Epstein-Barr virus tegument proteins BPLF1 and BGLF2 are viral antagonists of interferon production and signaling

Abstract

Epstein-Barr virus (EBV) successfully establishes a persistent infection in more than 95% of all adults but is etiologically associated with the development of lymphoid and epithelial malignancies, such as Burkitt’s lymphoma, Hodgkin’s lymphoma, nasopharyngeal carcinoma and gastric carcinoma, in a small subset of subjects latently infected with EBV. EBV has evolved to evade interferon (IFN)-dependent innate immune response using multiple counter-strategies. Here, we perform functional screens with an expression library of EBV-encoded proteins to search for interferon (IFN) antagonists. Two tegument proteins BPLF1 and BGLF2 are found to be IFNantagonizing proteins that potently suppress IFN production and signaling. BPLF1 is a large tegument protein with deubiquitinase activity. When type I IFN production is induced by DNA or RNA through their sensors either cGAS plus STING or RIG-I plus MAVS, BPLF1 exhibits a strong and deubiquitinase-dependent suppressive effect on the induction. BPLF1-mediated deubiquitination shows no ubiquitin linkage preference, with equally strong activity on both K63- and K48-linked ubiquitintion of STING and TBK1. Enforced expression of BPLF1 through CRISPRa in cells infected with EBV results in remarkable suppression of IFN production induced by DNA or RNA. We have also identified another EBV tegument protein BGLF2 as a suppressor of IFN signaling. The suppression effect is medicated though multiple targets including STAT1, STAT2 and JAK1. BGLF2 interacts with STAT2 to induce its K48-linked polyubiquitination and consequent proteasomal degradation. Additionally, BGLF2 inhibits tyrosine phosphorylation of JAK1 and STAT1 through recruitment of tyrosine phosphatase SHP1. IFN signaling is more robustly activated by a BGLF2-deficient EBV. Combined, we have delineated the IFN antagonism of EBV tegument proteins BPLF1 and BGLF2, which target ubiquitination and deubiquitination of key signal transducers to circumvent IFN production and signaling in EBV-infected cells. Supported by HMRF 17160822, HMRF 18170942 and RGC C7027-16G.