EMILIN2

EMILIN2 is a secreted extracellular matrix glycoprotein with an EMILIN1-like domain architecture (EMI domain, coiled-coil, collagenous stalk, C-terminal gC1q domain) that is incorporated into fibrillin microfibril networks and acts as a multifunctional regulator of apoptosis, growth-factor signaling, vascularization, and immune and hematopoietic processes (PMID:11278945, PMID:26945878). Its ECM deposition depends on fibronectin and intact fibrillin microfibrils, and it self-associates and hetero-associates with EMILIN1 through reciprocal gC1q–gC1q and gC1q–EMI domain contacts (PMID:25445627, PMID:26945878). A central activity is pro-apoptotic signaling: EMILIN2 directly binds the death receptor DR4 (and to a lesser extent DR5), driving receptor clustering, lipid-raft colocalization, DISC assembly, and caspase activation through the extrinsic pathway, so that its loss promotes transformed-cell survival (PMID:17698584). EMILIN2 also restrains canonical Wnt signaling by using its EMI domain to bind and sequester Wnt1, reducing LRP6 phosphorylation and β-catenin/TAZ activity (PMID:24374807); this tumor-suppressive function is subverted by HPV-18 E6, which promotes an EMILIN2–SNX27 interaction that blocks EMILIN2 secretion and relieves Wnt1 inhibition (PMID:38874360). In the vasculature, EMILIN2 promotes angiogenesis by directly engaging EGFR to drive IL-8/MIP-2 production, and supports vessel maturation by stimulating endothelial PDGF-BB and HB-EGF, serving as an α5β1/α6β1 integrin adhesion and haptotactic substrate for pericytes, and inducing pericyte N-cadherin via the sphingosine-1-phosphate receptor (PMID:29483644, PMID:37579864). Beyond these roles, EMILIN2 promotes platelet aggregation and outside-in signaling for clot retraction (PMID:25658937), activates TLR-4/MyD88/NF-κB signaling to drive macrophage M1 polarization (PMID:35148799), and acts as a macrophage-secreted chemoattractant for mesenchymal cells during bone regeneration while restraining MSC adipogenesis in marrow (PMID:35012633, PMID:38831448).

1. 2001 Medium

   Establishing EMILIN2 as a distinct secreted ECM glycoprotein with an EMILIN1-like multidomain architecture defined the molecular framework for all subsequent functional studies.

   Evidence Yeast two-hybrid using EMILIN1 gC1q as bait, cDNA cloning, secretion assay, and immunolocalization

   PMID:11278945

   Open questions at the time

   • No function assigned to any domain
   • Tissue distribution and physiological role unaddressed
2. 2007 High

   Identifying direct DR4/DR5 binding and DISC-dependent caspase activation revealed EMILIN2 as a pro-apoptotic ECM ligand engaging the extrinsic death pathway.

   Evidence Receptor binding assays, lipid raft fractionation, DISC and caspase assays, siRNA knockdown and overexpression in transformed cells

   PMID:17698584

   Open questions at the time

   • Domain mediating death-receptor binding not mapped
   • In vivo relevance of apoptotic role not tested
3. 2014 High

   Demonstrating EMI-domain-dependent Wnt1 sequestration showed EMILIN2 inhibits canonical Wnt/β-catenin/TAZ signaling at the ligand-receptor step, providing a tumor-suppressive mechanism.

   Evidence Co-IP, LRP6 phosphorylation and β-catenin/TAZ blots, EMI-deletion mutant, GSK3-inhibitor rescue, xenografts

   PMID:24374807

   Open questions at the time

   • Stoichiometry of Wnt1 sequestration unresolved
   • Cross-talk with apoptotic signaling unaddressed
4. 2014 Medium

   Mapping the domain basis of EMILIN1–EMILIN2 assembly clarified how these proteins build homo- and hetero-multimeric ECM networks.

   Evidence Quantitative Y2H, reciprocal Co-IP from co-transfected cells, immunofluorescence on cells and tissue

   PMID:25445627

   Open questions at the time

   • No high-resolution structure of multimers
   • Functional consequence of hetero-multimerization not tested
5. 2015 High

   Genetic and add-back studies defined EMILIN2 as a positive regulator of platelet aggregation and clot retraction via outside-in signaling, opposing EMILIN1.

   Evidence Global and platelet-specific KO mice, aggregation assays, purified protein add-back, ferric chloride injury, clot retraction assay

   PMID:25658937

   Open questions at the time

   • Platelet receptor for EMILIN2 not identified
   • Molecular basis of opposing EMILIN1/EMILIN2 effects unknown
6. 2016 Medium

   Showing that EMILIN2 deposition requires fibronectin and intact fibrillin microfibrils established how the protein is integrated into the ECM scaffold.

   Evidence Immunoelectron and immunofluorescence microscopy, ECM extraction, fibrillin-1 KO mice, dermal fibroblasts

   PMID:26945878

   Open questions at the time

   • Direct fibrillin–EMILIN2 binding not reconstituted
   • Domain mediating microfibril targeting not defined
7. 2018 High

   Identifying direct EGFR binding and downstream IL-8/MIP-2 induction established EMILIN2 as a pro-angiogenic factor with an in vivo rescuable phenotype.

   Evidence EGFR binding assay, IL-8/MIP-2 ELISA, Emilin2 KO retinal vascular development, MIP-2 rescue, tumor vascular analysis

   PMID:29483644

   Open questions at the time

   • EGFR-binding domain unmapped
   • Relationship between pro-angiogenic and pro-apoptotic activities unresolved
8. 2022 Medium

   Linking EMILIN2 to TLR-4/MyD88/NF-κB signaling defined it as a driver of macrophage M1 polarization shaping the tumor immune microenvironment.

   Evidence Emilin-2 KO AOM/DSS colorectal model, flow cytometry, ex vivo macrophage cultures, western blot for the pathway

   PMID:35148799

   Open questions at the time

   • Direct TLR-4 binding not demonstrated
   • Domain engaging TLR-4 unknown
9. 2022 Medium

   Bone-marrow studies showed EMILIN2 is MSC-secreted, restrains adipogenic differentiation, and supports HSPC frequency during aging.

   Evidence Bone marrow immunodetection, MSC cultures, adipogenic differentiation assay, HSPC flow cytometry in WT vs KO mice

   PMID:35012633

   Open questions at the time

   • Receptor/pathway mediating adipogenic inhibition unknown
   • Mechanism of HSPC support undefined
10. 2023 High

    Dissecting endothelial growth-factor induction, integrin engagement, and S1P-dependent N-cadherin induction established EMILIN2 as a multi-mechanism driver of pericyte recruitment and vascular stabilization.

    Evidence Recombinant Emilin2 endothelial stimulation, integrin binding/blocking, haptotaxis, N-cadherin blots, S1P receptor inhibition, KO tumor vascular analysis

    PMID:37579864

    Open questions at the time

    • Domains mediating integrin and S1P-axis effects not mapped
    • Integration with EGFR-driven angiogenesis unresolved
11. 2024 Medium

    Identifying E6-enhanced EMILIN2–SNX27 interaction revealed a viral mechanism that blocks EMILIN2 secretion to relieve Wnt1 inhibition and promote proliferation.

    Evidence GFP-SNX27 pulldown/MS, Co-IP, HPV-18 E6 PBM-mutant analysis, Wnt1 binding and proliferation assays

    PMID:38874360

    Open questions at the time

    • Trafficking fate of retained EMILIN2 not resolved
    • Generalizability beyond HPV-18 E6 untested
12. 2024 Medium

    Demonstrating macrophage-derived EMILIN2 as a chemoattractant for mesenchymal cells established its role in recruiting progenitors during bone regeneration.

    Evidence Migration assays, LC-MS/MS identification, Emilin2 KO bone injury model, histology, recombinant protein rescue

    PMID:38831448

    Open questions at the time

    • Receptor mediating mesenchymal chemotaxis unidentified
    • Relationship to MSC adipogenic and integrin functions unclear

• How EMILIN2's individual domains are partitioned among its many ligands (DR4/DR5, Wnt1, EGFR, integrins, TLR-4) and how these activities are coordinated in a single ECM protein remains unresolved.
• No structural model of the full-length protein with its receptors
• Domain-resolved ligand map incomplete for most partners
• No human Mendelian disease link established in the corpus