VEGF, a prosurvival factor, acts in concert with TGF-β1 to induce endothelial cell apoptosis

VEGF and TGF-β1 are potent angiogenesis inducers with opposing effects on endothelial cells. TGF-β1 induces apoptosis; VEGF protects endothelial cells from apoptosis. We found that TGF-β1 promotes endothelial cell expression of FGF-2, which up-regulates VEGF synthesis. Inhibition of VEGF signaling through VEGF receptor 2 (flk-1) abrogates TGF-β1-induced apoptosis and p38MAPK activation. Inhibition of p38MAPK blocks TGF-β1-induced apoptosis, showing that VEGF/flk-1-mediated activation of p38MAPK is required for TGF-β1 induction of apoptosis. In the absence of TGF-β1, VEGF activates p38MAPK and promotes endothelial cell survival. However, in context with TGF-β1, VEGF/flk-1-mediated activation of p38MAPK results in apoptosis. Thus, cross-talk between TGF-β1 and VEGF signaling converts VEGF/flk-1-activated p38MAPK into a proapoptotic signal. This finding illustrates an unexpected role of VEGF and indicates that VEGF can be pharmacologically converted into an apoptotic factor, a novel approach to antiangiogenesis therapy.