CAPRIN1 localizes to CD63-positive MVB-like SARS-CoV-2 egress compartments and limits cytopathic effects
Stress granules (SGs) are cytoplasmic condensates that assemble under cellular stress, including viral infection. The best-characterized evasion strategy in SARS-CoV-2 infection involves the viral nucleocapsid (N) protein hijacking the SG core protein G3BP1, thereby preventing SG assembly. By performing network analysis of N protein interactomes, we identified CAPRIN1 as an underexplored candidate, despite its central role alongside G3BP1 in SG assembly. Here, we provide the first high-resolution spatial and functional data on CAPRIN1 in SARS-CoV-2 infection. Using ultrastructure expansion microscopy (U-ExM), we localized CAPRIN1 and viral egress markers to enlarged, CD63- and LAMP1-positive, multivesicular body (MVB)-like egress compartments, refining the current model of SARS-CoV-2 egress. CAPRIN1 was found on both the limiting membrane of these compartments and within the intraluminal vesicles, a pattern distinct from G3BP1. Knockout of CAPRIN1 increased infection-associated cell death, promoted an aberrant cell-death phenotype, and enhanced syncytia formation. Together, our data reveal distinct activities of CAPRIN1 during infection and identify the egress compartments as MVB-like, raising the possibility that SARS-CoV-2 repurposes more than one cellular pathway for egress.