Abstract: BACKGROUND: Through sorting and identification of small cell lung cancer in vitro, the existence of tumor stem cells has been shown to be an important factor to promote the malignant proliferation of tumor cells. Tumorigenesis is closely related to the abnormal expression of various molecules in cells and the regulation of targeted genes. Previous studies have found that EVI1 has the characteristics of proto oncogene and can be up-regulated in lung cancer. miRNA-206 can target the expression of EVI1 gene and protein.
OBJECTIVE: To investigate the influence of miRNA-206 on cell proliferation and division cycle by targeted regulating the expression of EVI1 transcription gene in stem cells of small cell lung cancer.
METHODS: Firstly, miRNA-206 transfection experiment was used to verify the targeted regulation of EVI1 gene. The experiment was divided into three groups: miRNA-206 mimics, miR-206 inhibitor, and miR-NC. The expression of EVI1 protein in the stem cells was detected by western blot assay. miRNA-206 lentivirus transfection experiment was used to verify the signal transduction pathway and biological behavior of the cells. The experiment was divided into three groups: pLB-miR-206 group, empty vector group, and control group. The expression levels of miR-206 and EVI1 mRNA in stem cells were detected by RT-PCR. The expression levels of p-Akt and p-JNK protein were detected by western blot assay. The cell proliferation rate was detected by MTT method. Percentage of mitotic and apoptotic cells in cell cycle was detected by flow cytometry.  
RESULTS AND CONCLUSION: (1) The Evi1 protein level in the miR-206 mimics group was significantly higher than that in the miR-NC group (P < 0.05), and the Evi1 protein level in the miR-206 inhibitor group was significantly lower than that in the miR-NC group (P < 0.05). It was suggested that miR-206 may target the expression of EVI1 gene in stem cells. (2) After transfection with miRNA-206 lentivirus, the expression levels of miR-206 and EVI1 mRNA in pLB-miR-206 group were significantly lower than those in the empty vector and control groups; the protein expression levels of p-Akt and p-JNK decreased; the cell proliferation rate decreased; and the proportion of cell division cycle decreased (P < 0.05). It was found that miR-206 may target to regulate the expression of EVI1 transcription gene and the activation of Akt/JNK signaling pathway in stem cells of small cell lung cancer, which has an impact on cell proliferation and division cycle.

Key words: stem cells, cancer stem cells, lung cancer stem cells, small cell lung cancer, miR-206, EVI1 gene, signal pathway, proliferation, cell cycle