MicroRNA-34b Functions As A Tumor Suppressor And Acts As A Nodal Point In The Feedback Loop With Met

MicroRNAs(miRNAs) are a class of endogenous occurring small noncoding RNAs (approximately21-25nucleotides in length), which are derived from longer transcripts termed pri-miRNAs and pre-miRNAs. MiRNAs combine target mRNAs through partial complementarity to specific sequences located in the3’ untranslated region(3’-UTR) and act as post-transcriptional regulators of gene expression. It has been shown that human miRNA genes regions along with perturbed miRNA expression patterns have been detected in many human benign and malignant cancers. Therefore, it pocesses potential importance to elucidate the biological functions of miRNAs.Additionally, miRNAs have been shown to play important roles in invasion and metastasis of cancer as well. For example, miR-155may take part in the TGF-β-induced epithelial-mesenchymal transition(EMT) and in cell migration and invasion through targeting of the RhoA transcript. MiR-21possesses the possibility to stimulate cell invasion and metastasis in more than one tumor models, including breast cancer, colon cancer, and glioma. The pro-metastatic transcription factor TWIST1could activate miR-10b, which is essential for TWIST1-induced EMT involved in promotion of cell motility and invasiveness. Tumor invasion and metastasis are the critical indicators that define the prognosis of cancer patients. Therefore, it is very important to understand the specific roles of miRNAs in cancer progression, and it could lead to the identification of predictive markers and the development of novel therapeutic strategies for patients with metastases.Purpose:miRNAs, as a class of naturally occurring small noncoding RNAs, play profound and pervasive roles in cancer initiation and progression. Extensive decreases in miRNAs levels are frequently observed in human cancers, indicating that miRNAs may function intrinsically in tumor suppression. However, the underline mechanisms of miRNAs interactions with cellular pathways are little known. The aim of this study is to determine the role of miR-34b in the non-small cell lung cancer. In our study, the expression level of miR-34b was significantly decreased in NSCLC tissues in comparison with pericarcinous tissues of lung cancer. In vitro gain-of-function experiments indicated that miR-34b functioned as a tumor suppressor and inhibited cell proliferations by inducing cell apoptosis. After that, we analyzed the relations between miR-34b and Met and relevant proteins using IHC technology. These results suggest a miR-34b/Met axis with potential therapeutic implications.Methods:MiR-34b in non-small cell lung cancer(NSCLC) tissues was detected using quantitative Real-Time PCR. The relations between miR-34b expression level and pathological stage or lymph node metastasis were assessed using the Spearman correlation test. For in vitro studies, lung cancer cells were transfected with double stranded synthetic miRNA mimics (syn-hsa-miR-34b miScript miRNA) and scrambled controls. Immunohistochemistry technology was explored to validate the related downstream proteins of miR-34b.For qRT-PCR data, the statistical analysis of miR-34b expression level in NSCLC tissues and PTLC tissues were Iog2transformed. Values are expressed as the mean±SEM. Differences in miR-34b between NSCLC and PTLC were analyzed using two-sample t-test. Pearson Chi-Square and Fisher’s exact tests were used to determine the correlation between miR-34b expression and clinical stage and lymph node metastasis status. Spearman correlation analysis was used to determine the correlation between miR-34b expression and levels of phospho-Met, pS392p53and Mdm2.Results:Expression of miR-34b was lower in NSCLC tissues than that in pericarcinous tissues of lung cancer. Additionally, the Spearman correlation test showed lower miR-34b expression was correlated with higher lymph node metastasis. In vitro gain-of-function experiments indicated that miR-34b suppressed cell proliferation by inducing cell apoptosis. IHC results showed relations between lower miR-34b and over-expression of phospho-Met, p53(phospho S392) and Mdm2. Conclusion:Consistent with the opposing correlation between the expression of miR-34b and lymph node metastasis in NSCLC, miR-34b may play an important role in NSCLC progression. Furthermore, miR-34b down-regulates Met, following with subsequent changes of downstream p53(phospho S392) and Mdm2, and inversely p53up-regulates miR-34b in a feedback loop, which provides new insights into the roles of miR-34family members in the regulation of signaling pathways of NSCLC. As apoptosis and cell-cycle arrest are common end points of p53signal pathway activation, miR-34genes could be the potent regulators of tumor suppression by p53.The induction of miR-34genes permits p53to regulate the expression of a large number of proteins. Furthermore, targeting of p53-induced mRNAs by miR-34may devote to the tuneful response of the p53and prevent an uncontrolled response to p53activation.