Analysis of promoter methylation and epigenetic regulation of miR-32 in colorectal cancer cells.

MicroRNA-32 (miR-32) is upregulated in colorectal cancer (CRC) tissues; its overexpression leads to increased cell proliferation, migration and invasion, as well as reduced apoptosis of CRC cells, at least partly by inhibiting the target gene phosphatase and tensin homolog. However, the mechanisms of its upregulation have remained elusive. In the present study, the effects of methylation and acetylation on the expression of miR-32 were investigated. The promoter methylation status of miR-32 in the CRC cell lines HT-29 and HCT-116 and the normal colonic epithelial cell line NCM460 was investigated by bisulfate sequencing polymerase chain reaction (BSP). The potential role of methylation and histone acetylation in the regulation of miR-32 expression in CRC cells was investigated using the demethylation reagent 5-aza-2'-deoxycytidine (5-Aza-dC), the histone deacetylase inhibitor trichostatin A (TSA) and transfection of DNA methyltransferase 1 (DNMT1) overexpression plasmid. BSP revealed that CpG sites in the miR-32 promoter region of CRC and normal colonic epithelial cells were all hypomethylated, with methylation rates of 0.12, 1.14 and 0.64% in HCT-116, HT-29 and NCM460 cells, respectively. Treatment with 5-Aza-dC and/or TSA and transfection with DNMT1 plasmid did not significantly alter the expression of miR-32. Therefore, the present results suggest that methylation and histone acetylation do not affect miR-32 expression in CRC cells.