TRIM46

TRIM46 is a RING-domain E3 ubiquitin ligase and microtubule-associated protein that plays dual roles: organizing axonal microtubule architecture and regulating diverse signaling pathways through ubiquitin-mediated substrate degradation. In neurons, TRIM46 localizes to the axon initial segment where it forms the electron-dense cross-bridges that bundle parallel, plus-end-out microtubules; although knockout mice reveal that TRIM46 is essential for microtubule fasciculation, it is dispensable for axon specification and AIS formation in vivo (PMID:26671463, PMID:30967428, PMID:39251352). Its neuron-specific expression is achieved through PTBP2-regulated alternative splicing coupled to nonsense-mediated mRNA decay, and its transport to the AIS depends on a KIF3B-enriched kinesin-2 complex (PMID:35440129, PMID:41910726). Outside the nervous system, TRIM46 ubiquitinates and degrades multiple substrates—including PHLPP2, HDAC1, GPX4, IκBα, Axin1, DUSP1, and SLC7A11—thereby modulating AKT, NF-κB, Wnt/β-catenin, and ferroptosis pathways in contexts ranging from cancer chemoresistance to diabetic retinopathy and viral lung injury (PMID:35354796, PMID:34459501, PMID:34487731, PMID:36064447, PMID:35670901, PMID:39531094).

1. 2015 High

   The first functional characterization of TRIM46 established it as a microtubule-organizing protein that drives uniform plus-end-out microtubule polarity at the nascent axon and AIS, framing it as a key determinant of neuronal polarity.

   Evidence Overexpression/knockdown in cultured neurons with live imaging, Tau missorting readouts, and cargo trafficking assays

   PMID:26671463

   Open questions at the time

   • Whether TRIM46 directly cross-links microtubules or acts indirectly was unresolved
   • Whether TRIM46's role in cultured neurons reflects its requirement in vivo was untested
   • The E3 ligase activity of the RING domain was not examined in this neuronal context
2. 2019 High

   Ultrastructural analysis resolved that TRIM46 is the structural component of the electron-dense cross-bridges between fasciculated microtubules at the AIS, directly answering how microtubule bundling is achieved.

   Evidence Correlative light and electron microscopy with TRIM46 depletion in cultured rat hippocampal neurons

   PMID:30967428

   Open questions at the time

   • The minimal domain of TRIM46 sufficient for cross-bridge formation was not defined
   • Whether cross-bridge formation depends on the RING domain or a separate structural motif was unknown
3. 2020 Medium

   TRIM46 was shown to function as an E3 ubiquitin ligase for DUSP1, linking it to MAPK/NF-κB inflammatory signaling and revealing substrate activities beyond microtubule organization.

   Evidence Co-IP, ubiquitination assay, knockdown/overexpression, and in vivo mouse model of TcdB-induced inflammation

   PMID:31918570

   Open questions at the time

   • The ubiquitin chain type and RING-domain dependence were not demonstrated for DUSP1
   • No independent replication from a second laboratory
4. 2021 High

   Identification of GPX4 and HDAC1 as TRIM46 ubiquitination substrates extended its E3 ligase repertoire to ferroptosis regulation and epigenetic control of DNA replication/repair, respectively, with RING-domain mutant confirmation for HDAC1.

   Evidence Co-IP, ubiquitination assays, CRISPR knock-in of enhancer SNP (HDAC1 study), western blot, and in vivo tumor models

   PMID:34459501 PMID:34487731

   Open questions at the time

   • Whether GPX4 ubiquitination depends on the RING domain specifically was not tested
   • Whether substrate selectivity among diverse targets involves different adaptor proteins was unaddressed
5. 2022 High

   Mechanistic dissection of TRIM46 expression revealed that PTBP2-regulated alternative splicing and NMD control its neuron-specific accumulation during axonogenesis, explaining how a broadly transcribed gene achieves restricted protein expression.

   Evidence Alternative splicing analysis, NMD assays, PTBP2 manipulation, genetic exon deletion in neurons

   PMID:35440129

   Open questions at the time

   • Whether additional RNA-binding proteins regulate TRIM46 splicing in non-neuronal tissues was unknown
   • Genetic exon deletion showed TRIM46 is instructive but not always required for AnkG localization, leaving redundant pathways unidentified
6. 2022 High

   Additional E3 ligase substrates—PHLPP2, IκBα, and Axin1—were identified, showing TRIM46 activates AKT/glycolysis, NF-κB, and Wnt/β-catenin pathways in cancer and fibrosis contexts; RING-mutant analysis for PHLPP2 confirmed catalytic dependence.

   Evidence Co-IP, ubiquitination assays, RING-mutant overexpression, PDX models (PHLPP2), proteasome inhibitor rescue (Axin1), rat renal fibrosis model

   PMID:35354796 PMID:35670901 PMID:36064447

   Open questions at the time

   • The structural basis for TRIM46 recognizing such diverse substrates is uncharacterized
   • Whether these non-neuronal substrates are relevant under physiological (non-pathological) conditions was not tested
7. 2024 High

   TRIM46 knockout mice demonstrated that TRIM46 is dispensable for axon specification, AIS formation, and normal behavior in vivo—revising the prior model from cultured neurons—while confirming its requirement for microtubule fasciculation; AnkG was shown to restrict TRIM46 to the AIS.

   Evidence Constitutive TRIM46 knockout mice with immunohistochemistry, electron microscopy, and behavioral testing

   PMID:39251352

   Open questions at the time

   • Compensatory mechanisms that substitute for TRIM46 in axon specification in vivo remain unidentified
   • Whether microtubule fasciculation loss has functional consequences under stress or aging was not tested
8. 2024 Medium

   SLC7A11 was identified as a TRIM46 substrate linking it to ferroptosis and inflammation during influenza infection, and TRIM46 KO rats revealed roles in dendritic morphogenesis and interaction with FKBP5, expanding its neuronal functions beyond the AIS.

   Evidence Co-IP, cycloheximide chase, in vivo H1N1 mouse model (SLC7A11); CRISPR KO rats, Co-IP for FKBP5, morphological analysis

   PMID:38193537 PMID:39531094

   Open questions at the time

   • SLC7A11 ubiquitination site(s) and chain linkage type not mapped
   • The mechanistic link between TRIM46-FKBP5 interaction and dendritic spine phenotypes is correlative
   • No independent replication of either finding
9. 2026 Medium

   The mechanism of TRIM46 axonal delivery was resolved: a KIF3B-enriched, KAP3-associated kinesin-2 assembly distinct from the canonical KIF3A/B/KAP3 complex selectively transports TRIM46 to the AIS.

   Evidence Biochemical fractionation, co-immunoprecipitation, structural analyses, cellular localization assays

   PMID:41910726

   Open questions at the time

   • Whether this transport mechanism is regulated during development or plasticity is unknown
   • Structural details of the TRIM46-kinesin-2 interface at atomic resolution are lacking

• How TRIM46 achieves substrate selectivity across its many ubiquitination targets, whether its E3 ligase and microtubule-bundling activities are coordinated or independent, and what compensatory mechanisms maintain axon specification in its absence in vivo remain open questions.
• No structural model of TRIM46 exists to explain dual microtubule-binding and E3 ligase functions
• The identity of redundant factors that compensate for TRIM46 loss in axon specification is unknown
• Whether the diverse non-neuronal substrates reflect physiological or pathological roles has not been resolved