Alternative titles; symbols
HGNC Approved Gene Symbol: EFNB2
Cytogenetic location: 13q33.3 Genomic coordinates (GRCh38): 13:106,489,745-106,535,662 (from NCBI)
See 179610 for background on ephrins and the Eph subfamily of receptor protein-tyrosine kinases.
Hepatoma transmembrane kinase (HTK, or EPHB4; 600011) is a member of the Eph receptor family. It has a wide tissue distribution, including expression in several myeloid hematopoietic cell lines. Unlike most of the family members, HTK does not appear to be expressed in the central nervous system. As with other members, however, it is expressed in primary epithelia and epithelial cell-derived cell lines. Bennett et al. (1995) sought to define the functional role of HTK by cloning its cognate ligand from a kidney cell line. Both human and mouse EPLG5 clones were ultimately obtained. They found that the ligand cDNA encodes a transmembrane protein of 336 amino acids. Incubation of 3T3 cells expressing HTK with COS-7 cells expressing the ligand resulted in tyrosine phosphorylation of HTK. The ligand, like its receptor, is widely expressed and may function in a variety of tissues. Bennett et al. (1995) found that hematopoietic expression of HTK was localized to the monocytic lineage, suggesting that the ligand may play a role in differentiation and/or proliferation of these cells.
Cerretti et al. (1995) isolated human and murine cDNAs that encode a protein they termed LERK5 (also called EPLG5) that is a ligand for the EPH-related tyrosine kinases ELK (EPHB1; 600600) and HEK (EPHA3; 179611) and induces their phosphorylation. The human and mouse cDNAs encode predicted proteins of 333 and 336 amino acids, respectively, that share 97% amino acid identity. LERK5 shares 27% to 59% amino acid identity with other members of the LERK family. LERK5 is expressed in adult lung and kidney and in fetal heart, lung, kidney, and brain.
Sakano et al. (1996) further characterized the native and soluble forms of HTKL, which are heavily glycosylated. They also reported on the binding interactions between HTKL and HTK and the biologic function of HTKL on a HTK+ cell line.
By treating embryonic rat cortical neurons with Efnb2, followed by stimulation with glutamate, Takasu et al. (2002) observed a large increase in intracellular calcium that was dependent on the cytoplasmic domain of the ephrin receptor Ephb2 (600997). Treatment with Bdnf (113505) did not result in an increase in glutamate-stimulated intracellular calcium. Western blot analysis showed that Efnb2 treatment increased tyrosine phosphorylation of NMDA receptor 2B (Nr2b, or Grin2b; 138252) at positions 1252, 1336, and 1472 by the Src family tyrosine kinase Fyn (137025). Efnb2 treatment also increased phosphorylation of Creb (123810) at ser133, which was mediated by the NMDA receptor. In addition, Efnb2 treatment potentiated glutamate activation of Bdnf and Cpg15. Takasu et al. (2002) concluded that the EFNB-EPHB-NMDA receptor interaction may represent an early step in the initiation of synapse formation or maturation and may potentiate the ability of the NMDA receptor to respond to activity-dependent signals from the extracellular milieu. In a perspective, Ghosh (2002) noted that Grunwald et al. (2001) and Henderson et al. (2001) reported that mice lacking Ephb2 had defective synaptic plasticity, particularly at CA1 synapses, possibly due to a lack of proper clustering of NMDA receptors at the synapse.
Palmer et al. (2002) showed that SRC family kinases, or SFKs (see SRC; 190090), are positive regulators of ephrin-B phosphorylation and phosphotyrosine-mediated reverse signaling. EphB receptor engagement of ephrin-B caused rapid recruitment of SFKs to ephrin-B expression domains and transient SFK activation. With delayed kinetics, ephrin-B ligands recruited the cytoplasmic PDZ domain-containing protein tyrosine phosphatase PTPBL (see 600267) and were dephosphorylated. These data suggested the presence of a switch mechanism that allows a shift from phosphotyrosine-/SFK-dependent signaling to PDZ-dependent signaling.
In mouse hippocampal neurons, Grunwald et al. (2004) showed that ephrin B2 and B3 (602297) are predominantly located postsynaptically and are required for synaptic plasticity, including both long-term potentiation and long-term depression. The EphA4 receptor (602188) is also critically involved in long-term plasticity independent of its cytoplasmic domain, suggesting that the ephrin B proteins are the active signaling partner. Grunwald et al. (2004) suggested that ephrins can be used in converse manners, depending on the synaptic site.
Using immunofluorescence analysis, Foo et al. (2006) found that Efnb2 was expressed in arterial endothelium and, at lower levels, on arterial and venous mural cells (i.e., pericytes and vascular smooth muscle cells) in the developing mouse vascular system. Specific inactivation of Efnb2 in mural cells of various organs in transgenic mice resulted in perinatal lethality, vascular defects in skin, lung, gastrointestinal tract, and kidney glomeruli, and abnormal migration of smooth muscle cells to lymphatic capillaries. Cultured Efnb2-deficient mouse smooth muscle cells were defective in spreading, focal adhesion formation, and polarized migration, and they showed increased motility. Studies in these cells suggested the involvement of Crk (164762)-p130(Cas) (BCAR1; 602941) complex signaling downstream of Efnb2/Ephb receptor interactions in these processes. Foo et al. (2006) concluded that EFNB2 is a critical regulator of mural cell migration, spreading, and adhesion during blood vessel wall assembly, and that EFNB2 has both cell-autonomous and cell-cell contact-dependent functions.
Nipah virus (NiV) and the related, less pathogenic Hendra virus belong to the Henipavirus genus of paramyxoviruses. Since 1999, NiV outbreaks have occurred in Malaysia, Singapore, and Bangladesh, causing fatal infections in a broad range of animal species, including humans and pigs. Disease mortality has not been observed in fruit bats, the presumed native host of NiV. Endothelial cell syncytia in small blood vessels are a hallmark of the disease. Negrete et al. (2005) found that a fusion protein consisting of the ectodomain of the NiV attachment protein (NiV-G) and the Fc region of human IgG (NiV-G-Fc) bound to NiV-permissive cell lines, but not to nonpermissive cell lines. NiV-G-Fc immunoprecipitated a 48-kD protein from permissive cell lines, and tryptic fragment analysis identified the protein as EFNB2. Soluble NiV-G bound soluble EFNB2, but not EFNB1 (300035). Soluble EFNB2 or its cognate receptor, EPHB4, inhibited cell-cell fusion mediated by NiV-G or the NiV fusion protein (NiV-F). Transfection of EFNB2, but not EFNB1, rendered nonpermissive cells permissive to NiV envelope-mediated fusion. NiV-F/G also mediated infection of primary rat neurons, which express Efnb2. Negrete et al. (2005) proposed that small-molecule antagonists targeting NiV-G may be potential antiviral agents, whereas molecules targeting EFNB2 may be useful in studies of angiogenesis.
Independently, Bonaparte et al. (2005) identified EFNB2 as a functional receptor for NiV and Hendra virus.
Blood vessels form de novo (vasculogenesis) or upon sprouting of capillaries from preexisting vessels (angiogenesis). Using high-resolution imaging of zebrafish vascular development, Herbert et al. (2009) uncovered a third mode of blood vessel formation whereby the first embryonic artery and vein, 2 unconnected blood vessels, arise from a common precursor vessel. The first embryonic vein formed by selective sprouting of progenitor cells from the precursor vessel, followed by vessel segregation. Herbert et al. (2009) found that these processes were regulated by the ligand ephrin B2 and its receptor EphB4 (600011), which are expressed in arterial-fated and venous-fated progenitors, respectively, and interact to orient the direction of progenitor migration. Thus, Herbert et al. (2009) concluded that directional control of progenitor migration drives arterial-venous segregation and generation of separate parallel vessels from a single precursor vessel, a process essential for vascular development.
Wang et al. (2010) demonstrated with genetic experiments in mouse and zebrafish that ephrin-B2 (EFNB2), a transmembrane ligand for Ephrin receptor tyrosine kinases, promotes sprouting behavior and motility in the angiogenic endothelium. Wang et al. (2010) linked this proangiogenic function to a crucial role of ephrin-B2 in the VEGF signaling pathway, which they studied in detail for VEGFR3 (136352), the receptor for VEGFC (601528). In the absence of ephrin-B2, the internalization of VEGFR3 in cultured cells and mutant mice is defective, which compromises downstream signal transduction by the small GTPase Rac1 (602048), Akt (164730), and the mitogen-activated protein kinase Erk (601795). Wang et al. (2010) concluded that VEGFR3 signaling is coupled to receptor internalization. Ephrin-B2 is a key regulator of this process and thereby controls angiogenic and lymphangiogenic growth.
Sawamiphak et al. (2010) showed that ephrin-B2 reverse signaling involving PDZ interactions regulates endothelial tip cell guidance to control angiogenic sprouting and branching in physiologic and pathologic angiogenesis. In vivo, ephrin-B2 PDZ signaling-deficient mice exhibited a reduced number of tip cells with fewer filopodial extensions at the vascular front in the mouse retina. In pathologic settings, impaired PDZ signaling decreased tumor vascularization and growth. Mechanistically, Sawamiphak et al. (2010) showed that ephrin-B2 controls VEGF receptor (VEGFR2; 191306) internalization and signaling. Importantly, internalization of VEGFR2 is necessary for activation and downstream signaling of the receptor and is required for VEGF-induced tip cell filopodial extension. Sawamiphak et al. (2010) concluded that ephrin-B2 at the tip cell filopodia regulates the proper spatial activation of VEGFR2 endocytosis and signaling to direct filopodial extension.
Crystal Structure
EPHB receptors bind to and are activated by the transmembrane B-ephrins, resulting in the formation of discrete bidirectional signaling centers in which the EPH receptor tyrosine kinase domain transduces the forward signal into its cell and the ephrin transduces the reverse signal into its cell. Himanen et al. (2001) reported the crystal structure of the N-terminal ligand-binding globular domain of EPHB2 bound to the complete extracellular domain of EFNB2 at 2.7-angstrom resolution. The overall structure of each molecule in the complex is similar to that seen in the unbound molecule. Binding occurs through an expansive dimerization interface dominated by the insertion of an extended ephrin loop into a channel at the surface of the receptor. The EPHB-EFNB dimers then join to form a stable tetramer in which each molecule interacts with 2 complementary molecules, allowing transautophosphorylation and signal initiation.
Cerretti et al. (1995) mapped Lerk5 by interspecific backcross analysis to the proximal region of mouse chromosome 8. Bonaldo et al. (1994) mapped a cDNA later identified as that for human EPLG5 to human chromosome 13q33 by in situ hybridization.
Wang et al. (1998) achieved targeted disruption of the murine ephrin-B2 gene by homologous recombination in embryonic stem cells. Ephrin-B2 knockout mice display defects in angiogenesis by both arteries and veins in the capillary networks of the head and yolk sac as well as in myocardial trabeculation. The ephrin-B2 gene disruption prevents the remodeling of veins from a capillary plexus into properly branched structures. Moreover, it also disrupts the remodeling of arteries, suggesting that reciprocal interactions between prespecified arterial and venous endothelial cells are necessary for angiogenesis. These results provided evidence that differences between arteries and veins are in part genetically determined and suggested that reciprocal signaling between these 2 types of vessels is crucial for morphogenesis of the capillary beds.
To separate the ligand and receptor-like functions of Efnb2 in mice, Adams et al. (2001) replaced the endogenous gene by cDNAs encoding either C-terminally truncated (Efnb2 delta-C) or, as a control, full-length ligand (Efnb2 WT). While homozygous Efnb2 WT/WT animals were viable and fertile, loss of the Efnb2 cytoplasmic domain resulted in midgestation lethality similar to Efnb2 null mutants (Efnb2 -/-). The truncated ligand was sufficient to restore guidance of migrating cranial neural crest cells, but Efnb2 delta-C/delta-C embryos showed defects in vasculogenesis and angiogenesis similar to those observed in Efnb2 -/- animals. These results indicated distinct requirements of functions mediated by the Efnb2 C terminus for developmental processes in the vertebrate embryo.
Makinen et al. (2005) found that homozygous mutant mice lacking the C-terminal PDZ domain of Efnb2 survived the requirement of Efnb2 in embryonic blood vascular remodeling. However, they developed chylothorax and exhibited major lymphatic defects, including hyperplasia, lack of luminal valve formation, and failure in lymphatic remodeling.
Adams, R. H., Diella, F., Hennig, S., Helmbacher, F., Deutsch, U., Klein, R. The cytoplasmic domain of the ligand ephrinB2 is required for vascular morphogenesis but not cranial neural crest migration. Cell 104: 57-69, 2001. [PubMed: 11163240] [Full Text: https://doi.org/10.1016/s0092-8674(01)00191-x]
Bennett, B. D., Zeigler, F. C., Gu, Q., Fendly, B., Goddard, A. D., Gillett, N., Matthews, W. Molecular cloning of a ligand for the EPH-related receptor protein-tyrosine kinase Htk. Proc. Nat. Acad. Sci. 92: 1866-1870, 1995. [PubMed: 7534404] [Full Text: https://doi.org/10.1073/pnas.92.6.1866]
Bonaldo, M. F., Yu, M. T., Jelenc, P., Brown, S., Su, L., Lawton, L., Deaven, L., Efstratiadis, A., Warburton, D., Soares, M. B. Selection of cDNAs using chromosome-specific genomic clones: application to human chromosome 13. Hum. Molec. Genet. 3: 1663-1673, 1994. [PubMed: 7833926] [Full Text: https://doi.org/10.1093/hmg/3.9.1663]
Bonaparte, M. I., Dimitrov, A. S., Bossart, K. N., Crameri, G., Mungall, B. A., Bishop, K. A., Choudhry, V., Dimitrov, D. S., Wang, L.-F., Eaton, B. T., Broder, C. C. Ephrin-B2 ligand is a functional receptor for Hendra virus and Nipah virus. Proc. Nat. Acad. Sci. 102: 10652-10657, 2005. [PubMed: 15998730] [Full Text: https://doi.org/10.1073/pnas.0504887102]
Cerretti, D. P., Vanden Bos, T., Nelson, N., Kozlosky, C. J., Reddy, P., Maraskovsky, E., Park, L. S., Lyman, S. D., Copeland, N. G., Gilbert, D. J., Jenkins, N. A., Fletcher, F. A. Isolation of LERK-5: a ligand of the EPH-related receptor tyrosine kinases. Molec. Immun. 32: 1197-1205, 1995. [PubMed: 8559144] [Full Text: https://doi.org/10.1016/0161-5890(95)00108-5]
Foo, S. S., Turner, C. J., Adams, S., Compagni, A., Aubyn, D., Kogata, N., Lindblom, P., Shani, M., Zicha, D., Adams, R. H. Ephrin-B2 controls cell motility and adhesion during blood-vessel-wall assembly. Cell 124: 161-173, 2006. [PubMed: 16413489] [Full Text: https://doi.org/10.1016/j.cell.2005.10.034]
Ghosh, A. Learning more about NMDA receptor regulation. Science 295: 449-451, 2002. [PubMed: 11799227] [Full Text: https://doi.org/10.1126/science.1069391]
Grunwald, I. C., Korte, M., Adelmann, G., Plueck, A., Kullander, K., Adams, R. H., Frotscher, M., Bonhoeffer, T., Klein, R. Hippocampal plasticity requires postsynaptic ephrinBs. Nature Neurosci. 7: 33-40, 2004. [PubMed: 14699416] [Full Text: https://doi.org/10.1038/nn1164]
Grunwald, I. C., Korte, M., Wolfer, D., Wilkinson, G. A., Unsicker, K., Lipp, H.-P., Bonhoeffer, T., Klein, R. Kinase-independent requirement of EphB2 receptors in hippocampal synaptic plasticity. Neuron 32: 1027-1040, 2001. [PubMed: 11754835] [Full Text: https://doi.org/10.1016/s0896-6273(01)00550-5]
Henderson, J. T., Georgiou, J., Jia, Z., Robertson, J., Elowe, S., Roder, J. C., Pawson, T. The receptor tyrosine kinase EphB2 regulates NMDA-dependent synaptic function. Neuron 32: 1041-1056, 2001. [PubMed: 11754836] [Full Text: https://doi.org/10.1016/s0896-6273(01)00553-0]
Herbert, S. P., Huisken, J., Kim, T. N., Feldman, M. E., Houseman, B. T., Wang, R. A., Shokat, K. M., Stainier, D. Y. R. Arterial-venous segregation by selective cell sprouting: an alternative mode of blood vessel formation. Science 326: 294-298, 2009. [PubMed: 19815777] [Full Text: https://doi.org/10.1126/science.1178577]
Himanen, J.-P., Rajashankar, K. R., Lackmann, M., Cowan, C. A., Henkemeyer, M., Nikolov, D. B. Crystal structure of an Eph receptor-ephrin complex. Nature 414: 933-938, 2001. [PubMed: 11780069] [Full Text: https://doi.org/10.1038/414933a]
Makinen, T., Adams, R. H., Bailey, J., Lu, Q., Ziemiecki, A., Alitalo, K., Klein, R., Wilkinson, G. A. PDZ interaction site in ephrinB2 is required for the remodeling of lymphatic vasculature. Genes Dev. 19: 397-410, 2005. Note: Erratum: Genes Dev. 20: 1829 only, 2006. [PubMed: 15687262] [Full Text: https://doi.org/10.1101/gad.330105]
Negrete, O. A., Levroney, E. L., Aguilar, H. C., Bertolotti-Ciarlet, A., Nazarian, R., Tajyar, S., Lee, B. EphrinB2 is the entry receptor for Nipah virus, an emergent deadly paramyxovirus. Nature 436: 401-405, 2005. [PubMed: 16007075] [Full Text: https://doi.org/10.1038/nature03838]
Palmer, A., Zimmer, M., Erdmann, K. S., Eulenburg, V., Porthin, A., Heumann, R., Deutsch, U., Klein, R. EphrinB phosphorylation and reverse signaling: regulation by Src kinases and PTP-BL phosphatase. Molec. Cell 9: 725-737, 2002. [PubMed: 11983165] [Full Text: https://doi.org/10.1016/s1097-2765(02)00488-4]
Sakano, S., Serizawa, R., Inada, T., Iwama, A., Itoh, A., Kato, C., Shimizu, Y., Shinkai, F., Shimizu, R., Kondo, S., Ohno, M., Suda, T. Characterization of a ligand for receptor protein-tyrosine kinase HTK expressed in immature hematopoietic cells. Oncogene 13: 813-822, 1996. [PubMed: 8761303]
Sawamiphak, S., Seidel, S., Essmann, C. L., Wilkinson, G. A., Pitulescu, M. E., Acker, T., Acker-Palmer, A. Ephrin-B2 regulates VEGFR2 function in developmental and tumour angiogenesis. Nature 465: 487-491, 2010. [PubMed: 20445540] [Full Text: https://doi.org/10.1038/nature08995]
Takasu, M. A., Dalva, M. B., Zigmond, R. E., Greenberg, M. E. Modulation of NMDA receptor-dependent calcium influx and gene expression through EphB receptors. Science 295: 491-495, 2002. [PubMed: 11799243] [Full Text: https://doi.org/10.1126/science.1065983]
Wang, H. U., Chen, Z.-F., Anderson, D. J. Molecular distinction and angiogenic interaction between embryonic arteries and veins revealed by ephrin-B2 and its receptor Eph-B4. Cell 93: 741-753, 1998. [PubMed: 9630219] [Full Text: https://doi.org/10.1016/s0092-8674(00)81436-1]
Wang, Y., Nakayama, M., Pitulescu, M. E., Schmidt, T. S., Bochenek, M. L., Sakakibara, A., Adams, S., Davy, A., Deutsch, U., Luthi, U., Barberis, A., Benjamin, L. E., Makinen, T., Nobes, C. D., Adams, R. H. Ephrin-B2 controls VEGF-induced angiogenesis and lymphangiogenesis. Nature 465: 483-486, 2010. [PubMed: 20445537] [Full Text: https://doi.org/10.1038/nature09002]