| Objective: Lung cancer has the highest morbidity and mortality rates in the world,with the 5-year survival rate remaining about 15%-20%.Lung cancers are generally divided into two main categories: small cell lung cancer and non-small cell lung cancer(NSCLC).Lung adenocarcinoma(LUAD)is the most common subtype of NSCLC.Long non-coding RNAs(lncRNAs)are a class of functional molecules longer than 200 nucleotides.They cannot encode proteins,but they are capable of regulating gene expression,contributing to the occurrence and development of various tumors.lncRNA MYU(c-Myc-upregulated lncRNA)plays important roles in colon cancer and prostate cancer.However,its mechanisms in non-small cell lung cancer are still unclear.We aimed to investigate the function and possible mechanism of MYU in LUAD.Methods: Expression levels of LUAD clinical specimens from TCGA database were downloaded and analyzed;expression levels of MYU from 24 tumor specimens and 20 adjacent non-tumor(ANT)tissues of LUAD patients,as well as different LUAD cell lines and human normal bronchial epithelial cell line were detected and analyzed by quantitative real-time polymerase chain reaction assay.Expression levels of MYU and clinical correlation of LUAD were evaluated.Furthermore,MTT,colony formation assay,bromodeoxyuridine incorporation assay,wound-healing assay and flow cytometry were applied to study the effects of silencing or over-expressing of MYU on different biological processes,such as proliferation,migration,cell cycle progression,and apoptosis;Western blot was used to detect the modulation of MYU on c-Myc and its downstream key effector proteins.Finally,LUAD mouse model was used to study the effects of MYU knockdown on growth of tumor xenografts.Results: Results from TCGA database demonstrated that expression levels of MYU were significantly higher in LUAD tissues compared with ANT tissues;in our collected clinical specimens,expression levels of MYU were greatly increased in LUAD tissues compared with ANT tissues;at cell levels,expression levels of MYU were also significantly higher in LUAD cell lines PC9,A549 and HCC827 compared with human normal bronchial epithelial cell line.In PC9 and A549 cell lines,which with relative higher expression of MYU,knockdown of this gene significantly inhibited cell proliferation and migration capabilities,and induced cell cycle arrest and apoptosis;whereas in H1650 cell line,which with relative lower expression of MYU,overexpression of this gene significantly promoted cell proliferation and migration capabilities.When MYU was knocked down,protein levels of c-Myc and CDK6 was significantly down-regulated,while protein levels of p27 protein was significantly up-regulated.In vivo results from LUAD mouse model revealed that knockdown of MYU effectively inhibited the growth of tumor xenografts of PC9 in nude mice.Immunohistochemitry results showed that protein levels of c-Myc and CDK6 were decreased,while expression levels of p27 was increased,which were consistent with those results from in vitro Western blot experiments.Conclusion: Expression levels of MYU were significantly increased in TCGA and our collected clinical specimens of LUAD,as well as LUAD cell lines compared with ANT specimens and human normal bronchial epithelial cell line.Results from in vitro experiments showed that knockdown of MYU effectively inhibited proliferation and migration of lung adenocarcinoma cells,induced cell cycle arrest and promoted apoptosis,the function of which may highly correlate with c-Myc signaling pathway and its downstream effectors CDK6 and p27.Results from in vivo experiments indicated that knockdown of MYU effectively inhibited tumor growth of LUAD in nude mice.Collectively,our data combined with results from literatures suggest a positive regulatory loop which exists between MYU and c-Myc and results in higher expression of both genes to promote LUAD progression.Thus,silencing of MYU may serve as an effective therapy to inhibit tumor growth by targeting c-Myc signaling pathway for LUAD patients. |
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