Angiotensin-converting enzyme 2 (ACE2) is the primary entry receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but ACE2-independent entry has been observed in vitro for strains with the spike-E484D substitution. Here, we conduct a whole-genome CRISPR-Cas9 knockout screen using SARS-CoV-2 mouse adapted 1 (SARS-CoV-2), which carries spike-E484D, to identify the ACE2-independent entry mechanisms. SARS-CoV-2 infection in HEK293T cells relies on heparan sulfate and endocytic pathways, with TMEM106B, a transmembrane lysosomal protein, the most significant contributor. While SARS-CoV-2 productively infects human brain organoids and K18-hACE2 mouse brains, it does not infect C57BL/6J or Ifnar mouse brains. This suggests that ACE2-independent entry via TMEM106B, which is predominantly expressed in the brain, does not overtly increase the risk of SARS-CoV-2 neuroinvasiveness in mice with endogenous Ace2 expression. Importantly, SARS-CoV-2 does not replicate in the Ace2 mouse respiratory tract. Overall, this suggests that robust ACE2-independent infection by SARS-CoV-2 is likely an in vitro phenomenon with no apparent implications for infection in vivo.
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The naturally occurring mutation E484D in the spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can render viral entry ACE2 independent and imdevimab resistant. Here, we investigated whether the cellular proteins ASGR1, DC-SIGN, and TMEM106B, which interact with the viral S protein, can contribute to these processes. Employing S protein-pseudotyped particles, we found that expression of ASGR1 or DC-SIGN jointly with TMEM106B allowed for robust entry of mutant E484D into otherwise non-susceptible cells, while this effect was not observed upon separate expression of the single proteins and upon infection with SARS-CoV-2 wild type (WT).
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Angiotensin-converting enzyme 2 (ACE2) is the primary entry receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but ACE2-independent entry has been observed in vitro for strains with the spike-E484D substitution. Here, we conduct a whole-genome CRISPR-Cas9 knockout screen using SARS-CoV-2 mouse adapted 1 (SARS-CoV-2), which carries spike-E484D, to identify the ACE2-independent entry mechanisms. SARS-CoV-2 infection in HEK293T cells relies on heparan sulfate and endocytic pathways, with TMEM106B, a transmembrane lysosomal protein, the most significant contributor.
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- Excessive inflammation is a key cause of death in severe COVID-19, but the underlying mechanisms are not well understood.
- The study shows that the way SARS-CoV-2 enters different cell types (like epithelial and myeloid cells) affects how the virus replicates and triggers inflammation.
- Specific viral proteins, like NSP14 and ORF6, interact with signaling pathways (like NF-κB) to either enhance or suppress inflammatory responses, revealing important stages in COVID-19 progression.
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