The Regulation Of Transcription Factor FOXA2 In The Process Of Epithelial-mesenchymal Transition In Breast Cancer Cells

Epithelial-mesenchymal transition is an intricate process in which epithelial cells lose the epithelial characteristics. The cells lose their polarity and specialized cell-cell contacts, and acquire a mesenchymal-like phenotype and the ability of migratory, allowing them to move from the epithelial cell community to the cell matrix surrounding, and then to the remote locations. EMT plays an important role in embryo development and organ differentiation. Recent research also showed that EMT works in the progression of carcinoma and fibrosis of the tissues and organ. The prophase of breast cancer metastasis caused by EMT is a big challenge in the clinical treatment of the maliganant tumor. Many genes significantly change in their gene expression during EMT. To study gene regulatory mechanisms of certain transcription factors during the EMT of breast cancer cells will help us to understand the the metastasis of this tumor and to design new therapeutic strategies to treat this disease.In this study, we investigated the function of FOXA2 in the EMT process of breast cancer. The transcription factor FOXA2 is one of the Forkhead box family members and is required for embryonic development and for normal functions of multiple adult tissues, in which the maintained expression of FOXA2 is usually related to preventing the progression of malignant transformation. Our data have confirmed that FOXA2 is one of the key factors preventing EMT of breast cancer cells. So, we focused on the role of FOXA2 in the regulation of the EMT in breast cancer. Based on the data of the clinic breast cancer samples, we studied the stimulation of E-type genes and repression of M-type genes caused by FOXA2 in breast cell lines MCF-7(epithelial type) and MDA-MB-231(mesenchymal type), which was confirmed in vivo at last. We got results as follows:First, we measured the m RNA and protein levels of FOXA2 in the clinic breast cancer samples, and also in epithelial-type breast cancer cell line MCF-7 and mesenchymal-type breast cancer cell line MDA-MB-231. We found that the expression of FOXA2 were associated with EMT markers. The similar results were observed in the EGF-induced EMT in MCF-10 A breast cancer cells.To test whether FOXA2 is required for the epithelial phenotype of breast cancer cells, we repressed the FOXA2 in MCF-7 cells with si RNA, which enhanced the cell migration, decreased m RNA and protein of epithelial-related E-cadherin and increased m RNA and protein of mesenchymal-related Vimentin. We also infected MDA-MB-231 cells with a lentiviral expressing FOXA2 to get the MDA-MB-231 cell clones stably expressing FOXA2, which showed mesenchymal phenotype. All the reults indicated that FOXA2 was required for maintaining the epithelial characteristic of breast cancer cells and was able to prevent the EMT process.We also have found that FOXA2 bound to the promoter of E-cadherin for positive regulation and the promotor of ZEB2 for negative regulation. It has been indicated that FOXA can interact with the transcriptional co-repressor Grg3/TLE3. By assaying both of the m RNA and protein levels, we found that TLE3 expression was correlated with the expression of FOXA2 and the epithelial characteristic. Though Ch IP and Co-IP expreiments, we confirmed that FOXA2 and TLE3 bound together to the upsteam region of ZEB2 gene.At last, to determine the effect of FOXA2 on metastasis of breast cancer cells in vivo, we generated metastasis model in nude mice via tail vein injection of lentivirus-infected FOXA2-expressing MDA-MB-231 cells, which showed the prevention of the metastasis of breast cancer cells to lung.