Cited by 345Fungal and yeast genetics researchAntifungal resistance and susceptibilityFungal Infections and Studies

The DOI matches its Crossref record; 84 of the 84 references it cites were found in a registry or an index; none of the 46 sources its claims cite is checked for support yet.

A Sterol-Regulatory Element Binding Protein Is Required for Cell Polarity, Hypoxia Adaptation, Azole Drug Resistance, and Virulence in Aspergillus fumigatus

Open access

Abstract

At the site of microbial infections, the significant influx of immune effector cells and the necrosis of tissue by the invading pathogen generate hypoxic microenvironments in which both the pathogen and host cells must survive. Currently, whether hypoxia adaptation is an important virulence attribute of opportunistic pathogenic molds is unknown. Here we report the characterization of a sterol-regulatory element binding protein, SrbA, in the opportunistic pathogenic mold, Aspergillus fumigatus. Loss of SrbA results in a mutant strain of the fungus that is incapable of growth in a hypoxic environment and consequently incapable of causing disease in two distinct murine models of invasive pulmonary aspergillosis (IPA). Transcriptional profiling revealed 87 genes that are affected by loss of SrbA function. Annotation of these genes implicated SrbA in maintaining sterol biosynthesis and hyphal morphology. Further examination of the SrbA null mutant consequently revealed that SrbA plays a critical role in ergosterol biosynthesis, resistance to the azole class of antifungal drugs, and in maintenance of cell polarity in A. fumigatus. Significantly, the SrbA null mutant was highly susceptible to fluconazole and voriconazole. Thus, these findings present a new function of SREBP proteins in filamentous fungi, and demonstrate for the first time that hypoxia adaptation is likely an important virulence attribute of pathogenic molds.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper identifies SrbA, an SREBP homolog in *Aspergillus fumigatus*, as required for hypoxic growth, azole resistance, cell polarity, sterol biosynthesis, and virulence. Loss of SrbA renders the fungus avirulent in two murine models of invasive pulmonary aspergillosis and highly susceptible to fluconazole and voriconazole.

Key findings

  • The ΔsrbA mutant SDW1 showed no detectable hyphal growth under hypoxia (1% O₂, 5% CO₂, 94% N₂), whereas wild-type CEA10 and reconstituted SDW2 grew normally; under normoxia, growth rates were comparable (P>0.01).
  • SDW1 was highly susceptible to fluconazole (MIC 1 µg/ml) and voriconazole (MIC 0.012 µg/ml), while CEA10 and SDW2 were fluconazole-resistant and had voriconazole MICs of 0.125 µg/ml; all strains had equivalent MICs to amphotericin B (0.25 µg/ml) and caspofungin (0.125 µg/ml).
  • Microarray profiling in hypoxia identified 87 SrbA-affected genes, including *srbA* itself (38.59-fold), NRPS1 (23.36-fold), ERG25 (15.79-fold), ERG3 (13.57-fold), and ERG24 (11.98-fold) higher in wild type than mutant. GC-MS showed a C-4 methylated sterol-to-ergosterol ratio of 1.94 in SDW1 versus no C-4 methylated sterol accumulation in wild type, suggesting an ERG25 block.
  • SDW1 was avirulent in neutropenic CD1 mice (P=0.0002) and significantly attenuated in gp91phox−/− X-CGD mice (P=0.0054/0.005); no differences were found in oxidative stress resistance or RAW264.7 macrophage killing (P>0.01).

Methods

  • A *srbA* null mutant (SDW1) was generated in *A. fumigatus* CEA17 by replacing an ~2.2-kb internal *srbA* coding fragment with *A. parasiticus pyrG*; a reconstituted strain (SDW2) was created, and strains were confirmed by Southern blot and PCR.
  • Phenotypic assays included normoxic/hypoxic growth, microarray transcriptional profiling after 24 h hypoxia, E-test antifungal susceptibility, GC-MS sterol analysis, transmission electron microscopy, conidial germination, H₂O₂ sensitivity, and RAW264.7 macrophage killing.
  • Virulence was tested in two murine IPA models: outbred CD1 neutropenic mice (n=12 per strain) and gp91phox−/− X-CGD mice (n=6 per strain), inoculated with 10⁶ conidia; survival was analyzed by log-rank tests, with microarray analysis by SAM using a 2-fold cutoff and zero false discovery rate.

Limitations

  • The paper states that the mechanisms behind several phenotypes remain undefined, including how SrbA mediates hypoxia adaptation, azole resistance, and cell polarity; it also notes that no clear SCAP homolog was identified, that S1P/S2P protease mutants did not show expected hypoxic defects (unpublished data), and that SrbA regulation/activation was not elucidated.
  • Evident from the text: transcriptional profiling was limited to one hypoxic condition and time point (24 h), so many of the 87 genes may be indirect effects; oxygen tension was not directly measured in infected tissue; and some supporting data are described as unpublished or not shown.

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Integrity signals

Registry

Crossref · 10.1371/journal.ppat.1000200

Cites

84 of 84 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

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Show all 117 claims

  • It may state two separate claims as one. 30
  • Probably not a substantial claim. 35
  • The quote only partly states this claim. 1
58 of 58
  • The authors state this as an assumption.

    Sites of infection and inflammation in the neutropenic mouse model are hypoxic.

    “We hypothesize that these sites of infection and inflammation in this model are hypoxic.”
  • The authors state this as an assumption.

    The hyper-inflammatory response in X-CGD mice generates significant hypoxia in the lung.

    “with the hypothesis that the hyper-inflammatory response would generate significant hypoxia in the lung”
  • The paper relies on this without support.

    A. fumigatus must overcome significant hypoxia during pulmonary infections.

    “we believe that A. fumigatus must overcome significant hypoxia during pulmonary infections”
3 of 3

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Key sterol is identified as both dimethylated and demethylated

    Minor

    The results identify an accumulated sterol as 4,4-dimethylated, while the Figure 7 key identifies the corresponding sterol as 4,4-demethylated. Those descriptions disagree about the methyl groups central to the proposed C-4 demethylation defect.

  • Rox1p and Mot3p are said to repress and induce hypoxia-adaptation genes

    Minor

    The introduction first says Rox1p and Mot3p down-regulate genes needed for hypoxia adaptation, then says their expression under hypoxia leads to induction of those genes.

2 of 2

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Metadata

Authors
Willger, S. D., Puttikamonkul, S., Kim, K.-H., Burritt, J. B., Grahl, N., Metzler, L. J., Barbuch, R., Bard, M., Lawrence, C. B., & Cramer, R. A.
Affiliations
  • Montana State University (US)
  • Virginia Tech (US)
  • Indiana University – Purdue University Indianapolis (US)
Corresponding author
Cramer, Robert A.
Venue
PLoS Pathogens
Published
2008-11-07
Volume
4
Issue
11
Pages
e1000200
ISSN
  • 1553-7366 (ISSN-L)
  • 1553-7374
OpenAlex
W1973084729
Cited by
345
References
84
Citations by year
2026: 18 · 2025: 15 · 2024: 17 · 2023: 14 · 2022: 15 · 2021: 27 · 2020: 23 · 2019: 23 · 2018: 17 · 2017: 31 · 2016: 28 · 2015: 15 · 2014: 19 · 2013: 22 · 2012: 22
FWCI
5.21
Type
journal article
Language
en
Open access
Locations
  • PLoS Pathogens (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • IUScholarWorks (Indiana University) (submittedVersion, cc-by)
  • VTechWorks (Virginia Tech) (submittedVersion)
  • Publisher
Funders
  • Montana State University
  • National Institutes of Health (RR 020185)
  • National Institute of General Medical Sciences (R01GM062104, GM 62104)
  • National Institute of Allergy and Infectious Diseases (L40 AI084526)
  • National Center for Research Resources (P20RR020185, RR 020185)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Fungal and yeast genetics research
  • Health Sciences › Medicine › Infectious Diseases › Antifungal resistance and susceptibility
  • Health Sciences › Medicine › Infectious Diseases › Fungal Infections and Studies
Keywords
Aspergillus fumigatus, SREBP, hypoxia adaptation, cell polarity, fluconazole, voriconazole, ergosterol biosynthesis, sterol biosynthesis, hyphal morphology, invasive pulmonary aspergillosis, fungal virulence, gene expression profiling, filamentous fungi
MeSH terms
Adaptation, Physiological, Animals, Hypoxia, Aspergillus fumigatus, Azoles, Drug Resistance, Fungal Proteins, Mice, Inbred Strains, Transcription, Genetic, Virulence, Gene Expression Regulation, Fungal, Cell Polarity, Gene Expression Profiling, Mice, Sterol Regulatory Element Binding Proteins

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