miRNA independent hepacivirus variants suggest a strong evolutionary pressure to maintain miR-122 dependence

PLoS Pathog. 2017 Oct 30;13(10):e1006694. doi: 10.1371/journal.ppat.1006694. eCollection 2017 Oct.

Abstract

Hepatitis C virus (HCV) requires the liver specific micro-RNA (miRNA), miR-122, to replicate. This was considered unique among RNA viruses until recent discoveries of HCV-related hepaciviruses prompting the question of a more general miR-122 dependence. Among hepaciviruses, the closest known HCV relative is the equine non-primate hepacivirus (NPHV). Here, we used Argonaute cross-linking immunoprecipitation (AGO-CLIP) to confirm AGO binding to the single predicted miR-122 site in the NPHV 5'UTR in vivo. To study miR-122 requirements in the absence of NPHV-permissive cell culture systems, we generated infectious NPHV/HCV chimeric viruses with the 5' end of NPHV replacing orthologous HCV sequences. These chimeras were viable even in cells lacking miR-122, although miR-122 presence enhanced virus production. No other miRNAs bound this region. By random mutagenesis, we isolated HCV variants partially dependent on miR-122 as well as robustly replicating NPHV/HCV variants completely independent of any miRNAs. These miRNA independent variants even replicate and produce infectious particles in non-hepatic cells after exogenous delivery of apolipoprotein E (ApoE). Our findings suggest that miR-122 independent HCV and NPHV variants have arisen and been sampled during evolution, yet miR-122 dependence has prevailed. We propose that hepaciviruses may use this mechanism to guarantee liver tropism and exploit the tolerogenic liver environment to avoid clearance and promote chronicity.

MeSH terms

  • Apolipoproteins E / genetics
  • Apolipoproteins E / metabolism
  • Argonaute Proteins / genetics
  • Argonaute Proteins / metabolism
  • Cell Line, Tumor
  • Eukaryotic Initiation Factors / genetics
  • Eukaryotic Initiation Factors / metabolism
  • Evolution, Molecular*
  • Hepacivirus / genetics
  • Hepacivirus / metabolism*
  • Hepatitis C / genetics
  • Hepatitis C / metabolism*
  • Humans
  • MicroRNAs / genetics
  • MicroRNAs / metabolism*
  • Mutagenesis
  • Viral Tropism / physiology*

Substances

  • AGO1 protein, human
  • Apolipoproteins E
  • Argonaute Proteins
  • Eukaryotic Initiation Factors
  • MIRN122 microRNA, human
  • MicroRNAs