The effect of recombinant chimeric swine PKR-Apaf-1 proteins on viral-load reduction of PRRS and PED alpha-coronavirus infected cell lines

Abstract

The PRRS virus and PED alpha-coronavirus are the two main pig pathogens in the world. The current strategies to control these diseases are inadequate. The recombinant chimeric swine PKR-Apaf-1 protein (rcPAP) consists of the Human Immunodeficiency Virus Trans-activator transcription (HIV-TAT) domain, the dsRNA-binding domain of porcine Protein kinase R (PKR) gene and the caspase recruitment domain (CARD) domain of porcine Apoptotic Protease-Activating Factor-1 (Apaf-1) gene. In general, the rcPAP can detect viral dsRNA in virally infected cells and induces apoptosis and kills the virus-infected cells. In this study, the reducing viral-load efficacy of rcPAP (produced from bacteria) against PRRS virrus and PED alpha-coronavirus replication in the cell line was studied. The four concentrations of rcPAP (40, 60, 80 and 120 μg/ml) were studied at three different periods (24, 36 and 48 h post inoculation (hpi)). The results showed that no cytotoxicity in two cell lines was observed during rcPAP addition. The rcPAP (80 μg/ml) significantly increased the monkey active caspase-3 levels at 17.09 for the PRRS virus and at 15.96-fold for the PED alpha-coronavirus at 48 hpi, respectively (p < 0.05). The viral RNA copy numbers at 48 hpi were significantly reduced up to 84.47% of PRRS virus and up to 82.98% for PED alpha-coronavirus when treated with rcPAP (80 μg/ml) (p < 0.05), respectively. Interestingly, the viral titers at 48 hpi were dramatically decreased by 87.76% for PRRS virus and by 86.29% for PED alpha-coronavirus in virus-infected cells treated with rcPAP (80 μg/ml), respectively. The results also demonstrated that the rcPAP was able to reduce the viral load and viral N protein synthesis in both virus-infected cell lines. In conclusion, the results suggest that rcPAP is likely to be a valuable therapeutic agent against both PRRS virus and PED alpha-coronavirus infection.