Mechanistic or mammalian target of rapamycin (mTOR) is a central controller of cell growth and proliferation in response to mitogenic and nutrient signals. mTOR pathway is frequently hyper-activated in human cancers, leading to uncontrolled cancer growth. Because cancer cells are often 'addicted' to elevated mTOR signaling, rendering mTOR a desirable cancer drug target. The highly specific mTOR inhibitors rapamycin analogs (rapalogs) are FDA-approved anti-cancer drugs for advanced renal and breast cancers. However, their efficacy is limited by lack of understanding of what patients are responsive to rapalog therapy. Therefore, a detailed understanding of mTOR signaling will is of considerable significance to basic biology and cancer therapy. In this application, we will investigate the mechanism of stimulation of cell growth and cancer by Rab1, a novel mTOR activator we recently identified. We will further study the role of Rab1 in the pathobiology and targeted therapy of breast cancer. We anticipate that successful completion of this project will help answer some long-standing questions on cell regulation and enable individualized cancer therapy.