Affinage

EPHA8

Ephrin type-A receptor 8 · UniProt P29322

Length
1005 aa
Mass
111.0 kDa
Annotated
2026-06-09
20 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

EphA8 is an Eph-subclass receptor protein-tyrosine kinase, most highly expressed in brain, that governs axonal pathfinding and developmental cell-fate decisions in the mammalian nervous system (PMID:1648701, PMID:9214628). It functions as a GPI-linked ephrin-A-selective receptor, binding and being tyrosine-phosphorylated by ephrin-A ligands (A1, A4, A5) but not transmembrane ephrin-B ligands (PMID:9053851, PMID:10515610). Its juxtamembrane segment is a central signaling hub: it carries the autophosphorylation site Tyr-615 that selectively recruits Fyn, while Tyr-838 in the kinase domain sustains catalytic activity (PMID:10498895). Strikingly, several EphA8 outputs are kinase-independent — ligand-engaged EphA8 recruits the p110gamma isoform of PI 3-kinase through its juxtamembrane segment to drive integrin-mediated adhesion and migration on fibronectin (PMID:11416136, PMID:12681484), and the kinase domain (but not its catalytic activity) is required for sustained MAPK activation and neurite outgrowth (PMID:15782114). The same juxtamembrane region nucleates ligand-dependent recruitment of the Anks-family PTB scaffolds Odin and AIDA-1b, which restrain cell migration and promote neurite retraction (PMID:17875921), and couples receptor activation to Tiam-1-dependent, clathrin-mediated endocytosis and Rac activation (PMID:20496116); receptor turnover is further controlled by the Rab5 GEF RINL acting through Odin (PMID:22291991). EphA8 also engages a phosphatase feedback loop by phosphorylating and activating LMW-PTP, which in turn dephosphorylates the receptor (PMID:12787484). Beyond forward signaling, EphA8 can drive reverse signaling through ephrin-A5 to trigger caspase-dependent apoptosis of neural epithelial cells during brain development (PMID:23696555).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 1991 Medium

    Established the molecular identity of EphA8 as a brain-enriched Eph-family receptor tyrosine kinase, defining the protein class before any function was known.

    Evidence cDNA cloning and sequence analysis with Northern blot expression profiling

    PMID:1648701

    Open questions at the time
    • No ligand identified
    • No in vivo function established
    • Catalytic activity inferred from sequence, not demonstrated
  2. 1997 High

    Defined the in vivo requirement for EphA8, showing it is needed for correct axonal pathfinding rather than serving a dispensable role.

    Evidence Germline knockout mouse with anterograde and retrograde axonal tracing in the superior colliculus

    PMID:9214628

    Open questions at the time
    • Did not identify the ligand or downstream effectors mediating pathfinding
    • Cell-autonomy of the defect not resolved
  3. 1997 Medium

    Identified the activating ligands, establishing that EphA8 is engaged and phosphorylated by GPI-linked ephrin-A ligands.

    Evidence Fc-fusion ligand binding and receptor phosphorylation assays in transfected NIH3T3 cells

    PMID:9053851

    Open questions at the time
    • Ligand selectivity versus ephrin-B not yet tested
    • Downstream signaling not addressed
  4. 1999 Medium

    Confirmed exclusive ephrin-A (GPI-linked) ligand selectivity, ruling out transmembrane ephrin-B ligands.

    Evidence Ephrin-Fc chimera panel binding and receptor phosphorylation in NIH3T3 fibroblasts

    PMID:10515610

    Open questions at the time
    • Physiological ligand in vivo not pinpointed
    • Affinities not quantified
  5. 1999 High

    Mapped the key autophosphorylation sites and linked them to specific outputs, distinguishing a catalytic-sustaining site from an SH2-docking site.

    Evidence 2D phosphopeptide mapping, in vitro kinase assay, mutagenesis, in vitro SH2 binding, and Co-IP

    PMID:10498895

    Open questions at the time
    • Functional consequence of Fyn recruitment downstream not detailed
    • Stoichiometry of phosphorylation in vivo unknown
  6. 2001 High

    Revealed a kinase-independent adhesion mechanism in which EphA8 recruits p110gamma PI 3-kinase via its juxtamembrane segment to drive integrin-mediated adhesion.

    Evidence Cell adhesion assays with kinase-inactive and deletion mutants, in vitro pulldown, and dominant-negative lipid kinase-dead p110gamma

    PMID:11416136

    Open questions at the time
    • Structural basis of the p110gamma juxtamembrane interaction not resolved
    • In vivo relevance of the adhesion role untested
  7. 2003 Medium

    Extended the p110gamma axis to cell migration, showing ligand stabilizes the complex and that lipid kinase activity, not EphA8 catalysis, drives motility.

    Evidence PI 3-kinase activity assay, dominant-negative lipid kinase-dead p110gamma, and fibronectin migration assay

    PMID:12681484

    Open questions at the time
    • Downstream effectors of p110gamma in migration not identified
    • Connection to integrin signaling not mechanistically closed
  8. 2003 Medium

    Uncovered a phosphatase feedback loop in which EphA8 activates LMW-PTP, which then dephosphorylates the receptor.

    Evidence In vitro kinase and phosphatase activity assays with purified enzymes

    PMID:12787484

    Open questions at the time
    • In vitro reconstitution only; cellular relevance not established
    • Effect on downstream signaling not measured
  9. 2005 Medium

    Demonstrated a ligand- and catalysis-independent route to sustained MAPK signaling and neurite outgrowth requiring the kinase domain as a scaffold.

    Evidence Deletion mutants, kinase inhibitors, MAPK activity assay, and neurite outgrowth assay in NG108-15 cells

    PMID:15782114

    Open questions at the time
    • Adaptors linking the kinase domain to MAPK not identified
    • Reconciliation with kinase-dependent outputs unresolved
  10. 2007 High

    Identified Odin/AIDA-1b PTB scaffolds as ligand-induced juxtamembrane partners that restrain migration and promote neurite retraction, defining an inhibitory branch of signaling.

    Evidence Reciprocal Co-IP, PTB-domain pulldown, siRNA knockdown, dominant-negative PTB overexpression, and migration/retraction assays

    PMID:17875921

    Open questions at the time
    • Downstream effectors of Odin in EphA8 inhibition unmapped
    • Interplay with the p110gamma promigratory branch unclear
  11. 2010 Medium

    Linked receptor activation to clathrin-mediated endocytosis and Rac activation through juxtamembrane recruitment of the GEF Tiam-1.

    Evidence Endocytosis and Rac activity assays, deletion mutants, Co-IP, and Tiam-1 knockdown

    PMID:20496116

    Open questions at the time
    • Whether endocytosis terminates or propagates signaling not resolved
    • In vivo role of EphA8 internalization untested
  12. 2012 Medium

    Placed EphA8 in a degradative pathway, showing the Rab5 GEF RINL acts via Odin to lower receptor levels.

    Evidence Co-IP, GTP-Rab5 assay, RINL knockdown/overexpression with GEF-inactive mutant, and EphA8 Western blots

    PMID:22291991

    Open questions at the time
    • Lysosomal versus proteasomal fate not distinguished
    • Physiological context of receptor turnover unknown
  13. 2013 Medium

    Showed EphA8 can act as a ligand for reverse signaling, driving caspase-dependent apoptosis of ephrin-A5-expressing neural epithelium during brain development.

    Evidence Transgenic embryo ectopic EphA8-Fc expression, in vivo/in vitro apoptosis assays, and caspase inhibition

    PMID:23696555

    Open questions at the time
    • Ephrin-A5 reverse-signaling effectors not identified
    • Relevance to endogenous EphA8 spatial gradients unclear
  14. 2024 Low

    Implicated EphA8 as the relevant ephrin-A5 receptor mediating anti-proliferative signaling in human rhabdomyosarcoma cells.

    Evidence Fc-chimera binding, signaling, and proliferation assays in RMS cell lines (preprint)

    PMID:bio_10.1101_2024.12.23.629471

    Open questions at the time
    • Preprint, single lab with limited mechanistic detail
    • Signaling pathway driving growth arrest not defined
    • In vivo tumor relevance untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the competing promigratory (p110gamma/Tiam-1/Rac) and antimigratory (Odin) branches are integrated downstream of a single juxtamembrane hub, and how kinase-dependent and kinase-independent outputs are coordinated in vivo, remains unresolved.
  • No structural model of the juxtamembrane signaling complex
  • No in vivo dissection of which downstream branch mediates the axonal pathfinding phenotype

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0001618 virus receptor activity 2 GO:0060089 molecular transducer activity 2 GO:0140096 catalytic activity, acting on a protein 2
Localization
GO:0005768 endosome 2 GO:0005886 plasma membrane 2
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-1266738 Developmental Biology 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-5357801 Programmed Cell Death 1
Partners
ACP1ANKS1AANKS1BEFNA5FYNPIK3CGRINLTIAM1

Evidence

Reading pass · 14 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 amino acid residues in the catalytic domain of protein-tyrosine kinases, and is most highly expressed in brain. cDNA cloning, Northern blot analysis Oncogene Medium 1648701
1997 EphA8 (Eek) knockout mice show aberrant axonal projections: tectal neurons in the superior colliculus fail to reach contralateral inferior colliculus targets, and an abnormal ipsilateral tract projects to ventral cervical spinal cord, establishing EphA8 as required for axonal pathfinding in the mammalian nervous system. Homologous recombination knockout, axonal tracing (anterograde and retrograde labeling) The EMBO journal High 9214628
1997 EphA8 (Eek) receptor can be activated by at least three GPI-linked ephrin-A ligands (Elf-1/Cek7-L, Ehk1-L/Efl-2/Lerk3, and AL-1/RAGS), which bind to and tyrosine-phosphorylate EphA8 expressed in NIH3T3 cells. Chimeric Fc-fusion ligand binding assays, receptor phosphorylation assays in transfected NIH3T3 cells Oncogene Medium 9053851
1999 Tyr-615 (juxtamembrane) and Tyr-838 (kinase domain) are major autophosphorylation sites of EphA8. Mutation of Tyr-838 drastically reduces catalytic activity. Phospho-Tyr-615 selectively mediates binding to the Fyn SH2 domain over Src and RasGAP SH2 domains. Mutation of either site reduces EphA8-Fyn association in intact cells and attenuates cell attachment responses. 2D phosphopeptide mapping, in vitro kinase assay, site-directed mutagenesis, in vitro SH2 binding, co-immunoprecipitation Oncogene High 10498895
1999 EphA8 binds and is activated by ephrin-A1 and ephrin-A4 (GPI-linked), but not transmembrane ephrin-B1, -B2, or -B3, confirming EphA8 functions exclusively as a GPI-linked ephrin-A-dependent receptor tyrosine kinase. Chimeric Fc-fusion ligand binding assay, receptor tyrosine phosphorylation in transfected NIH3T3 fibroblasts Molecules and cells Medium 10515610
2001 EphA8 promotes cell adhesion to fibronectin via alpha5beta1 or beta3 integrins in a tyrosine kinase-independent manner. This function requires ephrin-A binding to the extracellular domain and the juxtamembrane intracellular segment. EphA8 associates with the p110gamma isoform of PI 3-kinase via its juxtamembrane segment, and p110gamma lipid kinase activity is required for integrin-mediated cell adhesion. Cell adhesion assay, kinase-inactive mutant analysis, EphA8 deletion/point mutants, PI 3-kinase activity assay, in vitro pulldown, dominant-negative p110gamma lipid kinase-inactive mutant Molecular and cellular biology High 11416136
2003 EphA8-stimulated cell migration on fibronectin requires p110gamma PI 3-kinase activity. Ephrin-A5 stimulation increases stability of the p110gamma–EphA8 complex and enhances PI 3-kinase activity. A lipid kinase-inactive p110gamma dominantly suppresses EphA8-stimulated migration. EphA8 tyrosine kinase activity is dispensable for this process. PI 3-kinase activity assay, dominant-negative lipid kinase-inactive p110gamma mutant, cell migration assay on fibronectin FEBS letters Medium 12681484
2003 EphA8 directly phosphorylates and activates low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) in vitro, and the phosphorylated LMW-PTP in turn dephosphorylates EphA8, suggesting a feedback-control mechanism of EphA8 autokinase activity. In vitro kinase assay, in vitro phosphatase activity assay Journal of biochemistry and molecular biology Medium 12787484
2005 EphA8 induces sustained MAP kinase (MAPK/ERK) activation and nuclear relocalization of activated MAPK, driving neurite outgrowth in NG108-15 neuronal cells. This requires the tyrosine kinase domain but not kinase catalytic activity, and is independent of ligand stimulation. Deletion mutant analysis, MAPK activity assay, immunofluorescence localization, kinase inhibitors, neurite outgrowth assay Oncogene Medium 15782114
2007 The PTB domain-containing proteins AIDA-1b and Odin (Anks family) associate with the juxtamembrane domain of EphA8 in response to ephrin-A5 ligand stimulation. This interaction is independent of EphA8 tyrosine kinase activity. Odin is identified as the more physiologically relevant partner; siRNA-mediated Odin knockdown diminishes EphA8-mediated inhibition of cell migration and neurite retraction. Overexpression of the Odin PTB domain alone (dominant-negative) attenuates EphA8-mediated cell migration inhibition. Co-immunoprecipitation, PTB domain pulldown, siRNA knockdown, dominant-negative overexpression, cell migration assay, neurite retraction assay 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 of EphA8-ephrinA5 complexes and for association with Tiam-1, a Rac-specific GEF. Tiam-1 knockdown impairs endocytosis of EphA8-ephrinA5 complexes, and an endocytosis-defective EphA8 juxtamembrane mutant shows reduced Rac activation after ephrin-A5 stimulation. Endocytosis assay, EphA8 deletion mutant analysis, Co-immunoprecipitation, siRNA knockdown of Tiam-1, Rac activity assay 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 its GEF activity and interaction with Odin; RINL knockdown increases EphA8 levels, placing RINL in the EphA8 degradation pathway via the endosomal/Rab5 system. Co-immunoprecipitation, GTP-bound Rab5 assay, RINL knockdown, RINL overexpression with GEF-inactive mutant, Western blot for EphA8 levels PloS one Medium 22291991
2013 Ectopic expression of EphA8-Fc in transgenic mouse embryos induces caspase-dependent apoptosis of ephrin-A5-expressing neural epithelial cells, causing a dramatic decrease in brain size, indicating that EphA8 can drive reverse signaling through ephrin-As to activate proapoptotic pathways during brain development. Transgenic mouse ectopic expression, in vivo and in vitro apoptosis assay, caspase inhibitor treatment, neuroepithelial cell culture Developmental neurobiology Medium 23696555
2024 In human rhabdomyosarcoma cells, ephrin-A5 binds and signals through EphA8 (not EphA7), and this signaling inhibits cell proliferation, identifying EphA8 as the relevant receptor for ephrin-A5-mediated anti-proliferative effects in this context. Binding assay with Fc chimeras, signaling assay, cell proliferation assay in human RMS cell lines bioRxivpreprint Low bio_10.1101_2024.12.23.629471

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 13 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) 1 38629918

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