The Autophagy Machinery Interacts with Epstein-Barr Virus Capsids for Viral Envelope Release

Abstract

Epstein-Barr virus (EBV) is a highly infectious !-herpesvirus and the causative agent of infectious mononucleosis. In addition to this acute disease, the infection with EBV may also lead to severe EBV-associated malignancies like Hodgkin or Burkitt lymphoma, due to its oncogenic potential. Approximately 95% of the human adult population is infected with EBV, which makes it one of the most prevalent and transmissible human viruses. Despite the EBV-associated global disease burden, there is still no vaccine or treatment available for EBV infections, which raises the need to further investigate this virus, its infectious cycle and identify its key targetable proteins. During replication, EBV exploits the cellular host machinery to generate and assemble all the components that form a new virus: DNA, capsid, tegument and envelope. However, upon the detection of pathogenic components, cell-intrinsic defense mechanisms are activated, such as the autophagy pathway, to counteract the infection. Indeed, autophagy can sequester cytoplasmic content, including pathogens, into double membrane-vesicles termed autophagosomes. While these vesicles normally fuse with the lysosome to degrade their cargo, some pathogens can manipulate this pathway to avoid their degradation or even to exploits its membranous compartment. Recent data suggest that EBV could hijack autophagy in order to undergo its final envelopment step. However, little is known of the molecular mechanism and key EBV proteins involved in the autophagy-mediated envelope acquisition.

In this PhD thesis, we aimed to investigate the requirements for EBV’s interaction with autophagy components during viral exocytosis. We first analyzed the composition of purified virions of EBV and found several components of the autophagy machinery, including membrane-associated LC3B-II, and numerous viral proteins, such as the capsid assembly proteins BVRF2 and BdRF1. Additionally, we showed that BVRF2 and BdRF1 interact with the hallmark of autophagosomes LC3B-II via a protein domain that they have in common. Using an EBV mutant, we identified BVRF2 as an essential protein for the assembly of mature capsids and consequently, for the production of infectious EBV. However, BdRF1 was sufficient for the release of non-infectious viral envelopes as long as autophagy was not compromised. These data suggests that BVRF2 and BdRF1 are not only important for capsid assembly but are also critical in recruiting autophagic membranes for the envelopment of EBV. This study highlights the importance of the interaction with LC3B for the virus assembly and egress and sheds light on new functions of these capsid proteins during EBV lytic cycle. Understanding the biology of EBV and its interactions with host cells is fundamental for research of new protein targets which could be used as treatments against EBV pathogenesis and transmission.