The role of Eph receptors and ephrin ligands in colorectal cancer

Eph receptors and their ephrin ligands constitute the largest subfamily of receptor tyrosine kinases and are components of the cell signaling pathways involved during development. Eph and ephrin overexpression have been documented in a variety of human cancers including gastrointestinal malignancies and in particular colorectal malignancies. EphB and ephrin B proteins have been implicated in the homeostasis of the gastrointestinal tract where EphB2- and EphB3-ephrin B signaling regulates cell sorting in the mature epithelium. These proteins are also reported to be upregulated in colon carcinomas. The EphA/ephrin A system has also been implicated in epithelial tissue structure and function. More recently, EphA receptors and their corresponding ligands have been implicated in numerous malignancies. Of these, EphA2 in particular has been intensively investigated and has been proposed as a therapeutic target. An interesting observation emerging from these studies is the role for Ephs and ephrins in critical aspects of cell adhesion, migration and positioning, and a crucial role in tumor progression and metastasis. However, the underlying role of Ephs and ephrins in these processes has generally been studied on individual Eph or ephrin genes. Given the multiplicity of Eph expression on gut epithelial cells, a more global approach is needed to define the precise role of Eph-ephrin interaction in malignant transformation. Here, we will review the recent advances on the role of Eph-ephrin signaling in colorectal malignancies.