Human coronavirus 229E infection inactivates pyroptosis executioner gasdermin D but ultimately leads to lytic cell death partly mediated by gasdermin E
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Abstract
Human coronavirus 229E (HCoV-229E) is associated with upper respiratory tract infections and causes local respiratory symptoms. It has been reported that HCoV-229E can cause cell death in a variety of cells in vitro . However, the molecular pathways that lead to virus-induced cell death remain poorly characterized. Here, we show that the main protease (Mpro) of HCoV-229E can cleave the pyroptosis executioner gasdermin D (GSDMD) within its active N-terminal domain at two different sites (Q29 and Q193) to generate fragments unable to cause pyroptosis. Despite GSDMD cleavage by HCoV-229E Mpro, we show that HCoV-229E infection leads to lytic cell death. We further demonstrate that virus-induced lytic cell death is partially dependent on the activation of caspases-3 and -8. Interestingly, inhibition of caspases does not only reduce lytic cell death upon infection, but also sustains the release of virus particles over time, which suggests that caspase-mediated cell death is a mechanism to limit virus replication and spread. Finally, we show that pyroptosis is partially dependent on another gasdermin family member, gasdermin E (GSDME). During HCoV-229E infection, GSDME is cleaved to yield its N-terminal pore-forming domain (p30). Accordingly, GSDME knockout cells show a significant decrease in lytic cell death upon virus, whereas this is not the case for GSDMD knockout cells, which aligns with the observation that GSDMD is also inactivated by caspase-3 during infection. These results suggest that GSDMD is inactivated during HCoV-229E infection, and point to GSDME as an important player in the execution of virus-induced cell death.
Importance
Recently, it has been shown that the Mpros of coronaviruses possess accessory functions other than their main role in the proteolytic processing of the viral polyproteins. Although the SARS-CoV-2 outbreak has fuelled the discovery of host cellular substrates of SARS-CoV-2 Mpro, less is known about the interplay of less pathogenic human coronavirus Mpros with host proteins. We demonstrate that HCoV-229E Mpro cleaves GSDMD at two sites within its pore-forming domain, which disrupts GSDMD-mediated pyroptosis. These results point to a new strategy for HCoV-229E to escape the host antiviral response. Additionally, we show that GSDME contributes to virus-induced lytic cell death upon activation by caspase-3, shedding light on a previously undescribed cell death mechanism occurring in HCoV-229E infected cells.
