DTX3

DTX3 is a RING finger-domain E3 ubiquitin ligase that negatively regulates Notch signaling and modulates diverse substrates through both canonical and non-canonical ubiquitylation. DTX3 ubiquitinates and promotes proteasomal degradation of NOTCH2, NOTCH4, and the Notch intracellular domain (NICD) via its C-terminal RING finger domain, suppressing Notch-dependent transcription, EMT, and tumor cell invasion (PMID:31854042, PMID:33300431, PMID:40127622). Beyond canonical protein substrates such as XRCC5 and mutant p53, DTX3 catalyzes ubiquitylation of nucleic acids (DNA and RNA) through ester bond formation and can monoubiquitylate tankyrase on mono-ADP-ribose rather than lysine, creating a hybrid ubiquitin-MAR mark that antagonizes PARylation-dependent degradation (PMID:39242775, PMID:35782979, PMID:33403043). DTX3 homodimerizes and heterodimerizes with other DTX family members, and a distinct N-terminal isoform (DTX3c) assembles with UBA1, UBE2N, and the Cdc48/p97 ATPase to target the EphB4 receptor kinase for degradation (PMID:12670957, PMID:37108544).

1. 2003 High

   Establishing DTX3 as an E3 ubiquitin ligase resolved whether DTX-family proteins possess intrinsic catalytic activity beyond their known role as Notch-pathway modulators in Drosophila.

   Evidence In vitro self-ubiquitination assay with purified DTX3 plus yeast two-hybrid and in vivo dimerization studies demonstrating homo- and heterodimerization among DTX family members

   PMID:12670957

   Open questions at the time

   • No physiological substrates identified at this stage
   • Functional consequence of DTX homo-/heterodimerization on substrate selection or E3 activity undefined
   • In vivo relevance of DTX3 E3 activity not tested
2. 2020 Medium

   Identification of NOTCH2 and NOTCH4 as direct ubiquitylation substrates established DTX3 as a negative regulator of Notch signaling through receptor degradation, answering whether DTX3 has physiological substrates.

   Evidence Yeast two-hybrid screen for DTX3-NOTCH2 interaction, ubiquitination assays, and gain/loss-of-function proliferation assays in esophageal carcinoma cells (NOTCH2); ARE-binding/mRNA stability assays showing DCAF13 controls DTX3 mRNA, plus ubiquitination assays confirming DTX3 targets NOTCH4 for degradation

   PMID:31854042 PMID:33300431

   Open questions at the time

   • NOTCH2 and NOTCH4 ubiquitylation studies each from single labs; independent replication lacking
   • Ubiquitin chain type and specific lysine sites on NOTCH2/NOTCH4 not mapped
   • Whether DTX3 acts on full-length receptors at the membrane versus cleaved intracellular domain not resolved at this point
3. 2020 Medium

   Discovery that DTX3 ubiquitinates mutant p53 to stabilize rather than degrade it revealed context-dependent outcomes of DTX3-mediated ubiquitylation, expanding its substrate repertoire beyond Notch receptors.

   Evidence Co-immunoprecipitation and ubiquitination assays in ovarian cancer cells showing DTX3 disrupts MDM2-mutant p53 interaction and stabilizes mutant p53, with in vivo tumor growth validation

   PMID:35782979

   Open questions at the time

   • Mechanism distinguishing DTX3-mediated stabilizing versus degradative ubiquitylation not elucidated
   • Ubiquitin chain linkage type on mutant p53 not determined
   • Single lab; not independently confirmed
4. 2021 Medium

   Identification of XRCC5/Ku80 as a DTX3 substrate linked DTX3 to DNA repair protein turnover and AKT signaling suppression, broadening its functional scope beyond Notch.

   Evidence IP-mass spectrometry, co-IP, immunofluorescence co-localization in the nucleus, and ubiquitination assays in papillary thyroid carcinoma cells

   PMID:33403043

   Open questions at the time

   • Whether DTX3-mediated XRCC5 ubiquitylation affects DNA repair function not tested
   • Mechanism linking XRCC5 ubiquitylation to AKT pathway suppression unclear
   • Single lab with no structural or in vivo validation
5. 2023 Medium

   Discovery of the DTX3c isoform and its assembly into a UBA1/UBE2N/Cdc48-p97 complex targeting EphB4 revealed isoform-specific complex formation and a mechanism coupling substrate recruitment to AAA-ATPase unfoldase activity.

   Evidence Targeted proteomics and reciprocal co-IP in malignant mesothelioma cells identifying complex members, plus functional perturbation of Cdc48/p97 ATPase activity

   PMID:37108544

   Open questions at the time

   • Only one cell system (mesothelioma) tested; generality of the DTX3c complex unknown
   • Direct in vitro reconstitution of the DTX3c-Cdc48/p97 complex not performed
   • Ubiquitin chain type on EphB4 and degradation pathway (proteasomal vs. lysosomal) not determined
6. 2024 High

   Demonstration that DTX3 ubiquitylates DNA and RNA via ester bonds established a fundamentally non-canonical catalytic activity, revealing DTX3 can act on nucleic acid substrates like DTX3L.

   Evidence Reconstituted in vitro ubiquitylation assays with purified proteins, ester bond characterization, and DUB reversal by USP2, JOSD1, and SARS-CoV-2 PLpro

   PMID:39242775

   Open questions at the time

   • Physiological function of nucleic acid ubiquitylation by DTX3 in cells not demonstrated
   • Whether DTX3 and DTX3L have redundant or distinct nucleic acid substrates in vivo unknown
   • Structural basis for DTX3 preference among nucleic acid substrates not resolved
7. 2025 Medium

   Mapping the DTX3-NICD interaction to the RING finger domain and demonstrating NICD ubiquitylation/degradation with epistasis via Notch inhibitor DAPT resolved how DTX3 directly suppresses Notch transcriptional output at the level of the active signaling fragment.

   Evidence Co-IP with domain truncation mapping, ubiquitination assay, and rescue with DAPT in bladder cancer cells in vitro and in vivo

   PMID:40127622

   Open questions at the time

   • Whether NICD ubiquitylation is the dominant mechanism across all tissue contexts or overlaps with NOTCH2/4 full-length receptor targeting is unresolved
   • Single lab study; independent confirmation needed
8. 2025 Medium

   Discovery that DTX3 monoubiquitylates tankyrase on mono-ADP-ribose (not lysine) introduced a novel non-canonical ubiquitylation modality — a ubiquitin-MAR hybrid mark — that antagonizes PARylation and stabilizes tankyrase by blocking RNF146-dependent degradation. (preprint)

   Evidence Cell-based ubiquitylation assays and biochemical characterization of ubiquitin-MAR hybrid mark; identification of RNF114/RNF166 as hybrid-mark readers (preprint)

   PMID:bio_10.1101_2025.04.09.648013

   Open questions at the time

   • Preprint; not yet peer-reviewed
   • In vivo significance of the ubiquitin-MAR hybrid mark for Wnt signaling or other tankyrase-dependent pathways not tested
   • Structural basis for DTX3 recognition of the MAR moiety not determined

• The rules governing whether DTX3 ubiquitylation leads to substrate degradation versus stabilization, and the physiological significance of its nucleic acid and ADP-ribose ubiquitylation activities, remain unresolved.
• No structural model of DTX3 or DTX3-substrate complexes exists
• Chain-type specificity (K48, K63, mono-Ub) dictating substrate fate not systematically characterized
• In vivo mouse knockout or genetic model for DTX3 has not been reported
• Relative contributions of canonical protein versus non-canonical nucleic acid/MAR ubiquitylation to DTX3 physiological function unknown