Classical swine fever virus can remain virulent after specific elimination of the interferon regulatory factor 3-degrading function of Npro

Nicolas Ruggli, Artur Summerfield, Ana R. Fiebach, Laurence Guzylack-Piriou, Oliver Bauhofer, Catherine G. Lamm, Sandro Waltersperger, Keita Matsuno, Luzia Liu, Markus Gerber, Kyung H. Choi, Martin A. Hofmann, Yoshihiro Sakoda, Jon Duri Tratschin

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68 Scopus citations


Pestiviruses prevent alpha/beta interferon (IFN-α/β) production by promoting proteasomal degradation of interferon regulatory factor 3 (IRF3) by means of the viral Npro nonstructural protein. Npro is also an autoprotease, and its amino-terminal coding sequence is involved in translation initiation. We previously showed with classical swine fever virus (CSFV) that deletion of the entire Npro gene resulted in attenuation in pigs. In order to elaborate on the role of the Npro-mediated IRF3 degradation in classical swine fever pathogenesis, we searched for minimal amino acid substitutions in Npro that would specifically abrogate this function. Our mutational analyses showed that degradation of IRF3 and autoprotease activity are two independent but structurally overlapping functions of Npro. We describe two mutations in Npro that eliminate Npro-mediated IRF3 degradation without affecting the autoprotease activity. We also show that the conserved standard sequence at these particular positions is essential for Npro to interact with IRF3. Surprisingly, when these two mutations are introduced independently in the backbones of highly and moderately virulent CSFV, the resulting viruses are not attenuated, or are only partially attenuated, in 8- to 10-week-old pigs. This contrasts with the fact that these mutant viruses have lost the capacity to degrade IRF3 and to prevent IFN-α/β induction in porcine cell lines and monocyte-derived dendritic cells. Taken together, these results demonstrate that contrary to previous assumptions and to the case for other viral systems, impairment of IRF3-dependent IFN-α/β induction is not a prerequisite for CSFV virulence.

Original languageEnglish (US)
Pages (from-to)817-829
Number of pages13
JournalJournal of virology
Issue number2
StatePublished - Jan 2009
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Insect Science
  • Virology


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