Abstract
VEGF and TGF-beta1 are potent angiogenesis inducers with opposing effects on endothelial cells. TGF-beta1 induces apoptosis; VEGF protects endothelial cells from apoptosis. We found that TGF-beta1 promotes endothelial cell expression of FGF-2, which up-regulates VEGF synthesis. Inhibition of VEGF signaling through VEGF receptor 2 (flk-1) abrogates TGF-beta1-induced apoptosis and p38(MAPK) activation. Inhibition of p38(MAPK) blocks TGF-beta1-induced apoptosis, showing that VEGF/flk-1-mediated activation of p38(MAPK) is required for TGF-beta1 induction of apoptosis. In the absence of TGF-beta1, VEGF activates p38(MAPK) and promotes endothelial cell survival. However, in context with TGF-beta1, VEGF/flk-1-mediated activation of p38(MAPK) results in apoptosis. Thus, cross-talk between TGF-beta1 and VEGF signaling converts VEGF/flk-1-activated p38(MAPK) 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.