Suppression of cGAS- and RIG-I-mediated innate immune signaling by Epstein-Barr virus deubiquitinase BPLF1

Author summaryEBV is an oncogenic virus causing Burkitt lymphoma and nasopharyngeal cancer. Elucidating how the virus evades human innate immune responses can provide a better understanding of how EBV causes cancer. In this study we have screened all EBV proteins to identify BPLF1 as a virulence factor that contributes to innate immune evasion. BPLF1 fulfills this function by removing the polyubiquitin marks on critical effector proteins including STING and TBK1. We have also established cell lines stably carrying a recombinant EBV that produces a catalytically inactive BPLF1. The recombinant virus has lost the ability to suppress antiviral responses induced by cGAS and STING in these cells. Our results provide mechanistic insight on the suppression of type I interferon production by BPLF1. Our study might also reveal new knowledge of EBV pathogenesis and new strategies for antiviral development. Epstein-Barr virus (EBV) has developed effective strategies to evade host innate immune responses. Here we reported on mitigation of type I interferon (IFN) production by EBV deubiquitinase (DUB) BPLF1 through cGAS-STING and RIG-I-MAVS pathways. The two naturally occurring forms of BPLF1 exerted potent suppressive effect on cGAS-STING-, RIG-I- and TBK1-induced IFN production. The observed suppression was reversed when DUB domain of BPLF1 was rendered catalytically inactive. The DUB activity of BPLF1 also facilitated EBV infection by counteracting cGAS-STING- and TBK1-mediated antiviral defense. BPLF1 associated with STING to act as an effective DUB targeting its K63-, K48- and K27-linked ubiquitin moieties. BPLF1 also catalyzed removal of K63- and K48-linked ubiquitin chains on TBK1 kinase. The DUB activity of BPLF1 was required for its suppression of TBK1-induced IRF3 dimerization. Importantly, in cells stably carrying EBV genome that encodes a catalytically inactive BPLF1, the virus failed to suppress type I IFN production upon activation of cGAS and STING. This study demonstrated IFN antagonism of BPLF1 mediated through DUB-dependent deubiquitination of STING and TBK1 leading to suppression of cGAS-STING and RIG-I-MAVS signaling.

Automated summary

This study identifies BPLF1 as a virulence factor of EBV that evades human innate immune responses by removing polyubiquitin marks on critical effector proteins. The study demonstrates the importance of the DUB activity of BPLF1 in suppressing antiviral responses and provides insights into the pathogenesis of EBV and potential antiviral strategies.