Pleiotrophin induces angiogenesis: Involvement of the phosphoinositide-3 kinase but not the nitric oxide synthase pathways

Pleiotrophin (PTN) is a developmentally regulated protein that has been sho wn to be involved in tumor growth and metastasis presumably by activating t umor angiogenesis. To clarify the potential angiogenic activity of PTN and to analyze the signaling pathways involved in this process, we used an in v itro model of Human Umbilical Vein Endothelial Cells (HUVEC). We show that PTN was mitogenic toward a variety of endothelial cells including HUVEC, st imulated HUVEC migration across a reconstituted basement membrane and induc ed the formation of capillary-like structures by HUVEC grown as 3D-cultures in Matrigel or collagen. The signaling pathways triggered following endoth elial cell stimulation by PTN were studied by using pharmacological inhibit ors of the Phosphoinositide-3 kinase (P13K) and endothelial Nitric Oxide Sy nthase (eNOS), two enzymes that have been shown to be crucial in the angiog enic response to Vascular Endothelial Growth Factor (VEGF). Whereas wortman nin (a P13K inhibitor) and L-NAME tan eNOS inhibitor) dramatically reduced HUVEC growth induced by VEGF, only the former inhibitor reduced the growth induced by PTN and to a lesser extent that stimulated by basic Fibroblast G rowth Factor. Thus, our results indicate that PTN induces angiogenesis and utilizes P13K- but not eNOS-dependent pathways for its angiogenic activity. (C) 2001 Wiley-Liss, Inc.