Ephrin receptors (EphRs) comprise the largest subfamily of receptor tyrosine kinases (RTKs). Class EphB receptors bind to transmembrane ephrin-B ligands. There are six vertebrate EhpB receptors (EphB1-6), which display promiscuous interactions with three ephrin-B ligands. EphB4 plays a role in osteoblast differentiation and has been linked to multiple myeloma. EphRs contain a ligand binding domain and two fibronectin repeats extracellularly, a transmembrane segment, and a cytoplasmic tyrosine kinase domain. Binding of the ephrin ligand to EphR requires cell-cell contact since both are anchored to the plasma membrane. The resulting downstream signals occur bidirectionally in both EphR-expressing cells (forward signaling) and ephrin-expressing cells (reverse signaling).
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