title: Autophagy is dispensable to overcome ER stress in the filamentous fungus Aspergillus niger.
abstract: Secretory proteins are subjected to stringent quality control systems in the endoplasmic reticulum (ER) which include the targeting of misfolded proteins for proteasomal destruction via the ER-associated degradation (ERAD) pathway. Since deletion of ERAD genes in the filamentous fungus Aspergillus niger had hardly any effect on growth, this study investigates whether autophagy might function as an alternative process to eliminate misfolded proteins from the ER. We generated A. niger double mutants by deleting genes essential for ERAD (derA) and autophagy (atg1 or atg8), and assessed their growth both under normal and ER stress conditions. Sensitivity toward ER stress was examined by treatment with dithiothreitol (DTT) and by expressing a mutant form of glucoamylase (mtGlaA::GFP) in which disulfide bond sites in GlaA were mutated. Misfolding of mtGlaA::GFP was confirmed, as mtGlaA::GFP accumulated in the ER. Expression of mtGlaA::GFP in ERAD and autophagy mutants resulted in a twofold higher accumulation in ΔderA and ΔderAΔatg1 strains compared to Δatg1 and wild type. As ΔderAΔatg1 mutants did not show increased sensitivity toward DTT, not even when mtGlaA::GFP was expressed, the results indicate that autophagy does not act as an alternative pathway in addition to ERAD for removing misfolded proteins from the ER in A. niger.
authors.affiliation: Molecular Microbiology and Biotechnology, Institute of Biology Leiden, Leiden University, Sylviusweg 72, 2333 BE, Leiden, The Netherlands.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Burggraaf
authors.affiliation: Molecular Microbiology and Biotechnology, Institute of Biology Leiden, Leiden University, Sylviusweg 72, 2333 BE, Leiden, The Netherlands.
authors.forename: Arthur F J
authors.initials: AF
authors.lastname: Ram
mesh_terms: D001234:Aspergillus niger / Q000502:physiology*; D001343:Autophagy / Q000235:genetics* / Q000502:physiology*; D000071190:Autophagy-Related Protein 8 Family / Q000235:genetics; D000071189:Autophagy-Related Protein-1 Homolog / Q000235:genetics; D004229:Dithiothreitol / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000502:physiology*; D060746:Endoplasmic Reticulum-Associated Degradation / Q000235:genetics* / Q000502:physiology*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D055786:Gene Knockout Techniques; D005087:Glucan 1,4-alpha-Glucosidase / Q000235:genetics; D017510:Protein Folding
chemical_list: D000071190:Autophagy-Related Protein 8 Family; D000071189:Autophagy-Related Protein-1 Homolog; D005087:Glucan 1,4-alpha-Glucosidase; D004229:Dithiothreitol
keywords: ERAD; UPR.; atg1; endoplasmic reticulum; misfolded protein; secretory protein