Analysis of the tumor-initiating and metastatic capacity of PDX1-positive cells from the adult pancreas

Pancreatic cancer is one of the deadliest human malignancies. A striking feature of pancreatic cancer is that activating Kras mutations are found in similar to 90% of cases. However, apart from a restricted population of cells expressing pancreatic and duodenal homeobox 1 (PDX1), most pancreatic cells are refractory to Kras-driven transformation. In the present study, we sought to determine which subsets of PDX1+ cells may be responsible for tumor growth. Using the Lox-Stop-Lox-KrasG12D genetic mouse model of pancreatic carcinogenesis, we isolated a population of KrasG12D-expressing PDX1+ cells with an inherent capacity to metastasize. This population of cells bears the surface phenotype of EpCAM+CD24+CD44+CD133-SCA1- and is closer in its properties to stem-like cells than to more mature cell types. We further demonstrate that the tumorigenic capacity of PDX1+ cells is limited, becoming progressively lost as the cells acquire a mature phenotype. These data are consistent with the hypothesis that the adult pancreas harbors a dormant progenitor cell population that is capable of initiating tumor growth under conditions of oncogenic stimulation. We present evidence that constitutive activation of the mitogen-activated protein kinase (MAPK/ERK) signaling and stabilization of the MYC protein are the two main driving forces behind the development of pancreatic cancer cells with stem-cell-like properties and high metastatic potential. Our results suggest that pancreatic cells bearing Kras mutation can be induced to differentiate into quasi-normal cells with suppressed tumorigenicity by selective inhibition of the MAPK/ERK/MYC signaling cascade.