Endosomal proteolysis by cathepsins is necessary for murine coronavirus mouse hepatitis virus type 2 spike-mediated entry

Zhaozhu Qiu, Susan T. Hingley, Graham Simmons, Christopher Yu, Jayasri Das Sarma, Paul Bates, Susan R. Weiss

Research output: Contribution to journalArticlepeer-review

Abstract

Most strains of murine coronavirus mouse hepatitis virus (MHV) express a cleavable spike glycoprotein that mediates viral entry and pH-independent cell-cell fusion. The MHV type 2 (MHV-2) strain of murine coronavirus differs from other strains in that it expresses an uncleaved spike and cannot induce cell-cell fusion at neutral pH values. We show here that while infection of the prototype MHV-A59 strain is not sensitive to pretreatment with lysosomotropic agents, MHV-2 replication is significantly inhibited by these agents. By use of an A59/MHV-2 chimeric virus, the susceptibility to lysosomotropic agents is mapped to the MHV-2 spike, suggesting a requirement of acidification of endosomes for MHV-2 spike-mediated entry. However, acidification is likely not a direct trigger for MHV-2 spike-mediated membrane fusion, as low-pH treatment is unable to overcome ammonium chloride inhibition, and it also cannot induce cell-cell fusion between MHV-2-infected cells. In contrast, trypsin treatment can both overcome ammonium chloride inhibition and promote cell-cell fusion. Inhibitors of the endosomal cysteine proteases cathepsin B and cathepsin L greatly reduce MHV-2 spike-mediated entry, while they have little effect on A59 entry, suggesting that there is a protcolytic step in MHV-2 entry. Finally, a recombinant virus expressing a cleaved MHV-2 spike has the ability to induce cell-cell fusion at neutral pH values and does not require low pH and endosomal cathepsins during infection. These studies demonstrate that endosomal proteolysis by cathepsins is necessary for MHV-2 spike-mediated entry; this is similar to the entry pathway recently described for severe acute respiratory syndrome coronavirus and indicates that coronaviruses may use multiple pathways for entry.

Original languageEnglish (US)
Pages (from-to)5768-5776
Number of pages9
JournalJournal of virology
Volume80
Issue number12
DOIs
StatePublished - Jun 2006
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Insect Science
  • Virology

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