Affinage

EPHA8

Ephrin type-A receptor 8 · UniProt P29322

Length
1005 aa
Mass
111.0 kDa
Annotated
2026-04-28
20 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

EphA8 is a receptor tyrosine kinase of the Eph family that transduces GPI-linked ephrin-A signals to regulate axonal pathfinding, cell adhesion, migration, and neurite dynamics during neural development. EphA8 autophosphorylates at Tyr-838 (required for catalytic activity) and Tyr-615 (which recruits Fyn via its SH2 domain), and signals through both kinase-dependent sustained MAPK activation for neurite outgrowth and kinase-independent recruitment of p110γ PI3-kinase and Odin/AIDA-1b scaffolds via its juxtamembrane segment to control integrin-mediated adhesion and migration (PMID:10498895, PMID:11416136, PMID:15782114, PMID:17875921). Ligand-stimulated EphA8 undergoes Tiam-1-regulated clathrin-mediated endocytosis and Rab5/RINL-dependent degradation (PMID:20496116, PMID:22291991). Loss of EphA8 in mice causes aberrant axonal projections from the superior colliculus, establishing its requirement for axonal pathfinding in vivo (PMID:9214628).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1991 Medium

    Identification of EphA8 (Eek) as a brain-enriched Eph-family receptor tyrosine kinase established the gene's molecular identity and tissue expression context.

    Evidence cDNA cloning, Northern blot, and sequence analysis from mouse cDNA

    PMID:1648701

    Open questions at the time
    • No functional data on kinase activity or ligand specificity
    • Expression data limited to Northern blot without cellular resolution
  2. 1997 High

    Knockout mice revealed that EphA8 is required for axonal pathfinding in the superior colliculus, with tectal neurons forming aberrant ipsilateral tracts to cervical spinal cord instead of reaching contralateral targets, establishing the first in vivo function.

    Evidence EphA8 knockout mice with axonal tracing and retrograde labeling

    PMID:9214628

    Open questions at the time
    • Downstream signaling pathways mediating the pathfinding phenotype unknown
    • Whether phenotype is cell-autonomous was not addressed
  3. 1997 Medium

    Ligand specificity was defined: EphA8 binds multiple GPI-linked ephrin-A ligands (ephrin-A1–A5) but not transmembrane ephrin-B ligands, classifying it as an EphA receptor.

    Evidence Fc-fusion ligand binding assays and receptor phosphorylation in NIH3T3 cells across two studies

    PMID:10515610 PMID:9053851

    Open questions at the time
    • Relative binding affinities for individual ephrin-A ligands not quantified
    • In vivo relevance of specific ephrin-A partners not resolved
  4. 1999 High

    Mapping of autophosphorylation sites (Tyr-838 for catalytic activation, Tyr-615 for Fyn SH2 recruitment) and demonstration of EphA8–Fyn physical association established the kinase-dependent signaling axis controlling cell adhesion.

    Evidence 2D phosphopeptide mapping, site-directed mutagenesis, in vitro SH2 binding, co-immunoprecipitation, dominant-negative Fyn

    PMID:10498895

    Open questions at the time
    • Fyn substrates downstream of EphA8 not identified
    • Structural basis of SH2 selectivity for Fyn over Src/RasGAP unknown
  5. 2001 High

    A kinase-independent signaling arm was uncovered: the juxtamembrane segment recruits p110γ PI3-kinase to activate α5β1/β3 integrins for fibronectin adhesion and migration, independent of EphA8 catalytic activity.

    Evidence Kinase-inactive and domain-deletion mutants, wortmannin inhibition, co-immunoprecipitation, dominant-negative p110γ in two cell lines

    PMID:11416136 PMID:12681484

    Open questions at the time
    • Direct binding interface between juxtamembrane segment and p110γ not mapped
    • How p110γ lipid kinase products activate integrins remains unclear
  6. 2005 Medium

    EphA8 drives neurite outgrowth via sustained MAPK activation and nuclear MAPK translocation, requiring the kinase domain but not kinase activity, revealing a scaffolding function of the kinase domain.

    Evidence Deletion and kinase-inactive mutants, pharmacological MAPK inhibitors, subcellular fractionation in NG108-15 neuronal cells

    PMID:15782114

    Open questions at the time
    • How the inactive kinase domain scaffolds MAPK activation is mechanistically undefined
    • Ligand-independent context limits physiological extrapolation
  7. 2007 High

    Odin and AIDA-1b were identified as PTB-domain scaffolds recruited to the EphA8 juxtamembrane region in a kinase-independent manner; Odin knockdown diminished ephrin-A5-induced inhibition of migration and neurite retraction, establishing Odin as a physiological effector.

    Evidence Reciprocal co-immunoprecipitation, PTB domain pulldown, siRNA knockdown with migration and neurite retraction assays

    PMID:17875921

    Open questions at the time
    • Odin downstream targets not identified
    • How Odin and p110γ share the juxtamembrane binding site is unresolved
  8. 2010 Medium

    EphA8 was shown to undergo clathrin-mediated endocytosis upon ephrin-A5 stimulation, regulated by Tiam-1 (a Rac GEF) binding to the juxtamembrane region, linking receptor trafficking to Rac activation.

    Evidence EphA8 deletion mutants, clathrin endocytosis assay, Tiam-1 co-immunoprecipitation and siRNA knockdown, Rac activity assay

    PMID:20496116

    Open questions at the time
    • Direct Tiam-1 binding site on juxtamembrane region not mapped
    • Functional consequence of impaired endocytosis on downstream signaling not tested in neurons
  9. 2012 Medium

    RINL, a Rab5-family GEF, was placed in the EphA8 degradation pathway: RINL forms a ternary complex with Odin and EphA8, and RINL GEF activity reduces EphA8 protein levels via Rab5-dependent trafficking.

    Evidence Co-immunoprecipitation, GEF activity assay, RINL knockdown and overexpression in HeLa cells

    PMID:22291991

    Open questions at the time
    • Lysosomal versus proteasomal route of EphA8 degradation not distinguished
    • In vivo relevance of RINL-mediated EphA8 turnover not tested
  10. 2013 Medium

    EphA8 ectodomain (EphA8-Fc) was shown to trigger caspase-dependent apoptosis in ephrin-A5-expressing neuroepithelial cells via reverse signaling, causing reduced brain size in transgenic embryos.

    Evidence Transgenic embryo EphA8-Fc expression, in vitro neuroepithelial culture with caspase inhibitors, apoptosis quantification

    PMID:23696555

    Open questions at the time
    • Intracellular pathway from ephrin-A5 reverse signal to caspase activation not defined
    • Contribution of reverse versus forward signaling to the brain size phenotype not fully separated

Open questions

Synthesis pass · forward-looking unresolved questions
  • No structural model of EphA8 signaling complexes exists, the mechanism by which the kinase domain scaffolds MAPK independently of catalytic activity is unresolved, and the in vivo signaling pathways responsible for the superior colliculus axon guidance phenotype remain uncharacterized.
  • No crystal structure of EphA8 intracellular domain or its complexes
  • Cell-type-specific conditional knockouts needed to resolve cell-autonomous functions
  • Integration of kinase-dependent and kinase-independent pathways in vivo not addressed

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 3 GO:0060090 molecular adaptor activity 2
Localization
GO:0005886 plasma membrane 4 GO:0005768 endosome 2
Pathway
R-HSA-162582 Signal Transduction 5 R-HSA-1266738 Developmental Biology 2
Partners
ANKS1AANKS1BEFNA5FYNPIK3CGRINLTIAM1

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1991 EphA8 (Eek) encodes a receptor protein-tyrosine kinase of the Eph subclass, containing all conserved catalytic domain residues, most abundantly expressed in brain. cDNA cloning, Northern blot, sequence analysis Oncogene Medium 1648701
1997 EphA8 loss-of-function in mice causes aberrant axonal projections: tectal neurons in the superior colliculus fail to reach contralateral inferior colliculus targets and form an abnormal ipsilateral tract to cervical spinal cord, establishing EphA8 as required for axonal pathfinding. EphA8 knockout mice, axonal tracing, retrograde labeling The EMBO journal High 9214628
1997 EphA8 (Eek) receptor can be activated by at least three GPI-linked ephrin ligands: Elf-1/Cek7-L, Ehk1-L/Efl-2/Lerk3, and AL-1/RAGS, as demonstrated by binding and receptor phosphorylation assays. Fc-fusion chimeric ligand binding assays, receptor phosphorylation in NIH3T3 cells Oncogene Medium 9053851
1999 EphA8 has two major autophosphorylation sites, Tyr-615 (juxtamembrane) and Tyr-838 (kinase domain); Tyr-838 phosphorylation is required for catalytic activity, while phospho-Tyr-615 mediates preferential binding to the Fyn SH2 domain over Src and RasGAP SH2 domains. EphA8 and Fyn physically associate in intact cells, and Fyn is a downstream target mediating EphA8 effects on cell adhesion. 2D phosphopeptide mapping, in vitro kinase assays, site-directed mutagenesis, in vitro SH2 binding, co-immunoprecipitation, dominant-negative Fyn overexpression Oncogene High 10498895
1999 EphA8 binds ephrin-A1 and ephrin-A4 (in addition to previously known ephrin-A2, -A3, -A5) but not transmembrane ephrin-B ligands, confirming EphA8 as a GPI-linked ephrin-dependent receptor tyrosine kinase. Fc-fusion chimeric ligand binding assays, receptor tyrosine phosphorylation in NIH3T3 fibroblasts Molecules and cells Medium 10515610
2001 EphA8 enhances cell adhesion to fibronectin via α5β1 and β3 integrins through a tyrosine kinase-independent mechanism that requires ephrin-A binding to the extracellular domain and the juxtamembrane segment of the intracellular domain. The p110γ isoform of PI3-kinase associates with EphA8 via the juxtamembrane segment and mediates integrin activation. Cell adhesion assays, kinase-inactive mutants, domain deletion mutants, wortmannin inhibition, in vitro binding, co-immunoprecipitation, dominant-negative p110γ overexpression Molecular and cellular biology High 11416136
2003 EphA8 phosphorylates and activates low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) in vitro, and activated LMW-PTP in turn dephosphorylates EphA8, suggesting a feedback-control mechanism for EphA8 autokinase activity. In vitro kinase assay, phosphatase activity assay Journal of biochemistry and molecular biology Medium 12787484
2003 Ligand-stimulated EphA8 signaling requires p110γ PI3-kinase activity to promote cell migration on fibronectin; a lipid kinase-inactive p110γ dominantly suppresses ephrin-A5-stimulated PI3-kinase activity and migration, in a manner independent of EphA8 tyrosine kinase activity. Ephrin-A5-Fc stimulation, lipid kinase-inactive dominant-negative p110γ, cell migration assay on fibronectin FEBS letters High 12681484
2005 EphA8 induces neurite outgrowth in NG108-15 neuronal cells in a ligand-independent manner, requiring the tyrosine kinase domain but not tyrosine kinase activity, through sustained MAPK activation that drives MAPK relocalization from cytoplasm to nucleus. Deletion mutants, kinase-inactive mutants, pharmacological inhibitors, MAPK activity assay, subcellular fractionation/immunofluorescence in NG108-15 cells Oncogene Medium 15782114
2007 Upon ephrin-A5 stimulation, PTB domain-containing Anks family proteins AIDA-1b and Odin associate with the juxtamembrane domain of EphA8 in a tyrosine kinase-independent manner. Odin acts as a physiologically relevant scaffold for EphA8 signaling; its knockdown diminishes ephrin-A5-induced inhibition of cell migration and neurite retraction. Co-immunoprecipitation, PTB domain pulldown, siRNA knockdown, cell migration assay, dominant-negative PTB domain overexpression Molecular and cellular biology High 17875921
2010 EphA8 undergoes clathrin-mediated endocytosis upon ephrin-A5 stimulation; the juxtamembrane region of EphA8 is required for endocytosis and for association with Tiam-1 (a Rac-specific GEF). Tiam-1 knockdown impairs endocytosis of EphA8-ephrin-A5 complexes and reduces Rac activation. EphA8 deletion mutants, clathrin-mediated endocytosis assay, co-immunoprecipitation with Tiam-1, Rac activity assay, Tiam-1 siRNA knockdown Molecules and cells Medium 20496116
2012 RINL (a Rab5 subfamily GEF) interacts with Odin and forms a ternary complex with EphA8. RINL expression reduces EphA8 protein levels in a manner dependent on both RINL GEF activity and Odin interaction, placing RINL in the EphA8 degradation pathway via Rab5-mediated trafficking. Co-immunoprecipitation, GEF activity assay (GTP-bound Rab measurement), RINL knockdown, overexpression in HeLa cells PloS one Medium 22291991
2013 EphA8-Fc ectopic expression in transgenic embryos induces caspase-dependent apoptosis of ephrin-A5-expressing neural epithelial cells via reverse signaling through ephrin-As, causing reduced brain size. Transgenic embryo expression of EphA8-Fc, in vitro neuroepithelial cell culture with EphA8-Fc, caspase inhibitor assays, apoptosis quantification Developmental neurobiology Medium 23696555

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1997 Aberrant axonal projections in mice lacking EphA8 (Eek) tyrosine protein kinase receptors. The EMBO journal 88 9214628
2001 The EphA8 receptor regulates integrin activity through p110gamma phosphatidylinositol-3 kinase in a tyrosine kinase activity-independent manner. Molecular and cellular biology 85 11416136
1991 eek and erk, new members of the eph subclass of receptor protein-tyrosine kinases. Oncogene 60 1648701
2015 miR-10a controls glioma migration and invasion through regulating epithelial-mesenchymal transition via EphA8. FEBS letters 55 25683004
2005 The EphA8 receptor induces sustained MAP kinase activation to promote neurite outgrowth in neuronal cells. Oncogene 40 15782114
1999 Phosphorylation at Tyr-838 in the kinase domain of EphA8 modulates Fyn binding to the Tyr-615 site by enhancing tyrosine kinase activity. Oncogene 28 10498895
2007 Identification of phosphotyrosine binding domain-containing proteins as novel downstream targets of the EphA8 signaling function. Molecular and cellular biology 24 17875921
2010 EphA8-ephrinA5 signaling and clathrin-mediated endocytosis is regulated by Tiam-1, a Rac-specific guanine nucleotide exchange factor. Molecules and cells 22 20496116
1997 The Eek receptor, a member of the Eph family of tyrosine protein kinases, can be activated by three different Eph family ligands. Oncogene 20 9053851
2013 Expression of EphA8-Fc in transgenic mouse embryos induces apoptosis of neural epithelial cells during brain development. Developmental neurobiology 19 23696555
2021 Bone marrow stromal cells derived exosomal miR-10a and miR-16 may be involved in progression of patients with multiple myeloma by regulating EPHA8 or IGF1R/CCND1. Medicine 12 33530159
2012 RINL, guanine nucleotide exchange factor Rab5-subfamily, is involved in the EphA8-degradation pathway with odin. PloS one 12 22291991
2003 The p110 gamma PI-3 kinase is required for EphA8-stimulated cell migration. FEBS letters 11 12681484
2007 Engineering lacZ Reporter gene into an ephA8 bacterial artificial chromosome using a highly efficient bacterial recombination system. Journal of biochemistry and molecular biology 10 17927897
2003 The EphA8 receptor phosphorylates and activates low molecular weight phosphotyrosine protein phosphatase in vitro. Journal of biochemistry and molecular biology 9 12787484
2000 Genomic structure and promoter analysis of the mouse EphA8 receptor tyrosine kinase gene. DNA and cell biology 9 10855796
2003 Identification of an enhancer region in the mouse ephA8 locus directing expression to the anterior region of the dorsal mesencephalon. Developmental dynamics : an official publication of the American Association of Anatomists 7 12666197
1999 Characterization of ephrin-A1 and ephrin-A4 as ligands for the EphA8 receptor protein tyrosine kinase. Molecules and cells 7 10515610
2010 Ectopic Expression of Ephrin-A5 Under the EphA8 Promoter at the Anterior Region of the Superior Colliculus. Experimental neurobiology 3 22110341
2024 LGP2 Facilitates Bacterial Escape through Binding Peptidoglycan via EEK Motif and Suppressing NOD2-RIP2 Axis in Cyprinidae and Xenocyprididae Families. Journal of immunology (Baltimore, Md. : 1950) 0 38629918