virulence in both an invertebrate and mouse model of invasive aspergillosis. RNA sequencing studies and phenotypic analysis revealed that brlA overexpression results in altered cell signaling, amino acid, and carbohydrate metabolism, including a marked upregulation of trehalose biosynthesis and a downregulation in the biosynthesis of the polysaccharide virulence factor galactosaminogalactan. This proof of concept study demonstrates that activation of the conidiation pathway in A. fumigatus can reduce virulence and suggests that brlA-inducing small molecules may hold promise as a new class of therapeutics for A. fumigatus infection. IMPORTANCE The mold Aspergillus fumigatus reproduces by the production of airborne spores (conidia), a process termed conidiation. In immunocompromised individuals, inhaled A. fumigatus conidia can germinate and form filaments that penetrate and damage lung tissues; however, conidiation does not occur during invasive infection. In this study, we demonstrate that forced activation of conidiation in filaments of A. fumigatus can arrest their growth and impair the ability of this fungus to cause disease in both an insect and a mouse model of invasive infection. Activation of conidiation was linked to profound changes in A. fumigatus metabolism, including a shift away from the synthesis of polysaccharides required for cell wall structure and virulence in favor of carbohydrates used for energy storage and stress resistance. Collectively, these findings suggest that activation of the conidiation pathway may be a promising approach for the development of new agents to prevent or treat A. fumigatus infection.

scholarly journals Two KTR Mannosyltransferases Are Responsible for the Biosynthesis of Cell Wall Mannans and Control Polarized Growth inAspergillus fumigatus

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Christine Henry ◽  
Jizhou Li ◽  
François Danion ◽  
Laura Alcazar-Fuoli ◽  
Emilia Mellado ◽  
...  
Keyword(s):  
Cell Wall ◽  
Invasive Aspergillosis ◽  
Aspergillus Fumigatus ◽  
Filamentous Fungi ◽  
Biosynthetic Pathway ◽  
Fungal Cell Wall ◽  
Polarized Growth ◽  
Biological Functions ◽  
Fungal Cell ◽  
Content Type

ABSTRACTFungal cell wall mannans are complex carbohydrate polysaccharides with different structures in yeasts and molds. In contrast to yeasts, their biosynthetic pathway has been poorly investigated in filamentous fungi. InAspergillus fumigatus, the major mannan structure is a galactomannan that is cross-linked to the β-1,3-glucan-chitin cell wall core. This polymer is composed of a linear mannan with a repeating unit composed of four α1,6-linked and α1,2-linked mannoses with side chains of galactofuran. Despite its use as a biomarker to diagnose invasive aspergillosis, its biosynthesis and biological function were unknown. Here, we have investigated the function of three members of the Ktr (also named Kre2/Mnt1) family (Ktr1, Ktr4, and Ktr7) inA. fumigatusand show that two of them are required for the biosynthesis of galactomannan. In particular, we describe a newly discovered form of α-1,2-mannosyltransferase activity encoded by theKTR4gene. Biochemical analyses showed that deletion of theKTR4gene or theKTR7gene leads to the absence of cell wall galactomannan. In comparison to parental strains, theΔktr4andΔktr7mutants showed a severe growth phenotype with defects in polarized growth and in conidiation, marked alteration of the conidial viability, and reduced virulence in a mouse model of invasive aspergillosis. In yeast, the KTR proteins are involved in protein 0- and N-glycosylation. This study provided another confirmation that orthologous genes can code for proteins that have very different biological functions in yeasts and filamentous fungi. Moreover, inA. fumigatus, cell wall mannans are as important structurally as β-glucans and chitin.IMPORTANCEThe fungal cell wall is a complex and dynamic entity essential for the development of fungi. It allows fungal pathogens to survive environmental challenge posed by nutrient stress and host defenses, and it also is central to polarized growth. The cell wall is mainly composed of polysaccharides organized in a three-dimensional network.Aspergillus fumigatusproduces a cell wall galactomannan whose biosynthetic pathway and biological functions remain poorly defined. Here, we described two new mannosyltransferases essential to the synthesis of the cell wall galactomannan. Their absence leads to a growth defect with misregulation of polarization and altered conidiation, with conidia which are bigger and more permeable than the conidia of the parental strain. This study showed that in spite of its low concentration in the cell wall, this polysaccharide is absolutely required for cell wall stability, for apical growth, and for the full virulence ofA. fumigatus.

scholarly journals α1,3 Glucans Are Dispensable in Aspergillus fumigatus

2011 ◽  
Vol 11 (1) ◽  
pp. 26-29 ◽  
Author(s):  
Christine Henry ◽  
Jean-Paul Latgé ◽  
Anne Beauvais
Keyword(s):  
Cell Wall ◽  
Aspergillus Fumigatus ◽  
Vegetative Growth ◽  
Conidial Germination ◽  
Glucan Synthase ◽  
Content Type ◽  
Chitin Content ◽  
A Cell

ABSTRACTA triple α1,3 glucan synthase mutant ofAspergillus fumigatusobtained by successive deletions of the three α1,3 glucan synthase genes (AGS1,AGS2, andAGS3) has a cell wall devoid of α1,3 glucans. The lack of α1,3 glucans affects neither conidial germination nor mycelial vegetative growth and is compensated by an increase in β1,3 glucan and/or chitin content.

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

2011 ◽  
Vol 11 (2) ◽  
pp. 129-140 ◽  
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.

scholarly journals Biosynthesis of β-(1→5)-Galactofuranosyl Chains of Fungal-Type and O-Mannose-Type Galactomannans within the Invasive Pathogen Aspergillus fumigatus

mSphere ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Yuria Chihara ◽  
Yutaka Tanaka ◽  
Minoru Izumi ◽  
Daisuke Hagiwara ◽  
Akira Watanabe ◽  
...  
Keyword(s):  
Cell Wall ◽  
Cell Surface ◽  
Aspergillus Fumigatus ◽  
Pathogenic Fungus ◽  
Cell Surface Hydrophobicity ◽  
Surface Hydrophobicity ◽  
Wall Structure ◽  
Fungal Cell ◽  
Content Type ◽  
Animal Pathogens

ABSTRACT The pathogenic fungus Aspergillus fumigatus contains galactomannans localized on the surface layer of its cell walls, which are involved in various biological processes. Galactomannans comprise α-(1→2)-/α-(1→6)-mannan and β-(1→5)-/β-(1→6)-galactofuranosyl chains. We previously revealed that GfsA is a β-galactofuranoside β-(1→5)-galactofuranosyltransferase involved in the biosynthesis of β-(1→5)-galactofuranosyl chains. In this study, we clarified the biosynthesis of β-(1→5)-galactofuranosyl chains in A. fumigatus. Two paralogs exist within A. fumigatus: GfsB and GfsC. We show that GfsB and GfsC, in addition to GfsA, are β-galactofuranoside β-(1→5)-galactofuranosyltransferases by biochemical and genetic analyses. GfsA, GfsB, and GfsC can synthesize β-(1→5)-galactofuranosyl oligomers at up to lengths of 7, 3, and 5 galactofuranoses within an established in vitro highly efficient assay of galactofuranosyltransferase activity. Structural analyses of galactomannans extracted from ΔgfsB, ΔgfsC, ΔgfsAC, and ΔgfsABC strains revealed that GfsA and GfsC synthesized all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans and that GfsB exhibited limited function in A. fumigatus. The loss of β-(1→5)-galactofuranosyl residues decreased the hyphal growth rate and conidium formation ability and increased the abnormal hyphal branching structure and cell surface hydrophobicity, but this loss is dispensable for sensitivity to antifungal agents and virulence toward immunocompromised mice. IMPORTANCE β-(1→5)-Galactofuranosyl residues are widely distributed in the subphylum Pezizomycotina of the phylum Ascomycota. Pezizomycotina includes many plant and animal pathogens. Although the structure of β-(1→5)-galactofuranosyl residues of galactomannans in filamentous fungi was discovered long ago, it remains unclear which enzyme is responsible for biosynthesis of this glycan. Fungal cell wall formation processes are complicated, and information concerning glycosyltransferases is essential for understanding them. In this study, we showed that GfsA and GfsC are responsible for the biosynthesis of all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans. The data presented here indicate that β-(1→5)-galactofuranosyl residues are involved in cell growth, conidiation, polarity, and cell surface hydrophobicity. Our new understanding of β-(1→5)-galactofuranosyl residue biosynthesis provides important novel insights into the formation of the complex cell wall structure and the virulence of the members of the subphylum Pezizomycotina.

scholarly journals The Putative APSES Transcription Factor RgdA Governs Growth, Development, Toxigenesis, and Virulence in Aspergillus fumigatus

mSphere ◽  
2020 ◽  
Vol 5 (6) ◽  
Author(s):  
Sang-Cheol Jun ◽  
Yong-Ho Choi ◽  
Min-Woo Lee ◽  
Jae-Hyuk Yu ◽  
Kwang-Soo Shin
Keyword(s):  
Transcription Factor ◽  
Aspergillus Fumigatus ◽  
Molecular Mechanisms ◽  
Pathogenic Fungus ◽  
Mrna Levels ◽  
Transcript Levels ◽  
Content Type ◽  
Asexual Sporulation ◽  
Human Pathogenic Fungus ◽  
Growth Development

ABSTRACT The APSES transcription factor (TF) in Aspergillus species is known to govern diverse cellular processes, including growth, development, and secondary metabolism. Here, we investigated functions of the rgdA gene (Afu3g13920) encoding a putative APSES TF in the opportunistic human-pathogenic fungus Aspergillus fumigatus. The rgdA deletion resulted in significantly decreased hyphal growth and asexual sporulation. Consistently, transcript levels of the key asexual developmental regulators abaA, brlA, and wetA were decreased in the ΔrgdA mutant compared to those in the wild type (WT). Moreover, ΔrgdA resulted in reduced spore germination rates and elevated transcript levels of genes associated with conidium dormancy. The conidial cell wall hydrophobicity and architecture were changed, and levels of the RodA protein were decreased in the ΔrgdA mutant. Comparative transcriptomic analyses revealed that the ΔrgdA mutant showed higher mRNA levels of gliotoxin (GT)-biosynthetic genes and GT production. While the ΔrgdA mutant exhibited elevated production of GT, ΔrgdA strains showed reduced virulence in the mouse model. In addition, mRNA levels of genes associated with the cyclic AMP (cAMP)-protein kinase A (PKA) signaling pathway and the SakA mitogen-activated protein (MAP) kinase pathway were increased in the ΔrgdA mutant. In summary, RgdA plays multiple roles in governing growth, development, GT production, and virulence which may involve attenuation of PKA and SakA signaling. IMPORTANCE Immunocompromised patients are susceptible to infections with the opportunistic human-pathogenic fungus Aspergillus fumigatus. This fungus causes systemic infections such as invasive aspergillosis (IA), which is one of the most life-threatening fungal diseases. To control this serious disease, it is critical to identify new antifungal drug targets. In fungi, the transcriptional regulatory proteins of the APSES family play crucial roles in controlling various biological processes, including mating, asexual sporulation and dimorphic growth, and virulence traits. This study found that a putative APSES transcription factor, RgdA, regulates normal growth, asexual development, conidium germination, spore wall architecture and hydrophobicity, toxin production, and virulence in A. fumigatus. Better understanding the molecular mechanisms of RgdA in human-pathogenic fungi may reveal a novel antifungal target for future drug development.

scholarly journals Position of O-Acetylation within the Capsular Repeat Unit Impacts the Biological Properties of Pneumococcal Serotypes 33A and 33F

2017 ◽  
Vol 85 (7) ◽  
Author(s):  
Brady L. Spencer ◽  
Jamil S. Saad ◽  
Anukul T. Shenoy ◽  
Carlos J. Orihuela ◽  
Moon H. Nahm
Keyword(s):  
Cell Wall ◽  
Repeat Unit ◽  
Biological Properties ◽  
Immune Recognition ◽  
Content Type ◽  
Pneumococcal Serotype ◽  
Membrane Bound ◽  
Biochemical Analyses ◽  
Opsonophagocytic Killing ◽  
Small Chemical

ABSTRACT Streptococcus pneumoniae (pneumococcus) produces many capsule types that differ in their abilities to evade host immune recognition. To explain these serotype-dependent protective capacities, many studies have investigated capsular thickness or the interaction of the capsule with complement proteins, but the effects of small chemical modifications of the capsule on its function have not been studied. One small chemical modification found frequently among pneumococcal capsules is O-acetylation. Pneumococcal serotype 33A has two membrane-bound O-acetyltransferase genes, wciG and wcjE. A 33A wcjE-deficient variant, 33F, occurs naturally and is increasing in prevalence in the wake of widespread conjugate vaccine use, but no wciG-deficient variants have been reported. To study the biological consequence of the loss of O-acetylation, we created wciG-deficient variants in both serotypes 33A and 33F, which we named 33X1 (ΔwciG) and 33X2 (ΔwciG ΔwcjE). Serotypes 33X1 and 33X2 express novel capsule types based on serological and biochemical analyses. We found that loss of WcjE-mediated O-acetylation appears not to affect cell wall shielding, since serotypes 33A and 33F exhibit comparable nonspecific opsonophagocytic killing, biofilm production, and adhesion to nasopharyngeal cells, though serotype 33F survived short-term drying better than serotype 33A. Loss of WciG-mediated O-acetylation in serotypes 33X1 and 33X2, however, resulted in a phenotype resembling that of nonencapsulated strains: increased cell wall accessibility, increased nonspecific opsonophagocytic killing, enhanced biofilm formation, and increased adhesion to nasopharyngeal cells. We conclude that WciG-mediated, but not WcjE-mediated, O-acetylation is important for producing protective capsules in 33A and that small chemical changes to the capsule can drastically affect its biological properties.

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