UBE2H

UBE2H is a ubiquitin-conjugating (E2) enzyme that catalyzes substrate ubiquitination, originally characterized through its ability to ubiquitinate histones in vitro, with its first 12 N-terminal residues required for substrate modification but dispensable for thiolester formation with ubiquitin (PMID:8132613). Its principal physiological role is as the cognate E2 for the CTLH/GID E3 ubiquitin ligase complex (PMID:36459484, PMID:38113892). This E2–E3 pairing is achieved through an unconventional catalytic assembly in which CK2-mediated multisite phosphorylation of acidic sequences in the UBE2H C-terminus anchors the enzyme to basic patches on the E3, with phosphorylation-dependent multivalency rigidifying the catalytic center to drive substrate ubiquitylation (PMID:38113892). UBE2H charging with ubiquitin is independently tuned by CDK and mTOR phosphorylation of N-terminal serines S3/S5, coupling CTLH ubiquitylation activity to mitotic state and nutrient status; preventing this phosphorylation enhances CTLH-mediated degradation of substrates including NEK9 and AAMP and produces proliferation and mitotic defects (PMID:41959163). Through the CTLH module, UBE2H is required for terminal erythroid maturation and enucleation (PMID:36459484) and supports mitochondrial proteostasis, a role conserved in yeast Ubc8 where it promotes TOM complex assembly and mitochondrial protein import (PMID:36253107). UBE2H is also required for normal neurogenesis, where its loss activates ATM-p53 signaling and induces apoptosis in differentiated neural cells (PMID:37208785), and it can act as an ISG15-conjugating E2 for protein ISGylation upon interferon stimulation (PMID:15485925).

1. 1994 High

   Establishing that human UBE2H is a catalytically active ubiquitin-conjugating enzyme answered whether it could transfer ubiquitin to substrates and localized substrate-recognition function to its N-terminus.

   Evidence in vitro ubiquitination and thiolester assays with N-terminal truncation mutagenesis, ortholog comparison to yeast UBC8

   PMID:8132613

   Open questions at the time

   • Physiological substrates beyond in vitro histones not defined
   • No cognate E3 partner identified at this stage
2. 2004 Medium

   Demonstrating UBE2H as an ISG15-conjugating E2 extended its activity beyond ubiquitin to a ubiquitin-like modifier in the interferon response.

   Evidence siRNA knockdown in HeLa cells with in-cell ISGylation readout and specificity testing against related E2s

   PMID:15485925

   Open questions at the time

   • ISG15 E3 partner for UBE2H not defined
   • Substrate specificity of ISGylation by UBE2H unresolved
3. 2022 High

   Identifying UBE2H as the cognate E2 for the CTLH E3 complex during erythropoiesis placed it in a defined physiological ubiquitylation pathway with a cellular phenotype.

   Evidence CRISPR-Cas9 loss-of-function and proteomics in an in vitro human erythropoiesis model

   PMID:36459484

   Open questions at the time

   • Erythroid CTLH substrates driving maturation/enucleation not enumerated
   • Molecular basis of the E2-E3 pairing not yet resolved
4. 2022 Medium

   Yeast Ubc8 work linked this E2 to mitochondrial proteostasis by showing it promotes TOM complex assembly and protein import.

   Evidence yeast genetic deletion with mitochondrial import assays, TOM assembly analysis, and quantitative proteomics

   PMID:36253107

   Open questions at the time

   • Direct E3 partner and substrates in the mitochondrial pathway not defined
   • Conservation of this role to human UBE2H not established in this study
5. 2023 High

   Cryo-EM and biochemistry resolved how UBE2H is selected by CTLH/GID, revealing phosphorylation-dependent anchoring of its C-terminus to the E3 distant from the active site.

   Evidence cryo-EM structure determination plus biochemistry, phospho-site mutagenesis, and cell biology

   PMID:38113892

   Open questions at the time

   • In vivo dynamics of CK2 phosphorylation/dephosphorylation cycling not fully resolved
   • Whether other E2s engage CTLH via similar mechanisms unaddressed
6. 2023 Medium

   Zebrafish loss-of-function tied UBE2H to neurogenesis and connected a human patient variant to disease-relevant neural apoptosis via ATM-p53 signaling.

   Evidence morpholino knockdown, transcriptomics, apoptosis assays, and functional validation of the p.Thr150Met patient variant in embryos

   PMID:37208785

   Open questions at the time

   • Mechanistic link between UBE2H loss and ATM-p53 activation unresolved
   • Relevant CTLH substrates in neural cells not identified
7. 2026 Medium

   Identifying CDK/mTOR phosphorylation of N-terminal S3/S5 as a brake on UBE2H ubiquitin-charging showed how CTLH activity is coupled to cell cycle and nutrient state, and uncovered new substrates.

   Evidence phospho-site mutagenesis, ubiquitin-charging and degradation assays, and mass spectrometry identifying NEK9 and AAMP (preprint)

   PMID:41959163

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Relative contribution of N-terminal vs C-terminal phospho-regulation in vivo unclear
   • C-degron recognition of NEK9 not fully mapped
8. 2026 Medium

   CRISPR screens defined UBE2H as an aneuploidy-specific dependency, linking its function to mitochondrial proteostasis under aneuploid stress.

   Evidence paired CRISPR loss-of-function screens with isogenic aneuploid/near-euploid validation and proteomics (preprint)

   PMID:42094535

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Direct mechanistic chain from UBE2H to mitochondrial protein abundance not established
   • Whether dependency is CTLH-dependent not resolved

• The full substrate repertoire of UBE2H-CTLH across tissues and the mechanistic basis connecting its activity to ATM-p53 signaling and mitochondrial proteostasis remain open.
• Comprehensive substrate map of UBE2H-CTLH lacking
• Integration of N-terminal and C-terminal phospho-regulation in vivo undefined
• Direct ISG15 vs ubiquitin partitioning of UBE2H activity unresolved