title: Coronavirus nsp6 proteins generate autophagosomes from the endoplasmic reticulum via an omegasome intermediate.
abstract: Autophagy is a cellular response to starvation which generates autophagosomes to carry cellular organelles and long-lived proteins to lysosomes for degradation. Degradation through autophagy can provide an innate defence against virus infection, or conversely autophagosomes can promote infection by facilitating assembly of replicase proteins. We demonstrate that the avian coronavirus, Infectious Bronchitis Virus (IBV) activates autophagy. A screen of individual IBV non-structural proteins (nsps) showed that autophagy was activated by IBV nsp6. This property was shared with nsp6 of mammalian coronaviruses Mouse Hepatitis Virus, and Severe Acute Respiratory Syndrome Virus, and the equivalent nsp5-7 of the arterivirus Porcine Reproductive and Respiratory Syndrome Virus. These multiple-spanning transmembrane proteins located to the endoplasmic reticulum (ER) where they generated Atg5 and LC3II-positive vesicles, and vesicle formation was dependent on Atg5 and class III PI3 kinase. The vesicles recruited double FYVE-domain containing protein (DFCP) indicating localised concentration of phosphatidylinositol 3 phosphate, and therefore shared many features with omegasomes formed from the ER in response to starvation. Omegasomes induced by viral nsp6 matured into autophagosomes that delivered LC3 to lysosomes and therefore recruited and recycled the proteins needed for autophagosome nucleation, expansion, cellular trafficking and delivery of cargo to lysosomes. The coronavirus nsp6 proteins activated omegasome and autophagosome formation independently of starvation, but activation did not involve direct inhibition of mTOR signalling, activation of sirtuin1 or induction of ER stress.
authors.affiliation: Biomedical Research Centre, Faculty of Health, School of Medicine, University of East Anglia, Norwich, UK.
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Cottam
authors.forename: Helena J
authors.initials: HJ
authors.lastname: Maier
authors.forename: Maria
authors.initials: M
authors.lastname: Manifava
authors.forename: Laura C
authors.initials: LC
authors.lastname: Vaux
authors.forename: Priya
authors.initials: P
authors.lastname: Chandra-Schoenfelder
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Gerner
authors.forename: Paul
authors.initials: P
authors.lastname: Britton
authors.forename: Nick T
authors.initials: NT
authors.lastname: Ktistakis
authors.forename: Tom
authors.initials: T
authors.lastname: Wileman
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D018018:Arterivirus / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D000071187:Autophagy-Related Protein 5; D002460:Cell Line; D018352:Coronavirus Infections / Q000473:pathology / Q000821:virology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000821:virology; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D016679:Genome, Viral / Q000235:genetics; D006801:Humans; D001351:Infectious bronchitis virus / Q000235:genetics / Q000378:metabolism*; D008561:Membrane Fusion / Q000187:drug effects; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D051742:Transcription Factor CHOP / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; D008869:Microtubule-Associated Proteins; D018129:Phosphatidylinositol Phosphates; D017361:Viral Nonstructural Proteins; C055525:phosphatidylinositol 3-phosphate; D051742:Transcription Factor CHOP; D058570:TOR Serine-Threonine Kinases; D000077191:Wortmannin