Tetherin restricts SARS-CoV-2 replication despite antagonistic effects of Spike and ORF7a (preprint)

ABSTRACT

SARS-CoV-2 infection induces interferon-stimulated genes, one of which encodes Tetherin, a transmembrane protein inhibiting the release of various enveloped viruses from infected cells. Previous studies revealed that SARS-CoV encodes two Tetherin antagonists the Spike protein (S) inducing lysosomal degradation of Tetherin, and ORF7a altering its glycosylation. SARS-CoV-2 ORF7a has also been shown to antagonize Tetherin. Therefore, we here investigated whether SARS-CoV-2 S is also a Tetherin antagonist and compared the abilities and mechanisms of S and ORF7a in counteracting Tetherin. SARS-CoV and SARS-CoV-2 S reduced Tetherin cell surface levels in a cell type-dependent manner, possibly related to the basal protein levels of Tetherin. In HEK293T cells, under conditions of high exogenous Tetherin expression, SARS-CoV-2 S and ORF7a reduced total Tetherin levels much more efficiently than the respective counterparts derived from SARS-CoV. Nevertheless, ORF7a from both strains was able to alter Tetherin glycosylation. The ability to decrease total protein levels of Tetherin was conserved among S proteins from different SARS-CoV-2 variants (D614G, Cluster 5, , {gamma}, {delta}, o). While SARS-CoV-2 S and ORF7a both colocalized with Tetherin, only ORF7a directly interacted with the restriction factor. Despite the presence of two Tetherin antagonists, however, SARS-CoV-2 replication in Caco-2 cells was further enhanced upon Tetherin knockout. Altogether, our data show that endogenous Tetherin restricts SARS-CoV-2 replication, and that the antiviral activity of Tetherin is partially counteracted by two viral antagonists with differential and complementary modes of action, S and ORF7a.