title: Repression of N-glycosylation triggers the unfolded protein response (UPR) and overexpression of cell wall protein and chitin in Aspergillus fumigatus.
abstract: Aspergillus fumigatus is the most common airborne fungal pathogen, causing fatal invasive aspergillosis in immunocompromised patients. The crude mortality is 60-90 % and remains around 29-42 % even with treatment. The main reason for patient death is the low efficiency of the drug therapies. As protein N-glycosylation is involved in cell wall biogenesis in A. fumigatus, a deeper understanding of its role in cell wall biogenesis will help to develop new drug targets. The Afstt3 gene encodes the essential catalytic subunit of oligosaccharyltransferase, an enzyme complex responsible for the transfer of the N-glycan to nascent polypeptides. To evaluate the role of N-glycosylation in cell wall biosynthesis, we constructed the conditional mutant strain CPR-stt3 by replacing the endogenous promoter of Afstt3 with the nitrogen-dependent niiA promoter. Repression of the Afstt3 gene in the CPR-stt3 strain led to a severe retardation of growth and a slight defect in cell wall integrity (CWI). One of the most interesting findings was that upregulation of the cell wall-related genes was not accompanied by an activation of the MpkA kinase, which has been shown to be a central element in the CWI signalling pathway in both Saccharomyces cerevisiae and A. fumigatus. Considering that the unfolded protein response (UPR) was found to be activated, which might upregulate the expression of cell wall protein and chitin, our data suggest that the UPR, instead of the MpkA-dependent CWI signalling pathway, is the major compensatory mechanism induced by repression but not abolition of N-glycosylation in A. fumigatus. Our finding is a key to understanding the complex compensatory mechanisms of cell wall biosynthesis and may provide a new strategy for drug development.
authors.affiliation: Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China.
authors.forename: Kai
authors.initials: K
authors.lastname: Li
authors.affiliation: Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China.
authors.forename: Haomiao
authors.initials: H
authors.lastname: Ouyang
authors.affiliation: Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Lü
authors.affiliation: Core Facility of Equipment, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China.
authors.forename: Jingnan
authors.initials: J
authors.lastname: Liang
authors.affiliation: Department of Chemistry, University of Natural Resources and Life Sciences, Vienna A-1190, Austria.
authors.forename: Iain B H
authors.initials: IBH
authors.lastname: Wilson
authors.affiliation: Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Jin
mesh_terms: D001232:Aspergillus fumigatus / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015153:Blotting, Western; D002473:Cell Wall / Q000378:metabolism*; D002686:Chitin / Q000096:biosynthesis*; D005656:Fungal Proteins / Q000096:biosynthesis*; D015870:Gene Expression; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005936:Glucans / Q000096:biosynthesis; D006031:Glycosylation; D006602:Hexosyltransferases / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D056811:Unfolded Protein Response
chemical_list: D005656:Fungal Proteins; D005936:Glucans; D008565:Membrane Proteins; D002686:Chitin; D006602:Hexosyltransferases; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase