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

Background

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.

Methods

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.

Results

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.

Conclusion
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.