Arch Virol . Trypsin enhances SARS-CoV-2 infection by facilitating viral entry

[tetano]

Arch Virol


. 2022 Jan 26.
doi: 10.1007/s00705-021-05343-0. Online ahead of print.
Trypsin enhances SARS-CoV-2 infection by facilitating viral entry


Yeeun Kim ^{# 1} , Guehwan Jang ^{# 1} , Duri Lee ¹ , Nara Kim ² , Jeong Won Seon ² , Young-Hoan Kim ² , Changhee Lee ³



Affiliations

• PMID: 35079901
• DOI: 10.1007/s00705-021-05343-0

Abstract

Coronaviruses infect cells by cytoplasmic or endosomal membrane fusion, driven by the spike (S) protein, which must be primed by proteolytic cleavage at the S1/S2 furin cleavage site (FCS) and the S2' site by cellular proteases. Exogenous trypsin as a medium additive facilitates isolation and propagation of several coronaviruses in vitro. Here, we show that trypsin enhances severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in cultured cells and that SARS-CoV-2 enters cells via either a non-endosomal or an endosomal fusion pathway, depending on the presence of trypsin. Interestingly, trypsin enabled viral entry at the cell surface and led to more efficient infection than trypsin-independent endosomal entry, suggesting that trypsin production in the target organs may trigger a high level of replication of SARS-CoV-2 and cause severe tissue injury. Extensive syncytium formation and enhanced growth kinetics were observed only in the presence of exogenous trypsin when cell-adapted SARS-CoV-2 strains were tested. During 50 serial passages without the addition of trypsin, a specific R685S mutation occurred in the S1/S2 FCS (⁶⁸¹PRRAR⁶⁸⁵) that was completely conserved but accompanied by several mutations in the S2 fusion subunit in the presence of trypsin. These findings demonstrate that the S1/S2 FCS is essential for proteolytic priming of the S protein and fusion activity for SARS-CoV-2 entry but not for viral replication. Our data can potentially contribute to the improvement of SARS-CoV-2 production for the development of vaccines or antivirals and motivate further investigations into the explicit functions of cell-adaptation-related genetic drift in SARS-CoV-2 pathogenesis.