ETS-Transcription Factor ETV1 Regulates Stromal Expansion and Metastasis in Pancreatic Cancer

Background & Aims The ETS-transcription factor ETV1 is involved in epithelial−mesenchymal transition during pancreatic development and is induced in mouse pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDAC). We investigated the function of ETV1 in stromal expansion of PDAC and metastasis, as well as its effects on a novel downstream target Sparc, which encodes a matricellular protein found in PDAC stroma that has been associated with invasiveness, metastasis and poor patient outcomes. Methods Pancreatic ductal cells were isolated from Pdx1Cre;Kras^G12D/+ mice (PanIN), Pdx1Cre;Kras^G12D/+;p53^fl/+ and Pdx1Cre;Kras^G12D/+;p53^fl/+;Rosa26^YFP mice (PDAC), and Pdx1Cre;Kras^G12D/+;p53^fl/+;Sparc^−/− mice. Cells were grown in 3-dimensional organoid culture to analyze morphology, proliferation, and invasion. Human PanIN and PDAC tissues were evaluated for ETV1 expression. Orthotopic pancreatic transplants of ETV1-overexpressing PDAC and respective control cells were performed. Results ETV1 expression was significantly increased in human PanINs and, even more so, in primary and metastatic PDAC. Analyses of mouse orthotopic xenografts revealed that ETV1 induced significantly larger primary tumors than controls, with significantly increased stromal expansion, ascites and metastases. In 3-dimensional organoids, ETV1 disrupted cyst architecture, induced EMT, and increased invasive capacity. Furthermore, we identified Sparc as a novel functional gene target of Etv1 by luciferase assays, and SPARC and ETV1 proteins co-localized in vivo. Disruption of Sparc abrogates the phenotype of stromal expansion and metastasis found with ETV1 overexpression in vivo. We identified hyaluronan synthase 2 (Has2) as another novel downstream factor of Etv1; that may mediate ETV1's significant expansion of hyaluronic acid in PDAC stroma. Conversely, disruption of Etv1 in PDAC mice (Pdx1Cre;Kras^G12D/+;p53^fl/+;Rosa26^YFP;Cre;Etv1^fl/fl) reduced levels of SPARC and hyaluronic acid in the stroma. Conclusions ETV1 is critical in the desmoplastic stromal expansion and metastatic progression of pancreatic cancer in mice, mediated functionally in part through Sparc and Has2.