It is conceivable that this inhibition of a particular signaling pathway could have a positive opinions loop for increasing other leptin-induced cytokine signaling pathways by inhibiting the production or levels of negative regulators. In Summary we have dissected what we believe to be the main signaling mechanisms involved in leptin-mediated increase in pro-angiogenic/pro-inflammatory factors in benign and malignancy EEC. MAPK, played a central role in leptin regulation of all cytokines and receptors. These results suggest that leptin’s effects are cell-specific and could confer a proliferative or cell survival advantage or possibly promote endometrial thickness. Leptin’s effects on pro-angiogenic molecules Nutlin carboxylic acid were more obvious in malignant versus benign cells and may imply that there is an underlying shift in leptin induced cell signaling pathways in endometrial malignancy cells. Keywords:leptin, pro-angiogenesis molecules, endometrial epithelial cells, endometrial malignancy, leptin signaling pathways, VEGF, VEGFR2, LIF, LIFR, IL1, IL-1R == INTRODUCTION == Leptin actions are more often than not related to energy balance. However, leptin is also acknowledged for its contributions to reproduction, angiogenesis, proliferation and inflammation. Therefore it is not surprising that leptin’s actions are now being linked to the development and pathogenesis of malignancy and endometriosis (1-9). The leptin sequence is highly conserved among mammalian species (10). In contrast, its receptor, OB-R has several isoforms (11) believed to Nutlin carboxylic acid be produced by alternate splicing. OB-Rb (full-length and functional isoform) and OB-Ra (a short isoform) are main isoforms found in diverse tissues (12), including the endometrium (13-15). Higher concentrations of OB-Ra to OB-Rb in endometrial malignancy cells have been explained (16) but the implication of this ratio is usually unclear. Leptin binds to OB-Rb in an complete Nutlin carboxylic acid specific way leading to the activation of any one of canonical signaling pathways (17) including JAK2/STAT3, PI-3K/AKT1 (18,19) and MAPK/ERK1/2 (20). Although not as common, other, kinases such as p38 protein kinase (21) and jun n terminal kinase (JNK) (22), protein kinase C (PKC) and AMP-activated protein kinase (AMPK) (23) are activated in response to leptin in some cell types. Endometrial epithelial cells (EEC) express OB-R and are targets for leptin actions (13-15,24). Accumulating evidence support the idea that leptin signaling is essential for the acquisition of endometrial receptivity and successful embryo implantation (25,26) but aberrant leptin actions have been found involved in pathological conditions (i.e., endometriosis and endometrial malignancy) (1,2,8,9,16,27-29). Leptin’s pleiotropic actions in the endometrium involve the increase in levels of pro-angiogenic and inflammatory cytokines (i.e., VEGF, LIF and IL-1), their cognate receptors and adhesion molecules (i.e., 3 integrin) (9,25,30,31). In this respect, leptin signaling could be essential for angiogenesis and inflammation required for endometrial cell adhesion, proliferation, survival and migration (1-3,6,9,25,30-34). In spite of the increasing evidence supporting leptin’s role as an important factor in endometrial biology, there is a lack of information on leptin-mediated signaling mechanisms in benign versus malignant cells. To this end, we have investigated how leptin induced signaling impacts levels of important cytokines/receptors for angiogenesis and inflammation in benign and malignant EEC. Our results suggest leptin triggers specific signaling NUFIP1 pathways in a hierarchal fashion and often differentially with respect to the regulation of VEGF, LIF, IL-1 and their cognate receptors in benign compared to malignant EEC. Our results further suggest that malignant-EEC are more sensitive to leptin induced stimulatory effects of pro-inflammatory/pro-angiogenic molecules. The differential responses of malignant EEC to leptin maybe related to a shift in the versatility of endometrial malignancy cells. == MATERIALS AND METHODS == == Materials == Antibodies for non-phosphorylated (F-2) and phosphorylated STAT3 (p-STAT3, B-7), non-phosphorylated and phosphorylated pAKT1, VEGF-R2 (flk-1 or KDR), all OB-R isoforms (extracellular domain name NH2 end) and OB-Rb (long.