In vitro inhibition of the replication of classical swine fever virus by porcine Mx1 protein

• This is the first report that porcine Mx1 can inhibit CSFV replication.
• The EGFP–poMx1 fusion proteins have a GTPase activity.
• The EGFP–poMx1 fusion proteins efficiently inhibit CSFV replication.
• The PTD–poMx1 fusion proteins can also inhibit CSFV replication.
• Porcine Mx1 may be developed into an antiviral agent against CSFV infection.

Classical swine fever virus (CSFV) is the causative pathogen of classical swine fever (CSF), a highly contagious disease of swine. Mx proteins are interferon-induced dynamin-like GTPases present in all vertebrates with a wide range of antiviral activities. Although Zhao et al. (2011) have reported that human MxA can inhibit CSFV replication, whether porcine Mx1 (poMx1) has anti-CSFV activity remains unknown. In this study, we generated a cell line designated PK-15/EGFP–poMx1 which expressed porcine Mx1 protein constitutively, and we observed that the proliferation of progeny virus in this cell line was significantly inhibited as measured by virus titration, indirect immune fluorescence assay, Q-PCR and Western blot. Furthermore, when PTD–poMx1 fusion protein expressed in Escherichia coli (Zhang et al., 2013) was used to treat CSFV-infected PK-15 cells, the results showed that PTD–poMx1 inhibited CSFV replication in a dose-dependent manner. Additionally, the proliferation of progeny virus was inhibited as measured by virus titration and Q-PCR. Overall, the results demonstrated that poMx1 effectively inhibited CSFV replication, suggesting that poMx1 may be a valuable therapeutic agent against CSFV infection.