Vascular endothelial growth factor (VEGF), binding to an appropriate receptor like FLT, is the main mitogen for endothelial cells and a strong inducer of angiogenesis. A soluble form of VEGF receptor, sFLT-1, specifically binds VEGF and inhibits its activity. The following expression plasmids were used in the experiments: pVEGF plasmid encoding VEGF165, pFGF-2 encoding FGF-2 and psFLT-1 plasmid encoding the soluble form of VEGF receptor, sFLT-1. The interaction between VEGF and sFLT-1 was evaluated using a migration test and ERK1/2 activity utilizing mouse sarcoma cells (L-1). Implication of the VEGF/sFLT-1 action was also visualized using in vivo angiogenesis assay. The conditioned medium (CM) from L-1 phVEGF-165 transfectants stimulated L-1 cell migration more than medium from non-transfected L-1 cells. Media collected from phVEGF-165 transfectants or original L-1 cells only slightly stimulated the migration of cells transfected with psFLT-1. The L-1 cells also showed intensive phospho-ERK1/2 activity when treated with the CM from VEGF transfectants. In vivo tests showed that sFLT-1 effectively suppressed VEGF-mediated angiogenesis without affecting FGF-2-driven angiogenesis. To summarize, this study documented that sFLT-1 released from transfected cells might inhibit cell functions induced by VEGF, but not by FGF. The results obtained from in vivo angiogenesis tests also confirm the antiangiogenic potency of cloned sFLT-1, which can be useful for planning cancer experimental therapy studies.

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