Epstein−Barr virus (EBV) successfully persists in the vast majority of adults but causes lymphoid and epithelial malignancies in a small fraction of latently infected individuals. Innate immunity is the first-line antiviral defense, which EBV has to evade in favor of its own replication and infection. EBV uses multiple strategies to perturb innate immune signaling pathways activated by Toll-like, RIG-I-like, NOD-like, and AIM2-like receptors as well as cyclic GMP-AMP synthase. EBV also counteracts interferon production and signaling, including TBK1-IRF3 and JAK-STAT pathways. However, activation of innate immunity also triggers pro-inflammatory response and proteolytic cleavage of caspases, both of which exhibit proviral activity under some circumstances. Pathogenic inflammation also contributes to EBV oncogenesis. EBV activates NFκB signaling and induces pro-inflammatory cytokines. Through differential modulation of the proviral and antiviral roles of caspases and other host factors at different stages of infection, EBV usurps cellular programs for death and inflammation to its own benefits. The outcome of EBV infection is governed by a delicate interplay between innate immunity and EBV. A better understanding of this interplay will instruct prevention and intervention of EBV-associated cancers.
The Epstein–Barr virus (EBV) successfully infects 95% of all adults but causes Burkitt’s lymphoma, Hodgkin’s lymphoma, gastric carcinoma, nasopharyngeal carcinoma or other malignancies in only a small subset of infected individuals. The virus must have developed effective viral countermeasures to evade host innate immunity. In this study, we performed functional screens to identify EBV-encoded interferon (IFN) antagonists. Several tegument proteins were found to be potent suppressors of IFN production and/or signaling. The large tegument protein and deubiquitinase BPLF1 antagonized type I IFN production induced by DNA sensors cGAS and STING or RNA sensors RIG-I and MAVS. BPLF1’s ability to suppress innate immune signaling required its deubiquitinase activity. BPLF1 functioned as a catalytically active deubiquitinase for both K63- and K48-linked ubiquitin chains on STING and TBK1, with no ubiquitin linkage specificity. Induced expression of BPLF1 in EBV-infected cells through CRISPRa led to effective suppression of innate DNA and RNA sensing. Another EBV tegument protein, BGLF2, was found to suppress JAK-STAT signaling. This suppression was ascribed to more pronounced K48-linked polyubiquitination and proteasomal degradation of BGLF2-associated STAT2. In addition, BGLF2 also recruited tyrosine phosphatase SHP1 to inhibit tyrosine phosphorylation of JAK1 and STAT1. A BGLF2-deficient EBV activated type I IFN signaling more robustly. Taken together, we characterized the IFN antagonism of EBV tegument proteins BPLF1 and BGLF2, which modulate ubiquitination of key transducer proteins to counteract type I IFN production and signaling in host cells. Supported by HMRF 17160822, HMRF 18170942, and RGC C7027-16G.
Abstract Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing global health emergency. Here we highlight nine most important research questions concerning virus transmission, asymptomatic and presymptomatic virus shedding, diagnosis, treatment, vaccine development, origin of virus and viral pathogenesis.
Latent infection with Epstein–Barr virus (EBV) is associated with several types of malignancies including nasopharyngeal carcinoma (NPC), which is particularly more prevalent in Southern China. EBV expresses at least 44 mature microRNAs (miRNAs) to modulate the activity of viral and cellular RNAs, but the targets of these EBV‐encoded miRNAs in NPC are not well understood. In this report, we characterized DICE1 tumor suppressor to be a cellular target of EBV miR‐BART3* miRNA. miR‐BART3* was abundantly expressed in NPC cells. The target site of miR‐BART3* located in the 3′‐untranslated region of DICE1 transcript was identified and characterized. Enforced expression of miR‐BART3* or its precursor pre‐miR‐BART3 led to down‐regulation of endogenous DICE1 expression. Inhibition of endogenous miR‐BART3* in NPC cells with anti‐miR‐BART3* oligonucleotide inhibitor resulted in increased expression of DICE1 protein. On the contrary, expression of miR‐BART3* overcame the growth suppressive activity of DICE1 and stimulated cell proliferation. Consistent with its tumor suppressive function, DICE1 was underexpressed in EBV‐expressing NPC tumor tissues. Taken together, our findings suggest that EBV encoded miR‐BART3* miRNA targets DICE1 tumor suppressor to promote cellular growth and transformation in NPC.
Epstein-Barr virus (EBV) infects more than 90% of the world’s adult population. Once established, latent infection of nasopharyngeal epithelial cells with EBV is difficult to eradicate and might lead to the development of nasopharyngeal carcinoma (NPC) in a small subset of individuals. In this study we explored the anti-EBV potential of CRISPR/Cas9 targeting of EBV genome in infected NPC cells. We designed gRNAs to target different regions of the EBV genome and transfected them into C666-1 cells. The levels of EBV DNA in transfected cells were decreased by about 50%. The suppressive effect on EBV DNA load lasted for weeks but could not be further enhanced by re-transfection of gRNA. Suppression of EBV by CRISPR/Cas9 did not affect survival of C666-1 cells but sensitized them to chemotherapeutic killing by cisplatin and 5-fluorouracil. Our work provides the proof-of-principle for suppressing EBV DNA load with CRISPR/Cas9 and a potential new strategy to sensitize EBV-infected NPC cells to chemotherapy.
Mouse p202 is a disease locus for lupus and a dominant-negative inhibitor of AIM2 inflammasome activation. A human homolog of p202 has not been identified so far. Here, we report a novel transcript isoform of human IFI16-designated IFI16-β, which has a domain architecture similar to that of mouse p202. Like p202, IFI16-β contains two HIN domains, but lacks the pyrin domain. IFI16-β is ubiquitously expressed in various human tissues and cells. Its mRNA levels are also elevated in leukocytes of patients with lupus, virus-infected cells, and cells treated with interferon-β or phorbol ester. IFI16-β co-localizes with AIM2 in the cytoplasm, whereas IFI16-α is predominantly found in the nucleus. IFI16-β interacts with AIM2 to impede the formation of a functional AIM2-ASC complex. In addition, IFI16-β sequesters cytoplasmic dsDNA and renders it unavailable for AIM2 sensing. Enforced expression of IFI16-β inhibits the activation of AIM2 inflammasome, whereas knockdown of IFI16-β augments interleukin-1β secretion triggered by dsDNA but not dsRNA Thus, cytoplasm-localized IFI16-β is functionally equivalent to mouse p202 that exerts an inhibitory effect on AIM2 inflammasome.