Control of apoptosis during angiogenesis by survivin expression in endothelial cells

Mechanisms controlling endothelial cell survival during angiogenesis were i nvestigated. Stimulation of quiescent endothelial cells with mitogens, incl uding vascular endothelial growth factor and basic fibroblast growth factor , induced up to approximate to 16-fold up-regulation of the cell cycle-regu lated apoptosis inhibitor survivin. Mitogen stimulation rapidly increased s urvivin RNA expression in endothelial cells, which peaked after 6 to 10 hou rs in culture and decreased by 24 hours. Inflammatory cytokines, tumor necr osis factor alpha, and interleukin-1 did not induce survivin expression in endothelial cells. Formation of three-dimensional vascular tubes in vitro w as associated with strong induction of survivin in endothelial cells, as co mpared with two-dimensional cultures. By immunohistochemistry, survivin was minimally expressed in endothelium of nonproliferating capillaries of norm al skin, whereas it became massively upregulated in newly formed blood vess els of granulation tissue in vivo. Recombinant expression of green fluoresc ent protein survivin in endothelial cells reduced caspase-3 activity and co unteracted apoptosis induced by tumor necrosis factor alpha/cycloheximide, These findings identify survivin as a novel growth factor-inducible protect ive gene expressed by endothelial cells during angiogenesis. Therapeutic ma nipulation of survivin expression and function in endothelium may influence compensatory or pathological (tumor) angiogenesis.