CDB15:0000468 EFNA1 — EPHA2

ABSTRACT: Ephrins are ligands for the Eph receptor tyrosine kinases, which play important roles in patterning nervous and vascular systems. Ephrin-A1 is a glycosylphosphatidylinositol-anchored ligand that binds to the EphA receptor tyrosine kinases. In the present study, we have identified a new ephrin-A1 isoform, denoted ephrin-A1b (ephrin-A1 isoform b). Compared with the originally described ephrin-A1 sequence, ephrin-A1a [Holzman, Marks and Dixit (1990) Mol. Cell. Biol. 10, 5830-5838], ephrin-A1b lacks a segment of 22 amino acids (residues 131-152). At the transcript level, exon 3 is spliced out in the transcript encoding ephrin-A1b. Transfection of HEK-293T cells (human embryonic kidney 293 cells) with an ephrin-A1b-expressing plasmid resulted in a significant expression of the protein on the cell surface. However, soluble EphA2 receptor (EphA2-Fc) bound weakly to ephrin-A1b-expressing transfectants, but bound strongly to ephrin-A1a-expressing transfectants. Ephrins have been shown to undergo regulated cleavage after interaction with their receptors. This process is inhibited by co-expression of ephrin-A1a and ephrin-A1b, indicating that ephrin-A1b influences the cleavage process. Taken together, these findings indicate that this newly described isoform may regulate the function of its ephrin-A1a counterpart.

ABSTRACT: In mammals, 14 members of the Eph receptor tyrosine kinase family have been described so far. Here we present a not yet described member of this family denoted EphA10. We report the identification of three putative EphA10 isoforms: one soluble and two transmembrane isoforms. One of the latter isoforms lacked the sterile alpha motif commonly found in Eph receptors. The gene encoding EphA10 is located on chromosome 1p34 and expression studies show that EphA10 mRNA is mainly expressed in testis. Binding studies to ephrin ligands suggests that this receptor belongs to the EphA subclass of Eph receptors binding mainly to ephrin-A ligands.

ABSTRACT: The Eph receptor tyrosine kinase family includes many members, which are often expressed together in various combinations and can promiscuously interact with multiple ephrin ligands, generating intricate networks of intracellular signals that control physiological and pathological processes. Knowing the entire repertoire of Eph receptors and ephrins expressed in a biological sample is important when studying their biological roles. Moreover, given the correlation between Eph receptor/ephrin expression and cancer pathogenesis, their expression patterns could serve important diagnostic and prognostic purposes. However, profiling Eph receptor and ephrin expression has been challenging. Here we describe a novel and straightforward approach to catalog the Eph receptors present in cultured cells and tissues. By measuring the binding of ephrin Fc fusion proteins to Eph receptors in ELISA and pull-down assays, we determined that a mixture of four ephrins is suitable for isolating both EphA and EphB receptors in a single pull-down. We then used mass spectrometry to identify the Eph receptors present in the pull-downs and estimate their relative levels. This approach was validated in cultured human cancer cell lines, human tumor xenograft tissue grown in mice, and mouse brain tissue. The new mass spectrometry approach we have developed represents a useful tool for the identification of the spectrum of Eph receptors present in a biological sample and could also be extended to profiling ephrin expression.

ABSTRACT: Embryonic Stem Cell (ESC) differentiation requires complex cell signalling network dynamics, although the key molecular events remain poorly understood. Here, we use phosphoproteomics to identify an FGF4-mediated phosphorylation switch centred upon the key Ephrin receptor EPHA2 in differentiating ESCs. We show that EPHA2 maintains pluripotency and restrains commitment by antagonising ERK1/2 signalling. Upon ESC differentiation, FGF4 utilises a bimodal strategy to disable EPHA2, which is accompanied by transcriptional induction of EFN ligands. Mechanistically, FGF4-ERK1/2-RSK signalling inhibits EPHA2 via Ser/Thr phosphorylation, whilst FGF4-ERK1/2 disrupts a core pluripotency transcriptional circuit required for Epha2 gene expression. This system also operates in mouse and human embryos, where EPHA receptors are enriched in pluripotent cells whilst surrounding lineage-specified trophectoderm expresses EFNA ligands. Our data provide insight into function and regulation of EPH-EFN signalling in ESCs, and suggest that segregated EPH-EFN expression coordinates cell fate with compartmentalisation during early embryonic development.