Antagonizing JAK-STAT signaling by porcine reproductive and respiratory syndrome virus

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The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway is activated by numerous cytokines. JAK-STAT pathways involve in regulation of cell growth, proliferation, differentiation, apoptosis, angiogenesis, immunity and inflammatory response. Because of their significance in immune response, they are often targeted by pathogens, including porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV causes reproductive failure in sows and severe respiratory disease in pigs of all ages. A typical feature of the immune response to PRRSV infection in pigs is delayed production and low titer of virus neutralizing antibodies, and weak cell-mediated immune response. One possible reason for the weak protective immune response is that PRRSV interferes with innate immunity and modulates cytokine signaling, including JAK-STAT pathways. The objective of this project was to elucidate the mechanisms of PRRSV interference with JAK-STAT2 and JAK-STAT3 signaling. This study demonstrates that PRRSV antagonizes interferon (IFN)-activated JAK-STAT2 signaling and oncostatin M (OSM)-activated JAK-STAT3 pathway via inducing STAT2 and STAT3 degradation. Mechanistically, PRRSV non-structural protein 11 (nsp11) and nsp5 induce the degradation of STAT2 and STAT3, respectively, via the ubiquitin-proteasome pathway. Notably, PRRSV manipulates karyopherin alpha 6 (KPNA6), an importin that is responsible for STAT3 nuclear translocation in the JAK-STAT signaling, to facilitate viral replication. Knockdown of KPNA6 expression led to significant reduction in PRRSV replication. These data demonstrate that PRRSV interferes with different JAK-STAT pathways to evade host antiviral response while harnessing cellular factors for its own replication. These findings provide new insights into PRRSV-cell interactions and its molecular pathogenesis in interference with the host immune response, and facilitate the development of novel antiviral therapeutics.