CADM3

CADM3 (Necl-1/SynCAM3) is a neural tissue-specific, calcium-independent immunoglobulin superfamily cell adhesion molecule that mediates homophilic and heterophilic trans-cellular adhesion—principally with Cadm4 at axon–glia interfaces—and organizes synaptic and myelinated fiber domains in both the central and peripheral nervous systems. Its N-terminal V-type Ig domain dimerizes through a Phe82-dependent interface to drive cell–cell adhesion, while its cytoplasmic tail recruits MAGUK scaffolds (Dlg3, Pals2, CASK) (PMID:15741237, PMID:16467305). On myelinated axons, Cadm3 is the dominant ligand for Schwann cell Cadm4, organizing Caspr and Kv1 channel distribution and negatively regulating myelination by dampening ErbB3/PI3K/Akt signaling; loss-of-function variants (Tyr172Cys, Gly368Cys) that reduce surface expression cause axonal Charcot–Marie–Tooth neuropathy (PMID:33397712, PMID:27658374, PMID:33889941, PMID:38074074). Cadm3 also directs cone-to-OFF bipolar cell synapse formation in the retina, maintains prefrontal noradrenergic homeostasis, promotes synaptogenesis, and acts as a tumor suppressor in glioma whose silencing is regulated by Sp1/HDAC1-dependent histone deacetylation (PMID:38623325, PMID:41308882, PMID:18686604, PMID:19062177).

1. 2005 High

   Establishing that CADM3 mediates Ca²⁺-independent homophilic and heterophilic adhesion and couples to MAGUK scaffolds resolved its basic molecular mode of action as a synaptic/junctional adhesion molecule.

   Evidence Cell-cell adhesion assays, co-immunoprecipitation, immunoelectron microscopy in transfected cells

   PMID:15741237

   Open questions at the time

   • Relative affinities for different heterophilic partners not quantified
   • In vivo relevance of MAGUK interactions not tested
2. 2006 High

   Solving the crystal structure of the V-domain dimer and identifying Phe82 as critical for adhesion defined the atomic basis of Cadm3 homophilic interaction.

   Evidence 2.4 Å crystal structure, size-exclusion chromatography, cross-linking, site-directed mutagenesis

   PMID:16467305

   Open questions at the time

   • Structure of heterophilic complexes (e.g., Cadm3–Cadm4) not determined
   • No in vivo mutagenesis to confirm Phe82 requirement
3. 2008 Medium

   Demonstrating that CADM3 overexpression induces synapse formation between neurons and non-neuronal cells established it as a synaptogenic adhesion molecule.

   Evidence Overexpression in HEK293-neuron co-culture, synaptosome fractionation

   PMID:18686604

   Open questions at the time

   • Loss-of-function synaptogenic phenotype not shown in this study
   • Specific synaptic partners and downstream signaling not identified
4. 2009 High

   Showing that CADM3 re-expression suppresses glioma proliferation, migration, and invasion while its silencing is governed by Sp1/HDAC1 at the promoter established its tumor suppressor function and epigenetic regulation.

   Evidence Cell cycle analysis, nude mouse xenograft, ChIP, co-IP for Sp1/HDAC1/p300, zymography, invasion assays

   PMID:19062177 PMID:20078932

   Open questions at the time

   • Mechanism linking Cadm3 adhesion to cell cycle arrest undefined
   • Whether HDAC-mediated silencing occurs in other neural tumor types not tested
5. 2011 Medium

   In vitro binding assays in zebrafish demonstrated that Cadm3 preferentially binds Cadm4 heterophilically, identifying the key axon–glia adhesion partnership.

   Evidence In vitro binding assays with zebrafish Cadm proteins, immunohistochemistry

   PMID:21456004

   Open questions at the time

   • Quantitative affinity measurements not reported
   • Binding studied in zebrafish orthologs—mammalian specificity assumed but not directly shown
6. 2016 High

   Bidirectional manipulation of axonal Cadm3 revealed that it negatively regulates PNS myelination by selectively dampening ErbB3/PI3K/Akt signaling, resolving how Cadm3 tunes myelin formation.

   Evidence shRNA knockdown and overexpression in DRG neuron–Schwann cell co-cultures, phospho-Western blots for ErbB3, Akt, Erk1/2

   PMID:27658374

   Open questions at the time

   • Mechanism by which Cadm3 extracellular domain interferes with ErbB3 activation unresolved
   • In vivo confirmation of signaling effects not provided in this study
7. 2021 High

   Genetic epistasis in triple-KO mice proved that Cadm3 is the dominant axonal ligand for glial Cadm4 in organizing myelinated fiber domains (Caspr, Kv1 channels), while the Tyr172Cys disease variant demonstrated that reduced surface expression and impaired Cadm4 interaction cause axonal CMT neuropathy.

   Evidence Single/double/triple Cadm1/2/3 KO mice, Cadm3-Y170C knock-in mice, STORM imaging, mass spectrometry, electrodiagnostics

   PMID:33397712 PMID:33889941

   Open questions at the time

   • Whether Cadm3 signaling function (ErbB3 regulation) contributes to CMT pathology not tested
   • Structural basis of Cadm3–Cadm4 trans interaction not resolved at atomic level
8. 2022 Medium

   SynCAM3 deletion reduced glial scar formation after spinal cord injury by preventing reactive-to-scar astrocyte transformation, revealing a CNS injury role for Cadm3.

   Evidence Cadm3 KO mice, spinal cord compression injury, scRNA-seq, behavioral assessment

   PMID:35682897

   Open questions at the time

   • Mechanism by which Cadm3 promotes scar astrocyte transformation unknown
   • Not independently replicated
9. 2023 Medium

   A second CADM3 missense variant (Gly368Cys) causing autosomal dominant axonal CMT confirmed CADM3 as a bona fide CMT disease gene and extended the loss-of-surface-expression pathomechanism.

   Evidence Whole exome sequencing, membrane protein level quantification by Western blot, structural prediction

   PMID:38074074

   Open questions at the time

   • No knock-in animal model for this variant
   • Limited to structural prediction without experimental structural data
10. 2024 High

    Cadm3 KO mice showed dislocated cone–OFF bipolar cell synapses and impaired short-wavelength cone signal transmission rescued by AMPA receptor potentiation, establishing Cadm3 as a retinal synapse organizer.

    Evidence Cadm3 KO mice, immunofluorescence, electroretinography, optokinetic response, pharmacological rescue

    PMID:38623325

    Open questions at the time

    • Whether Cadm3 acts through Cadm4 or a different partner in retina not determined
    • Mechanism linking Cadm3 loss to AMPA receptor dislocation unresolved
11. 2025 High

    Cadm3 KO in rats causes prefrontal norepinephrine depletion, spine loss, and Adra2a upregulation rescued by PFC-targeted reconstitution, establishing Cadm3 as a synaptic–noradrenergic integrator in prefrontal circuits.

    Evidence Constitutive KO rats and mice, PFC-targeted viral rescue, mirtazapine pharmacology, NE measurement, behavioral assays

    PMID:41308882

    Open questions at the time

    • Direct molecular link between Cadm3 adhesion and noradrenergic terminal maintenance unknown
    • Whether this reflects a developmental or maintenance role not distinguished

• Key unresolved questions include the atomic structure of the Cadm3–Cadm4 heterophilic complex, the mechanism by which the Cadm3 ectodomain dampens ErbB3 activation, and whether its synaptic, myelination-regulatory, and tumor-suppressive functions share common intracellular signaling intermediates.
• No structure of Cadm3–Cadm4 complex
• Intracellular signaling downstream of Cadm3 adhesion poorly characterized beyond ErbB3/PI3K
• Relationship between MAGUK scaffold recruitment and functional outcomes untested in vivo