Vascular endothelial growth factor mediates intracrine survival of breast cancer cells through vascular endothelial growth factor receptor-1*Authors contributed equally

2523 Vascular endothelial growth factor (VEGF) expression in breast tumors has been correlated with a poor outcome in the pathogenesis of breast cancer. Moreover, the expression, localization and function of VEGF receptors (VEGFR), VEGFR-1 and VEGFR-2 as well as neurophilin-1 (NP-1), in breast cancer are controversial. Therefore, we investigated the expression and function of VEGF, VEGFR-1 and VEGFR-2 in breast cancer cells. We observed that VEGFR-1 expression was abundant, VEGFR-2 expression was low and NP-1 expression was variable. MDA-MB-231 and MCF-7 breast cancer cells, transfected with antisense VEGF cDNA or with small-interfering RNA (siRNA) for VEGF (siVEGF), resulted in a significant reduction in VEGF expression and increased apoptosis as compared to the control cells. Additionally, specific targeted knockdown of VEGFR-1 expression by siVEGFR-1 significantly decreased the survival of breast cancer cells through down-regulation of AKT phosphorylation, while targeted knockdown of VEGFR-2 or neuropilin-1 (NP-1) expression had no effect on the survival of these cancer cells. Since a VEGFR-1 specific ligand, the placenta growth factor (PIGF), surprisingly, did not inhibit the breast cancer cell apoptosis induced by siVEGF, and since VEGFR-1 antibody also had no effects on the survival of these cells, we examined VEGFR-1 localization. VEGFR-1 was found to be predominantly expressed internally in MDA-MB-231 and MCF-7 breast cancer cells. Specifically, VEGFR-1 was found to be colocalized with Lamin A/C and was expressed mainly in the nuclear envelope in breast cancer cell lines and primary breast cancer tumors. Breast cancer cells treated with siVEGFR-1 showed significant decrease of VEGFR-1 expression and lack of VEGFR-1 expression in the nuclear envelope. These results provide evidence of a unique survival system in breast cancer cells by which VEGF can act as an internal autocrine (intracrine) survival factor through its binding to VEGFR-1, and may provide a more optimal strategy for tumor therapy based on the inhibition of angiogenesis.