Demethylation of miR-9-3 and miR-193a Genes Suppresses Proliferation and Promotes Apoptosis in Non-Small Cell Lung Cancer Cell Lines

Background: MicroRNAs miR-9-3 and miR-193a have recently been found to be hypermethylated in a variety of non-small cell lung cancer (NSCLC) cells and primary human tumors. The objectives of this study were to investigate the role of demethylation of miR-9-3 and miR-193a genes in regulating proliferation and apoptosis in NSCLCs, and to decipher the potential mechanisms underlying the properties. Methods: MTT and population doubling time by flow cytometry were used to assess cell proliferation. Enzyme-Linked Immunosorbent Assay and caspase-3 activity assay were employed to evaluate apoptosis. Real-time RT-PCR and Western blot were used to quantify gene expression at mRNA and protein levels, respectively. Methylation-specific PCR was utilized to assess methylation status. Results: We found that demethylation agent 5-Aza-2'-deoxycytidine (5-AzaC) reduced cell numbers and prolonged population doubling time (PDT), and promoted doxorubicin-induced apoptosis in seven NSCLC cell lines with different methylation statuses on miR-9-3 and miR-193a promoter regions: NCI-H1993/NCI-H1915 (miR-9-3+/miR-193a+), NCI-H1975/NCI-H200 (miR-9-3+/miR-193a-), A427/NCI-H2073 (miR-9-3-/miR-193a+), and NCI-H1703 (miR-9-3-/miR-193a-). Treatment with 5-AzaC concomitantly upregulated expression of miR-9-3 and miR-193a, and downregulated their respective target genes NF-κB and Mcl-1. The effects of 5-AzaC were abolished by concomitant knockdown of miR-9-3 and miR-193a using the complex antisense technique, whereas forced ectopic expression of miR-9-3 and miR-193a mimicked the effects of 5-AzaC. We further observed that the strength of proliferation inhibition and apoptosis promotion elicited by 5-AzaC was in the order of NCI-H1993/NCI-H1915 > A427/NCI-H2073 > NCI-H1975/NCI-H200 > NCI-H1703. Conclusions: Methylation-silencing of miR-9-3 and miR-193a may be an important epigenetic mechanisms favoring NSCLC cell growth and survival for carcinogenesis and cancer progression, and demethylation to reactivate expression of miR-9-3 and miR-193a genes contributes, at least partially, to the anti-cancer properties of 5-AzaC and thereby may be worthy of future studies for the possibility of being a new therapeutic strategy for the treatment of human NSCLCs.