Pancreatic cancer is the fourth to fifth leading cause of cancer-related death in western societies with an average overall 5-year survival of less than 5% and a median survival period of less than 6 months . CSCs are a small subpopulation of cells capable of self-renewal and differentiation and have been identified in a variety of tumors. CSCs may be responsible for tumor initiation, progression, metastasis and resistance to therapy. The expression patterns of the stem cell surface markers CD44, CD24 and ESA in pancreatic adenocarcinoma cell lines are diverse and not all CSCs sorted from pancreatic adenocarcinoma cell lines develop cell spheres , PANC-1 is a common pancreatic adenocarcinoma cell line used for study of CSCs [28–32]. In this study, we sorted CD44+CD24+ESA+ CSCs in pancreatic adenocarcinoma cell line PANC-1. Stem cell features are controlled by a small group of transcription factors, like Nanog and Oct4 . Coexpression of Oct4 and Nanog is associated with pancreatic carcinogenesis and is negatively correlated with the survival prognosis of oral squamous cell carcinoma patients . Oct4 and Nanog induce cancer stem cell–like properties and have correlations with EMT . Our study also demonstrates that the expressions of Oct4 and Nanog were increased in CSCs of PANC-1.
Emerging evidence suggests the role of microRNA (miRNA) in many biological processes. Among many miRNAs, miR-200 family is known as tumor suppressor and they are usually down-regulated in some tumors including prostate cancer and the loss of expression of miR-200 family contributes to the acquisition of EMT phenotype and drug resistance. Down-regulation of miR-200 by siRNA technique has been shown to be associated with EMT phenotype while reexpression of miR-200 can result in the reversal of EMT phenotype. We determined the expression levels of miR-200a, miR-200b and miR-200c in CSCs of PANC-1 by real time RT-PCR. Among the family of miR-200, only miR-200a expression was dramatically decreased.
EMT induction in cancer cells results in the acquisition of invasive and metastatic properties. Recent reports indicate that the emergence of CSCs occurs in part as a result of EMT, for example, through cues from tumor stromal components. CSCs and EMT-type cells, which shares molecular characteristics with CSCs, have been believed to play critical roles in drug resistance and early cancer metastasis as demonstrated in several human malignancies including pancreatic cancer. Interestingly, recent studies have also shown that miR-200 family could regulate the processes of EMT by targeting E-box binding protein ZEB1 and ZEB2 . Thus, the discovery of molecular knowledge of drug resistance and metastasis in relation to miR-200 family, CSCs and EMT in pancreatic cancer are becoming an important area of research, and such knowledge is likely to be helpful in the discovery of newer drugs as well as designing novel therapeutic strategies for the treatment and/or prevention of pancreatic cancer with better outcome. E-cadherin, occludin and cytokeratin are downregulated during EMT, while N-cadherin, vimentin, fibronectin, SNAI1/SAIL, SNAI2/SLUG, ZEB2/SIP1, and TWIST1 are upregulated class switch from E-cadherin to Ncadherin results in the loss of epithelial phenotype and the acquisition of mesenchymal phenotype. Transcriptional repression of E-cadherin gene or functional repression of E-cadherin protein is the critical step for EMT. Upregulation of EMT regulators is associated with more malignant phenotypes in a variety of human cancer, such as gastric cancer, pancreatic cancer, breast cancer, and ovarian cancer . In the present study, miR-200a inhibits epithelial-mesenchymal transition by inhibiting the expression of vimentin, N-cadherin and ZEB1, and also retards CSCs migration and invasion. The inhibition of EMT markers by these agents suggests that they could inhibit early metastasis of pancreatic CSCs.
The EMT is an embryonic key developmental program that is often activated during cancer invasion and metastasis. It is a process by which cells undergo a morphological switch from the epithelial polarized phenotype to the mesenchymal fibroblastoid phenotype. Many signalling pathways have contributed to the induction of EMT, including TGFβ-1, Wnt, Hedgehog, Notch, and nuclear factor-kappa B (NF-kB) [38–42]. Kyoung-Ok Hong et al. have shown that activation of PI3K/Akt axis is one of the key mechanisms in the process of EMT and it seems that its inhibition by treatment with phosphatidylinositol ether lipid analogues (PIA) may regulate the reverse process MET leading to the re-expression of both E-cadherin and β-catenin, and reducing expression of vimentin, mesenchymal marker, in oral squamous lines carcinoma stabilized . Further stuty was needed to probe the signalling pathways participatived in MET of CSCs.