| Three cell membrane receptor tyrosine kinases Flt-1 (also designated VEGF-R1), Flk-1 (also designated VEGF-R2 or KDR) and Flt-4 (putatively involved in the growth of endothelial cells) are characterized by the presence of seven immunoglobulin-like sequences in their extracellular domains. Two members of this receptor class, Flt-1 and Flk-1, represent high affinity receptors for vascular endothelial growth factor (VEGF). On the basis of structural similarity to Flt-1 and Flk-1, Flt-4 may represent a third receptor for either VEGF or a VEGF-related ligand. Flt-3/ Flk-2 and its human homolog, STK-1, are expressed at high levels in hematopoietic cells and also in neural, gonadal, hepatic and placental tissues. |
