Many viruses trigger the
type I interferon (IFN) pathway upon
infection, resulting in the transcription of hundreds of
interferon-stimulated genes (ISGs), which define the
antiviral state of the host. Classical swine fever virus (CSFV) is the causative agent of
classical swine fever (CSF), a highly contagious
viral disease endangering the pig industry in many countries. However, anti-CSFV ISGs are poorly documented. Here we screened 20 ISGs that are commonly induced by type I IFNs against CSFV in lentivirus-delivered cell lines, resulting in the identification of guanylate-
binding protein 1 (GBP1) as a potent anti-CSFV ISG. We observed that overexpression of GBP1, an IFN-induced
GTPase, remarkably suppressed CSFV replication, whereas knockdown of endogenous GBP1 expression by small interfering RNAs significantly promoted CSFV growth. Furthermore, we demonstrated that GBP1 acted mainly on the early phase of CSFV replication and inhibited the translation efficiency of the
internal ribosome entry site of CSFV. In addition, we found that GBP1 was upregulated at the transcriptional level in CSFV-infected PK-15 cells and in various organs of CSFV-infected pigs. Coimmunoprecipitation and
glutathione S-transferase (GST) pulldown assays revealed that GBP1 interacted with the NS5A
protein of CSFV, and this interaction was mapped in the N-terminal globular
GTPase domain of GBP1. Interestingly, the K51 of GBP1, which is crucial for its
GTPase activity, was essential for the inhibition of CSFV replication. We showed further that the NS5A-GBP1 interaction inhibited
GTPase activity, which was critical for its
antiviral effect. Taking our findings together, GBP1 is an anti-CSFV ISG whose action depends on its
GTPase activity.
IMPORTANCE: Classical swine fever virus (CSFV) is the causative agent of
classical swine fever (CSF), an economically important
viral disease affecting the pig industry in many countries. To date, only a few host restriction factors against CSFV, including
interferon-stimulated genes (ISGs), have been characterized. Using a minilibrary of porcine ISGs, we identify porcine guanylate-
binding protein 1 (GBP1) as a potent
antiviral ISG against CSFV. We further show that the anti-CSFV action of GBP1 depends on its
GTPase activity. The K51 of GBP1, critical for its
GTPase activity, is essential for the
antiviral action of GBP1 against CSFV replication, and the binding of the NS5A
protein to GBP1 antagonizes the
GTPase activity and thus the
antiviral effect. This study will facilitate the development of anti-CSFV therapeutic agents by targeting host factors and may provide a new strategy for the control of CSF.