The Epstein-Barr virus EBNA2 protein induces a subset of NOTCH target genes in thyroid cancer cell lines but fails to suppress proliferation

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

EBNA2 mediates lipid metabolism and tumorigenesis through activation of ATF4 pathway

Epstein-Barr virus (EBV) can infect the majority of the human population with no obvious symptoms and is associated with tumor development, although the mechanism is still largely unknown. In this study, we investigated the role and the underlying mechanism of EBV nuclear antigen 2 (EBNA2) in tumorigenesis. We found that the infection of EBNA2 in human B lymphocytes (HBL) upregulated the expression of activating transcription factor 4 (ATF4). Furthermore, we used gene expression or knockdown approach to demonstrate the effect of EBNA2 on redox balance, mitochondrial function, lipid metabolism, and cell proliferation in both HBL and EBV-transformed lymphocyte cell line (LCL). More importantly, we applied in vivo xenograft tumor mouse model to explore the contribution of EBNA2 and ATF4 in tumor growth and mouse survival. Mechanistically, we revealed that EBNA2 exposure caused persistent expression of ATF4 via EBNA2-mediated epigenetic changes, which increased the binding ability of upstream stimulating factor 1 (USF1) on the ATF4 promoter. ATF4 activation in HBL cells modulated the expression of lipid metabolism-related genes and potentiated fatty acid oxidation and lipogenesis. Conversely, knockdown of either EBNA2 or ATF4 in LCL suppressed lipid metabolism, modulated redox balance and mitochondrial function, as well as inhibited tumor cell proliferation. In consistent with these findings from in vitro study, an in vivo xenograft model confirmed that knockdown of either EBNA2 or ATF4 inhibited the gene expression of SREBP1, ChREBP, and FAS, as well as suppressed tumor growth and prolonged animal survival. Collectively, this study demonstrates that EBNA2 mediates tumorigenesis through ATF4 activation and the modulation of lipid metabolism; therefore, our findings provide a novel avenue for the clinical treatment of EBV-mediated cancer.