Oncogenic K-Ras triggers cellular senescence by raising intracellular levels of reactive oxygen species. K-Ras- expressing cells need to bypass the oncogene-induced senescence (OIS) barrier to progress to higher grades of malignancy. Non-small cell lung cancer (NSCLC) is the most common form of lung cancer and adenocarcinoma is the most common type of NSCLC. K-Ras mutations represent the most common molecular change in lung adenocarcinomas. Progression from pre-malignant lesions to malignant adenocarcinomas is a hallmark of NSCLC pathogenesis. Our proposed investigations will directly address Provocative Question #1 by identifying and functionally characterizing novel molecular mechanisms that control the transition from premalignant lung lesions to adenocarcinomas and whose inhibition has the potential to prevent NSCLC development. Central hypothesis: we advance the novel paradigm that caveolin-1 controls the fate of lung epithelial cells in response to oncogenic Ras. We propose that oncogenic K-Ras induces senescence in premalignant lung lesions through a caveolin-1-mediated pro-oxidative signaling and that downregulation of caveolin-1 expression is necessary to bypass OIS and drive the progression to malignant adenocarcinomas. This hypothesis will be tested by pursuing three specific aims: Aim 1: Determine how caveolin-1 promotes oncogenic K-Ras-induced cellular senescence. Hypothesis: inhibition of MTH1 function by caveolin-1 is promoted by oncogenic K-Ras via mTOR activation, which leads to enhanced purine oxidation, sustained DNA damage response (DDR) and cellular senescence in lung epithelial cells. Aim 2: Identify how oncogenic K-Ras-expressing cells bypass OIS. Hypothesis: a selective pressure exists in oncogenic K-Ras-expressing cells that downregulates caveolin-1 gene expression to elude OIS. Aim 3: Determine if a lack of caveolin-1 promotes the progression to adenocarcinomas in mouse models of oncogene-induced lung cancer. Hypothesis: Caveolin-1-mediated OIS is a tumor suppressor mechanism: the genetic ablation of caveolin-1 inhibits the formation of premalignant and senescent-positive lung lesions in favor of malignant and senescent-negative adenocarcinomas. These investigations propose the novel concept that targeting K-Ras-dependent signaling that bypasses OIS through downregulaton of caveolin-1 expression, which will be identified in this proposal, is an alternative and better therapeutic option then targeting K-Ras itself: it will allow the selective inhibition of pro-tumorigenic K- Ras signaling while rescuing pro-senescent K-Ras pathways. This new information has the potential to directly impact the development of novel therapeutic interventions to prevent the progression to lung adenocarcinomas.