Interferon-Inducible Oligoadenylate Synthetase-Like Protein Acts as an Antiviral Effector against Classical Swine Fever Virus via the MDA5-Mediated Type I Interferon-Signaling Pathway

Abstract

Classical swine fever virus (CSFV) is the causative agent of classical swine fever (CSF), which poses a serious threat to the global pig industry. Interferons (IFNs) and IFN-stimulated genes (ISGs) play a key role in host antiviral defense. We have previously screened the porcine 2′-5′-oligoadenylate synthetase-like protein (pOASL) as a potential anti-CSFV ISG using a reporter CSFV. This study aimed to clarify the underlying antiviral mechanism of pOASL against CSFV. We confirmed that CSFV replication was significantly suppressed in lentivirus-delivered, pOASL-overexpressing PK-15 cells, whereas silencing the expression of endogenous pOASL by small interfering RNAs markedly enhanced CSFV growth. In addition, the transcriptional level of pOASL was upregulated both in vitro and in vivo upon CSFV infection. Interestingly, the anti-CSFV effects of pOASL are independent of the canonical RNase L pathway but depend on the activation of the type I IFN response. Glutathione S-transferase pulldown and coimmunoprecipitation assays revealed that pOASL interacts with MDA5, a double-stranded RNA sensor, and further enhances MDA5-mediated type I IFN signaling. Moreover, we showed that pOASL exerts anti-CSFV effects in an MDA5-dependent manner. In conclusion, pOASL suppresses CSFV replication via the MDA5-mediated type I IFN-signaling pathway.IMPORTANCE The host innate immune response plays an important role in mounting the initial resistance to viral infection. Here, we identify the porcine 2′-5′-oligoadenylate synthetase-like protein (pOASL) as an interferon (IFN)-stimulated gene (ISG) against classical swine fever virus (CSFV). We demonstrate that the anti-CSFV effects of pOASL depend on the activation of type I IFN response. In addition, we show that pOASL, as an MDA5-interacting protein, is a coactivator of MDA5-mediated IFN induction to exert anti-CSFV actions. This work will be beneficial to the development of novel anti-CSFV strategies by targeting pOASL.

MERTK is a host factor that promotes classical swine fever virus entry and antagonizes innate immune response in PK-15 cells

“…To further verify that MERTK antagonizes the host innate immune response to CSFV, we quantified the mRNA levels of IFN-β and suppressor of cytokine signalling protein 1 (SOCS1) in MERTK-knockdown cells infected with CSFV at 24 hpi. Our results showed that silencing of MERTK resulted in increased mRNA levels of IFN-β and SOCS1, as well as of GBP1 and OASL ( Figure 6E), which have been identified as potent anti-CSFV interferon-stimulated genes (ISGs) [27,40]. Taken together, these findings suggest that MERTK facilitates CSFV entry and enhances viral replication.…”

“…Genomic RNA copies of CSFV were quantified by realtime RT-PCR (RT-qPCR) as previously described [27].…”

Antiviral activity of ISG15 against classical swine fever virus replication in porcine alveolar macrophages via inhibition of autophagy by ISGylating BECN1

“…The expression of many ISGs is induced following type I IFN treatment. However, some of them exert independent antiviral functions that may affect CSFV replication [6,7,9]. This knowledge helps to explain why knockdown of ISG15 notably enhanced CSFV replication but did not totally neutralize the anti-CSFV activity of IFN-α ( Figures 2D, E).…”

“…RNA viruses of the family Flaviviridae are sensitive to type I IFN, and replication of CSFV is attenuated by treatment with IFN-α [5]. Although many studies have focused on screening and identifying antiviral ISGs and elucidating their antiviral mechanisms, only 2′,5′-oligoadenylate synthetase-like protein (OASL), myxovirus resistance protein 1 (Mx1), viperin, guanylate-binding protein 1 (GBP1), and IFN-inducible transmembrane proteins (IFITMs) have been identified to inhibit CSFV infection or replication [6][7][8][9][10][11].…”

Genetic responses of inbred chicken lines illustrate importance of eIF2 family and immune-related genes in resistance to Newcastle disease virus

“…After being activated, OAS promotes the synthesis of 2-5 oligoadenylate, which activates RNase L. Upon binding 2′-5′-linked oligoadenylates (2-5 A), activated RNase L degrades cellular and viral RNA 34 . This RNase L-dependent pathway is best characterized; however, recent studies have described OAS antiviral activity through a RNase L-independent pathway 35,36 . In chickens, OAS has been shown to be encoded by only one gene (OASL) 37 and to be upregulated after infection with different viruses 38,39 including NDV 3,4,21 .…”