Cells in our body need to communicate together. For that, they use so called signaling pathways. Among these, the Notch signaling pathway is conserved in all animal species studied so far. It is involved in the control of cell proliferation, of cell death and for the maintenance of stem cells. Notch is directly involved in many cancers since excessive activity of this pathway leads to overproliferation of tissues and/or to an increase of stem cells. We are using the fruit fly and cell culture assays as model systems to understand how Notch is regulated. We focus on the role of a particular transport route inside the cell. Indeed, recent evidences has shown that the receptor Notch has to enter the cell and reach a specific vesicular compartment to be activated. Genes regulating this transport are involved in divers cancers including breast cancer and leukemia. In this proposal, we will study a new regulator of Notch, that acts as a tumor suppressor in Drosophila. Modulating the vesicular transport of Notch might allow a control of its signaling activity and might thus open new therapeutic avenues.