Addition of a c-myc epitope tag within the VEGF protein does not affect in vitro biological activity

The overexpression of vascular endothelial growth factor (VEGF) has been strongly implicated in diseases involving neovascularization. VEGF exists in as many as six different isoforms, each showing a unique pattern of tissue distribution and activity. To investigate the effect of individual VEGF isoform overexpression in neovascular disease models, we inserted c-myc epitope tags into the three VEGF isoforms expressed in retinal pigment epithelial cells, VEGF(121), VEGF(165), and VEGF(189). We found that the 12-amino acid insertion between the receptor binding and heparin binding domains did not affect VEGF transcription, translation, or secretion. In addition, VEGF isoforms containing the c-myc epitope tag were able to stimulate endothelial cell proliferation as efficiently as non-tagged VEGF isoforms and they could be individually identified by Western blotting and immunocytochemistry using the c-myc epitope specific monoclonal antibody 9E10.