55: African swine fever virus include multiple mechanisms for the manipulation of interferon responses

Abstract

The African Swine Fever Virus (ASFV) is an acute virus with a tropism for the pig macrophage and the ability to persist. In spite of these characteristics, no individual ASFV gene has been described which interferes with the impact of interferon (IFN) response. Moreover, bioinformatic searching failed to detect any ASFV genes with any homology to the IFN system. Therefore, we cloned and screened a total of 16 early expressed, non-homologous ASFV genes in luciferase reporter assays for their effect on the induction and impact of IFN responses. Five of these viral genes were demonstrated to inhibit the impact of IFN. One, the ASFV open reading frame (ORF) DP148R coding for protein MGF360-18R, inhibited luciferase reporter assays monitoring activation of the host cell response to both type I and type II IFN’s. Cells expressing this viral protein exhibited a clear reduction in the levels of STAT1, a critical transcription factor of the Jak-STAT pathway. Inhibition of the ubiquitin–proteasome pathway using the 26S proteasome inhibitor MG132 reversed the MGF360-18R-mediated degradation of STAT1. We conclude that ASFV has evolved multiple mechanisms for the manipulation of IFN responses and that MGF360-18R, in particular, manipulates the polyubiquitination system to induce degradation of STAT1, a critical signalling intermediate of the Jak-STAT pathway. Finally, the hypothesis that early expressed, non-homologous ASFV genes might include mechanisms for the inhibition of IFN responses, and indeed for host cell manipulation in general, has been confirmed.