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Coronavirus NSP6 restricts autophagosome expansion.

ABSTRACT: Autophagy is a cellular response to starvation that generates autophagosomes to carry long-lived proteins and cellular organelles to lysosomes for degradation. Activation of autophagy by viruses can provide an innate defense against infection, and for (+) strand RNA viruses autophagosomes can facilitate assembly of replicase proteins. We demonstrated that nonstructural protein (NSP) 6 of the avian coronavirus, infectious bronchitis virus (IBV), generates autophagosomes from the ER. A statistical analysis of MAP1LC3B puncta showed that NSP6 induced greater numbers of autophagosomes per cell compared with starvation, but the autophagosomes induced by NSP6 had smaller diameters compared with starvation controls. Small diameter autophagosomes were also induced by infection of cells with IBV, and by NSP6 proteins of MHV and SARS and NSP5, NSP6, and NSP7 of arterivirus PRRSV. Analysis of WIPI2 puncta induced by NSP6 suggests that NSP6 limits autophagosome diameter at the point of omegasome formation. IBV NSP6 also limited autophagosome and omegasome expansion in response to starvation and Torin1 and could therefore limit the size of autophagosomes induced following inhibition of MTOR signaling, as well as those induced independently by the NSP6 protein itself. MAP1LC3B-puncta induced by NSP6 contained SQSTM1, which suggests they can incorporate autophagy cargos. However, NSP6 inhibited the autophagosome/lysosome expansion normally seen following starvation. Taken together the results show that coronavirus NSP6 proteins limit autophagosome expansion, whether they are induced directly by the NSP6 protein, or indirectly by starvation or chemical inhibition of MTOR signaling. This may favor coronavirus infection by compromising the ability of autophagosomes to deliver viral components to lysosomes for degradation.

SUBMITTER: Cottam EM

PROVIDER: S-EPMC4203519 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Coronavirus NSP6 restricts autophagosome expansion.

Cottam Eleanor M EM Whelband Matthew C MC Wileman Thomas T

Autophagy 20140611 8

Autophagy is a cellular response to starvation that generates autophagosomes to carry long-lived proteins and cellular organelles to lysosomes for degradation. Activation of autophagy by viruses can provide an innate defense against infection, and for (+) strand RNA viruses autophagosomes can facilitate assembly of replicase proteins. We demonstrated that nonstructural protein (NSP) 6 of the avian coronavirus, infectious bronchitis virus (IBV), generates autophagosomes from the ER. A statistical ...[more]

PMID: 24991833

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Project description:Macroautophagy/autophagy is a conserved ubiquitous pathway that performs diverse roles in health and disease. Although many key, widely expressed proteins that regulate autophagosome formation followed by lysosomal fusion have been identified, the possibilities of cell-specific elements that contribute to the autophagy fusion machinery have not been explored. Here we show that a macrophage-specific isoform of the vacuolar ATPase protein ATP6V0D2/subunit d2 is dispensable for lysosome acidification, but promotes the completion of autophagy via promotion of autophagosome-lysosome fusion through its interaction with STX17 and VAMP8. Atp6v0d2-deficient macrophages have augmented mitochondrial damage, enhanced inflammasome activation and reduced clearance of Salmonella typhimurium. The susceptibility of atp6v0d2 knockout mice to DSS-induced colitis and Salmonella typhimurium-induced death, highlights the in vivo significance of ATP6V0D2-mediated autophagosome-lysosome fusion. Together, our data identify ATP6V0D2 as a key component of macrophage-specific autophagosome-lysosome fusion machinery maintaining macrophage organelle homeostasis and, in turn, limiting both inflammation and bacterial infection. Abbreviations: ACTB/β-actin: actin, beta; ATG14: autophagy related 14; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); ATP6V0D1/2: ATPase, H+ transporting, lysosomal V0 subunit D1/2; AIM2: absent in melanoma 2; BMDM: bone marrow-derived macrophage; CASP1: caspase 1; CGD: chronic granulomatous disease; CSF1/M-CSF: colony stimulating factor 1 (macrophage); CTSB: cathepsin B; DSS: dextran sodium sulfate; IL1B: interleukin 1 beta; IL6: interleukin 6; IRGM: immunity-related GTPase family M member; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LC3: microtubule-associated protein 1 light chain 3; LPS: lipo-polysaccaride; NLRP3: NLR family, pyrin domain containing 3; PYCARD/ASC: PYD and CARD domain containing; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; SNAP29: synaptosomal-associated protein 29; SQSTM1/p62: sequestosome 1; STX17: syntaxin 17; TLR: toll-like receptor; TNF: tumor necrosis factor ; TOMM20: translocase of outer mitochondrial membrane 20; ULK1: unc-51 like kinase 1; VAMP8: vesicle-associated membrane protein 8; WT: wild type; 3-MA: 3-methyladenine.

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Coronavirus NSP6 restricts autophagosome expansion.

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Coronavirus NSP6 restricts autophagosome expansion.

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