UBE3D

UBE3D is a HECT_2-family E3-like ubiquitin ligase whose principal characterized role is to stabilize the pre-mRNA 3'-end processing endonuclease CPSF73/CPSF3, thereby maintaining cleavage and polyadenylation capacity and the downstream gene expression programs it controls (PMID:35992060, PMID:36519931, PMID:40075082). It binds the E2 ubiquitin-conjugating enzyme UbcH10/UBE2C through residues 235–257, displays HECT-dependent self-ubiquitinylation, and ubiquitinylates cyclin B in vitro (PMID:15749827). Mechanistically, UBE3D is a cytoplasmic binding partner of CPSF73 that uses a conserved cysteine to coordinate the enzyme's active-site metal ions, and its loss—by siRNA depletion or CRISPR knockout—lowers CPSF73/CPSF3 protein, produces pre-mRNA cleavage defects, and globally dysregulates mRNAs; overexpression of UBE3D or CPSF73 rescues the resulting phenotypes, placing UBE3D genetically upstream of CPSF73 (PMID:35992060, PMID:36519931, PMID:39032490). In mice, UBE3D interacts with and can de-ubiquitinate CPSF3, and its deficiency reduces CPSF3 and downregulates Homeobox gene expression, while dominant-negative CPSF3 reproduces this loss (PMID:40075082). UBE3D additionally functions in DNA double-strand break repair: it is recruited to damage sites via a PIP-box interaction with PCNA, binds KAP1 through residues R377/R378, and its depletion impairs chromatin relaxation and KAP1 recruitment, implicating it in homologous recombination via heterochromatin de-condensation; the AMD-associated V379M mutation abolishes KAP1 binding upon oxidation (PMID:36094642). Its yeast ortholog Ipa1 belongs to the same HECT_2 family, requires conserved cysteines for activity, interacts with multiple E2 enzymes, and modulates proteasome activity (PMID:29519818).

1. 2005 Medium

   Established that UBE3D (H10BH) is an E3-like ubiquitin ligase by showing it pairs with a specific E2 enzyme and can ubiquitinylate a substrate, defining its biochemical activity.

   Evidence Yeast two-hybrid, in vitro ubiquitinylation, and deletion mutagenesis mapping UbcH10 binding and HECT-dependent activity

   PMID:15749827

   Open questions at the time

   • Single lab without independent replication
   • Physiological substrates beyond cyclin B not identified
   • In vitro activity not validated in cells
2. 2018 Medium

   Showed the yeast ortholog Ipa1 defines a conserved HECT_2 family with essential active-site cysteines and links the family to proteasome regulation, framing UBE3D within proteostasis.

   Evidence Genetic mutant analysis, in vivo E2 interaction assays, Rpn4 reporter and substrate turnover in yeast

   PMID:29519818

   Open questions at the time

   • Findings are in yeast ortholog, not human UBE3D
   • Direct proteasome substrates not defined
   • Mechanism linking Ipa1 to Rpn4 regulon unresolved
3. 2022 Medium

   Identified the primary cellular role of UBE3D as a stabilizer of CPSF73, connecting it to pre-mRNA 3'-end processing rather than substrate destruction.

   Evidence siRNA depletion with CPSF73 western blot, pre-mRNA cleavage assays, gene expression analysis

   PMID:35992060

   Open questions at the time

   • Mechanism by which UBE3D blocks CPSF73 degradation not resolved
   • Direct ubiquitin chain editing on CPSF73 not demonstrated
   • Single lab
4. 2022 Medium

   Confirmed via genetic knockout and rescue that UBE3D acts upstream of CPSF73 and that this axis is required for a physiological output, adipogenic differentiation.

   Evidence CRISPR/Cas9 knockout in 3T3-L1, overexpression rescue, RNA-seq, western blot, differentiation assay

   PMID:36519931

   Open questions at the time

   • Direct enzymatic mechanism on CPSF73 not shown
   • Generality beyond adipocytes untested in this work
   • Single lab
5. 2022 Medium

   Revealed a second, distinct function in DNA double-strand break repair, showing UBE3D is recruited via PCNA and engages KAP1 to drive heterochromatin de-condensation.

   Evidence I-SceI GFP reporter, IP-MS, Co-IP, pulldown, MNase assays, site-directed mutagenesis

   PMID:36094642

   Open questions at the time

   • Whether repair role depends on ligase activity unknown
   • Relationship between repair function and CPSF73 stabilization unclear
   • AMD V379M mechanism shown only at the binding level
6. 2024 Medium

   Provided a structural rationale for CPSF73 stabilization, proposing UBE3D uses a conserved cysteine to coordinate CPSF73 active-site metals analogous to BRAT1-INTS11.

   Evidence Structural analysis using a paralogous cryo-EM template, binding partner identification, functional complementation analogy

   PMID:39032490

   Open questions at the time

   • Direct structure of the UBE3D-CPSF73 complex not reported
   • Cysteine-metal coordination not biochemically validated
   • Reconciliation with ligase/de-ubiquitination activities pending
7. 2025 Medium

   Extended the CPSF3 axis in vivo and reframed UBE3D activity as de-ubiquitination of CPSF3, linking the interaction to developmental Homeobox gene expression.

   Evidence CRISPR/Cas9 knockout mice, Co-IP, de-ubiquitination assay, RNA-seq, dominant-negative CPSF3, in situ hybridization

   PMID:40075082

   Open questions at the time

   • Apparent de-ubiquitinase activity not reconciled with reported E3 ligase activity
   • Catalytic residues for CPSF3 de-ubiquitination not mapped
   • Single lab

• Whether UBE3D's enzymatic activity is fundamentally that of a ubiquitin ligase, a de-ubiquitinase, or a non-catalytic protective binder of CPSF73/CPSF3 remains unresolved, as does how its 3'-end processing and DSB-repair roles are coordinated.
• No direct structure of any UBE3D-substrate complex
• Catalytic mechanism toward CPSF73/CPSF3 undefined
• Functional link between RNA processing and DNA repair roles unknown