Distinct signal transduction pathways are utilized during the tube formation and survival phases of in vitro angiogenesis

Angiogenesis, the formation of new blood vessels from preexisting ones, occ urs during development, wound healing and cancer and involves stages that o rchestrate a network of cooperative interactions, Peptide growth factors an d extracellular matrix (ECM) components are two major groups of angiogenesi s mediators. Among the different ECM proteins, collagens have been well-ass ociated with in vivo angiogenesis. Using human umbilical vein endothelial c ells (HUVEC) grown in 3-D collagen gels we show that: (1) HUVEC do not surv ive well in 3-D collagen gels due to rapid induction of apoptosis. (2) VEGF , a potent in vivo angiogenic factor, fails to induce tube formation. (3) P MA was effective in inducing tube formation and survival in HUVEC dispersed in 3-D collagen gels, activating MAP kinase, phosphoinositide 3-OH kinase (PI-3-kinase) and Akt/PKB (protein kinase B) pathways. (4) VEGF was effecti ve in preventing PMA-induced tube-like structure regression after PMA-withd rawal by (5) activating the mitogen activated protein kinase (MAPK), rather than the Akt/PKB, signaling pathway.