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Ivermectin inhibits porcine reproductive and respiratory syndrome virus in cultured porcine alveolar macrophages

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating viral pathogen of swine that causes huge financial losses in the pig industry worldwide. Ivermectin is known to be a potent inhibitor of importin α/β-mediated nuclear transport and exhibits antiviral activity towards several RNA viruses by blocking the nuclear trafficking of viral proteins. Although PRRSV replication occurs exclusively in the cytoplasm of infected cells, the nucleocapsid (N) protein has been shown to distinctly localize in the nucleus and nucleolus throughout infection. Here, we sought to assess whether ivermectin suppresses PRRSV replication in cultured porcine alveolar macrophage (PAM) cells and to investigate the effect of ivermectin on the subcellular localization of the PRRSV N protein. Our data demonstrate that ivermectin treatment inhibits PRRSV infection in PAM-pCD163 cells in a dose-dependent manner. The antiviral activity of ivermectin on PRRSV replication was most effective when cells were treated during the early stage of infection. Treatment of PRRSV-infected cells with ivermectin significantly suppressed viral RNA synthesis, viral protein expression, and progeny virus production. However, immunofluorescence and cell fractionation assays revealed that ivermectin was incapable of disrupting the nuclear localization of the N protein, both in PRRSV-infected PAM-pCD163 cells and in PAM cells stably expressing the PRRSV N protein. This finding suggests that an alternative mechanism of action accounts for the ability of ivermectin to diminish PRRSV replication. Taken together, our results suggest that ivermectin is an invaluable therapeutic or preventative agent against PRRSV infection.

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Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2013R1A2A2A01004355) and Technology Development Program for Bio-industry, Ministry for Agriculture, Food and Rural Affairs, Republic of Korea (311007-05-1-HD120).

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Correspondence to Changhee Lee.

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705_2015_2653_MOESM1_ESM.tif

Fig. A1. Nuclear and cytoplasmic fractionation of PRRSV-infected PAM cells treated with ivermectin. Each nuclear and cytosolic fraction was prepared from PAM-pCD163 cells infected with PRRSV and treated with different concentrations of ivermectin for 48 h (A) or with a constant concentration of ivermectin (10 μM) at the indicated time points post-infection (B). These fractions were subjected to western blot analysis with an antibody specific for PRRSV N protein (top panel), α-tubulin as a cytosol protein marker (middle panel), or SP1 as a nuclear protein marker (bottom panel) (TIFF 11586 kb)

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Lee, Y.J., Lee, C. Ivermectin inhibits porcine reproductive and respiratory syndrome virus in cultured porcine alveolar macrophages. Arch Virol 161, 257–268 (2016). https://doi.org/10.1007/s00705-015-2653-2

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Keywords

  • Ivermectin
  • Ivermectin Treatment
  • Viral Protein Expression
  • Porcine Alveolar Macrophage
  • Functional Nuclear Localization Signal