Guido PAPA

Wednesday, 14 April 2021 | 12:00 noon

MRC Laboratory of Molecular Biology, Cambridge, UK

Role of SARS-CoV-2 Spike cleavage in virus entry and cell-cell fusion

(Host: L. Banks)

Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) infects cells by binding to the host cell receptor ACE2 and undergoing virus-host membrane fusion. Fusion is triggered by the membrane- associated protease TMPRSS2, which processes the viral Spike (S) protein to reveal the fusion peptide. SARS-CoV-2 Spike has evolved a multibasic site (RRAR) at the S1-S2 boundary, which is thought to be cleaved by furin in order to prime S protein for TMPRSS2 processing.

Combining a CRISPR-Cas9 knockout approach with multibasic site Spike mutants we dissected the cleavage mechanism of the Spike protein and its role in virus infection, demonstrating that depletion of furin protease reduces, but does not completely prevent, production of infectious SARS-CoV-2 virus. SARS-CoV-2 Spike protein also mediates cell-cell fusion, potentially allowing virus to spread virion- independently. Using our dual colour cell-cell fusion assay we studied the role of furin in triggering formation of multinucleated cells and revealed that the presence of furin in either donor or acceptor cells is not essential for a TMPRSS2-dependent cell-cell fusion event.

Despite the rapid development of effective vaccines against SARS-CoV-2, antiviral drugs and specific inhibitors of enzymes involved in viral replication are urgently needed. Our findings indicate that, since furin is not essential for virus replication, inhibitors currently developed against this cellular protease may be ineffective to completely block viral infection.

Our study also suggests a key role of TMPRSS2 protease in promoting S-mediated cell-cell fusion, paving the way for targeting this process and utilising a cocktail of inhibitors to efficiently treat SARS-CoV-2 infections.