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Published on: March 1, 2019
Synergistic activation of bat SARS-like coronaviruses spike protein by elastase and TMPRSS2
Yuichiro Yamamoto1, Tetsuya Inoue1, Naoto Sugiyama1
1Laboratory of Molecular Targeted Therapy, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 6-3-1, Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan.
Abstract:
Although numerous sarbecoviruses have been identified in bats, but most lack the ability to infect human cells. Some barriers limit coronavirus zoonosis, including susceptibility to host proteases. Here, we investigated whether exogenous protease treatment can circumvent host restrictions in two severe acute respiratory syndrome (SARS)-related bat coronaviruses. We found that the spike proteins of RaTG13 and Khosta-2, which are sarbecoviruses obtained from horseshoe bats in China and Russia, respectively, facilitated the ACE2-mediated entry of pseudotyped viruses into VeroE6/TMPRSS2 cells following elastase treatment. In contrast, trypsin and thermolysin exhibited no effects. Elastase-enhanced infectivity correlated with increased fusogenicity driven by the cleavage of spike proteins. This process was TMPRSS2-dependent and was inhibited by nafamostat, a TMPRSS2 inhibitor. Additionally, mutation of residue 809 within the S2 subunit of the RaTG13 spike protein (S809D) impaired elastase-induced cleavage and infectivity. Hence, proteolytic processing of the spike protein serves as a restriction to RaTG13 and Khosta-2 infections, which can be overcome by elastase. This suggests that elastase secreted in inflamed tissues during viral infection may increase the zoonotic potential of sarbecoviruses by facilitating human cell entry.
Insights
Certain bat coronaviruses, like RaTG13 and Khosta-2, can infect human cells if treated with elastase. This protease treatment overcomes natural barriers, suggesting a potential increase in zoonotic risk for these severe acute respiratory syndrome (SARS)-related viruses.
Area of Science:
- Virology
- Molecular Biology
- Infectious Diseases
Background:
- Numerous sarbecoviruses exist in bats, but most cannot infect human cells due to host restrictions.
- Protease susceptibility is a key barrier limiting coronavirus zoonosis.
Purpose of the Study:
- To investigate if exogenous protease treatment can overcome host restrictions for SARS-related bat coronaviruses.
- To determine the role of spike protein cleavage in viral entry and infectivity.
Main Methods:
- Used pseudotyped viruses expressing spike proteins of RaTG13 and Khosta-2.
- Treated VeroE6/TMPRSS2 cells with various proteases (elastase, trypsin, thermolysin).
- Assessed viral entry, infectivity, and spike protein cleavage, including effects of TMPRSS2 inhibition and specific spike protein mutations.
Main Results:
- Elastase treatment facilitated ACE2-mediated entry of RaTG13 and Khosta-2 pseudotyped viruses into cells.
- Elastase enhanced infectivity by increasing spike protein cleavage and fusogenicity, dependent on TMPRSS2.
- Trypsin and thermolysin had no effect; a specific mutation (S809D) impaired elastase-induced infectivity.
Conclusions:
- Proteolytic processing of the spike protein is a restriction for RaTG13 and Khosta-2 infections.
- Elastase can overcome this restriction, enhancing viral entry and infectivity.
- Secreted elastase in inflamed tissues may increase the zoonotic potential of sarbecoviruses.
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