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Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway is activated by myriad cytokines, which are involved in regulation of cell growth, proliferation, differentiation, apoptosis, angiogenesis, immunity and inflammatory response. Because of its significance in immune response, JAK-STAT pathway is often targeted by pathogens, including porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV causes reproductive failure in sows and 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 of the possible reasons for the weak protective immune response is that PRRSV interferes with cytokine-mediated JAK-STAT signaling. PRRSV inhibits interferon-activated JAK-STAT signaling by blocking nuclear translocation of STAT1 and STAT2. The mechanism is that PRRSV non-structural protein 1β (nsp1β) induces degradation of karyopherin α1 (KPNA1), a critical adaptor in nucleo-cytoplasmic transport. PRRSV also antagonizes IL6-activated JAK-STAT3 signaling via inducing degradation of STAT3. In this review, we briefly introduce JAK-STAT signaling, summarize the PRRSV interference with it, and provide perspective on the perturbation in the context of PRRSV-elicited immune response. [ABSTRACT FROM AUTHOR]

Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of a contagious disease characterized by reproductive failure in sows and respiratory disease in piglets. This infectious disease results in significant losses in the swine industry and specific anti-PRRSV drugs are needed. In this study, we evaluated a novel class of antisense compounds, peptide-conjugated phosphorodiamidate morpholino oligomers (P-PMOs), for their ability to suppress PRRSV replication in cell culture. P-PMOs are analogs of single-stranded DNA and contain a modified backbone that confers highly specific binding to RNA and resistance to nucleases. Of six P-PMOs tested, one (‘5UP1’), with sequence complementary to the 5′-terminal 21 nucleotides of the PRRSV genome, was found to be highly effective at reducing PRRSV replication in a specific and dose-dependent manner in CRL11171 cells in culture. 5UP1 treatment generated up to a 4.5log reduction in infectious PRRSV yield, while a control P-PMO had no effect on viral titer. Immunofluorescence assay with an anti-PRRSV monoclonal antibody confirmed the titer observations. The sequence-specificity of 5UP1 effect was confirmed in part by a cell-free luciferase reporter assay system, which showed that 5UP1-mediated inhibition of translation decreased if the target-RNA contained mispairings in relation to the 5UP1 P-PMO. Real-time RT-PCR showed that the production of PRRSV negative-sense RNA was reduced if 5UP1 was added to cells at up to 6h post-virus inoculation. Cell viability assays detected no cytotoxicity of 5UP1 within the concentration-range of this study. These results indicate that P-PMO 5UP1 has potential as an anti-PRRSV agent. [Copyright &y& Elsevier]

The interferon-induced double-strand RNA activated protein kinase (PKR) plays an important role in antiviral response. The objective of this study was to assess the effect of porcine reproductive and respiratory syndrome virus (PRRSV) on PKR activation. Here we report that PRRSV inhibited PKR activation during its early stage infection of primary pulmonary alveolar macrophages (PAMs). PRRSV infection led to lower level of phosphorylated PKR in comparison with mock-infected cells. The PKR inhibition was sustained until 10 h post infection in the presence of polyI:C, a synthetic analog of double-stranded RNA activating PKR. PKR-mediated phosphorylation of the eukaryotic translation initiation factor eIF2α was also lower in the PRRSV-infected PAMs during the early stage infection. Interestingly, inactivated PRRSV was capable to inhibit the PKR activation until 6 h post infection. This suggests that structural components of PRRSV virions were responsible for the inhibition, although PRRSV replication was needed for longer inhibition. These results indicate that the downregulation of PKR activation during early infection stage should be essential for PRRSV to avoid the antiviral response to initiate replication. This finding contributes to our understanding on PRRSV interaction with host innate immune response and reveal a target for control of PRRSV infection. [ABSTRACT FROM AUTHOR]

Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV) is a positive-sense single-strand RNA virus that has contributed to substantial losses to the swine industry. The objective of this study was to examine the interference of interferon (IFN)-activated signaling by PRRSV viral proteins and compare the effects of several PRRSV strains on the IFN signaling. Three non-structural proteins (nsp 1β, 7 and 12) and two structural proteins (GP3 and N) of VR-2385 were found to significantly inhibit the expression of IFN-stimulated response element (ISRE) luciferase reporter. Nsp1β and N showed robust inhibition and their-encoding sequences from the six PRRSV strains (VR-2385, Ingelvac PRRS MLV, VR-2332, NVSL97-7895, MN184, and Lelystad) were cloned for further characterization. The nsp1βs of all the strains except MLV inhibited expression of IFN-induced ISRE reporter, interferon-stimulated gene 56 (ISG56) and signal transducer and activator of transcription 2 (STAT2). The N proteins inhibited the IFN-induced ISRE reporter expression and STAT2 elevation and blocked nuclear translocation of STAT1. In MARC-145 cells, all the six PRRSV strains with the exception of MN184 blocked the activity of exogenous IFN-α. In primary porcine pulmonary alveolar macrophages (PAMs), only MLV and NVSL failed to inhibit the activity of IFN-α. These results indicate that some PRRSV strains, such as NVSL and MN184, have variable effects on IFN-activated signaling in the two types of cells. [Copyright &y& Elsevier]