CRM1-dependent nuclear export of TRIM28 promotes MAVS K48-linked ubiquitination and suppresses RIG-I-mediated...

Ubiquitination is a pivotal post-translational mechanism regulating antiviral innate immunity. TRIM28, a member of the transcription intermediary factor 1 (TIF1) subfamily of the TRIM protein family, has been implicated in the modulation of retinoic acid-inducible gene I (RIG-I) signaling. However, the molecular basis and in vivo relevance remain unclear.

TRIM28 overexpression and knockdown systems were used to evaluate type I interferon (IFN) responses and RNA virus replication in vitro, and an AAV-mediated lung-specific TRIM28 knockdown model was used for in vivo validation. Virus-induced nucleocytoplasmic trafficking of TRIM28 was analyzed by confocal microscopy. Protein interactions and ubiquitination events were examined by co-immunoprecipitation and in-cell ubiquitination assays. TRIM28 domain deletion constructs and MAVS lysine mutants were used to assess domain requirements and to probe functionally relevant ubiquitination sites on MAVS.

TRIM28 knockdown enhanced type I IFN responses and inhibited RNA virus replication in vitro and in vivo. Viral infection predominantly triggered CRM1-dependent nuclear export of TRIM28, leading to its cytoplasmic accumulation. Cytoplasmic TRIM28 associated with MAVS and promoted K48-linked polyubiquitination in an RBCC domain-dependent manner, reducing TBK1 and IRF3 activation and attenuating IFN production. Mutation of MAVS Lys136 or Lys461 impaired TRIM28-mediated ubiquitination and restored downstream signaling.

TRIM28 functions as a negative regulator of RIG-I-mediated antiviral signaling by promoting K48-linked ubiquitination of MAVS. These findings define the TRIM28-MAVS axis as a regulatory checkpoint in innate antiviral immunity and suggest its potential as a target for antiviral intervention.