VEGFR1 (also called Flt-1) is one of the five receptor tyrosine kinases (RTKs) (VEGFR1, KDR/Flk-1, Flt-4, Tie-1, and Tek/Tie-2) whose expression is almost exclusively restricted to the endothelial cells. Tie-1 and Tie-2/Tek define a class of RTKs containing two immunoglobulin-like domains, three EGF homology domains and three fibronectin type III domains in their extracellular regions. VEGFR1/Flt-1, VEGFR2/KDR/Flk-1, VEGFR3/Flt-4 are members of the class III subfamily of RTKs containing seven immunoglobulin-like repeats in their extracellular domains. All five RTKs are likely to play central roles in vasculogenesis and angiogenesis.
Full length mouse VEGFR1 mRNA encodes a 1333 amino acid (aa) residue precursor with a 22 aa residue signal peptide. Mature VEGFR1 is composed of a 737 aa residue extracellular domain, a 22 aa residue transmembrane domain and a 552 aa residue cytoplasmic domain. As a result of alternative splicing of the mRNA, a cDNA encoding a truncated form of VEGFR1, lacking the seventh immunoglobulin-like domain, the transmembrane and intracellular domains, has been cloned. The recombinant soluble VEGFR1/Fc chimera binds VEGF and PlGF with high affinity and is a potent VEGF antagonist.