Multiple forms of mouse vascular endothelial growth factor-D are generatedby RNA splicing and proteolysis

The secreted glycoprotein vascular endothelial growth factor-D (VEGF-D) is angiogenic, lymphangiogenic, and promotes metastatic spread of tumor cells via lymphatic vessels. VEGF-D consists of a receptor-binding domain (VEGF h omology domain) and N- and G terminal propeptides. Proteolytic processing p roduces numerous forms of human VEGF-D, including fully processed derivativ es (containing only the VEGF homology domain), partially processed, and unp rocessed derivatives. Proteolysis is essential to generate human VEGF-D tha t binds the angiogenic receptor VEGF receptor-2 (VEGFR-2) and the lymphangi ogenic receptor VEGFR-3 with high affinity. Here, we report that alternativ e use of an RNA splice donor site in exon 6 of the mouse VEGF-D gene produc es two different protein isoforms, VEGF-D-358 and VEGF-D-326, with distinct C termini. The two isoforms were both expressed in all adult mouse tissues and embryonic stages of development analyzed. Both isoforms are proteolyti cally processed in a similar fashion to human VEGF-D to generate a range of secreted derivatives and bind and cross-link VEGFR-3 with similar potency. The isoforms are differently glycosylated when expressed in vitro. This st udy demonstrates that RNA splicing, protein glycosylation, and proteolysis are mechanisms for generating structural diversity of mouse VEGF-D.