Silencing of miR-137 by aberrant promoter hypermethylation in surgically resected lung cancer.

Abstract

Recent studies demonstrated that miR-137 is downregulated in various tumors, and that it functions as a tumor suppressor. miR-137 could be silenced by its aberrant promoter hypermethylation. The purpose of this study was to investigate the significance of MIR137 promoter methylation on its expression in lung cancer. Lung cancer cell lines were treated with either a DNA methyltransferase inhibitor (5-azacytidine, AZA) and/or an HDAC inhibitor (trichostatin A, TSA) to determine whether miR-137 expression was reactivated. Paired lung tumor and adjacent non-tumor lung tissues were obtained (n=50). Quantitative methylation-specific PCR and bisulfite sequencing were used to analyze the methylation status of MIR137, and real-time RT-PCR was performed to analyze miR-137 expression. miR-137 was reactivated by treatment with either AZA and/or TSA in lung cancer cell lines. Methylation-specific PCR showed increased MIR137 promoter methylation in lung tumors compared with adjacent non-tumor tissues, which was further validated by bisulfite sequencing. The expression of miR-137 was downregulated significantly in lung tumors, which was correlated with level of MIR137 promoter methylation inversely. miR-137 downregulation was related to its promoter hypermethylation in lung cancer. Further studies are needed to assess its value as a prognostic factor and potential therapeutic applications in lung cancer.