Immunomodulatory effects of coronavirus membrane proteins E, M, and S.

Abstract: COronaVIrus Disease 2019 (COVID-19) is caused by a human coronavirus, SARS-CoV-2. This viruscaused a large outbreak in China that was associated with a high human-to-human transmission rate and mortalityand subsequently led to a pandemic in the human population. SARS-CoV-2 is member of the â-coronaviruses andis highly related to SARS-CoV. In an ongoing evolutionary arms race, viruses have evolved factors that facilitatetheir replication while the host cell has evolved signaling networks to detect and eradicate invading viruses. Theinnate immune system is a conserved defense strategy critical for the initial detection and restriction of pathogensand later activation of the adaptive immune response. Activation of innate immunity relies on the recognition ofpathogen-associated molecular patterns (PAMP) by pattern recognition receptors (PRRs) such as Toll-likereceptors, RNA and DNA sensors. Upon activation by PAMPs, PRRs recruit adaptor proteins that initiate signalingpathways involving modifying enzymes such as kinases, phosphatases, E3 ubiquitin ligases that ultimately leadto the activation of crucial transcription factors including IRF3 and NF-êB. Synergistically, these factors promotethe production of antiviral type I interferons (IFN-I), inflammatory cytokines, NK cell immunity, apoptosis, andautophagy. Thus, the pathogenicity and spread of a virus in the host is in part determined by the ability of the virusto evade host cell innate responses. The SARS-CoV-2 virion has three transmembrane proteins [envelope (E),membrane (M), and spike (S)] that are necessary for viral assembly and infectivity. They also have importantimmunomodulatory functions as they trigger or antagonize innate immune responses within infected cells. TheE proteins from other coronaviruses have been shown to form an oligomeric structure with ion channel activity thatcan alter calcium homeostasis with implications on viral pathogenesis. The M protein of other coronaviruses wasshown to have a range of immunomodulatory effects through TLR-dependent and independent mechanisms andthe S protein can exert its effects by modulating surface signaling responses. It also causes the degradation ofBST-2 (tetherin), which functions to prevent release of progeny virus. We hypothesize that theimmunomodulatory properties of SARS-CoV-2 membrane proteins will determine the outcome of theinfection and viral mediated pathogenesis. To test this, in Aim 1, we propose to examine E, M, and S proteinsfrom SARS-CoV-2 and compare their impact in modulating innate immunity, proinflammatory responses,autophagy, and apoptosis with the same proteins from SARS-CoV, MERS-CoV, and HCoV-OC43. In Aim 2, wewill determine the immunomodulatory effects of virus-like particles (VLPs) formed by the membrane proteins ofthe four viruses. We will also determine the immunoevasion capabilities of of SARS-CoV-2 and compare themwith SARS-CoV, MERS and HCoV-OC43. Overall, the results of these studies will further our knowledge ofimmunoevasion strategies of human coronaviruses and guide in the development of efficacious vaccines.