TMPRSS2 and furin are both essential for proteolytic activation of SARS-CoV-2 in human airway cells

TLDR

SARS‑CoV‑2 spreads worldwide, causing severe respiratory disease, and its spike protein must be cleaved by host proteases such as furin and TMPRSS2, making these enzymes attractive drug targets. The study shows that furin cleaves the spike at the S1/S2 site while TMPRSS2 cleaves at S2′, that TMPRSS2 is essential for viral activation in airway cells, and that combined inhibition of TMPRSS2 and furin with MI‑1851 markedly suppresses replication, indicating strong therapeutic potential.

Abstract

The novel emerged SARS-CoV-2 has rapidly spread around the world causing acute infection of the respiratory tract (COVID-19) that can result in severe disease and lethality. For SARS-CoV-2 to enter cells, its surface glycoprotein spike (S) must be cleaved at two different sites by host cell proteases, which therefore represent potential drug targets. In the present study, we show that S can be cleaved by the proprotein convertase furin at the S1/S2 site and the transmembrane serine protease 2 (TMPRSS2) at the S2′ site. We demonstrate that TMPRSS2 is essential for activation of SARS-CoV-2 S in Calu-3 human airway epithelial cells through antisense-mediated knockdown of TMPRSS2 expression. Furthermore, SARS-CoV-2 replication was also strongly inhibited by the synthetic furin inhibitor MI-1851 in human airway cells. In contrast, inhibition of endosomal cathepsins by E64d did not affect virus replication. Combining various TMPRSS2 inhibitors with furin inhibitor MI-1851 produced more potent antiviral activity against SARS-CoV-2 than an equimolar amount of any single serine protease inhibitor. Therefore, this approach has considerable therapeutic potential for treatment of COVID-19.