Study On The Expression Of Let-7a And MiR-21 In Breast Cancer And Their Role In Breast Cancer Cells

Objective:MicroRNA(miRNA) are small, endogenous noncoding RNA that regulate a variety of biological processes, such as cell differentiation, proliferation, and survival. Recent studies suggested that abnormal expression of miRNA was present in a variety of cancers and played critical roles in cancer initiation, progression, and chemoresistance, including let-7a and miR-21.In this study, firstly we investigated the different expression of let-7a and miR-21 in breast cancer tissues and adjacent tissues to find new markers for the diagnosis of breast cancer. Then we Changed the expression of let-7a and miR-21 in breast cancer cells to analyze their effect on breast cancer cells and elucidate their application value in diagnosis and treatment of breast cancer by detecting changes in cell biological characteristics and the influence of the expression of target genes.Methods:(1)30 human fresh breast cancer tissues and adjacent tissues (more than 5 cm distance from neoplastci foci) were collected during the operation and conserved in the -80℃ low temperature refrigerator.(2)The expression of let-7a and miR-21 of breast cancer and adjacent tissue were detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction, respectively. The expression differences of them were analyzed by statistical method.(3)The breast cancer cells MCF-7 and MDA-MB-231 were transfected with let-7a and miR-21 mimics or let-7a and miR-21 inhibitor by Lipofectamin, respectively. The biological characteristics changes of cell proliferation and migration ability were evaluated in transfected cells.(4)The possible target genes of let-7a and miR-21 were forecasted by bioinformatics tools. The level of high mobility group protein Al(HMGAl) and Signal Transducer and Activator of Transcription3 (STAT3) were detected in the breast cancer cells MCF-7 and MDA-MB-231 transfected with let-7a and miR-21 mimics or let-7a and miR-21 inhibitor by western blot, to determin targeted regulation relationship of let-7a vs HMGA1 and miR-21 vs STAT3.Results:(1)The expression of let-7a in breast cancer tissue was evident lower than in adjacent tissue (P<0.001), and the expression of miR-21 in breast cancer tissue was outstanding higher than in adjacent tissue (P<0.05) by real-time fluorescent quantitative PCR.(2)MTT cell proliferation assay, colony formation assay, wound-healing assay, transwell migration assay showed that, comparing with mimics negative control (mimics NC) groups or inhibitor negative control (inhibitor NC) groups, respectively, there was a significant reduction of proliferation capacity, colony formation capacity, migration capacity in the breast cancer cells MCF-7 and MDA-MB-231 transfected with let-7a mimics and miR-21 inhibitor, there was a significant enhancement of proliferation capacity, colony formation capacity, migration capacity in cells transfected with let-7a inhibitor and miR-21 mimics. Each group was statistically significant by the statistical analysis(P<0.05).(3)The potential target genes of let-7 and miR-21 were predicted by bioinformatics methods, and the expression of proteins was detected by western blot, respectively.The expression of HMGA1 was decreased in the breast cancer cells MCF-7 and MDA-MB-231 transfected with let-7a mimics; the expression of HMGA1 was increased in the cells transfected with let-7 a inhibitor; the expression of STAT3 was decreased in the breast cancer cells MCF-7 and MDA-MB-231 transfected with miR-21 mimics; the expression of STAT3 was increased in the cells transfected with miR-21 inhibitor.Conclusions:(1)Low expression of let-7a and high expression of miR-21 in breast cancer tissue indicated that they played an important role in the development of breast cancer. They can be used as one of the indicators in distinguishing benign and malignant.(2)Let-7a negatively regulated the proliferation and migration of the breast cancer cells MCF-7 and MDA-MB-231, and miR-21 positively regulated the proliferation and migration of the breast cancer cells MCF-7 and MDA-MB-231.(3)Let-7a regulated the breast cancer cells MCF-7 and MDA-MB-231 through targeting of HMGA1, miR-21 regulated the breast cancer cells MCF-7 and MDA-MB-231 through targeting of STAT3...