Effects of a defective endoplasmic reticulum-associated degradation pathway on the stress response, virulence, and antifungal drug susceptibility of the mold pathogen Aspergillus fumigatus.
Proteins that are destined for release outside the eukaryotic cell, insertion into the plasma membrane, or delivery to intracellular organelles are processed and folded in the endoplasmic reticulum (ER). An imbalance between the level of nascent proteins entering the ER and the organelle's ability to manage that load results in the accumulation of unfolded proteins. Terminally unfolded proteins are disposed of by ER-associated degradation (ERAD), a pathway that transports the aberrant proteins across the ER membrane into the cytosol for proteasomal degradation. The ERAD pathway was targeted in the mold pathogen Aspergillus fumigatus by deleting the hrdA gene, encoding the A. fumigatus ortholog of Hrd1, the E3 ubiquitin ligase previously shown to contribute to ERAD in other species. Loss of HrdA was associated with impaired degradation of a folding-defective ERAD substrate, CPY*, as well as activation of the unfolded-protein response (UPR). The ΔhrdA mutant showed resistance to voriconazole and reduced thermotolerance but was otherwise unaffected by a variety of environmental stressors. A double-deletion mutant deficient in both HrdA and another component of the same ERAD complex, DerA, was defective in secretion and showed hypersensitivity to ER, thermal, and cell wall stress. However, the ΔhrdA ΔderA mutant remained virulent in mouse and insect infection models. These data demonstrate that HrdA and DerA support complementary ERAD functions that promote survival under conditions of ER stress but are dispensable for virulence in the host environment.
Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA.
Karthik
K
Krishnan
Xizhi
X
Feng
Margaret V
MV
Powers-Fletcher
Gregory
G
Bick
Daryl L
DL
Richie
Laura A
LA
Woollett
David S
DS
Askew
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D001228:Aspergillosis / Q000382:microbiology / Q000401:mortality; D001232:Aspergillus fumigatus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D003600:Cytosol / Q000187:drug effects; D025141:Drug Resistance, Fungal / Q000187:drug effects* / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000235:genetics; D060746:Endoplasmic Reticulum-Associated Degradation / Q000187:drug effects / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding; D011743:Pyrimidines / Q000494:pharmacology; D016019:Survival Analysis; D014230:Triazoles / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism; D014774:Virulence; D065819:Voriconazole
D000935:Antifungal Agents; D005656:Fungal Proteins; D011743:Pyrimidines; D014230:Triazoles; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; D065819:Voriconazole