Pancreatic cancer is the fourth most common cause of
cancer death in the United States, and the aggressiveness of
pancreatic cancer is in part due to its intrinsic and extrinsic drug resistance characteristics, which are also associated with the acquisition of epithelial-to-mesenchymal transition (EMT). Emerging evidence also suggests that the processes of EMT are regulated by the expression status of many
microRNAs (
miRNA), which are believed to function as key regulators of various
biological and
pathologic processes during
tumor development and progression. In the present study, we compared the expression of
miRNAs between
gemcitabine-sensitive and
gemcitabine-resistant
pancreatic cancer cells and investigated whether the treatment of cells with "natural agents" [3,3'-
diindolylmethane (DIM) or
isoflavone] could affect the expression of
miRNAs. We found that the expression of miR-200b, miR-200c, let-7b, let-7c, let-7d, and let-7e was significantly down-regulated in
gemcitabine-resistant cells, which showed EMT characteristics such as elongated fibroblastoid morphology, lower expression of epithelial marker
E-cadherin, and higher expression of mesenchymal markers such as
vimentin and ZEB1. Moreover, we found that reexpression of miR-200 by transfection studies or treatment of
gemcitabine-resistant cells with either DIM or
isoflavone resulted in the down-regulation of ZEB1, slug, and
vimentin, which was consistent with morphologic reversal of EMT phenotype leading to epithelial morphology. These results provide experimental evidence, for the first time, that DIM and
isoflavone could function as
miRNA regulators leading to the reversal of EMT phenotype, which is likely to be important for designing novel
therapies for
pancreatic cancer.