Uncovering the mechanisms and implications of BST2 antagonism by SARS-CoV-2

PROJECT SUMMARY BST2/Tetherin is a key factor of the cellular intrinsic immune response that broadly restricts enveloped viruses. BST2 tethers nascent virions to the cell surface by embedding itself into cellular and viral membranes. Tethering not only limits viral release, but also facilitates adaptive immune recognition of the infecting virus. Tethered virions are opsonized by antibodies, which can be recognized by Fc receptors on both natural killer cells and macrophages, activating their ability to kill or phagocytose the infected cell. We have recently reported that SARS-CoV-2 is susceptible to BST2 restriction. However, the virus has evolved to use its Spike to downregulate BST2. Downregulation is achieved by an interaction between Spike and the extracellular domains of BST2, routing BST2 for lysosomal degradation in a Clathrin- and Ubiquitin-dependent manner. Remarkably, newly emerged variants of concern (VOC) have enhanced their ability to counteract BST2, suggesting that BST2 antagonism is a contributing factor to the host adaptation of SARS-CoV-2. Therefore, my long-term goal is to block the ability of SARS-CoV-2 to evade BST2 restriction. My overall objective is to understand the mechanism and implications of BST2 evasion by SARS-CoV-2. My central hypothesis is that mutations accumulated in the Spike of SARS-CoV-2 allow for more efficient counteraction of BST2, increasing virion release and reducing the susceptibility of SARS-CoV-2 to BST2-dependent antibody-mediated cellular responses. I will achieve my overall objective by exploring these two specific aims: (1) elucidate the mechanism of enhancement of BST2 antagonism across VOC, and (2) identify the driving pressures of BST2 antagonism. This work is significant as it will (1) fill the critical gap in knowledge of how SARS-CoV-2 evades BST2 restriction, and how VOC enhance this activity; (2) define the extent to which evasion of BST2 allows for evasion of antibody-mediated responses, and how this translates to vaccine efficacy; and (3) provide proof-of-concept for the design of antivirals to disable SARS-CoV- 2 antagonism of BST2 with the goal of both blocking viral replication and enhancing clearance of infected cells. The support provided by this F31 award will enhance my education by (1) facilitating my training in Surface Plasmon Resonance by Dr. Jermaine Jenkins and the URMC Structural Biology Core Facility (see letter of support), (2) allowing me to travel to the University of Wisconsin-Madison to gain hands-on training from my co- sponsor, Dr. David Evans (see co-sponsor statement), who developed assays to measure Fc receptor-mediated killing of infected cells, which we are proposing to use here, and (3) expanding my experience in scientific writing and communication as I publish my findings and present at both national and international conferences.