DLL3 (Q9NYJ7) — curation notes

Deep research providers were unavailable in this environment (just deep-research-falcon human DLL3 --fallback perplexity-lite failed: "agentapi not found in PATH"; perplexity
provider not configured). Research below was done directly from the cached publications,
the UniProt record and PubMed.

Protein architecture

UniProt Q9NYJ7: signal peptide 1-26, extracellular topological domain 27-492,
transmembrane 493-513, cytoplasmic 514-618 — a single-pass type I membrane protein with a
DSL domain and six EGF-like repeats.
[file:human/DLL3/DLL3-uniprot.txt "SUBCELLULAR LOCATION: Membrane {ECO:0000305}; Single-pass type I membrane protein"]
The DSL domain is the Notch-binding module
[file:human/DLL3/DLL3-uniprot.txt "The DSL domain is required for binding to the Notch receptor."]

Function: a divergent, cis-inhibitory Notch ligand

DLL3 is a DSL-family member that does not trans-activate Notch. Chapman et al. showed
it inhibits signalling in the cell that expresses it, by interacting with Notch1 in the
late endocytic compartment and routing newly synthesised Notch1 to lysosomal degradation
before the receptor reaches the surface.
PMID:21147753
PMID:21147753

Geffers et al. showed DLL1 and DLL3 are not interchangeable in vivo: Dll3 knocked into the
Dll1 locus does not rescue, and DLL1 but not DLL3 activates Notch in Drosophila wing discs.
PMID:17664336

Localization — important for this review

Endogenous DLL3 is an intracellular, Golgi/late-endosomal membrane protein, not a
cell-surface ligand under physiological conditions.
PMID:17664336
PMID:21147753

The exception is pathological overexpression: in SCLC and LCNEC, DLL3 is upregulated and
aberrantly trafficked to the plasma membrane, which is the basis of the DLL3-directed ADC
and T-cell-engager therapeutics (rovalpituzumab tesirine, tarlatamab).
PMID:26311731
PMID:26311731
PMID:37355629

Conclusion for GO: the primary location is Golgi membrane plus late endosome; cell surface is a genuine but condition-specific (tumour) location; plasma membrane as the
site where DLL3 is active is not supported for the normal protein.

Disease

Biallelic DLL3 mutations cause autosomal recessive spondylocostal dysostosis (vertebral
segmentation defects), reflecting a requirement in somitogenesis.
PMID:10742114

Review decisions

• plasma membrane (IBA is_active_in; IEA located_in): MODIFY to Golgi membrane. The
  PAINT node assertion is right for the Delta/Serrate clade but DLL3 has target-specific
  evidence of divergence in trafficking (Geffers, Chapman).
• Notch signaling pathway (IBA, IEA): MODIFY to negative regulation of Notch signaling
  pathway — a sign correction, not a refinement.
• membrane (IEA, NAS): MODIFY to Golgi membrane.
• animal gross anatomical part developmental process (ARBA IEA): TOO_GENERAL; skeletal
  system development, accepted here, entails it.