Grape seed extract inhibits VEGF expression via reducing HIF-1α protein expression

Grape seed extract (GSE) is a widely consumed dietary supplement that has antitumor activity. Here, we have investigated the inhibitory effect of GSE on the expression of vascular endothelial growth factor (VEGF) and the mechanism underlying this action. We found that GSE inhibited VEGF messenger RNA (mRNA) and protein expression in U251 human glioma cells and MDA-MB-231 human breast cancer cells. GSE inhibited transcriptional activation of the VEGF gene through reducing protein but not mRNA expression of hypoxia-inducible factor (HIF) 1 alpha. The inhibitory effect of GSE on HIF-1 alpha expression was mainly through inhibiting HIF-1 alpha protein synthesis rather than promoting protein degradation. Consistent with this result, GSE-suppressed phosphorylation of several important components involved in HIF-1 alpha protein synthesis, such as Akt, S6 kinase and S6 protein. Furthermore, in the MDA-MB-231 tumor, we found that GSE treatment inhibited the expression of VEGF and HIF-1 alpha and the phosphorylation of S6 kinase without altering the subcellular localization of HIF-1 alpha, correlating with reduced vessel density and tumor size. Depletion of polyphenol with polyvinylpyrrolidone abolished the inhibitory activity of GSE, suggesting a water-soluble fraction of polyphenol in GSE is responsible for the inhibitory activity. Taken together, our results indicate that GSE inhibits VEGF expression by reducing HIF-1 alpha protein synthesis through blocking Akt activation. This finding provides new insight into the mechanisms of anticancer activity of GSE and reveals a novel molecular mechanism underlying the antiangiogenic action of GSE.