TIE-1 (Tyrosine Kinase with Ig and EGF Homology domains 1) and TIE-2/Tek comprise a receptor tyrosine kinase (RTK) subfamily. These receptors are expressed on endothelial and hematopoietic progenitor cells and play critical roles in angiogenesis, vasculogenesis and hematopoiesis. Human TIE-1 cDNA encodes a 1124 amino acid (aa) residue precursor protein with an 18aa signal peptide, a 727 aa extracellular domain and a 354 aa cytoplasmic domain. so far, two ligands have been described for TIE-2 [angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2)], but no ligand was found for TIE-1.