NEURL4

NEURL4 is a multidomain scaffold and enzyme that operates at centrosomes, in mitochondria, and within HERC2-centered ubiquitin-signaling networks to control centriole homeostasis, genome integrity, and cell-fate signaling (PMID:22441691, PMID:35157000, PMID:29097665). At the centrosome, NEURL4 localizes to procentrioles and daughter centrioles through its Neuralized homology repeat and drives ubiquitylation and destabilization of the centriolar capping protein CP110; its loss causes CP110 accumulation, ectopic microtubule organizing centres, and aberrant mitotic spindles (PMID:22441691). This CP110-removing activity is recruited to the centriole by ODF2 and is sufficient to license primary cilia biogenesis (PMID:37681926), and the upstream Neurl4→CP110 epistasis is conserved in Drosophila where it maintains primordial germ cell integrity (PMID:26116656). NEURL4 physically engages the E3 ligase HERC2—being itself a HERC2 substrate—through a region distinct from its CP110-binding site, and the HERC2–NEURL4 association is required for normal centrosome and pericentriolar material architecture (PMID:22261722). Beyond the centrosome, NEURL4 directly binds the p53 C-terminus via its Neuralized domains 3 and 4 to promote p53 tetramerization and transcriptional activity without altering p53 stability, acting with HERC2 and MDM2 in a DNA-damage-responsive regulatory complex (PMID:28977907, PMID:31665549). NEURL4 also participates in a cytoplasmic RNF8–UBC13–HERC2 ubiquitin-signaling network that suppresses synapse formation in cerebellar neurons (PMID:29097665) and in a LRRK2–NEURL4–HERC2 complex that modulates endosomal recycling of the Notch ligand Dll1 to regulate neural stem cell differentiation (PMID:26355680). Independently of these scaffolding roles, NEURL4 is the principal mitochondrial ADP-ribosyltransferase, accounting for most mitochondrial ART activity and poly-ADP-ribosylating the base excision repair ligase mtLIG3 to maintain mtDNA integrity (PMID:35157000).

1. 2009 Medium

   Establishing the structural basis of Neuralized homology repeats addressed how these domains recognize ligands and showed that the human NEURL4 NHR domain belongs to a distinct subfamily that does not bind the Tom peptide.

   Evidence NMR solution structure of Drosophila Neur NHR1 with ITC, compared to human NEURL4 NHR1

   PMID:19683535

   Open questions at the time

   • Human NEURL4 NHR domain function was inferred structurally without functional validation
   • No NEURL4 ligand identified by this structural comparison
   • Full-length NEURL4 architecture not resolved
2. 2012 High

   Discovery that NEURL4 localizes to centrioles and promotes CP110 ubiquitylation defined its first cellular function: preventing ectopic MTOC formation and preserving spindle and centrosome integrity.

   Evidence siRNA depletion, ubiquitylation assays, domain mutants, and AP-MS/Co-IP defining NEURL4–CP110 and NEURL4–HERC2 interactions in human cells

   PMID:22261722 PMID:22441691

   Open questions at the time

   • The catalytic identity of the ligase directly ubiquitylating CP110 within the complex not pinned down
   • Whether NEURL4 acts as adaptor or has intrinsic enzymatic role at the centrosome unresolved at this stage
3. 2012 Medium

   Mapping NEURL4 into a high-molecular-weight HERC2–MAPK6 complex that also associates with E6AP/UBE3A placed it within a broader ubiquitin-regulatory assembly.

   Evidence Affinity purification/mass spectrometry with Co-IP validation, single lab

   PMID:22645313

   Open questions at the time

   • Functional consequence of the MAPK6 and E6AP associations not established
   • Stoichiometry and architecture of the complex unknown
4. 2015 Medium

   Identifying the LRRK2–NEURL4–HERC2 complex connected NEURL4 to endosomal trafficking, showing it modulates Dll1 recycling to negatively regulate Notch and accelerate neural stem cell differentiation.

   Evidence Co-IP, domain mapping, cell-based trafficking assays, and Drosophila genetics, single lab

   PMID:26355680

   Open questions at the time

   • Direct mechanism linking the complex to endosomal sorting machinery unclear
   • Whether ubiquitin transfer onto trafficking cargo is involved not shown
5. 2015 Medium

   Conservation of the Neurl4→CP110 epistasis in Drosophila confirmed CP110 downregulation as the core ancestral function and extended it to germ cell biology.

   Evidence Drosophila loss-of-function genetics and double-mutant suppressor analysis with immunofluorescence

   PMID:26116656

   Open questions at the time

   • The germ plasm role appears separable from CP110 regulation and remains mechanistically undefined
   • Molecular link between CP110 control and PGC morphology not detailed
6. 2017 Medium

   Demonstrating direct NEURL4–p53 binding via NHR domains 3–4 revealed a non-degradative role: NEURL4 promotes p53 tetramerization and transcriptional output, expanding its function into tumor-suppressor signaling.

   Evidence Co-IP, domain mapping, luciferase reporter and clonogenic assays, knockdown/overexpression, single lab

   PMID:28977907

   Open questions at the time

   • Structural basis of how NEURL4 binding favors p53 tetramers not resolved
   • Whether HERC2 ubiquitin activity contributes mechanistically unclear
7. 2017 High

   Placing NEURL4 within the neuronal cytoplasmic RNF8–UBC13–HERC2 network established its role in suppressing synapse formation in cerebellum.

   Evidence AP-MS, in vivo RNAi, conditional knockout, electrophysiology, and confocal imaging with genetic epistasis (KD phenocopy)

   PMID:29097665

   Open questions at the time

   • Synaptic substrate(s) ubiquitylated by this network not identified
   • How a cytoplasmic ubiquitin signal limits bouton number mechanistically unknown
8. 2019 Medium

   Defining a DNA-damage-responsive p53/HERC2/NEURL4/MDM2 complex showed how NEURL4-bound oligomeric p53 is modified and partitioned between HERC2 and the MDM2 promoter, linking the scaffold to the p53–MDM2 feedback loop.

   Evidence Co-IP, siRNA knockdown, promoter reporter assays, Western blot, and RT-PCR after bleomycin treatment

   PMID:31665549

   Open questions at the time

   • Direct contribution of NEURL4 (versus HERC2) to MDM2 promoter regulation not separated
   • Kinetics of complex dissociation after DNA damage incompletely defined
9. 2022 High

   Identifying NEURL4 as the principal mitochondrial ADP-ribosyltransferase that poly-ADP-ribosylates mtLIG3 defined an enzymatic, organelle-specific function in mtDNA base excision repair, distinct from its scaffolding roles.

   Evidence In vitro ART activity assays on mitochondrial extracts, NEURL4 KO/KD, ADP-ribosylome mass spectrometry, and mtDNA integrity readout

   PMID:35157000

   Open questions at the time

   • Catalytic domain/residues mediating ART activity within NEURL4 not mapped
   • How NEURL4 enzymatic activity is regulated and coordinated with its centrosomal/nuclear roles unknown

• How NEURL4 partitions and coordinates its distinct enzymatic (mitochondrial ART) and scaffolding (centrosomal, p53, synaptic, trafficking) activities, and which domains confer each, remains unresolved.
• No structure of full-length human NEURL4 or its catalytic ART module
• No unified model linking subcellular pools to specific functions
• Regulation of NEURL4 by its own HERC2-mediated ubiquitylation across compartments unexplored