ChIP-seq and in vivo transcriptome analyses of the Aspergillus fumigatus SREBP SrbA reveals a new regulator of the fungal hypoxia response and virulence.
The Aspergillus fumigatus sterol regulatory element binding protein (SREBP) SrbA belongs to the basic Helix-Loop-Helix (bHLH) family of transcription factors and is crucial for antifungal drug resistance and virulence. The latter phenotype is especially striking, as loss of SrbA results in complete loss of virulence in murine models of invasive pulmonary aspergillosis (IPA). How fungal SREBPs mediate fungal virulence is unknown, though it has been suggested that lack of growth in hypoxic conditions accounts for the attenuated virulence. To further understand the role of SrbA in fungal infection site pathobiology, chromatin immunoprecipitation followed by massively parallel DNA sequencing (ChIP-seq) was used to identify genes under direct SrbA transcriptional regulation in hypoxia. These results confirmed the direct regulation of ergosterol biosynthesis and iron uptake by SrbA in hypoxia and revealed new roles for SrbA in nitrate assimilation and heme biosynthesis. Moreover, functional characterization of an SrbA target gene with sequence similarity to SrbA identified a new transcriptional regulator of the fungal hypoxia response and virulence, SrbB. SrbB co-regulates genes involved in heme biosynthesis and demethylation of C4-sterols with SrbA in hypoxic conditions. However, SrbB also has regulatory functions independent of SrbA including regulation of carbohydrate metabolism. Loss of SrbB markedly attenuates A. fumigatus virulence, and loss of both SREBPs further reduces in vivo fungal growth. These data suggest that both A. fumigatus SREBPs are critical for hypoxia adaptation and virulence and reveal new insights into SREBPs' complex role in infection site adaptation and fungal virulence.
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Dawoon
D
Chung
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Bridget M
BM
Barker
Bioinformatics Core, Department of Microbiology, Montana State University, Bozeman, Montana, United States of America.
Charles C
CC
Carey
Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, United States of America.
Brittney
B
Merriman
Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
Ernst R
ER
Werner
Division of Molecular Biology, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
Beatrix E
BE
Lechner
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Sourabh
S
Dhingra
Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Chao
C
Cheng
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.
Wenjie
W
Xu
Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, United States of America.
Sara J
SJ
Blosser
Center for Applied Plant Sciences, The Ohio State University, Columbus, Ohio, United States of America.
Kengo
K
Morohashi
Bioinformatics Core, Department of Microbiology, Montana State University, Bozeman, Montana, United States of America.
Aurélien
A
Mazurie
Department of Plant Pathology, The Ohio State University, Columbus, Ohio, United States of America.
Thomas K
TK
Mitchell
Division of Molecular Biology, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
Hubertus
H
Haas
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.
Aaron P
AP
Mitchell
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Robert A
RA
Cramer
D001232:Aspergillus fumigatus / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics; D059014:High-Throughput Nucleotide Sequencing; D051779:Sterol Regulatory Element Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D059467:Transcriptome
D005656:Fungal Proteins; D051779:Sterol Regulatory Element Binding Proteins