HECTD4

HECTD4 is a HECT-domain E3 ubiquitin ligase that shapes diverse cellular programs by directing substrate ubiquitination, with in vitro reconstitution of ubiquitin conjugation using purified protein establishing its catalytic activity (PMID:40768362). In epithelial cancer, HECTD4 is induced upon loss of matrix adhesion and ubiquitinates COX-2 (PTGS2) and its regulatory kinase MKK7, so that its depletion stabilizes COX-2 and drives anchorage-independent proliferation, tumorigenesis, and metastasis—phenotypes reversed by COX-2 suppression (PMID:40768362). In neurons, HECTD4 ubiquitinates GluN2B and MALT1, and its downregulation in ischemic stroke weakens GluN2B engagement, elevating GluN2B phosphorylation through MALT1-dependent loss of STEP61, raising intracellular calcium and worsening excitotoxic injury (PMID:36527595). HECTD4 also targets METTL3 for degradation, reducing RANK m6A modification to suppress osteoclast differentiation (PMID:42141331). Biallelic loss-of-function variants in HECTD4 cause an Angelman-like neurodevelopmental syndrome with seizures and movement disorders (PMID:36401616). Beyond these substrate-defined axes, the structural basis of substrate recognition and the determinants of HECTD4 regulation across tissues have not been characterized in the available corpus.

1. 2022 Medium

   Establishing HECTD4 as a human disease gene answered whether its loss has organismal consequence, linking it to an Angelman-like neurodevelopmental phenotype.

   Evidence Exome sequencing across unrelated families with RNA-level confirmation of loss-of-function in patient cells

   PMID:36401616

   Open questions at the time

   • Does not identify the molecular substrate(s) whose dysregulation drives the neurodevelopmental phenotype
   • No mechanistic link from variant to ubiquitination defect
2. 2022 Medium

   Defining GluN2B and MALT1 as ubiquitination targets answered how HECTD4 protects neurons, placing it upstream of STEP61-controlled GluN2B phosphorylation and calcium homeostasis.

   Evidence MS-based interaction mapping, ubiquitination assays, MALT1 siRNA/inhibitor epistasis, and calcium readouts in an ischemia-reperfusion rat model

   PMID:36527595

   Open questions at the time

   • No in vitro reconstitution of GluN2B or MALT1 ubiquitination with purified components
   • Single lab study without reciprocal interaction validation
3. 2022 Low

   Linking HECTD4 to ethanol-responsive hepatic signaling raised the question of whether it participates in ethanol metabolism, showing its expression is ROS-dependently induced and tied to CYP2E1, lipogenic, and ALDH2 expression.

   Evidence HECTD4 knockdown in ethanol-treated cells with gene expression readouts and alcohol-treated mouse liver

   PMID:35713687

   Open questions at the time

   • No ubiquitination substrate identified in this context
   • Gene-expression association only, no direct mechanistic evidence
4. 2025 High

   In vitro reconstitution settled whether HECTD4 is itself a catalytically active E3 ligase and identified COX-2 and MKK7 as substrates governing anchorage-independent growth.

   Evidence In vitro ubiquitin conjugation with purified protein, genome-wide CRISPR screen, ubiquitin remnant profiling, and genetic/pharmacologic COX-2 rescue

   PMID:40768362

   Open questions at the time

   • Structural basis of substrate recognition unresolved
   • Mechanism of adhesion-loss-induced HECTD4 induction not defined
5. 2026 Medium

   Identifying METTL3 as a degradation target extended HECTD4's reach into m6A-dependent gene regulation, defining a HECTD4 → METTL3 → RANK m6A → osteoclast differentiation axis.

   Evidence Ubiquitination assays, MeRIP-qPCR, TRAP staining, and METTL3/RANK epistasis with exosome-delivered HECTD4

   PMID:42141331

   Open questions at the time

   • Single lab and single publication
   • No direct demonstration HECTD4 ubiquitinates METTL3 with purified components
6. 2026 Low

   Proteomic profiling in prostate cancer broadened the candidate substrate landscape, associating HECTD4 with ubiquitination of cell-cycle and signaling proteins.

   Evidence HECTD4 knockdown with LC-MS/MS ubiquitination profiling and pathway analysis in prostate cancer cell lines

   PMID:42055625

   Open questions at the time

   • No direct in vitro ubiquitination assays for individual candidate substrates (NUSAP1, CDK6, MED13L)
   • Association-level evidence only

• The structural and regulatory logic by which a single HECT ligase selects such distinct substrates across cancer, neurons, and bone remains unresolved.
• No structural model of substrate engagement
• Determinants of tissue-specific substrate selection unknown
• Mechanism linking disease variants to substrate dysregulation undefined