Autophagy plays a critical role in viral replication and the regulation of host immune responses. Although the TOM1-TOLLIP complex has been implicated in immune signaling, cargo trafficking, and endocytosis, its role in viral replication has not been defined. Here, we demonstrate that the SARS-CoV-2 main protease (NSP5) cleaves TOM1 at residue Q354 through its protease activity. This cleavage is also observed with the main proteases of SARS-CoV and MERS-CoV. Importantly, TOM1 overexpression suppresses SARS-CoV-2 replication in HEK293T-hACE2 and Vero cells, while TOM1 knockout via CRISPR-Cas9 significantly enhances viral propagation, indicating that TOM1 functions as a novel restriction factor against SARS-CoV-2 infection. Moreover, various TOM1 orthologs from diverse species, including cattle, bats, monkeys, mice, and ducks, show similar restriction to SARS-CoV-2, but they all are antagonized by NSP5 cleavage. Mechanistically, we found that TOM1 recruits the autophagy receptor TOLLIP to target SARS-CoV-2 envelope (E) protein for autophagic degradation, thereby limiting viral replication. These findings highlight the importance of the TOM1-TOLLIP complex in host defense and discover that SARS-CoV-2 exploits a conserved NSP5-mediated TOM1 cleavage mechanism to evade host antiviral defenses.IMPORTANCEViruses must overcome the body's natural defenses in order to replicate and spread. One important cellular defense mechanism is autophagy, a process that helps cells remove harmful proteins and pathogens. In this study, we discovered that a host protein called TOM1 acts as a restriction factor that helps limit the replication of SARS-CoV-2, the virus responsible for COVID-19. TOM1 works together with another protein, TOLLIP, to direct envelope proteins to the cell's degradation system, thereby reducing viral replication. However, SARS-CoV-2 has evolved a strategy to counter this defense. The viral main protease (NSP5) cleaves TOM1, disabling its antiviral activity. This mechanism is conserved among several coronaviruses, including SARS-CoV and MERS-CoV. Our findings reveal a previously unrecognized antiviral role of the TOM1-TOLLIP complex and demonstrate how coronaviruses evade this host defense, providing new insight into virus-host interactions and potential targets for antiviral therapies.
Zhang et al. (Fri,) studied this question.