Reseach On The Role Of MiR-139-5p Regulated By EZH2 In The Metastasis And Chemoresistance Of Colorectal Cancer

Backgroud:Epigenetic alterations such as DNA CpG island methylation, No-coding RNA, Histone modification and chromatin remodeling have been proved to be critical in the carcinogensis and progression of colorectal cancer.miR-139-5p is a novel down-regulated MicroRNA in colorectal cancer, its prognostic value need to be validated in large clinical tissue specimen. The effect of miR-139-5p on metastasis and chemoresistance of colorectal cancer remains unknown. EZH2 was frequently over-expressed in a variety kinds of tumors including colorectal cancer, and was closely associated with aggressiveness and clinical outcomes of colorectal cancer. EZH2 represses the transcription of multiple target genes including MicroRNAs, through histone methylation.Methods:Expression level of miR-139-5p was determined in 115 coloractal cancer tissue and 51 paired adjacent nontumorous tissue by TaqMan MicroRNA Assay. The association of miR-139-5 and clinical outcomes of colorectal cancer was analyzed. The biological function of miR-139-5p including cell proliferation, migration/invasion, cell cycle and apoptosis were investigated in vitro. The alteration of epithelial-mesenchymal transition and chemosensiticity of cancer cell with ectopic over-expression of miR-139-5p were detected. Novel target gene of miR-139-5p were predicted by bioinformatics and fully proved in molecular level, cell level and tissue level to further underline the mechanismof miR-139-5p in metastasis and chemoresistance. RNA interference and chromatin inmmunoprecipitation were used to investigate the regulation role of EZH2 on miR-139-5p.Results:Lower level of miR-139-5p was measured in 51 colorectal cancer tissue compare to paired adjacent nontumorous tissue. In stage Ⅱ and Ⅲ disease, higher expression of miR-139-5p was associated with inferior DFS and OS. Furthermore, miR-139-5p was proved to be an independent negative prognostic factor for DFS in multivariate survival analysis. Ectopic expression of miR-139-5p in colorectal cancer cell showed no significant effect on proliferation, cell cycle and apoptosis, but decreased the migration and invasion potential dramatically. ZEB1 and BCL2 was novel target gene of miR-139-5p as proved by luciferase. miR-139-5p represses epithelial-mesenchymal transition by targeting ZEB1 which is a critical transcriptional factor in the metastatic initialization. Ectopic expression of miR-139-5p sensitized cancer cells to 5-fluorouracil and oxaliplatin mediated cell apoptosis through targeting BCL2. miR-139-5p is down-regulated in colorectal cancer by EZH2 mediated H3K27me3. The expression level of miR-139-5p, target gene BCL2, ZEB1 and upstream regulator EZH2 were correlated in colorectal tissue. Conclusion:Down-regulated miR-139-5p by EZH2 through H3K27me3 demonstrated multiple tumor-suppressive functions of inhibiting metastatic initialization and chemoresistance by restoring target oncogenic genes:ZEB1 and BCL2, invoving epithelial-mesenchymal transition and chemoagents mediated apoptosis.