Lower miR-340 expression predicts poor prognosis of non-small cell lung cancer and promotes cell proliferation by targeting CDK4.

Aberrantly microRNAs (miRs) expression is reported to be involved in tumorigenesis and development in non-small cell lung cancer (NSCLC). MiR-340 had been identified to be downregulated in NSCLC in the previous study. However, the underlying mechanisms of miR-340 involved in NSCLC progression still needed to be well known. In the present study, we confirmed that miR-340 expression was notably down-regulated in NSCLC tissues compared to matched adjacent noncancerous lung tissues by quantitative real time PCR (qRT-PCR) analyses. Lower miR-340 expression positively related to lymph node metastasis, larger tumor size, advanced TNM stage and poor prognosis of NSCLC patients. In vitro assays, we demonstrated that upregulation of miR-340 expression suppressed cell proliferation ability. Bioinformatics analysis and luciferase reporter assays revealed that miR-340 directly targeted the 3'-untranslated (3'UTR) region of CDK4 mRNA. Over-expression of miR-340 suppressed cell proliferation by regulating CDK4 expression in NSCLC cells. Additionally, we showed that increased miR-340 expression promoted the expression of cell proliferation related protein CDK6 expression, but decreasing the P15 and P21 expression. In vivo, we verified that miR-340 overexpression also inhibited tumor growth by regulating CDK4 expression. Therefore, these findings revealed miR-340 functions as a tumor suppressor in NSCLC cells and may provide a potential target of NSCLC treatment.