Chromatin dynamics regulated by epigenetic modification is crucial in genome stability and gene expression. Various epigenetic mechanisms have been identified in the pathogenesis of human diseases. Here, we examined the effects of ten epigenetic agents on pseudorabies virus (PRV) infection by using GFP-reporter assays. Inhibitors of bromodomain protein 4 (BRD4), which receives much more attention in cancer than viral infection, was found to exhibit substantial anti-viral activity against PRV as well as a range of DNA and RNA viruses. We further demonstrated that BRD4 inhibition boosted a robust innate immune response. BRD4 inhibition also de-compacted chromatin structure and induced the DNA damage response, thereby triggering the activation of cGAS-mediated innate immunity and increasing host resistance to viral infection both in vitro and in vivo. Mechanistically, the inhibitory effect of BRD4 inhibition on viral infection was mainly attributed to the attenuation of viral attachment. Our findings reveal a unique mechanism through which BRD4 inhibition restrains viral infection and points to its potent therapeutic value for viral infectious diseases. Author summaryBRD4 has been well investigated in tumorigenesis for its contribution to chromatin remodeling and gene transcription. BRD4 inhibitors are used as promising chemotherapeutic drugs for cancer therapy. Here, we show a unique mechanism through which BRD4 inhibition broadly inhibits attachment of DNA and RNA viruses through DNA damage-dependent antiviral innate immune activation via the cGAS-STING pathway, in both cell culture and an animal model. STING-associated innate immune signaling has been considered to be a new possibility for cancer therapy, and STING agonists have been tested in early clinical trials. Our data identify BRD4 inhibitors as a potent therapy not only for viral infection but also for cancer immunotherapy. PLOS PATHOGENSPLOS Pathogens | https://doi.

Cholesterol 25-hydroxylase (CH25H) catalyses the production of 25-hydroxycholesterol (25HC) from cholesterol by adding a second hydroxyl group at position 25. The aim of this study was to examine the antiviral effect of CH25H on pseudorabies virus (PRV), a swine pathogen that can cause devastating disease and economic losses worldwide. The results showed that porcine ch25h was induced by either interferon or PRV infection. PRV infection of porcine alveolar macrophages (3D4/21 cells) was attenuated by CH25H overexpression and enhanced by silencing of CH25H. Furthermore, treatment of 3D4/21 cells with 25HC inhibited the growth of PRV in vitro, suggesting that CH25H may restrict PRV replication by 25HC production. We further identified that the anti-PRV role of CH25H and 25HC was subject to their inhibitory effect on PRV attachment and entry. Collectively, these findings demonstrate that CH25H is an intrinsic host restriction factor in PRV infection of porcine alveolar macrophages.

Autophagy maintains cellular homeostasis by degrading organelles, proteins, and lipids in lysosomes. Autophagy is involved in the innate and adaptive immune responses to a variety of pathogens. Some viruses can hijack host autophagy to enhance their replication. However, the role of autophagy in porcine reproductive and respiratory syndrome virus (PRRSV) infection is unclear. Here, we show that N-Myc downstream-regulated gene 1 (NDRG1) deficiency induced autophagy, which facilitated PRRSV replication by regulating lipid metabolism. NDRG1 mRNA is expressed ubiquitously in most porcine tissues and most strongly in white adipose tissue. PRRSV infection downregulated the expression of NDRG1 mRNA and protein, while NDRG1 deficiency contributed to PRRSV RNA replication and progeny virus assembly. NDRG1 deficiency reduced the number of intracellular lipid droplets (LDs), but the expression levels of key genes in lipogenesis and lipolysis were not altered. Our results also show that NDRG1 deficiency promoted autophagy and increased the subsequent yields of hydrolyzed free fatty acids (FFAs). The reduced LD numbers, increased FFA levels, and enhanced PRRSV replication were abrogated in the presence of an autophagy inhibitor. Overall, our findings suggest that NDRG1 plays a negative role in PRRSV replication by suppressing autophagy and LD degradation. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV), an enveloped single-positive-stranded RNA virus, causes acute respiratory distress in piglets and reproductive failure in sows. It has led to tremendous economic losses in the swine industry worldwide since it was first documented in the late 1980s. Vaccination is currently the major strategy used to control the disease. However, conventional vaccines and other strategies do not provide satisfactory or sustainable prevention. Therefore, safe and effective strategies to control PRRSV are urgently required. The significance of our research is that we demonstrate a previously unreported relationship between PRRSV, NDRG1, and lipophagy in the context of viral infection. Furthermore, our data point to a new role for NDRG1 in autophagy and lipid metabolism. Thus, NDRG1 and lipophagy will have significant implications for understanding PRRSV pathogenesis for developing new therapeutics.

a b s t r a c tKeywords: PRV IFITMs GAS/STING/TBK1/IRF3 innate immune pathway Viral entry Interferon-inducible transmembrane proteins (IFITMs) restrict infection by several viruses, such as influenza A virus, West Nile virus and dengue virus. It has not been determined whether porcine IFITMs (pIFITMs) inhibit infection by pseudorabies virus (PRV), an enveloped, double-stranded DNA virus, which is the etiological agent of Aujeszky's disease in pigs. Here, we report that PRV infection elicited pIFITM1 expression in PK15 porcine kidney epithelial cells and 3D4/21 alveolar macrophages. pIFITM2 and pIFITM3 expression was only elevated in PK15 cells during PRV infection. Depletion of pIFITM1 using RNA interference, either in PK15 or in 3D4/21 cells, enhanced PRV infection while overexpression of pIFITM1 had the opposite effect. Knockdown of pIFITM2 and pIFITM3 did not influence PRV infection, suggesting that pIFITM2 and pIFITM3 are independent of PRV infection. PRV-induced pIFITM1 expression was dependent on the cGAS/STING/TBK1/IRF3 innate immune pathway and interferon-alpha receptor-1, suggesting that pIFITM1 is up-regulated by the type I interferon signaling pathway. The anti-PRV role of pIFITM1 was inhibited upon PRV entry. Our data demonstrate that pIFITM1 is a host restriction factor that inhibits PRV entry that may shed light on a strategy for prevention of PRV infection.

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