Epigenetic regulation of miR-129-2 and its effects on the proliferation and invasion in lung cancer cells

MicroRNAs (miRNAs) play a pivotal role in carcinogenesis. Dysregulation of miRNAs, both oncogenic miRNAs and tumour-suppressive miRNAs, is closely associated with cancer development and progression. The levels of miRNAs could be changed epigenetically by DNA methylation in the 5 untranslated region (UTR) of pre-mature miRNAs. To investigate whether DNA methylation alters the expression of miR-129 in lung cancer, we did DNA methylation assays and found that 5 UTR region of miR-129-2 gene was absolutely methylated in both A549 and SPCA-1 lung cancer cells, but totally un-methylated in 95-D cells. The expression of miR-129 was restored by 5-Aza-2'-deoxycytidine (DAC), a de-methylation agent, in both A549 and SPCA-1 cells, resulting in attenuated cell migration and invasion ability, and decreased protein level of NF-B, which indicates the involvement of NF-B pathway. To further illustrate the roles of miR-129 in lung tumourigenesis, we overexpressed miR-129 in lung cancer cells by transfection of miR-129 mimics, and found arrested cell proliferation at G2/M phase of cell cycle and inhibited cell invasion. These findings strongly suggest that miR-129 is a tumour suppressive miRNA, playing important roles in the development and progression of human lung cancer.