Die epithelial-mesenchymale Transition in der Metastasierung des duktalen Adenokarzinoms des Pankreas Epithelial to mesenchymal transition in the metastatic process of pancreatic ductal adenocarcinoma

Introduction: Epithelial to mesenchymal transition (EMT) is recognized as a key process during tumor invasion and metastasis. During EMT, tumor cells of epithelial origin undergo a series of changes such as loss of cell-cell adhesion and acquisition of motility. However, it has been observed that cells having undergone EMT do not form metastases and that metastases retain the original epithelial phenotype devoid of EMT characteristics. This study investigates the phenotype of the primary tumor and its metastases for pancreatic ductal adenocarcinoma (PDAC). Methods: Using 4 PDAC cell lines in an orthotopic mouse model for PDAC, we collected tissue from primary tumors and lymph node metastases. mRNA and miRNA expression profiles were determined by micro array for both sample types and expression of relevant genes was validated by quantitative RT-PCR. Staining for ECAD and β-Catenin was performed by immune histochemistry and histological appearance of primary tumors and metastatic lesions was graded by a pathologist. Statistical analysis was performed using SPSS 16.0 and GeneSpring 7.3.1 (t-test, Bonferroni Correction). Results: Key EMT suppressing miRNAs were significantly upregulated (let-7-family (P < 0.001)) and non differentially regulated (miR-200 family (P = 0.64)) in metastatic lesions vs. primary tumors. Expression of connected EMT relevant mRNAs was not significantly different between tissues (ECAD, HMGA2, ZEB1). Histologically, primary tumors displayed epithelial differentiation in central areas with typical ECAD and β-Catenin distribution while showing a mesenchymal phenotype at the invasive front. Metastases presented an epithelial phenotype. Discussion: Our results support the thesis that only cells with an epithelial differentiation are able to successfully form metastases. Whether these cells undergo a reversal of EMT and regain their original epithelial phenotype or whether non EMT cells are able to invade the bloodstream and colonize distant sites remains unclear and is the focus of current research. Einleitung Der Vorgang der epithelial mesenchymalen Transition (EMT) erlaubt es polarisierten, epithelialen Zellen durch Veranderungen in Genexpression und Proteinlokalisation einen mesenchymalen Phanotyp anzunehmen, der erhohte Migrationsfahigkeit und Invasivitat, erhohte Apoptoseresistenz und erhohte Produktion von Komponenten der extrazellularen Matrix besitzt [1]. Die EMT hat physiologische Bedeutung in der Embryogenese (EMT Typ I), der Regeneration von Organen und der Wundheilung (EMT Typ II) und gilt als zentraler Mechanismus in der Entwicklung und Aussaat epithelialer Tumoren (EMT Typ III) [2]. Die verschiedenen Faktoren, die eine Zelle zum Durchlaufen einer EMT befahigen werden als Nachweis des Vorgangs genutzt. Beispiele solcher Proteine sind CDH1, β-Catenin, ZEB1 und HMGA2 deren Expression teilweise durch miRNAs wie die miRNA-200- und miRNA-let-7-Familie reguliert wird. Diese mRNAs und miRNAs wurden als EMT-Marker in dieser Studie eingesetzt.