Pancreatic ductal adenocarcinoma (PDAC) is the most aggressive human malignancy and intrinsically resistant to conventional therapies. YAP1, as a key downstream effector of the Hippo pathway, plays an important role in tumorigenesis including PDAC. Alternative mRNA splicing of YAP1 results in at least 8 protein isoforms, which are divided into two subgroups (YAP1-1 and YAP1-2) based on the presence of either a single or double WW domains. We investigated the functions and regulatory mechanisms of YAP1-1 and YAP1-2 in PDAC cells induced by TGF-β to undergo epithelial-to-mesenchymal transition (EMT). CRISPR-Cas9 and shRNA were used to silence YAP1 expression in pancreatic cancer cells. Re-constituted lentivirus mediated overexpression of each single YAP1 isoform was generated in the parental knockout L3.6 cells. EMT was induced by treatment with TGF-β, EGF and bFGF in parental and the constructed stable cell lines. Western blot and qPCR were used to detect the expression of EMT markers. Scratch wound healing and transwell assays were used to detect cell migration. The stability and subcellular localization of YAP1 proteins were determined by Western blot analysis, immunofluorescence, as well as ubiquitination assays. We showed that TGF-β, EGF and bFGF all significantly promoted EMT in PDAC cells, which was inhibited by knockdown of YAP1 expression. Interestingly, YAP1-1 stable cells exhibited a stronger migratory ability than YAP1-2 cells under normal culture condition. However, upon TGF-β treatment, L3.6-YAP1-2 cells exhibited a stronger migratory ability than L3.6-YAP1-1 cells. Mechanistically, TGF-β treatment preferentially stabilizes YAP1-2 and enhances its nuclear localization. Furthermore, TGF-β-induced EMT and YAP1-2 activity were both blocked by inhibition of AKT signaling. Our results showed that both YAP1-1 and YAP1-2 isoforms are important mediators in the EMT process of pancreatic cancer. However, YAP1-2 is more important in mediating TGF-β-induced EMT, which requires AKT signaling.

ABSTRACT. Pancreatic ductal adenocarcinoma (PDAC) is characterized by a poor prognosis and high mortality rate. In this study, we investigated the expression of Rab23 in non-tumor pancreatic tissues and PDACs via immunohistochemistry. Rab23 was found in 39 of 58 (67.2%) and in 11 of 30 (36.7%) of the PDAC and non-tumor pancreatic tissue samples (P = 0.0073), respectively. There were significant correlations between Rab23 expression and unfavorable variables, including cancer differentiation level (P = 0.0089), lymph nodal (P = 0.0099), and distant metastases (P = 0.0173). Inactivation with small interfering RNA against Rab23 in the human pancreatic cancer cell line Panc-1 inhibited the migration and invasive potential of the cells. Our data provide new insight into the essential role of Rab23 in PDAC invasion and metastasis and suggest that Rab23 expression is a useful indicator of metastatic potential; hence, it may be a new therapeutic target for this common malignancy.

Non-small cell lung cancer (NSCLC) accounts for over 80% of all cases of lung cancer, a leading cause of cancer-related death worldwide. NSCLC patients frequently harbour activating mutations in the epidermal growth factor receptor (EGFR) gene, particularly in the first four exons (exons 18-21) of the EGFR tyrosine kinase domain, which is strikingly high in East Asian populations. 1 EGFR signalling plays a pivotal role in cellular proliferation, survival and metastatic progression, as well as chemoresistance. 2