The Relationship Of MiR-17 Expression In Breast Cancer Between Clinical Features And The Effection Of MiR-17 On Biological Characteristics Of Breast Cancer

BACKGROUNDIn China,breast cancer has become one of the highest incidence malignant tumors in women.with differences among tumors that are driven by multiple genetic/epigenetic alterations and molecular events.Despite the improved prognosis of breast cancer patients because of early diagnosis,radical surgery and the development of adjuvant therapy,breast cancer remains the most common type of cancer among women.Prognostic factors that are frequently used for making clinical decisions in breast cancer are age,tumor size,status of lymph nodes,histological types of the tumor,pathological grade,and hormone receptor status.However,more biomarkers are needed for therapy and prediction of outcome because human breast cancers are diverse in their genetic nature and their response to therapy.Therefore,a better understanding of the genetic and molecular characteristics of breast cancer is urgently needed for early diagnosis,choice of the appropriate treatment and an improved prognosis for patients with breast cancer.MicroRNAs(miRNAs)are small noncoding endogenous RNA of 20-25 nucleotides that negatively regulate expression of target genes at the posttranscriptional level through mRNA degradation and translational repression.Numerous studies have demonstrated that aberrantly expressed miRNAs are involved in diverse diseases,including cancer,some miRNAs act as tumor suppressors or oncogenes and play critical roles in many aspects of breast cancer carcinogenesis including cell proliferation,differentiation,metastasis,and angiogenesis.there is growing recognition of the possibility of miRNAs as biomarkers for cancer diagnosis,prognosis and prediction of treatment response.Recently,miR-17 has been shown to play a significant role in the pathogenesis of various cancers,however,little is known about the associated between the level of miR-17 expression and the tumorigenesis and development of breast cancer.OBJECTIVEMicroRNAs(miRNAs)have been shown to be involved in the initiation and progression of cancers in the literature.In this study,we aimed to evaluate the clinicopathological role of miR-17 in breast cancer.METHODSWe have collected 132 patients with breast cancer from Changzhou No 2 People's Hospital Affiliated to Nanjing Medical University.The expression of miR-17 was measured in breast cancer tissues and paired adjacent normal tissues by using real-time quantitative polymerase chain reaction.We compared the expression of miR-17 in cancer tissues with which in adjacent normal tissues,and we analyze the expression of miR-17 with different pathological stages of breast cancer.We also investigated the association between the expression of miR-17 and clinicopathological characteristics,such as age,cyclooxygenase-2,CD44,epidermal growth factor receptor,progesterone receptor,P-glycoprotein status,and lymph node metastasis.Then,we calculated the Overall survival as the time from the date of surgery resection to the date of last contact or death.Survival analyses were performed using the Kaplan-Meier method and the log-rank test.We hypothesized that miR-17 may act as oncogenes in breast cancer.To validate this hypothesis,we detected miR-17 expression in the breast cancer cell lines MCF-7,MDA-MB-435S,and MDA-MB-231,and then compared the expression of miR-17 in cancer cell lines with MCF10A cells.To investigate the role of miR-17 in the regulation of breast cancer cells.we transfected MCF-7 and MDA-MB-231 cells with miR-17 mimics or an inhibitor.and the cells were subjected to MTT assay.In addition to cell proliferation,we also investigated the role of miR-17 on cell cycle progression.Cell cycle profile was examined by flow cytometry with propidium iodide staining,and the cell numbers were counted according to the DNA content of G0/G1,S,and G2/M phases.To measure the effect of miR-17 on tumor growth in vivo,exnograft tumor model assay in nude mice were used.All animal experiments in this study were approved by the ethics committee of Nanjing Medical University,and the guidelines of National Animal Care and Use Committee were followed.Twenty mice were randomly divided into two groups,and each mouse was injected subcutaneously with 1×108 cells.The agomiR-17 expression constructs were generated by GenePharma,and miR-17 expression was confirmed by quantitative reverse transcription(qRT)-PCR.The tumor volume(mm3)was measured every 7 days and was calculated using the following formula:volume = width × width × height/2.The animals were sacrificed 42 days after seeding the tumor cells.All tumor grafts were excised,weighed,and harvested.RESULTSThe expression of miR-17 was significantly increased in cancer tissues compared with adjacent normal tissues(p<0.0001,n=40).In addition,the expression of miR-17 was higher in tumors with pathological stages(Stage1 and Stage 2,p=0.5612;Stagel and Stage3,P<0.05;Stage1 and Stage 4,p<0.05).The data showed that the expression of miR-17 differed significantly according to estrogen receptor status(p<0.05)and human epidermal growth factor receptor 2 status(p<0.05),no difference was found between miR-17 expression and other clinical features,such as age,cyclooxygenase-2,CD44,epidermal growth factor receptor,progesterone receptor,P-glycoprotein status,and lymph node metastasis.Breast cancer patients with a low expression of miR-17 had a significantly longer survival time compared with those with a high expression of miR-17(p=0.0044,p<0.05,n=36).the expression of miR-17 was significantly higher in cancer cell lines compared with MCF10A cells.miR-17 mimics promoted miR-17 expression and miR-17 inhibitor inhibited miR-17 expression in breast cancer cells.miR-17 mimics induced breast cancer cell proliferation.In contrast,miR-17 inhibitor suppressed cell proliferation in breast cancer cells.In addition to cell proliferation,we also found that miR-17 inhibitor arrested cell cycle in S phases.With the experiment in vivo,we observed faster tumor growth in the agomiR-17 group compared with the control group.The average weight of tumors from the two groups was significantly different.These results showed that overexpression of miR-17 induced tumor growth in vivo.Conclusion:This study analyzed the association between miR-17 and the prognosis of breast cancer.We found that miR-17 was upregulated in breast cancer tissues and induced breast cancer cell proliferation.We provided evidence to verify that breast cancer patients with a low expression of miR-17 had a significantly longer survival time.These findings suggested that miR-17 might be a novel prognostic indicator and a potential target for diagnosis and gene therapy in breast cancer.