Activation of ERAD pathway by human hepatitis B virus modulates viral and subviral particle production

PLoS One. 2012;7(3):e34169. doi: 10.1371/journal.pone.0034169. Epub 2012 Mar 26.

Abstract

Hepatitis B virus (HBV) belongs to the Hepadnaviridae family of enveloped DNA viruses. It was previously shown that HBV can induce endoplasmic reticulum (ER) stress and activate the IRE1-XBP1 pathway of the unfolded protein response (UPR), through the expression of the viral regulatory protein X (HBx). However, it remained obscure whether or not this activation had any functional consequences on the target genes of the UPR pathway. Of these targets, the ER degradation-enhancing, mannosidase-like proteins (EDEMs) are thought to play an important role in relieving the ER stress during UPR, by recognizing terminally misfolded glycoproteins and delivering them to the ER-associated degradation (ERAD). In this study, we investigated the role of EDEMs in the HBV life-cycle. We found that synthesis of EDEMs (EDEM1 and its homologues, EDEM2 and EDEM3) is significantly up-regulated in cells with persistent or transient HBV replication. Co-expression of the wild-type HBV envelope proteins with EDEM1 resulted in their massive degradation, a process reversed by EDEM1 silencing. Surprisingly, the autophagy/lysosomes, rather than the proteasome were involved in disposal of the HBV envelope proteins. Importantly, inhibition of the endogenous EDEM1 expression in HBV replicating cells significantly increased secretion of both, enveloped virus and subviral particles. This is the first report showing that HBV activates the ERAD pathway, which, in turn, reduces the amount of envelope proteins, possibly as a mechanism to control the level of virus particles in infected cells and facilitate the establishment of chronic infections.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autophagy
  • Blotting, Western
  • Calcium-Binding Proteins
  • Cell Line, Tumor
  • Endoplasmic Reticulum-Associated Degradation*
  • Gene Expression
  • Glycoproteins / genetics
  • Glycoproteins / metabolism
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • HEK293 Cells
  • Hep G2 Cells
  • Hepatitis B virus / genetics*
  • Hepatitis B virus / physiology
  • Host-Pathogen Interactions / genetics
  • Humans
  • Lysosomes / metabolism
  • Mannosidases
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Microscopy, Fluorescence
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • RNA Interference
  • Reverse Transcriptase Polymerase Chain Reaction
  • Virion / genetics*
  • Virion / physiology
  • Virus Replication / genetics*
  • alpha-Mannosidase / genetics
  • alpha-Mannosidase / metabolism

Substances

  • Calcium-Binding Proteins
  • EDEM1 protein, human
  • Glycoproteins
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • light chain 3, human
  • Green Fluorescent Proteins
  • Mannosidases
  • EDEM2 protein, human
  • EDEM3 protein, human
  • alpha-Mannosidase