MPZL2

MPZL2 (EVA/EVA1) is an immunoglobulin superfamily transmembrane protein that mediates homophilic cell-cell adhesion and associates with the cytoskeleton, functioning to organize epithelial architecture and tissue integrity (PMID:9585423). At epithelial cell-cell junctions it co-localizes with E-cadherin and assembles into a complex with CLCA2 (bound through its transmembrane segment) and ZO-1, and its loss in mammary epithelial cells triggers epithelial-to-mesenchymal transition, marking it as a maintainer of the differentiated epithelial state (PMID:26930581). In the inner ear, MPZL2 localizes to auditory hair cells (PMID:29982980), and loss-of-function variants cause autosomal recessive nonsyndromic sensorineural hearing loss; mutant mice show progressive hearing impairment with disorganization and degeneration of the organ of Corti and spiral ganglion neurons, establishing that MPZL2-mediated adhesion is essential for cochlear structural integrity (PMID:29961571). Restoration of MPZL2 function by in vivo base editing of a humanized mutant allele rescues hearing and cochlear structure, demonstrating the phenotype is directly attributable to MPZL2 loss (PMID:40764318). Beyond adhesion, MPZL2 has cell-type-specific signaling roles: it is required for early thymocyte development and thymus organization through epithelial-haematopoietic crosstalk (PMID:17362876, PMID:19851463), it promotes glioblastoma-initiating cell self-renewal by recruiting TRAF2 to its cytoplasmic tail to activate RelB-dependent noncanonical NF-κB signaling (PMID:26677976), it suppresses protective autophagy in endothelial cells under proatherogenic disturbed flow downstream of TWIST1 (PMID:36794585), and macrophage-derived MPZL2 drives obesity-induced visceral adipose inflammation in conjunction with a TLR4 interaction (PMID:40118448).

1. 1998 Medium

   Established MPZL2 as a novel immunoglobulin superfamily molecule capable of homophilic adhesion and cytoskeletal association, framing it as a candidate organizer of thymic epithelial structure.

   Evidence RNA fingerprinting, expression analysis in thymic epithelial lines, detergent fractionation, and cell adhesion assay

   PMID:9585423

   Open questions at the time

   • No structural model or adhesion-interface mutagenesis
   • Binding partner mediating adhesion not identified
   • Cytoskeletal linkage inferred from solubility, not a defined interaction
2. 1998 Low

   Mapped MPZL2 expression to spongiotrophoblast and invasive glycogen cells during placentation, raising the possibility of a role in trophoblast invasion.

   Evidence In situ hybridization across mouse placental development

   PMID:9883583

   Open questions at the time

   • Expression only; no loss-of-function test of placental function
   • No mechanistic link to adhesion activity established
3. 2007 Medium

   Showed that gain of MPZL2 in the thymic cortex enlarges the stromal compartment and increases thymocyte numbers, supporting a structural-organizational role in thymus development.

   Evidence Transgenic mouse overexpression with histology and flow cytometry

   PMID:17362876

   Open questions at the time

   • Gain-of-function only; does not define the requirement
   • Molecular mechanism linking adhesion to stromal expansion unresolved
4. 2009 Medium

   Demonstrated a cell-autonomous requirement for MPZL2 in early T lymphocyte development, advancing from correlation to functional necessity.

   Evidence RNAi knockdown in hematopoietic progenitors, OP9-DL1 co-culture, and Rag2-γc DKO reconstitution with flow cytometry

   PMID:19851463

   Open questions at the time

   • Signaling pathway downstream of MPZL2 in thymocytes not defined
   • Adhesion partner driving the DN1-DN3 transition unknown
5. 2015 Medium

   Identified a signaling output for MPZL2 by showing it recruits TRAF2 to its cytoplasmic tail to drive noncanonical NF-κB activation supporting glioblastoma stem cell self-renewal, extending its role beyond passive adhesion.

   Evidence Knockdown/overexpression in glioblastoma-initiating cells, TRAF2 co-immunoprecipitation, NF-κB reporter and western blot

   PMID:26677976

   Open questions at the time

   • Cytoplasmic motif mediating TRAF2 binding not mapped
   • Whether this pathway operates in normal epithelia untested
   • Upstream ligand/adhesion event triggering signaling unknown
6. 2016 Medium

   Placed MPZL2 in a defined junctional complex with CLCA2 and ZO-1 alongside E-cadherin and showed its loss drives EMT, mechanistically tying it to maintenance of the epithelial state.

   Evidence Membrane dihybrid screen, reciprocal co-IP with transmembrane deletion mapping, siRNA with EMT readout, immunofluorescence co-localization

   PMID:26930581

   Open questions at the time

   • Functional consequence of CLCA2 binding for adhesion not dissected
   • Connection between junctional complex and EMT signaling unresolved
7. 2018 High

   Established MPZL2 as a Mendelian deafness gene and showed its adhesion function is essential for cochlear structural integrity, with hair-cell localization supporting the site of action.

   Evidence Homozygosity mapping and exome sequencing in families, Mpzl2-mutant mouse audiometry and cochlear histology, plus immunolocalization to inner ear hair cells

   PMID:29961571 PMID:29982980

   Open questions at the time

   • Adhesion partner in the organ of Corti not identified
   • Why degeneration is progressive rather than developmental unclear
8. 2023 High

   Revealed a non-adhesion, organelle-associated role in which MPZL2 suppresses protective autophagy and promotes endothelial apoptosis under disturbed flow, placing it downstream of TWIST1 in a flow-dependent atherogenic circuit.

   Evidence siRNA in human ECs, autophagic flux assays, flow chamber, ChIP/TF analysis, and zebrafish morpholino knockdown

   PMID:36794585

   Open questions at the time

   • Molecular mechanism by which MPZL2 inhibits autophagy not defined
   • Relationship between adhesion role and autophagy suppression unresolved
9. 2025 Medium

   Defined macrophage-derived MPZL2 as the functionally relevant driver of obesity-induced visceral adipose inflammation, with a TLR4 interaction as candidate mechanism.

   Evidence Whole-body and adipocyte-specific knockout mice, HFD model, macrophage transplantation rescue, and TLR4 co-immunoprecipitation

   PMID:40118448

   Open questions at the time

   • TLR4 interaction shown by Co-IP only, not reciprocally validated functionally
   • Whether MPZL2 modulates TLR4 signaling output directly untested
10. 2025 High

    Demonstrated that restoring MPZL2 function is sufficient to reverse hearing loss, confirming the gene's causal role and establishing therapeutic tractability.

    Evidence Dual-AAV adenine base editor correction of c.220C>T in a humanized Mpzl2 knock-in mouse with ABR audiometry, cochlear histology, and RNA-seq

    PMID:40764318

    Open questions at the time

    • Durability and developmental timing window of rescue not fully defined
    • Does not resolve the molecular adhesion mechanism in the cochlea

• The unifying biochemical mechanism connecting MPZL2's homophilic adhesion to its diverse signaling outputs (TRAF2/NF-κB, autophagy suppression, TLR4) remains unresolved.
• No structure of the adhesion interface or cytoplasmic signaling motifs
• The physiological homophilic/heterophilic ligand in each tissue is undefined
• Whether adhesion and signaling roles are separable functions is untested