Enhancer Of Zeste Homolog 2 Epigenetically Promotes Cell Proliferation And Migration Of Breast Cancer By Targeting MiR-125b

Background: Breast cancer is the most common cancer for female and have a strong impact on the health of female. EZH2(Enhancer of Zeste Homolog 2) is a kind of human homolog from enhancer element of zeste gene in fruit fly, and core component of PRC2(polycomb repressor complex 2) which is a kind of compound with the inside enzyme activity of histone methyltransferase. Recently, the research result of epigenetics shows EZH2 is commonly related to the harmful progress of breast cancer. MiRNA is a kind of non-coding RNA which keep mRNA-- silent at post transcriptional level. The dysregulation is very common in the course of occurrence and development of various diseases including breast cancer. Objective: This study was to conducted to explore the relationship between EZH2 and miR-125 b in breast cancer, and preliminarily explore the interactive relationship between EZH2 and miR-125 b and their roles for the course of proliferation and migration in breast cancer cell. Methods: 1. Immunohistochemical and Western blot are used to respectively verify the EZH2 expression level differentiation between breast cancer tissue, cells and normal tissue, cells. Then the mRNA expression level tendency in some different breast cell lines were tested by use of real-time PCR. 2. After targeted restrained siRNA-EZH2 was transfecting to different breast carcinoma cell lines, then relative transcript level of miR-125 b was tested by use of real-time PCR. Then transfect EZH2 palsmid to non-oncogenicity mammary epithelial cell lines, and test relative transcript level of miR-125 by use of real-time PCR after overexpression of EZH2. 3. siRNA-EZH2 and mi R-125binhibitor( chemical modification inhibitor aimed at specific miR-125 b in the cells) were divided into groups and were cotransfected to MDA-MB-231 cells. Changed circumstances of cell proliferation in different treatment groups were tested by use of MTT assay, and transformation of cell migration ability was tested by transwell assay. 4. EZH2 plasmid and miR-125bmimics(compounded in chemosynthetic method, which can strengthen miR-125 b of simulated living body endogenesis with endogenous function of miR-125b)were divided into groups and were cotransfected to HMEC cells. Changed circumstances of cell proliferation in different treatment groups were tested by use of MTT assay, and transformation of cell migration ability was tested by transwell assay. Result: 1. EZH2 expression level in breast cells or tissue is apparently higher than that in nononcogenicity mammary epithelial cells or tissue, and the mi R-125 b level in the breast carcinoma cell lines is apparently lower than that in non- oncogenicity mammary epithelial cells. 2. After the test, miR-125 b levels in the different breast carcinoma cell lines of transfecting siRNA-EZH2 in varying degrees; and miR-125 b level in non- oncogenicity mammary epithelial cells of transfecting EZH2 plasmid dramatically declined. 3. In the MDA-MB-231 cell line, MTT testing result showed that cell reproductive capacity dramatically declined after transfecting siRNA-EZH2, correspondingly transwell experiment result also showed that cell metastasis ability declined dramatically; however the cell reproductive capacity in inhibitor groups of cotransfecting siRNA-EZH2 and miR-125 b dramatically improved than that in the groups of transfecting siRNA-EZH2, so did the cell metastasis ability. 4. In the HMEC cell line, MTT testing result showed that the cell reproductive capacity in the groups of transfecting EZH2 plasmid dramatically improved than that in the control group; howerver cell reproductive capacity in the groups of cotransfecting EZH2 plasmid and miR-125 bmimics remarkably inhibited than that in the group of transfecting EZH2 plasmid. Conclusion: The results showed that the decline of cell proliferation activity and transfer ability caused by lower EZH2 would be likely to be closely related to increasing expression of miR-125 b caused by lower EZH2; and the promotion of cell proliferation activity caused by overexpression of EZH2 would be likely to be closely related to down-regulated expression of miR-125 b caused by overexpression of EZH2. EZH2 maybe targetedly improve proliferation and migration of breast cancer cell, which will provide a new understanding for molecular mechanism of breast cancer metastasis, and maybe provide new research direction for biological targeted therapy.