LEPTIN-VEGFR-2 AXIS INDUCES NOTCH IN ENDOTHELIAL CELLS

 Notch signaling is essential for breast cancer (BC) angiogenesis and its dysfunction is implicated in many cancers.  Leptin (a pro-angiogenic, pro-inflammatory and mitogenic factor) induces the expression of VEGF/VEGFR-2 and Notch in BC cells.  The binding of leptin to its receptor (OB-Rb) in endothelial cells (EC) was shown to phosphorylate/transactivate VEGFR-2 inducing angiogenic features.    We hypothesize that leptin is an inducer of Notch in endothelial cells and that this effect could occur upon leptin-mediated transactivation of VEGFR-2, thereby, inducing angiogenic changes in EC.  Human endothelial umbilical cells (HUVEC) were challenged with leptin, a potent leptin inhibitor (LPrA2) and pharmacological inhibitors for VEGFR-2 kinase (SU5416) and Notch signaling (DAPT). Leptin-dose and time-course effects on expression of Notch (receptors: Notch1, Notch2, Notch3 and Notch4; ligands: JAG1, DLL-4 and target: Survivin were determined by Western blot and Real-Time RT PCR.  Phosphorylation/Transactivation of VEGFR-2 was determined by ELISA. Formation of tubules was determined using a Matrigel Assay.  Our studies show for the first time that leptin is a potent inducer of Notch signaling in EC. Moreover, leptin-induced VEGFR-2 phosphorylation was essential for leptin effects on Notch and probably to the leptin-induced angiogenic features of EC.  Leptin secreted either by adipose tissue or BC cells may contribute to tumor angiogenesis by acting directly on cancer cells inducing VEGF secretion or through EC inducing VEGFR-2/Notch crosstalk.   Leptin is a pro-survival factor that increases BC proliferation and expression of anti-apoptotic molecules and, reduces the effects of chemotherapeutics.  Combinatory therapies targeting both Notch and leptin signaling could be a new strategy for Breast Cancer treatment.