Identification of Ppy-lineage cells as a novel origin of pancreatic ductal adenocarcinoma

The Ppy-gene encodes the pancreatic polypeptide (PP) secreted by PP- or - cells, an endocrine cell type located in the islet periphery. For a detailed characterization of PP cells, we aimed to establish PP cell lines. To this end, we generated Ppy-Cre;Rosa26-CAG-LSL-Large T mice, in which the SV40 large T antigen (TAg) is expressed in Ppy-expressing cells upon Cre-loxP-mediated recombination. Ppy-Cre;Rosa26-CAG-LSL-Large T mice, surprisingly, developed pancreatic ductal adenocarcinoma (PDAC) rapidly by 3 to 4 weeks of age, while mice with insulin2-Cre-mediated activation of TAg developed insulinomas. This suggests that PDACs could arise from the islet/endocrine cells, which is rather unexpected as PDACs are generally believed to originate from the pancreatic acinar or ductal cells. RNA-seq analysis of transformed Ppy-lineage cells in 7-day old islets showed downregulation of endocrine genes, upregulation of exocrine, ductal genes, and upregulation of PDAC-related genes and pathways, respectively. These results suggest that expression of an oncogene in Ppy-lineage cells leads to a fate switch in these endocrine precursors that causes them to adopt a PDAC cell fate. Our findings revealed that Ppy-lineage cells may be one of the origins of PDAC and provide novel insights into the heterogeneity in pathogenesis of pancreatic cancer and its personalized therapy. To determine the molecular characteristics and gene expression profile of Ppy-lineage lesion-forming cells, we performed RNA-seq and gene ontology analysis of Ppy-lineage cells with and without antigen activation using7-day oldreporter mice which express both tdTomato and TAg. We profiled total of 100 PpyCre/+; Rosa26tdTomato/+ (control) cells and 100 RTT (transformed) cells pooled from n=3 mice for each group using RNA-seq analysis.