INHIBITION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR (VEGF)-INDUCED ENDOTHELIAL-CELL PROLIFERATION BY A PEPTIDE CORRESPONDING TO THE EXON 7-ENCODED DOMAIN OF VEGF(165)

Vascular endothelial growth factor (VEGF) is a potent mitogen for endo thelial cells (EC) in vitro and a major regulator of angiogenesis in v ivo. VEGF(121) and VEGF(165) are the most abundant of the five known V EGF isoforms. The structural difference between these two is the prese nce in VEGF(165) of 44 amino acids encoded by exon 7 lacking in VEGF(1 21). It was previously shown that VEGF(165) and VEGF(121) both bind to KDR/Flk-1 and Flt-1 but that VEGF(165) binds in addition to a novel r eceptor (Soker, S., Bidder, Il., Neufeld, G., and Klagsbrun, M. (1996) J. Biol. Chem. 271, 5761-5767). The binding of VEGF(165) to this VEGF (165)-specific receptor (VEGF(165)R) is mediated by the exon 7-encoded domain. To investigate the biological role of this domain further, a glutathione S-transferase fusion protein corresponding to the VEQF(165 ) exon 7-encoded domain was prepared. The fusion protein inhibited bin ding of I-125-VEGF(165) to VEGF(165)R on human umbilical vein-derived EC (HUVEC) and MDA-MB-231 tumor cells. The fusion protein also inhibit ed significantly I-125-VEGF(165) binding to KDR/Flk-1 on HUVEC but not on porcine EC which express KDR/Flk-1 alone. VEGF(165) had a 2-fold h igher mitogenic activity for HUVEC than did VEGF(121). The exon 7 fusi on protein inhibited VEGF(165)-induced HUVEC proliferation by 60% to a bout the level stimulated by VEGF(121). Unexpectedly, the fusion prote in also inhibited HUVEC proliferation in response to VEGF(121). Deleti on analysis revealed that a core inhibitory domain exists within the C -terminal 23-amino acid portion of the exon 7-encoded domain and that a cysteine residue at position 22 in exon 7 is critical for inhibition . It was concluded that the exon 7-encoded domain of VEGF(165) enhance s its mitogenic activity for HUVEC by interacting with VEGF(165)R and modulating KDR/Flk-1-mediated mitogenicity indirectly and that exon 7- derived peptides may be useful VEGF antagonists in ansogenesis-associa ted diseases.