Study On MiRNA-134Impact Epithelial-mesenchymal Transition(EMT) Process Of Human Tumor Cell

Metastasis is a characteristic of malignant tumors, and is one of the leading causes of death of cancer patients. It has been found that the epithelial-mesenchymal transition (EMT) of tumor cells is the main reason for tumor metastasis. The characteristics of EMT include the loss of epithelial phenotype, the acquisition of mesenchymal phenotype, and the process of gaining the ability of migrating freely in the cell matrix for tumor cells. TGF-β is an important factor to induce EMT of tumor cells and TGF-β-induced EMT process has been used as a classical model for studying tumor cell invasion and metastasis in vitro.Acting as important regulatory factors of gene expression, miRNAs inhibit the translation of their target genes by binding to the3’untranslated region (3’UTR) of their target mRNAs through imperfect base-pairing to the mRNA sequences, called microRNA response elements (MREs). It is known that miRNAs play roles in the regulation of cell cycle, cell migration and invasion, cell anoikis, and apoptosis. The abnormal expression of miRNAs has been found in many types of tumors, suggesting that miRNAs might be used as potential prognostic markers of tumors. Among more than200human miRNAs found so far, miR-134is an adult brain-specific miRNA, which is involved in regulating the development of neurons. In this study, we have found that miR-134is expressed in epithelial cells but not in mesenchymal cells of human breast and lung cancer, implicating its roles in EMT of tumor cells.We have found that the expression levels of miR-134in epithelial cell line MCF-7are higher than that in mesenchymal cell line MDA-MB-231of human breast cancer. Similarly, the expression levels of miR-134in epithelial cell line A549are higher than that in mesenchymal cell line H1299of human lung cancer. Further studies have shown that the inhibition of miR-134enhances the migration ability of A549cells and the overexpression of miR-134blocks the migration of H1299cells. With the in vitro TGF-β-induced A549cell EMT model, we have found that the expression of miR-134decreases gradually during the EMT process. Furthermore, while the TGF-β treatment increases the migration of A549cells, the overexpression of miR-134inhibits the migration of the cells during TGF-β-induced EMT process. These results suggest that miR-134can maintain the epithelial phenotype of the tumor cells and block the cell migration.Belonging to the Forkhead Box (FOX) transcription factor family, FOXM1is involved in regulating many important physiological processes, such as cell proliferation and senescence, DNA damage repair, organogenesis. It also plays important roles in the pathological processes of tumorigenesis, tumor progression, invasion, and migration. It has been found that FOXM1is highly expressed in a variety of human tumors and the higher expression levels of FOXM1in tumors predict a worse prognosis of patients. Our study found that FOXM1is highly expressed in the mesenchymal cells of human breast and lung cancer and its expression is negatively correlated with the expression levels of miR-134. The clinical samples of patients with lung cancer are used to detect the expression levels of miR-134and FOXM1. We found that the expression levels of miR-134are higher in patient samples with no metastasis than that in metastasis samples, while the expression levels of FOXM1in the two groups are in contrast. Sequence analysis predicts that FOXM13’UTR contains a MRE for miR-134. Interestingly, overexpression of miR-134inhibits the upregulation of FOXM1protein during TGF-β-induced EMT process in A549cells. On the other hand, the maintained expression of FOXM1in A549cells counteracts the inhibitory role of the transfection of miR-134during the EMT process, allowing the cells transfected with miR-134to restore the migration ability and to express mesenchymal cell marker N-cadherin. These results suggest that miR-134prevents the EMT process through inhibiting translation of FOXM1mRNA in human lung cancer cells.In addition, we have also verified the inhibition of FOXM1expression by miR-134in different systems. During the human embryonic carcinoma cells NT2/D1differentiation induced by retinoic acid (RA), the expression levels of miR-134increase and the expression levels of FOXM1decline. We have confirmed that FOXM13’UTR mediates the repression of FOXM1expression during RA-induced differentiation. Overexpression of miR-134represses the expression of FOXM1protein but not mRNA. The results suggest that the miR-134attenuates the expression of FOXM1during pluripotent NT2/D1embryonal carcinoma cell differentiationTogether, this study provides new clues to better understand the mechanism of miRNAs in tumor metastasis and establishes the roles of miR-134during EMT process of human tumor cell. We have determined that miR-134involves in maintaining the epithelial phenotype of tumor cells and inhibits the migration ability of the cells. Furthermore, we have proved that the miR-134is able to block the tumor cell EMT process by negatively regulating the translation of FOXM1through targeting the FOXM13’UTR.