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Macroautophagy/autophagy is a cellular degradation and recycling process that maintains the homeostasis of organisms. The protein degradation role of autophagy has been widely used to control viral infection at multiple levels. In the ongoing evolutionary arms race, viruses have developed various ways to hijack and subvert autophagy in favor of its replication. It is still unclear exactly how autophagy affects or inhibits viruses. In this study, we have found a novel host restriction factor, HNRNPA1, that could inhibit PEDV replication by degrading viral nucleocapsid (N) protein. The restriction factor activates the HNRNPA1-MARCHF8/MARCH8-CALCOCO2/NDP52-autophagosome pathway with the help of transcription factor EGR1 targeting the HNRNPA1 promoter. HNRNPA1 could also promote the expression of IFN to facilitate the host antiviral defense response for antagonizing PEDV infection through RIGI protein interaction. During viral replication, we found that PEDV can, in contrast, degrade the host antiviral proteins HNRNPA1 and others (FUBP3, HNRNPK, PTBP1, and TARDBP) through its N protein through the autophagy pathway. These results reveal the dual function of selective autophagy in PEDV N and host proteins, which could promote the ubiquitination of viral particles and host antiviral proteins and degradation both of the proteins to regulate the relationship between virus infection and host innate immunity. Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; Baf A1: bafilomycin A1; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; ChIP: chromatin immunoprecipitation; Co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI: 4′,6-diamidino-2-phenylindole; GPI: glycosyl-phosphatidylinositol; hpi: hours post infection; MARCHF8/MARCH8: membrane-associated ring-CH-type finger 8; MOI: multiplicity of infection; N protein: nucleocapsid protein; PEDV: porcine epidemic diarrhea virus; siRNA: small interfering RNA; TCID50: 50% tissue culture infectious doses. [ABSTRACT FROM AUTHOR]

Senecavirus A (SVA), an important emerging porcine virus, has outbreaks in different regions and countries each year, becoming a virus with global prevalence. SVA infection has been reported to induce macroautophagy/autophagy; however, the molecular mechanisms of autophagy induction and the effect of SVA on autophagy remain unknown. This study showed that SVA infection induced the autophagy process in the early stage of SVA infection, and the rapamycin-induced autophagy inhibited SVA replication by degrading virus 3 C protein. To counteract this, SVA utilized 2AB protein inhibiting the autophagy process from promoting viral replication in the late stage of SVA infection. Further study showed that SVA 2AB protein interacted with MARCHF8/MARCH8 and LC3 to degrade the latter and inhibit the autophagy process. In addition, we found that MARCHF8 was a positive regulator of type I IFN (IFN-I) signaling. During the autophagy process, the SVA 2AB protein targeted MARCHF8 and MAVS forming a large complex for degradation to deactivate IFN-I signaling. Together, our study reveals the molecular mechanisms of selective autophagy in the host against viruses and reveals potential viral strategies to evade the autophagic process and IFN-I signaling for successful pathogenesis. Abbreviations: Baf A1: bafilomycin A1; Co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI: 4′,6-diamidino-2-phenylindole; hpi: hours post-infection; IFN: interferon; ISG: IFN-stimulated gene; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCHF8/MARCH8: membrane associated ring-CH-type finger 8; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; Rapa: rapamycin; RT: room temperature; siRNA: small interfering RNA; SVA: Senecavirus A; TCID50: 50% tissue culture infectious doses. [ABSTRACT FROM AUTHOR]

Interferon-induced BST2 (bone marrow stromal cell antigen 2) inhibits viral replication by tethering enveloped virions to the cell surface to restrict viral release and by inducing the NFKB-dependent antiviral immune response. However, the mechanism by which BST2 uses the selective autophagy pathway to inhibit viral replication is poorly understood. In this study, we showed that BST2 expression was significantly increased during porcine epidemic diarrhea virus (PEDV) infection of Vero cells by IRF1 targeting its promoter. We also showed that BST2 suppressed PEDV replication by binding and degrading the PEDV-encoded nucleocapsid (N) protein. The downregulation of N protein was blocked by macroautophagy/autophagy inhibitors but not a proteasome inhibitor, implying that the N protein was degraded via the selective autophagy pathway. Both the BST2 and N protein interacted with the E3 ubiquitin ligase MARCHF8/MARCH8 and the cargo receptor CALCOCO2/NDP52, and the ubiquitination of N protein was necessary for the degradation of N mediated by the BST2-MARCHF8 axis. The knockdown of MARCHF8 or ATG5 with small interfering RNAs blocked the selective autophagy pathway, rescued the protein abundance of PEDV N in 293T cells, and prevented the inhibition of PEDV replication by BST2 in Vero cells. Together, our data demonstrate the novel mechanism of BST2-mediated virus restriction, in which BST2 recruits MARCHF8 to catalyze the ubiquitination of the PEDV N protein. The ubiquitinated N protein is then recognized by CALCOCO2/NDP52, which delivers it to autolysosome for degradation through the selective autophagy pathway. Abbreviations: 3MA: 3-methyladenine; ATG: autophagy-related; Baf A1: bafilomycin A1; BST2: bone marrow stromal cell antigen 2; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CC: coiled-coil; ChIP: chromatin immunoprecipitation; Co-IP: co-immunoprecipitation; CQ: chloroquine; CT: cytoplasmic tail; DAPI: 4′,6-diamidino-2-phenylindole; GPI: glycosyl-phosphatidylinositol; hpi: hours post infection; IRF1: interferon regulatory factor 1; ISG: IFN-stimulated gene; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCHF8/MARCH8: membrane-associated ring-CH-type finger 8; MOI: multiplicity of infection; N protein: nucleocapsid protein; PED: porcine epidemic diarrhea; PEDV: porcine epidemic diarrhea virus; RT: room temperature; siRNA: small interfering RNA; STAT: signal transducer and activator of transcription; TCID50: 50% tissue culture infectious doses; TM: transmembrane. [ABSTRACT FROM AUTHOR]

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Copyright of Avian Pathology is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)