NEURL1

NEURL1 is a RING-type E3 ubiquitin ligase that regulates intercellular signaling and protein turnover by targeting specific substrates for ubiquitination (PMID:18077452, PMID:31068605). It monoubiquitinates the Notch ligand Jagged1 in vitro, reducing cellular Jagged1 levels and blocking Notch signaling from ligand-presenting cells to neighboring Notch-expressing cells; this activity depends on its ubiquitin ligase function (PMID:18077452). NEURL1 is N-myristoylated at its N-terminus, which targets it to the plasma membrane, and this localization is required for its down-regulation of Jagged1 and suppression of Notch signaling (PMID:18077452). Through both of its Neuralized Homology Repeat (NHR) domains, NEURL1 also directly binds the cGMP-hydrolyzing phosphodiesterase PDE9A and promotes its K27-linked polyubiquitination and proteasomal degradation (PMID:31068605); in bladder cancer cells this RING-domain-dependent degradation of PDE9A is accompanied by inhibited cell growth and increased apoptosis (PMID:40442542). Beyond its ligase activity and substrate targeting, NEURL1 mRNA is itself subject to dendritic transport in neurons via 3'UTR targeting elements (PMID:27780737).

1. 2007 High

   Established NEURL1 as an enzymatically active E3 ubiquitin ligase with a defined substrate, resolving how it intersects the Notch pathway by acting on the ligand rather than the receptor.

   Evidence In vitro ubiquitination assay, cell-based Notch signaling assay, and ligase-dead point mutations in mouse Neurl1

   PMID:18077452

   Open questions at the time

   • Monoubiquitination linkage type and the lysine residues on Jagged1 not defined
   • Whether endogenous Jagged1 turnover depends on NEURL1 in vivo untested
2. 2007 High

   Showed that NEURL1 activity toward Jagged1 requires correct subcellular targeting, linking N-myristoylation-driven plasma membrane localization to its signaling function.

   Evidence Myristoylation-site mutagenesis, subcellular fractionation, and signaling readout

   PMID:18077452

   Open questions at the time

   • Whether membrane targeting also governs non-Jagged1 substrates not addressed
3. 2019 High

   Identified a second, mechanistically distinct substrate, demonstrating that NEURL1 uses its NHR domains to bind PDE9A and direct an atypical K27-linked polyubiquitin signal for proteasomal degradation.

   Evidence Yeast two-hybrid, reciprocal co-IP, NHR domain mapping, ubiquitination assay, and proteasome inhibitor rescue

   PMID:31068605

   Open questions at the time

   • Physiological context of PDE9A regulation by NEURL1 not established
   • Functional consequence of cGMP signaling changes not measured
4. 2025 Medium

   Placed the NEURL1-PDE9A axis in a disease context, showing RING-dependent PDE9A degradation correlates with tumor-suppressive cellular phenotypes.

   Evidence Stable full-length vs RING-deleted NEURL1 overexpression, MG-132 rescue, viability and apoptosis assays in bladder cancer cells

   PMID:40442542

   Open questions at the time

   • Single study without independent replication
   • Causal link between PDE9A degradation and apoptosis not formally separated from other NEURL1 effects
5. 2016 Medium

   Revealed a layer of post-transcriptional control over NEURL1 itself by mapping 3'UTR elements that drive dendritic mRNA localization in neurons.

   Evidence Reporter mRNA localization in primary hippocampal neurons with systematic 3'UTR deletion mapping

   PMID:27780737

   Open questions at the time

   • Trans-acting factors binding the dendritic targeting element not identified
   • Functional consequence of local NEURL1 translation in dendrites untested

• How NEURL1 substrate selection (Jagged1 vs PDE9A), ubiquitin linkage choice (mono- vs K27-linked), and tissue-specific roles are coordinated remains unresolved.
• No structural model of NEURL1 RING or NHR domains engaging substrates
• Determinants of mono- vs poly- and K27-linkage specificity unknown
• In vivo physiological substrates and phenotypes not established