Identification of cancer initiating cells in K-Ras driven lung adenocarcinoma

Ubiquitous expression of a resident K-RasG12V oncogene in adult mice revealed that most tissues are resistant to K-Ras oncogenic signals. Indeed, K-RasG12V expression only induced overt tumors in lungs. To identify these transformation-permissive cells, we induced K-RasG12V expression in a very limited number of adult lung cells (0.2%) and monitored their fate by X-Gal staining, a surrogate marker coexpressed with the K-Ras G12V oncoprotein. Four weeks later, 30% of these cells had proliferated to form small clusters. However, only SPC+ alveolar type II (ATII) cells were able to form hyperplastic lesions, some of which progressed to adenomas and adenocarcinomas. In contrast, induction of K-Ras G12V expression in lung cells by intratracheal infection with adenoviral-Cre particles generated hyperplasias in all regions except the proximal airways. Bronchiolar and bronchioalveolar duct junction hyperplasias were primarily made of CC10+ Clara cells. Some of them progressed to form benign adenomas. However, only alveolar hyperplasias, exclusively made up of SPC+ ATII cells, progressed to yield malignant adenocarcinomas. Adenoviral infection induced inflammatory infiltrates primarily made of T and B cells. This inflammatory response was essential for the development of K-RasG12V-driven bronchiolar hyperplasias and adenomas, but not for the generation of SPC+ ATII lesions. Finally, activation of K-RasG12V during embryonic development under the control of a Sca1 promoter yielded CC10+, but not SPC+, hyperplasias, and adenomas. These results, taken together, illustrate that different types of lung cells can generate benign lesions in response to K-Ras oncogenic signals. However, in adult mice, only SPC+ ATII cells were able to yield malignant adenocarcinomas.Work was supported by European Research Council Grant ERC-AG/250297-RAS AHEAD; EU-Framework Programme Grants LSHG-CT-2007-037665/CHEMORES, HEALTH-F2-2010-259770/LUNGTARGET, and HEALTH-010-260791/EUROCANPLATFORM; Spanish Ministry of Economy and Competitiveness Grant SAF2011-30173; Autonomous Community of Madrid S2011/BDM-2470/ONCOCYCLE (to M.B.); National Institutes of Health Grant R01 CA109335-04A1; Spanish Ministry of Economy and Competitivenes Grant SAF2012-32810; and EU-Framework Programme Grant FP7-ENV-2011/ARIMMORA (to I.S.-G.). S.M. was supported by a predoctoral fellowship from Fundación La Caixa.Peer Reviewe