1
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Ror S, Stamnes MA, Moye-Rowley WS. Gene-specific transcriptional activation by the Aspergillus fumigatus AtrR factor requires a conserved C-terminal domain. mSphere 2024; 9:e0042524. [PMID: 38975761 PMCID: PMC11288021 DOI: 10.1128/msphere.00425-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2024] [Accepted: 06/12/2024] [Indexed: 07/09/2024] Open
Abstract
Treatment of fungal infections associated with the filamentous fungus Aspergillus fumigatus is becoming more problematic as this organism is developing resistance to the main chemotherapeutic drug at an increasing rate. Azole drugs represent the current standard-of-care in the treatment of aspergillosis with this drug class acting by inhibiting a key step in the biosynthesis of the fungal sterol ergosterol. Azole compounds block the activity of the lanosterol α-14 demethylase, encoded by the cyp51A gene. A common route of azole resistance involves an increase in transcription of cyp51A. This transcriptional increase requires the function of a Zn2Cys6 DNA-binding domain-containing transcription activator protein called AtrR. AtrR was identified through its action as a positive regulator of expression of an ATP-binding cassette transporter (abcC/cdr1B here called abcG1). Using both deletion and alanine scanning mutagenesis, we demonstrate that a conserved C-terminal domain in A. fumigatus is required for the expression of abcG1 but dispensable for cyp51A transcription. This domain is also found in several other fungal pathogen AtrR homologs consistent with a conserved gene-selective function of this protein segment being conserved. Using RNA sequencing (RNA-seq), we find that this gene-specific transcriptional defect extends to several other membrane transporter-encoding genes including a second ABC transporter locus. Our data reveal that AtrR uses at least two distinct mechanisms to induce gene expression and that normal susceptibility to azole drugs cannot be provided by maintenance of wild-type expression of the ergosterol biosynthetic pathway when ABC transporter expression is reduced. IMPORTANCE Aspergillus fumigatus is the primary human filamentous fungal pathogen. The principal chemotherapeutic drug used to control infections associated with A. fumigatus is the azole compound. These drugs are well-tolerated and effective, but resistance is emerging at an alarming rate. Most resistance is associated with mutations that lead to overexpression of the azole target enzyme, lanosterol α-14 demethylase, encoded by the cyp51A gene. A key regulator of cyp51A gene expression is the transcription factor AtrR. Very little is known of the molecular mechanisms underlying the effect of AtrR on gene expression. Here, we use deletion and clustered amino acid substitution mutagenesis to map a region of AtrR that confers gene-specific activation on target genes of this transcription factor. This region is highly conserved across AtrR homologs from other pathogenic species arguing that its importance in transcriptional regulation is maintained across evolution.
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Affiliation(s)
- Shivani Ror
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Mark A. Stamnes
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - W. Scott Moye-Rowley
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
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2
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Dladla M, Gyzenhout M, Marias G, Ghosh S. Azole resistance in Aspergillus fumigatus- comprehensive review. Arch Microbiol 2024; 206:305. [PMID: 38878211 DOI: 10.1007/s00203-024-04026-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Revised: 05/28/2024] [Accepted: 05/31/2024] [Indexed: 06/23/2024]
Abstract
Aspergillus fumigatus is a ubiquitous filamentous fungus commonly found in the environment. It is also an opportunistic human pathogen known to cause a range of respiratory infections, such as invasive aspergillosis, particularly in immunocompromised individuals. Azole antifungal agents are widely used for the treatment and prophylaxis of Aspergillus infections due to their efficacy and tolerability. However, the emergence of azole resistance in A. fumigatus has become a major concern in recent years due to their association with increased treatment failures and mortality rates. The development of azole resistance in A. fumigatus can occur through both acquired and intrinsic mechanisms. Acquired resistance typically arises from mutations in the target enzyme, lanosterol 14-α-demethylase (Cyp51A), reduces the affinity of azole antifungal agents for the enzyme, rendering them less effective, while intrinsic resistance refers to a natural resistance of certain A. fumigatus isolates to azole antifungals due to inherent genetic characteristics. The current review aims to provide a comprehensive overview of azole antifungal resistance in A. fumigatus, discusses underlying resistance mechanisms, including alterations in the target enzyme, Cyp51A, and the involvement of efflux pumps in drug efflux. Impact of azole fungicide uses in the environment and the spread of resistant strains is also explored.
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Affiliation(s)
- Mthokozisi Dladla
- Department of Genetics, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, 9301, South Africa
| | - Marieka Gyzenhout
- Department of Genetics, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, 9301, South Africa.
| | - Gert Marias
- Department of Plant Sciences, Division of Plant Pathology, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, South Africa
| | - Soumya Ghosh
- Department of Genetics, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, 9301, South Africa.
- Natural and Medical Sciences Research Center, University of Nizwa, Nizwa 616, Birkat Al Mawz, Oman.
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3
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Ror S, Stamnes MA, Moye-Rowley WS. Loss of a conserved C-terminal region of the Aspergillus fumigatus AtrR transcriptional regulator leads to a gene-specific defect in target gene expression. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.22.595332. [PMID: 38826412 PMCID: PMC11142210 DOI: 10.1101/2024.05.22.595332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Treatment of fungal infections associated with the filamentous fungus Aspergillus fumigatus is becoming more problematic as this organism is developing resistance to the main chemotherapeutic drug at an increasing rate. Azole drugs represent the current standard-of-care in treatment of aspergillosis with this drug class acting by inhibiting a key step in biosynthesis of the fungal sterol ergosterol. Azole compounds block the activity of the lanosterol α-14 demethylase, encoded by the cyp51A gene. A common route of azole resistance involves an increase in transcription of cyp51A. This transcriptional increase requires the function of a Zn2Cys6 DNA-binding domain-containing transcription activator protein called AtrR. AtrR was identified through its action as a positive regulator of expression of an ATP-binding cassette transporter (abcC/cdr1B here called abcG1). Using both deletion and alanine scanning mutagenesis, we demonstrate that a conserved C-terminal domain in A. fumigatus is required for expression of abcG1 but dispensable for cyp51A transcription. This domain is also found in several other fungal pathogen AtrR homologues consistent with a conserved gene-selective function of this protein segment being conserved. Using RNA-seq, we find that this gene-specific transcriptional defect extends to several other membrane transporter-encoding genes including a second ABC transporter locus. Our data reveal that AtrR uses at least two distinct mechanisms to induce gene expression and that normal susceptibility to azole drugs cannot be provided by maintenance of wild-type expression of the ergosterol biosynthetic pathway when ABC transporter expression is reduced.
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Affiliation(s)
- Shivani Ror
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Mark A Stamnes
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - W Scott Moye-Rowley
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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4
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Kühbacher A, Merschak P, Haas H, Liebl M, Müller C, Gsaller F. The cytochrome P450 reductase CprA is a rate-limiting factor for Cyp51A-mediated azole resistance in Aspergillus fumigatus. Antimicrob Agents Chemother 2023; 67:e0091823. [PMID: 37815358 PMCID: PMC10648939 DOI: 10.1128/aac.00918-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 08/12/2023] [Indexed: 10/11/2023] Open
Abstract
Azole antifungals remain the "gold standard" therapy for invasive aspergillosis. The world-wide emergence of isolates resistant to this drug class, however, developed into a steadily increasing threat to human health over the past years. In Aspergillus fumigatus, major mechanisms of resistance involve increased expression of cyp51A encoding one of two isoenzymes targeted by azoles. Yet, the level of resistance caused by cyp51A upregulation, driven by either clinically relevant tandem repeat mutations within its promoter or the use of high expressing heterologous promoters, is limited. Cytochrome P450 enzymes such as Cyp51A rely on redox partners that provide electrons for their activity. A. fumigatus harbors several genes encoding putative candidate proteins including two paralogous cytochrome P450 reductases, CprA and CprB, and the cytochrome b 5 CybE. In this work, we investigated the contribution of each cprA, cprB, and cybE overexpression to cyp51A-mediated resistance to different medical and agricultural azoles. Using the bidirectional promoter PxylP, we conditionally expressed these genes in combination with cyp51A, revealing cprA as the main limiting factor. Similar to this approach, we overexpressed cprA in an azole-resistant background strain carrying a cyp51A allele with TR34 in its promoter, which led to a further increase in its resistance. Employing sterol measurements, we demonstrate an enhanced eburicol turnover during upregulation of either cprA or cyp51A, which was even more pronounced during their simultaneous overexpression. In summary, our work suggests that mutations leading to increased Cyp51A activity through increased electron supply could be key factors that elevate azole resistance.
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Affiliation(s)
- Alexander Kühbacher
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Petra Merschak
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Hubertus Haas
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Maximilian Liebl
- Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians Universität München, Munich, Germany
| | - Christoph Müller
- Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians Universität München, Munich, Germany
| | - Fabio Gsaller
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
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5
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Paul S, Stamnes MA, Moye-Rowley WS. Interactions between the transcription factors FfmA and AtrR are required to properly regulate gene expression in the fungus Aspergillus fumigatus. G3 (BETHESDA, MD.) 2023; 13:jkad173. [PMID: 37523774 PMCID: PMC10542180 DOI: 10.1093/g3journal/jkad173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 06/05/2023] [Accepted: 07/17/2023] [Indexed: 08/02/2023]
Abstract
Transcriptional regulation of azole resistance in the filamentous fungus Aspergillus fumigatus is a key step in development of this problematic clinical phenotype. We and others have previously described a C2H2-containing transcription factor called FfmA that is required for normal levels of voriconazole susceptibility. Null alleles of ffmA exhibit a strongly compromised growth rate even in the absence of any external stress. Here, we employ an acutely repressible doxycycline-off form of ffmA to rapidly deplete FfmA protein from the cell. Using this approach, we carried out RNA-seq analyses to probe the transcriptome cells acutely deprived of FfmA. A total of 2,000 genes were differentially expressed upon acute depletion of FfmA, illustrating the broad transcriptomic effect of this factor. Interestingly, the transcriptome changes observed upon this acute depletion of FfmA expression only shared limited overlap with those found in an ffmAΔ null strain analyzed by others. Chromatin immunoprecipitation coupled with high throughput DNA sequencing analysis (ChIP-seq) identified 530 genes that were bound by FfmA. More than 300 of these genes were also bound by AtrR, a transcription factor important in azole drug resistance, demonstrating striking regulatory overlap with FfmA. However, while AtrR is an upstream activation protein with known specificity, our data suggest that FfmA is a chromatin-associated factor that binds DNA in a manner dependent on other factors. We provide evidence that AtrR and FfmA interact in the cell and show reciprocal expression modulation. Interaction of AtrR and FfmA is required for normal gene expression in A. fumigatus.
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Affiliation(s)
- Sanjoy Paul
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Mark A Stamnes
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - W Scott Moye-Rowley
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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Yap A, Volz R, Paul S, Moye-Rowley WS, Haas H. Regulation of High-Affinity Iron Acquisition, Including Acquisition Mediated by the Iron Permease FtrA, Is Coordinated by AtrR, SrbA, and SreA in Aspergillus fumigatus. mBio 2023; 14:e0075723. [PMID: 37093084 PMCID: PMC10294635 DOI: 10.1128/mbio.00757-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Accepted: 03/29/2023] [Indexed: 04/25/2023] Open
Abstract
Iron acquisition is crucial for virulence of the human pathogen Aspergillus fumigatus. Previous studies indicated that this mold regulates iron uptake via both siderophores and reductive iron assimilation by the GATA factor SreA and the SREBP regulator SrbA. Here, characterization of loss of function as well as hyperactive alleles revealed that transcriptional activation of iron uptake depends additionally on the Zn2Cys6 regulator AtrR, most likely via cooperation with SrbA. Mutational analysis of the promoter of the iron permease-encoding ftrA gene identified a 210-bp sequence, which is both essential and sufficient to impart iron regulation. Further studies located functional sequences, densely packed within 75 bp, that largely resemble binding motifs for SrbA, SreA, and AtrR. The latter, confirmed by chromatin immunoprecipitation (ChIP) analysis, is the first one not fully matching the 5'-CGGN12CCG-3' consensus sequence. The results presented here emphasize for the first time the direct involvement of SrbA, AtrR, and SreA in iron regulation. The essential role of both AtrR and SrbA in activation of iron acquisition underlines the coordination of iron homeostasis with biosynthesis of ergosterol and heme as well as adaptation to hypoxia. The rationale is most likely the iron dependence of these pathways along with the enzymatic link of biosynthesis of ergosterol and siderophores. IMPORTANCE Aspergillus fumigatus is the most common filamentous fungal pathogen infecting humans. Iron acquisition via siderophores has previously been shown to be essential for virulence of this mold species. Here, we demonstrate that AtrR, a transcription factor previously shown to control ergosterol biosynthesis, azole resistance, and adaptation to hypoxia, is essential for activation of iron acquisition, including siderophore biosynthesis and uptake. Dissection of an iron-regulated promoter identified binding motifs for AtrR and the two previously identified regulators of iron acquisition, SrbA and SreA. Altogether, this study identified a new regulator required for maintenance of iron homeostasis, revealed insights into promoter architecture for iron regulation, and emphasized the coordinated regulation of iron homeostasis ergosterol biosynthesis and adaptation to hypoxia.
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Affiliation(s)
- Annie Yap
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Ricarda Volz
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Sanjoy Paul
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - W. Scott Moye-Rowley
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Hubertus Haas
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
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7
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Paul S, Stamnes MA, Moye-Rowley WS. Transcription factor FfmA interacts both physically and genetically with AtrR to properly regulate gene expression in the fungus Aspergillus fumigatus. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543935. [PMID: 37333080 PMCID: PMC10274792 DOI: 10.1101/2023.06.06.543935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Transcriptional regulation of azole resistance in the filamentous fungus Aspergillus fumigatus is a key step in development of this problematic clinical phenotype. We and others have previously described a C2H2-containing transcription factor called FfmA that is required for normal levels of voriconazole susceptibility and expression of an ATP-binding cassette transporter gene called abcG1 . Null alleles of ffmA exhibit a strongly compromised growth rate even in the absence of any external stress. Here we employ an acutely repressible doxycycline-off form of ffmA to rapidly deplete FfmA protein from the cell. Using this approach, we carried out RNA-seq analyses to probe the transcriptome of A. fumigatus cells that have been deprived of normal FfmA levels. We found that 2000 genes were differentially expressed upon depletion of FfmA, consistent with the wide-ranging effect of this factor on gene regulation. Chromatin immunoprecipitation coupled with high throughput DNA sequencing analysis (ChIP-seq) identified 530 genes that were bound by FfmA using two different antibodies for immunoprecipitation. More than 300 of these genes were also bound by AtrR demonstrating the striking regulatory overlap with FfmA. However, while AtrR is clearly an upstream activation protein with clear sequence specificity, our data suggest that FfmA is a chromatin-associated factor that may bind to DNA in a manner dependent on other factors. We provide evidence that AtrR and FfmA interact in the cell and can influence one another's expression. This interaction of AtrR and FfmA is required for normal azole resistance in A. fumigatus .
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Affiliation(s)
- Sanjoy Paul
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA. 52242 USA
| | - Mark A. Stamnes
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA. 52242 USA
| | - W. Scott Moye-Rowley
- Department of Molecular Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, IA. 52242 USA
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Biochemical Identification of a Nuclear Coactivator Protein Required for AtrR-Dependent Gene Regulation in Aspergillus fumigatus. mSphere 2022; 7:e0047622. [PMID: 36374043 PMCID: PMC9769526 DOI: 10.1128/msphere.00476-22] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Azole drugs represent the primary means of treating infections associated with the filamentous fungal pathogen Aspergillus fumigatus. A central player in azole resistance is the Zn2Cys6 zinc cluster-containing transcription factor AtrR. This factor stimulates expression of both the cyp51A gene, which encodes the azole drug target enzyme, as well as an ATP-binding cassette transporter-encoding gene called abcG1 (cdr1B). We used a fusion protein between AtrR and the tandem affinity purification (TAP) moiety to purify proteins that associated with AtrR from A. fumigatus. Protein fractions associated with AtrR-TAP were subjected to multidimensional protein identification technology mass spectrometry, and one of the proteins identified was encoded by the AFUA_6g08010 gene. We have designated this protein NcaA (for nuclear coactivator of AtrR). Loss of ncaA caused a reduction in voriconazole resistance and drug-induced abcG1 expression, although it did not impact induction of cyp51A transcription. We confirmed the association of AtrR and NcaA by coimmunoprecipitation from otherwise-wild-type cells. Expression of fusion proteins between AtrR and NcaA with green fluorescent protein allowed determination that these two proteins were localized in the A. fumigatus nucleus. Together, these data support the view that NcaA is required for nuclear gene transcription controlled by AtrR. IMPORTANCE Aspergillus fumigatus is a major filamentous fungal pathogen in humans and is susceptible to the azole antifungal class of drugs. However, loss of azole susceptibility has been detected with increasing frequency in the clinic, and infections associated with these azole-resistant isolates have been linked to treatment failure and worse outcomes. Many of these azole-resistant strains contain mutant alleles of the cyp51A gene, which encodes the azole drug target. A transcription factor essential for cyp51A gene transcription has been identified and designated AtrR. AtrR is required for azole-inducible cyp51A transcription, but we know little of the regulation of this transcription factor. Using a biochemical approach, we identified a new protein called NcaA that is involved in regulation of AtrR at certain target gene promoters. Understanding the mechanisms controlling AtrR function is an important goal in preventing or reversing azole resistance in this pathogen.
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