Researchers at the University of Liverpool have demonstrated how SARS-CoV-2 viral proteases assault the host cell and how this may be targeted to limit virus replication in cell culture using medicines that are already in clinical trials or are in development.
The new results, which were published in Nature Communications today (September 21, 2021), provide a valuable resource for understanding proteolysis in the context of viral infection and informing the development of tailored methods to combat the virus that causes Covid-19.
During the epidemic, SARS-CoV-2 was responsible for roughly 227 million infections and 4.6 million fatalities globally. An increased knowledge of SARS-basic CoV-2’s biology will aid efforts to test, treat, and vaccine against the virus.
SARS-CoV-2 reproduction requires both viral and cellular proteases, and drugs targeting proteases have already been demonstrated to suppress SARS-CoV-2 replication in cell culture models.
Researchers from the University of Liverpool and the Institut Pasteur in Paris utilized mass spectrometry to investigate proteolytic cleavage events during SARS-CoV-2 infection in this study.
“Mass spectrometry-based approaches to identify protease substrates have existed for a number of years, but they have only seen limited application to the study of viral substrates, and had not previously been applied to the study of proteolysis during coronavirus infection,” says lead author Dr. Emmott Edward, a Tenure-Track Fellow at the University’s Institute of Systems, Molecular, and Interdisciplinary Research.
Multiple viral proteins, including key antigenic proteins S and N, which are the principal targets for vaccine and antibody testing, were discovered to have hitherto undiscovered cleavage sites.
They observed substantial increases in cellular cleavage events consistent with SARS-CoV-2 major protease (Mpro) cleavage and identified 14 putative high-confidence substrates of the main and papain-like proteases, with in vitro tests confirming a subset.
They went on to show that siRNA depletion of these cellular proteins suppresses SARS-CoV-2 replication and that medicines targeting two of these proteins, the tyrosine kinase SRC and the Ser/Thr kinase MYLK, reduced SARS-CoV-2 titers in a dose-dependent manner.
In a human cell line model of infection, both Bafetinib (an investigational cancer medication) and Sorafenib (an authorized medicine used to treat kidney and liver cancer) inhibited SARS-CoV-2 at doses that did not cause cytotoxicity.
“A better knowledge of how proteolytic cleavage is controlled, regulates protein function, and aids viral reproduction will be critical for targeting cellular substrates of viral proteases as a therapeutic strategy,” Dr. Emmott stated.
“As more SARS-CoV-2 variations emerge, including post-translational modification data from research like these might help predict phenotypes from genomic data on future variants.”