| Background and Objective:Breast cancer is the most commonly diagnosed malignancy and is the leading cause of cancer-related mortality among females worldwide.Although the morbidity of breast cancer in China is relatively lower than other country,but it has been increasing steadily in recent years,which seriously threatens the health and quality of life of women.At present,the main treatment for breast cancer is surgery and the adjuvant therapy includes chemotherapy,radiotherapy,endocrine therapy and molecular target therapy.Among these,molecular targeted therapy is the areas of research focus in oncotherapy and represents the future directions of oncology drug therapy.In the present,herceptin is the major therapeutic in molecular target therapy of breast cencer,which is a monoclonal antibody that interferes with the HER2/neu receptor.Evidence-based medicine has confirmed that herceptin combined with postoperative chemotherapy can significantly reduce the recurrence and metastasis of breast cancer.Triple-negative breast cancer(TNBC)is a subclass of breast cancer.It lacks ER,PR,and HER2 expression and accounts for about 10% to 17% of all breast cancers.Endocrine therapy and molecular target therapy are ineffective treatments for patients with TNBC and chemotherapy is the only systemic treatment.So it urgently needs to find a more reliable and effective molecular target in the present areas of molecular target therapy of breast caner.Non-coding RNAs(nc RNAs)is recently discovered RNA molecules that are transcribed by DNA but do not encode proteins.RNA profiling technologies have improved over the past few decades.Recent advances in high-throughput sequencing have facilitated the understanding of nc RNAs.In fact,it is estimated that approximately 2% of the total genomic sequence in humans is transcribed into protein-coding RNAs,with the remainder considered nc RNAs.Long nc RNAs(lnc RNAs)are a major subclass of nc RNAs ranging from 200 nt to >100kb in length and specific base pairing regions confer on lnc RNAs the ability to fold into complex secondary structures.They are initially regarded as a consequence of transcriptional noise and do not have biological function.Hower,researchers recently reveal that lnc RNAs play important roles in a repertoire of biological processes including cell differentiation,proliferation,apoptosis,and metabolism through controlling gene expression through different mechanisms,including DNA methylation,histone modification,chromatin remodeling,and gene silencing.Furthermore,dysregulated lnc RNA expression is associated with various human diseases,including cancer.At present,the researchers attempt to explore the role played by lnc RNAs in tumor progression.Emerging evidence indicates that aberrant expression of lnc RNAs play an important role in breast cancer development and progression.It is not only a result,but also an important actor.TUG1 is a 7561 bp lnc RNA that was originally identified as a transcript upregulated in response to taurine treatment in developing mouse retinal cells.Functional studies further revealed that knockdown of TUG1 inhibited mouse retinal development.Studies have shown that TUG1 exerts its biological function through binding to PRC2.PRC2 harbours methyltransferase activity and catalyses the methylation of H3K27 to repress gene expression.Knockdown of TUG1 improves the expression of more than 120 genes,most of which involve in the regulation of cell cycle.It is suggested that TUG1 may plays an important role in the regulation of cell proliferation.In addition,recent studies have found that TUG1 promoter contains many highly conserved p53 binding sites and that TUG1 was induced by p53.P53 is an important tumor suppressor in breast cancer,and its mutation is associated with the formation of tumor.Base on the above,it is speculated that TUG1 is aberrantly expressed in breast cancer and its dysregulation is associated with the development and progression of breast cancer.Therefore,this study aimed to determine the clinical significance and biological functions of TUG1 in breast cancer.Methods:To assess the putative clinical significance of TUG1 in breast cancer,we first tested to determine whether there was an aberrant expression of TUG1 in breast cancer and evidence of an association between TUG1 expression and clinicopathological characteristics of patients with breast cancer.Quantitative real-time polymerase chain reaction(q RT-PCR)was performed to measure TUG1 expression in cells from breast cancer cell lines and in 58 matched pairs of breast cancer and normal tissue samples from patients with clinicopathological comparisons.Gain-and loss-of-function experiments were performed in vitro to investigate the biological role of TUG1.We performed cell transfection and lentivirus infection to establish TUG1 overexpression and knockdown breast cancer cell model,and observe the cell proliferation and metastasis ability of breast cancer.CCK-8,colony formation,and Ed U assays were performed to detecte cell proliferation.Cell cycle and cell apoptosis were determined by flow cytometry.Cell invasion and migration ability were assessed by Transwell assay.To further explore the mechanism of TUG1 on breast cancer cell proliferation,we used western blot and q RT-PCR to measure the expression of the cell cycle regulators Cyclin D1 and CDK4,and a rescue experiment was performed to determine the influence of TUG1 on cell proliferation.Results:We found that TUG1 expression was downregulated in 91%(53/58)of breast cancer tissue samples compared to controls and TUG1 expression in cells from breast cancer cell lines was significantly decreased compared to that found in MCF-10 A cells.In addition,decreased TUG1 expression was significantly correlated with p53 mutation and lymph node metastasis.In vitro experiments revealed that TUG1 overexpression significantly suppressed cell proliferation by causing cell cycle arrest and inducing apoptosis in breast cancer cells,while TUG1 knockdown caused increased cell growth via promoting cell cycle progression and regulating the expression of Cyclin D1 and CDK4.Further functional assays indicated that TUG1 overexpression significantly promoted cell migration and invasion while TUG1 knockdown had the opposite effects.Western blot showed that Cyclin D1 and CDK4 levels were greatly increased in the TUG1 knockdown group compared to the control group.At the transcriptional level,Cyclin D1 and CDK4 expression was markedly increased with TUG1 knockdown.Rescue experiment indicated that knockdown of Cyclin D1 and CDK4 reversed the increased proliferation induced by TUG1 silencing.Conclusion:1.TUG1 expression is downregulated in breast cancer and decreased TUG1 expression is significantly correlated with p53 mutation and lymph node metastasis;2.TUG1 inhibits cell proliferation of breast cancer through suppressing the expression of cell cycle regulators Cyclin D1 and CDK4;3.TUG1 has a role in breast cancer cell migration and invasion;4.TUG1 acts as a tumor suppressor in breast cancer and may serve as a potential molecular target for therapy,which may have a role and provide a new method in the treatment of breast cancer. |
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