CHARACTERIZATION OF MURINE FLT4 LIGAND VEGF-C

Flt4 is a receptor protein tyrosine kinase that is expressed in the ad ult lymphatic endothelium and high endothelial venules. We have used a BIAcore assay to identify rodent and human cell conditioned media con taining the ligand of Flt4 (Flt4-L). Receptor-based affinity chromatog raphy was used to purify this growth factor, followed by amino acid se quencing and molecular cloning of the murine cDNA, the orthologue of h uman vascular endothelial growth factor-C and vascular endothelial gro wth factor related protein. The murine flt4-L gene was localized to ch romosome 8 and demonstrated to be widely expressed. Flt4-L was found t o have a hydrophobic signal sequence and a pro-peptidelike sequence th at is removed to generate the mature N-terminus. In addition, the C-te rminal region of Flt4-L has four repeats of a cysteine-rich motif that is presumably also proteolytically processed to generate the 21 000 M -r polypeptide subunit of the Flt4-L homodimer. Recombinant Flt4-L act ivated Flt4 as judged by induction of tyrosyl phosphorylation, and ind uced mitogenesis in vitro of lymphatic endothelial cells.