! PROJECT SUMMARY Lung cancer is the leading cause of cancer deaths in both men and women in the United States, with over 155,000 patients dying each year in this country alone. Cancer genome sequencing has begun to uncover the compendium of mutations within human lung adenocarcinoma, but despite these advances we still have a very limited understanding of the molecular and cellular mechanisms by which even the most frequently mutated genes drive cancer growth. In particular, the molecular and cellular consequences of tumor suppressor gene function have been difficult to understand, slowing our understanding of these pathways and stalling personalized oncology approaches aimed at tailoring therapies based on tumor suppressor genotypes. In this proposal, we will employ several innovative methods to uncover the mechanisms by which the Lkb1 tumor suppression constrains lung cancer growth. This will enable a detailed understanding of the tumor suppressive function of Lkb1. While current tools have led to important insights into tumor biology, the inability to restore tumor-suppressor genes of interest at will in established tumors in vivo, has hampered our understanding of their molecular and cellular functions. We have generated mice with a conditionally-inactivable and conditionally-restorable genetic system which allows Lkb1 inactivation and subsequent restoration in autochthonous tumors. To characterize Lkb1-mediated tumor suppression, we will use this allele system to restore Lkb1 expression in lung tumors in vivo. Cellular and molecular analysis both in cell culture and in vivo will extend preliminary findings which linkLkb1 to changes in chromatin accessibility. To further understand the impact of the chromatin landscape on Lkb1-mediated tumor suppression, we will perform cell culture and in vivo experiments focused on the epistatic relationship between Lkb1 and epigenetic modifying enzymes identified in a genome-scale screen for suppressors of Lkb1-mediated growth suppression. Finally, we will investigate the relative importance of the Sik family of kinases which we have found to be tumor suppressive Lkb1-substrates. Our overall goals are to understand the molecular and cellular responses of lung tumors to Lkb1/Sik-mediated tumor suppression as well as to uncover how this response is related to changes in chromatin state. Our preliminary data, novel genetic systems, and strong collaborative team make us uniquely positioned to conduct these studies. Our proposed research is significant because it will increase our fundamental understanding of how Lkb1 limits lung tumor growth, illuminate the connection between Lkb1 and chromatin state dynamics, and potentially uncover novel and therapeutically targetable pro-tumorigenic pathways. !