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Downregulation of miR-218 by porcine reproductive and respiratory syndrome virus facilitates viral replication via inhibition of type I interferon responses.

ABSTRACT: Porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating pathogen in the swine industry worldwide. miRNAs are reported to be involved in virus-host interaction. Here, we used high-throughput sequencing and miRNA inhibitors to screen possible miRNAs that can inhibit PRRSV infection on its target cell, porcine alveolar macrophages. We observed that miR-218 was downregulated upon virus infection, and knockdown of miR-218 significantly enhanced PRRSV replication. Overexpression of miR-218 resulted in a decrease in PRRSV replication, and this overexpression did not alter viral genomic RNA levels, but rather increased antiviral interferon signaling. Further analysis revealed that miR-218 regulated PRRSV replication by directly targeting porcine suppressor of cytokine signaling 3 (SOCS3), a JAK2 kinase inhibitor. Knockdown of the endogenous SOCS3 expression led to augmentation of type I interferon genes and resulted in decreased PRRSV replication, and vice versa. During PRRSV infection in vivo and in vitro, cellular miR-218 expression was downregulated and SOCS3 expression was upregulated, further supporting the inverse correlation between miR-218 and SOCS3 expression. The data on SOCS3 depletion in combination with miR-218 inhibition suggested that the antiviral activity of miR-218 required the SOCS3-mediated signaling pathway. Similarly, miR-218 negatively regulated PRRSV replication in Marc-145 cells, as well as the replication of porcine epidemic diarrhea virus and transmissible gastroenteritis virus in Vero and ST cells respectively. Taken together, these results demonstrate that PRRSV-induced miR-218 downregulation serves to inhibit the type I interferon response and may provide a novel therapeutic target for treatment of PRRSV and other viral infections.

SUBMITTER: Zhang L

PROVIDER: S-EPMC8131720 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:MicroRNAs (miRNAs) play an important role in the regulation of immune responses. Previous studies have indicated that dysregulating the miRNAs leads to the immunosuppression of porcine reproductive and respiratory syndrome virus (PRRSV). However, it is not clear how PRRSV regulates the expression of host miRNA, which may lead to immune escape or promote the replication of the virus. The present work suggests that PRRSV upregulated the expression of miR-373 through elevating the expression of specificity protein 1 (Sp1) in MARC-145 cells. Furthermore, this work demonstrated that miR-373 promoted the replication of PRRSV, since miR-373 was a novel negative miRNA for the production of beta interferon (IFN-β) by targeting nuclear factor IA (NFIA), NFIB, interleukin-1 receptor-associated kinase 1 (IRAK1), IRAK4, and interferon regulatory factor 1 (IRF1). We also found that both NFIA and NFIB were novel proteins for inducing the production of IFN-β, and both of them could inhibit the replication of PRRSV. In conclusion, PRRSV upregulated the expression of miR-373 by elevating the expression of Sp1 and hijacked the host miR-373 to promote the replication of PRRSV by negatively regulating the production of IFN-β. PRRSV causes one of the most economically devastating diseases of swine, and there is no effective method for controlling PRRSV. It is not clear how PRRSV inhibits the host's immune response and induces persistent infection. Previous studies have shown that PRRSV inhibited the production of type I IFN, and the treatment of type I IFN could efficiently inhibit the replication of PRRSV, so it will be helpful to design new methods of controlling PRRSV by understanding the molecular mechanism by which PRRSV modulated the production of IFN. The current work shows that miR-373, upregulated by PRRSV, promotes PRRSV replication, since miR-373 impaired the production of IFN-β by targeting NFIA, NFIB, IRAK1, IRAK4, and IRF1, and both NFIA and NFIB were antiviral proteins to PRRSV. In conclusion, this paper revealed a novel mechanism of PRRSV that impaired the production of type I IFN by upregulating miR-373 expression in MARC-145 cells.

Project description:Porcine reproductive and respiratory syndrome (PRRS) is of great concern to the swine industry due to pandemic outbreaks of the disease, current ineffective vaccinations, and a lack of efficient antiviral strategies. In our previous study, a PRRSV Nsp9-specific nanobody, Nb6, was successfully isolated, and the intracellularly expressed Nb6 could dramatically inhibit PRRSV replication in MARC-145 cells. However, despite its small size, the application of Nb6 protein in infected cells is greatly limited, as the protein itself cannot enter the cells physically. In this study, a trans-activating transduction (TAT) peptide was fused with Nb6 to promote protein entry into cells. TAT-Nb6 was expressed as an inclusion body in Escherichia coli, and indirect enzyme-linked immunosorbent assays and pulldown assays showed that E. coli-expressed TAT-Nb6 maintained the binding ability to E. coli-expressed or PRRSV-encoded Nsp9. We demonstrated that TAT delivered Nb6 into MARC-145 cells and porcine alveolar macrophages (PAMs) in a dose- and time-dependent manner, and TAT-Nb6 efficiently inhibited the replication of several PRRSV genotype 2 strains as well as a genotype 1 strain. Using a yeast two-hybrid assay, Nb6 recognition sites were identified in the C-terminal part of Nsp9 and spanned two discontinuous regions (Nsp9aa454-551 and Nsp9aa599-646). Taken together, these results suggest that TAT-Nb6 can be developed as an antiviral drug for the inhibition of PRRSV replication and controlling PRRS disease.IMPORTANCE The pandemic outbreak of PRRS, which is caused by PRRSV, has greatly affected the swine industry. We still lack an efficient vaccine, and it is an immense challenge to control its infection. An intracellularly expressed Nsp9-specific nanobody, Nb6, has been shown to be able to inhibit PRRSV replication in MARC-145 cells. However, its application is limited, because Nb6 cannot physically enter cells. Here, we demonstrated that the cell-penetrating peptide TAT could deliver Nb6 into cultured cells. In addition, TAT-Nb6 fusion protein could suppress the replication of various PRRSV strains in MARC-145 cells and PAMs. These findings may provide a new approach for drug development to control PRRS.

Project description:Porcine reproductive and respiratory syndrome virus (PRRSV) infection eliminates production of type I interferons (IFNs) in host cells, which triggers an antiviral immune response through the induction of downstream IFN-stimulated genes (ISGs), thus escaping the fate of host-mediated clearance. The IFN-induced transmembrane 3 (IFITM3) has recently been identified as an ISG and plays a pivotal role against enveloped RNA viruses by restricting cell entry. However, the role of IFITM3 in PRRSV replication is unknown. The present study demonstrated that overexpression of IFITM3 suppresses PRRSV replication, while silencing of endogenous IFITM3 prominently promoted PRRSV replication. Additionally, it was shown that IFITM3 undergoes S-palmitoylation and ubiquitination modification, and both posttranslational modifications contribute to the anti-PRRSV activity of IFITM3. Further study showed that PRRSV particles are transported into endosomes and then into lysosomes during the early stages of infection, and confocal microscopy results revealed that PRRSV particles are transported to IFITM3-positive cellular vesicles. By using a single virus particle fluorescent labeling technique, we confirmed that IFITM3 can restrict PRRSV membrane fusion by inducing accumulation of cholesterol in cellular vesicles. Additionally, we found that both endogenous and exogenous IFITM3 are incorporated into newly producing PRRS virions and diminish viral intrinsic infectivity. By using cell coculture systems, we found that IFITM3 effectively restricted PRRSV intercellular transmission, which may have been caused by disrupted membrane fusion and reduced viral infectivity. In conclusion, our results demonstrate, for the first time, that swine IFITM3 interferes with the life cycle of PRRSV, and possibly other enveloped arteritis viruses, at multiple steps.IMPORTANCE Porcine reproductive and respiratory syndrome (PRRS), which is caused by PRRS virus (PRRSV), is of great economic significance to the swine industry. Due to the complicated immune escape mechanisms of PRRSV, there are no effective vaccines or therapeutic drugs currently available against PRRS. Identification of cellular factors and underlying mechanisms that establish an effective antiviral state against PRRSV can provide unique strategies for developing antiviral vaccines or drugs. As an interferon (IFN)-stimulated gene, the role of IFN-induced transmembrane 3 (IFITM3) in PRRSV infection has not been reported as of yet. In the present study, it was shown that IFITM3 can exert a potent anti-PRRSV effect, and PRRS virions are trafficked to IFITM3-containing cell vesicles, where viral membrane fusion is impaired by cholesterol accumulation that is induced by IFITM3. Additionally, both endogenous and exogenous IFITM3 are incorporated into newly assembled progeny virions, and this decreased their intrinsic infectivity.

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Downregulation of miR-218 by porcine reproductive and respiratory syndrome virus facilitates viral replication via inhibition of type I interferon responses.

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