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Cell-type-specific activation of the oligoadenylate synthetase-RNase L pathway by a murine coronavirus

Ling Zhao1, L Dillon Birdwell, Ashley Wu

  • 1Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Journal of Virology
|May 24, 2013
PubMed

Insights

Mouse hepatitis virus ns2 protein inhibits the OAS-RNase L pathway. Its enzymatic activity is crucial for MHV replication in macrophages and hepatitis induction, but not brain infection.

Area of Science:

  • Virology
  • Immunology
  • Molecular Biology

Background:

  • Murine coronavirus (MHV) nonstructural protein 2 (ns2) functions as a 2',5'-phosphodiesterase.
  • MHV ns2 inhibits the interferon-induced oligoadenylate synthetase (OAS)-RNase L pathway.
  • Enzymatically active ns2 is essential for MHV replication in macrophages and hepatitis induction in mice.

Purpose of the Study:

  • To investigate the cell type-specific role of MHV ns2 enzymatic activity in viral replication and innate immune response.
  • To compare the replication kinetics of wild-type MHV and an ns2 mutant in various primary cell types.
  • To determine the conditions for RNase L activation during MHV infection.

Main Methods:

  • Replication assays of MHV strain A59 (A59) and ns2-H126R mutant in primary hepatocytes, neurons, astrocytes, oligodendrocytes, macrophages, and microglia.
  • Assessment of RNase L activity via rRNA cleavage.
  • Measurement of type I interferon and OAS mRNA levels.
  • Interferon pretreatment and poly(I·C) stimulation experiments.

Main Results:

  • MHV and ns2-H126R replicated similarly in hepatocytes, neurons, astrocytes, and oligodendrocytes.
  • RNase L activity was induced by ns2-H126R but not A59, specifically in macrophages and microglia.
  • RNase L activation correlated with type I interferon and OAS mRNA induction in myeloid cells.
  • Interferon pretreatment restricted viral replication but did not activate RNase L in non-myeloid cells.
  • Poly(I·C) induced rRNA degradation in astrocytes and oligodendrocytes, indicating RNase L potential.

Conclusions:

  • MHV ns2 enzymatic activity is critical for inhibiting the OAS-RNase L pathway in macrophages and microglia.
  • RNase L activation during MHV infection is cell type-specific, requiring high OAS gene expression.
  • While OAS expression is necessary, it is not sufficient for an effective RNase L antiviral response in all cell types.

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