Tie receptors and their angiopoietin ligands play a critical role in angiogenesis or blood vessel formation. They are considered to control numerous signaling pathways that are involved in diverse cellular processes, such as cell migration, proliferation, survival and reorganization of the actin cytoskeleton.
Tie (tyrosine kinase with immunoglobulin and epidermal growth factor homology domains) represents a class of receptor tyrosine kinases (RTKs) that are predominately expressed by vascular endothelial cells. The angiopoietins are a family of growth factors that are largely specific for endothelium and they bind to Tie2/Tek RTKs.
Tie2 signaling initially involves the activation of Tie2 by the interaction of angiopoietin 1. Angiopoietin interacts with the Tie2 receptor with its fibrinogen like domain (FLD). This interaction leads to the dimerization of both the receptor and the ligand, and later initiate the trans-phosphorylation of Tie2.