Vascular endothelial growth factor (VEGF) is an important regulator of endothelial cell proliferation and migration during embryonic vasculogenesis and angiogenesis as well as in pathological angiogenesis. The recently cloned new factors structurally homologous to VEGF were designated as VEGF-B/VRF and VEGF-C/VRP. The receptor for VEGF-B is unknown. VEGF-C is the ligand for FLT4, a receptor tyrosine kinase whose expression becomes restricted largely to lymphatic endothelia during development and that is related to VEGF receptors FLT1 and KDR.
In this study keratin 14-promoter-directed VEGF-C over-expression in the basal epidermis of transgenic mice was capable of promoting an abundant growth of extensive lymphatic-like vessel structures in the dermis, including large vessel lacunae resembling in their histopathology the human condition known as lymphangioma. Thus, VEGF-C appears to induce selective angiogenesis of the lymphatic vessels in vivo. In contrast, preliminary data on mice, which over-express VEGF-B under the same promoter, does not yet allow us draw any conclusions about its possible biological function.
Recombinant biologically active human VEGF-C was produced using the baculovirus system. Unpurified and purified VEGF-C were used to confirm the interaction of VEGF-C with KDR, a fact recently missed by others. The recombinant protein is going to be used in a large number of future experiments. The production of VEGF-B seems to be intrinsically difficult in non-mammalian cells. Although quantitatively satisfying results could not be obtained yet, the purified growth factor will be used in experiments to identify its receptor.