NPTXR

NPTXR is a transmembrane neuronal pentraxin receptor that cooperates with NPTX2 to cluster GluA4-containing AMPA receptors at excitatory synapses onto parvalbumin-expressing fast-spiking interneurons, thereby controlling circuit maturation, rhythmogenesis, and seizure susceptibility (PMID:25754824). NPTXR participates in a trans-synaptic adhesion complex with C1QL3 and ADGRB3/BAI3, linking presynaptic secreted factors to postsynaptic signaling at excitatory synapses (PMID:33337553), and functions as the cognate receptor for NPTX2 in peripheral sensory neurons where it mediates NPTX2–IL-31 synergistic signaling through p-ERK to regulate itch behavior (PMID:41564473). In cancer cells, NPTXR activates PI3K–AKT–mTOR, FAK–JNK, and YAP signaling pathways, and its silencing or antibody-mediated blockade suppresses proliferation, invasion, and peritoneal metastasis in gastric and esophageal squamous cell carcinoma models (PMID:32847597, PMID:38717547).

1. 2015 High

   Whether neuronal pentraxins are functionally required at specific synapse types was unknown; double knockout of NPTX2 and NPTXR revealed their essential, cooperative role in clustering GluA4-AMPARs at excitatory synapses onto parvalbumin interneurons, establishing NPTXR as a critical organizer of inhibitory circuit maturation and network oscillations.

   Evidence NPTX2/NPTXR double-KO mice analyzed by electrophysiology, GluA4 immunostaining, and in vivo circuit recordings

   PMID:25754824

   Open questions at the time

   • Individual contributions of NPTXR versus NPTX2 to GluA4 clustering were not separable in the double KO
   • Structural basis for NPTXR–GluA4 interaction not determined
   • Whether NPTXR functions similarly at non-PV interneuron synapses is untested
2. 2020 Medium

   Whether NPTXR has signaling functions outside the CNS was unclear; knockdown and antibody blockade in gastric cancer cells demonstrated that NPTXR activates PI3K–AKT–mTOR, FAK–JNK, and YAP pathways to promote proliferation, survival, and peritoneal metastasis.

   Evidence siRNA knockdown, xenograft models, intracellular signaling assays, and anti-NPTXR monoclonal antibody treatment in vivo

   PMID:32847597

   Open questions at the time

   • Direct mechanism linking NPTXR transmembrane domain to PI3K/FAK/YAP activation is undefined
   • Whether cancer-context signaling reflects a ligand-dependent or constitutive activity is unknown
   • Findings not yet independently replicated outside a single laboratory
3. 2021 Medium

   The identity of trans-synaptic adhesion complexes incorporating neuronal pentraxins was unknown; interactome analysis revealed that NPTXR forms a tripartite complex with C1QL3 and ADGRB3/BAI3, establishing a new trans-synaptic bridge at excitatory synapses.

   Evidence In vivo Co-IP/pulldown, snRNA-seq co-expression analysis, cell-cell adhesion assay

   PMID:33337553

   Open questions at the time

   • No reciprocal Co-IP or reconstituted binding assay to confirm direct NPTXR–BAI3 interaction
   • Functional consequence of disrupting this specific complex at synapses is untested
   • Stoichiometry and domain requirements for complex assembly are undetermined
4. 2024 Medium

   Extending the oncogenic role of NPTXR beyond gastric cancer, knockdown and antibody blockade confirmed that NPTXR promotes proliferation and survival in esophageal squamous cell carcinoma, generalizing its pro-tumorigenic function.

   Evidence siRNA knockdown and anti-NPTXR monoclonal antibody treatment with proliferation/apoptosis/adhesion assays in ESCC cells

   PMID:38717547

   Open questions at the time

   • Downstream signaling pathway activation in ESCC not characterized
   • In vivo validation in ESCC xenograft models not performed
   • Whether NPTXR's cancer role depends on its pentraxin domain or ligand engagement is unknown
5. 2025 Medium

   Whether NPTXR functions as a receptor for NPTX2 outside the CNS was untested; siRNA knockdown in trigeminal ganglion neurons demonstrated that NPTXR is the cognate receptor mediating NPTX2–IL-31 synergistic p-ERK signaling and itch behavior in peripheral sensory neurons.

   Evidence Intra-TG siRNA injection, immunolocalization in CGRP+/IB4+ neurons, p-ERK signaling assay, scratching behavioral assay in atopic dermatitis mouse model

   PMID:41564473

   Open questions at the time

   • Direct binding between NPTX2 and NPTXR in sensory neurons not biochemically demonstrated
   • Mechanism of NPTXR–IL-31 receptor cross-talk is uncharacterized
   • Whether NPTXR regulates other somatosensory modalities beyond itch is unknown

• The atomic structure of NPTXR and the molecular basis by which its pentraxin domain engages GluA4, NPTX2, and C1QL3 remain unresolved; NMR backbone assignments of the PTX domain have been completed but no structure or binding interface has been defined.
• No 3D structure of NPTXR pentraxin domain or full ectodomain available
• Binding interfaces with GluA4, NPTX2, and C1QL3 are unmapped
• Whether NPTXR signaling in cancer versus neurons uses distinct or overlapping ligand-binding surfaces is unknown