Tumor cells secrete vascular endothelial growth factor (VEGF), a potent angiogenic factor that mediates endothelial cell migration and proliferation through activation of specific tyrosine kinase receptors. Recently tumor cells have been shown to express vascular endothelial growth factor receptors. Potential functions mediated by these receptors are poorly defined. We hypothesized that stimulation of VEGFR-1 in tumor cells, through a Src family-dependent mechanism, increases migration and proliferation of human colon cancer cells. HT29 human colon carcinoma cells (which express VEGFR-1, but not VEGFR-2) were stimulated with VEGF-A (10ng/ml) or VEGF-B (50ng/ml). Activities of Src and Yes were determined by an immune complex kinase assay at various times after stimulation and quantified with densitometric analysis. Migration was assessed in a Boyden chamber assay in the presence of 1) FBS or 2) FBS + VEGF-A. After 72h, cells were stained and counted under light microscopy. Proliferation was estimated by an MTT assay. To determine specificity of signaling through VEGFR-1, the above assays were performed in the presence of a specific VEGFR-1 blocking antibody (18F1). To determine specificity of signaling through Src, the identical assays were performed in the presence of the selective Src kinase inhibitor, PP2. VEGF-A induced a ∼2- fold increase in Src kinase activity and a ∼3- fold increase in Yes activity compared to control cells after 10 minutes. VEGF-B induced a similar increase in Src and Yes kinase activity indicating specificity of signaling through VEGFR-1. VEGF-A induced a 5-fold increase in migration versus control cells, but did not increase proliferation. Pretreatment with 18F1 abrogated Src kinase induction by VEGF-A and -B at all time points and VEGF-A induced migration, while PP2 abrogated VEGF-A induced migration and basal proliferation in FBS. We conclude that the expression of VEGFR-1 on HT29 cells mediates a biologic response requiring activation of Src family protein tyrosine kinases and that expression of VEGFR on tumor cells may contribute to tumorigenic growth and/or tumor progression via a Src-dependent pathway.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]