Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease with a 5 year-survival rate of approximately 6%. Despite recent efforts in developing novel therapies, chemotherapy remains the standard of care for advance pancreatic cancer patients. MicroRNAs (miRNAs) are short non-coding RNAs that act as post-transcriptional negative regulators of gene expression. Our laboratory is interested in investigating how miRNAs dysregulation contribute to PDAC tumourigenesis. One of the major signalling pathways that drives tumourigenesis in PDAC is the TGF-β pathway. This pathway promotes epithelial-to-mesenchymal transition (EMT), metastasis and stemness. In this study we aimed to find out whether miRNAs were involved in the TGF-β response, as this was yet largely unknown. We used miRNA expression profiling and identified miRNAs regulated by TGF-β. We then focused on the top two miRNAs upregulated by TGF-β and characterized their role in PDAC. We used several strategies to inhibit the function of these miRNAs, including the genome editing approach CRISPR. With these systems we showed that silencing of these miRNAs impaired EMT, motility, stemness in vitro and tumourigenesis and metastasis in vivo. Furthermore, we identified globally the targets of these miRNAs by integrating AGO2-RIP sequencing with RNA-sequencing upon overexpression of the miRNA of interest. We found that the candidate miRNA targets significantly overlap and mainly inhibit p53 and cell to cell junctions’ pathways, which are all important in PDAC progression. We also showed that the candidate miRNAs were up-regulated in PDAC patient samples, and their specific tumoral expression strongly correlated with reduced overall survival and disease-free survival. These findings demonstrate a fundamental role of miRNAs within the TGF-β response and represent potential novel targets for therapeutic intervention in PDAC.
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