Endoplasmic Reticulum-Associated Degradation Controls Virus Protein Homeostasis, Which Is Required for Flavivirus Propagation

J Virol. 2021 Jul 12;95(15):e0223420. doi: 10.1128/JVI.02234-20. Epub 2021 Jul 12.

Abstract

Many positive-stranded RNA viruses encode polyproteins from which viral proteins are generated by processing the polyproteins. This system produces an equal amount of each viral protein, though the required amounts for each protein are not the same. In this study, we found the extra membrane-anchored nonstructural (NS) proteins of Japanese encephalitis virus and dengue virus are rapidly and selectively degraded by the endoplasmic reticulum-associated degradation (ERAD) pathway. Our gene targeting study revealed that ERAD involving Derlin2 and SEL1L, but not Derlin1, is required for the viral genome replication. Derlin2 is predominantly localized in the convoluted membrane (CM) of the viral replication organelle, and viral NS proteins are degraded in the CM. Hence, these results suggest that viral protein homeostasis is regulated by Derlin2-mediated ERAD in the CM, and this process is critical for the propagation of these viruses. IMPORTANCE The results of this study reveal the cellular ERAD system controls the amount of each viral protein in virus-infected cells and that this "viral protein homeostasis" is critical for viral propagation. Furthermore, we clarified that the "convoluted membrane (CM)," which was previously considered a structure with unknown function, serves as a kind of waste dump where viral protein degradation occurs. We also found that the Derlin2/SEL1L/HRD1-specific pathway is involved in this process, whereas the Derlin1-mediated pathway is not. This novel ERAD-mediated fine-tuning system for the stoichiometries of polyprotein-derived viral proteins may represent a common feature among polyprotein-encoding viruses.

Keywords: Derlin2; ERAD; Flavivirus; VCP; convoluted membrane; endoplasmic reticulum-associated degradation; valosin-containing protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Chlorocebus aethiops
  • Dengue Virus / growth & development
  • Dengue Virus / metabolism*
  • Encephalitis Virus, Japanese / growth & development
  • Encephalitis Virus, Japanese / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum-Associated Degradation / physiology*
  • Genome, Viral / genetics
  • HCT116 Cells
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Membrane Proteins / metabolism*
  • Proteins / metabolism*
  • RNA Interference
  • RNA, Small Interfering / genetics
  • Ubiquitin-Protein Ligases / metabolism
  • Valosin Containing Protein / metabolism
  • Vero Cells
  • Viral Nonstructural Proteins / metabolism*
  • Virus Replication / physiology

Substances

  • DERL1 protein, human
  • DERL2 protein, human
  • Membrane Proteins
  • Proteins
  • RNA, Small Interfering
  • SEL1L protein, human
  • Viral Nonstructural Proteins
  • SYVN1 protein, human
  • Ubiquitin-Protein Ligases
  • VCP protein, human
  • Valosin Containing Protein