EphB4 (D1C7N) Rabbit mAb (BSA and Azide Free) #78650

The Eph receptors are the largest known family of receptor tyrosine kinases (RTKs). They can be divided into two groups based on sequence similarity and on their preference for a subset of ligands: EphA receptors bind to a glycosylphosphatidylinositol-anchored ephrin A ligand; EphB receptors bind to ephrin B proteins that have a transmembrane and cytoplasmic domain (1,2). Research studies have shown that Eph receptors and ligands may be involved in many diseases including cancer (3). Both ephrin A and B ligands have dual functions. As RTK ligands, ephrins stimulate the kinase activity of Eph receptors and activate signaling pathways in receptor-expressing cells. The ephrin extracellular domain is sufficient for this function as long as it is clustered (4). The second function of ephrins has been described as "reverse signaling", whereby the cytoplasmic domain becomes tyrosine phosphorylated, allowing interactions with other proteins that may activate signaling pathways in the ligand-expressing cells (5). Various stimuli can induce tyrosine phosphorylation of ephrin B, including binding to EphB receptors, activation of Src kinase, and stimulation by PDGF and FGF (6). Tyr324 and Tyr327 have been identified as major phosphorylation sites of ephrin B1 in vivo (7).

The ephrin receptor B4 (EphB4) is normally expressed on venous endothelial cells, while arterial endothelial cells express its ligand, EphrinB2. Together, EphB4 and EphrinB2 play an important roll in vasculature development and maintenance (8). Research studies show that various cancers, including breast, colorectal, esophageal, and pancreatic cancers, express EphB4 (9-12). However, as EphB4 has been shown to have both tumor suppressive and promoting properties, its role in tumorigenesis and tumor progression remains uncertain (13).