This is an application for a NIDDK Mentored Clinical Scientist Development Award for Peter E. Clark, M.D. and is in response to NOT-DK-03-004: NIDDK Career Development Programs for Urologic Surgeons. Advanced renal cell carcinoma (RCC) is a deadly, chemotherapy resistant disease usually treated with biologic therapy such as interferon alpha (IFNa). New forms of therapy for advanced RCC are needed. Apo2 ligand/Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is a member of the TNF superfamily and is an attractive potential anti-tumor agent as it induces apoptosis preferentially in malignant cells. TRAIL is well tolerated in animal tumor models and preliminary clinical trials are ongoing in various cancers, including RCC. TRAIL mediated apoptosis is dependent on its death domain (DD) containing cognate receptors, DR4 and DR5, as well as the DD adaptor molecule FADD. TRAIL mediated signaling may be modulated by two receptors that lack a functional DD, DcR1 and DcR2 and by other downstream regulators of apoptosis (FLIP, Bel family members, etc.). This project examines three complementary aspects of TRAIL receptor signaling in RCC. Our preliminary studies indicate that IFNa and TRAIL cooperate to increase RCC cell death. In aim one we will determine the molecular mechanism by which this occurs. In other cancers the expression of TRAIL and its receptors predicts outcome but this has not been studied in RCC. In aim two we will analyze a large well characterized cohort of RCC patients to determine the expression level of TRAIL and its cognate receptors and test if this predicts clinical outcome. Finally, functionally significant somatic mutations exist in DR4 and DR5 in a variety of cancers but this has not been studied in RCC. In aim 3 we will identify mutations in RCC and determine their functional significance. Together, these studies provide a detailed picture of the role of TRAIL in RCC and could provide a mechanistic basis for combining TRAIL with IFNa as therapy for RCC and using TRAIL receptor levels and/or mutations as clinical prognostic markers.