Vascular endothelial growth factor (VEGF-A) is a major regulator of blood vessel formation and function. It controls several processes in endothelial cells, such as proliferation, survival, and migration, but it is not known how these are coordinately regulated to result in more complex morphogenetic events, such as tubular sprouting, fusion, and network formation. We show here that VEGF-A controls angiogenic sprouting in the early postnatal retina by guiding filopodial extension from specialized endothelial cells situated at the tips of the vascular sprouts. The tip cells respond to VEGF-A only by guided migration; the proliferative response to VEGF-A occurs in the sprout stalks. These two cellular responses are both mediated by agonistic activity of VEGF-A on VEGF receptor 2. Whereas tip cell migration depends on a gradient of VEGF-A, proliferation is regulated by its concentration. Thus, vessel patterning during retinal angiogenesis depends on the balance between two different qualities of the extracellular VEGF-A distribution, which regulate distinct cellular responses in defined populations of endothelial cells.

No growth factors specific for the lymphatic vascular system have yet been described. Vascular endothelial growth factor (VEGF) regulates vascular permeability and angiogenesis, but does not promote lymphangiogenesis. Overexpression of VEGF-C, a ligand of the VEGF receptors VEGFR-3 and VEGFR-2, in the skin of transgenic mice resulted in lymphatic, but not vascular, endothelial proliferation and vessel enlargement. Thus, VEGF-C induces selective hyperplasia of the lymphatic vasculature, which is involved in the draining of interstitial fluid and in immune function, inflammation, and tumor metastasis. VEGF-C may play a role in disorders involving the lymphatic system and may be of potential use in therapeutic lymphangiogenesis.

We have identified a member of the VEGF family by computer-based homology searching and have designated it VEGF-D. VEGF-D is most closely related to VEGF-C by virtue of the presence of N- and C-terminal extensions that are not found in other VEGF family members. In adult human tissues, VEGF-D mRNA is most abundant in heart, lung, skeletal muscle, colon, and small intestine. Analyses of VEGF-D receptor specificity revealed that VEGF-D is a ligand for both VEGF receptors (VEGFRs) VEGFR-2 (Flk1) and VEGFR-3 (Flt4) and can activate these receptors. However, VEGF-D does not bind to VEGFR-1. Expression of a truncated derivative of VEGF-D demonstrated that the receptor-binding capacities reside in the portion of the molecule that is most closely related in primary structure to other VEGF family members and that corresponds to the mature form of VEGF-C. In addition, VEGF-D is a mitogen for endothelial cells. The structural and functional similarities between VEGF-D and VEGF-C define a subfamily of the VEGFs.

Metastasis is a frequent and lethal complication of cancer. Vascular endothelial growth factor‐C (VEGF‐C) is a recently described lymphangiogenic factor. Increased expression of VEGF‐C in primary tumours correlates with dissemination of tumour cells to regional lymph nodes. However, a direct role for VEGF‐C in tumour lymphangiogenesis and subsequent metastasis has yet to be demonstrated. Here we report the establishment of transgenic mice in which VEGF‐C expression, driven by the rat insulin promoter (Rip), is targeted to β‐cells of the endocrine pancreas. In contrast to wild‐type mice, which lack peri‐insular lymphatics, RipVEGF‐C transgenics develop an extensive network of lymphatics around the islets of Langerhans. These mice were crossed with Rip1Tag2 mice, which develop pancreatic β‐cell tumours that are neither lymphangiogenic nor metastatic. Double‐transgenic mice formed tumours surrounded by well developed lymphatics, which frequently contained tumour cell masses of β‐cell origin. These mice frequently developed pancreatic lymph node metastases. Our findings demonstrate that VEGF‐C‐induced lymphangiogenesis mediates tumour cell dissemination and the formation of lymph node metastases.

The recently identified vascular endothelial growth factor C (VEGF‐C) belongs to the platelet‐derived growth factor (PDGF)/VEGF family of growth factors and is a ligand for the endothelial‐specific receptor tyrosine kinases VEGFR‐3 and VEGFR‐2. The VEGF homology domain spans only about one‐third of the cysteine‐rich VEGF‐C precursor. Here we have analysed the role of post‐translational processing in VEGF‐C secretion and function, as well as the structure of the mature VEGF‐C. The stepwise proteolytic processing of VEGF‐C generated several VEGF‐C forms with increased activity towards VEGFR‐3, but only the fully processed VEGF‐C could activate VEGFR‐2. Recombinant ‘mature’ VEGF‐C made in yeast bound VEGFR‐3 ( K D = 135 pM) and VEGFR‐2 ( K D = 410 pM) and activated these receptors. Like VEGF, mature VEGF‐C increased vascular permeability, as well as the migration and proliferation of endothelial cells. Unlike other members of the PDGF/VEGF family, mature VEGF‐C formed mostly non‐covalent homodimers. These data implicate proteolytic processing as a regulator of VEGF‐C activity, and reveal novel structure–function relationships in the PDGF/VEGF family.