The antiviral role of TRIM25 in mammalian embryonic stem cells

Mammalian embryonic stem cells (ESCs), despite lacking functional interferon (IFN) signaling, are remarkably resistant to viral infection. However, the mechanistic basis of their antiviral defenses remains incompletely characterized. In this study, we investigated the antiviral functional role and molecular mechanism of tripartite motif-containing protein 25 (TRIM25), a well-known key driver of IFN-dependent innate immunity, in IFN-deficient mouse ESCs (mESCs). TRIM25 exhibited a broad spectrum of antiviral activity in mESCs. RNAi depletion or CRISPR-mediated knockout of TRIM25 markedly enhanced the replication and propagation of both encephalomyocarditis virus (EMCV) and vesicular stomatitis virus (VSV). Mechanistically, the antiviral activity of TRIM25 in mESCs is independent of both IFN production and constitutive ISG expression. In virus-infected mESCs, TRIM25 translocated from the nucleus to the cytoplasm and directly bound viral RNA, where it formed cytoplasmic condensates with GTPase-activating protein-binding protein 1 (G3BP1) that colocalized with dsRNA foci. Genetic perturbation of G3BP1 similarly compromised the antiviral defenses of mESCs, revealing an essential synergism between TRIM25 and stress granule components in restricting viral replication. Our study identifies TRIM25 as a pivotal RNA-sensing effector in ESCs, delineating a previously unrecognized IFN-independent axis of intrinsic immunity that bridges viral RNA surveillance with stress granule-mediated suppression, thereby expanding the paradigm of pluripotent cell-autonomous antiviral strategies.