Intracrine VEGF signaling mediates the activity of prosurvival pathways in human colorectal cancer cells

The effects of vascular endothelial growth factor-A (VEGFA/ VEGF) and its receptors on endothelial cells function have been studied extensively, but their effects on tumor cells are less well defined. Studies of human colorectal cancer cells where the VEGF gene has been deleted suggest an intracellular role of VEGF as a cell survival factor. In this study, we investigated the role of intracrine VEGF signaling in colorectal cancer cell survival. In human colorectal cancer cells, RNAi-mediated depletion of VEGF decreased cell survival and enhanced sensitivity to chemotherapy. Unbiased reverse phase protein array studies and subsequent validation experiments indicated that impaired cell survival was a consequence of disrupted AKT and ERK1/2 (MAPK3/1) signaling, as evidenced by reduced phosphorylation. Inhibition of paracrine or autocrine VEGF signaling had no effect on phospho-AKT or phospho-ERK1/2 levels, indicating that VEGF mediates cell survival via an intracellular mechanism. Notably, RNAi-mediated depletion of VEGF receptor VEGFR1/FLT1 replicated the effects of VEGF depletion on phospho-AKT and phospho-ERK1/2 levels. Together, these studies show how VEGF functions as an intracrine survival factor in colorectal cancer cells, demonstrating its distinct role in colorectal cancer cell survival.