The 5' flanking region of miR-378 is hypomethylated in acute myeloid leukemia.

BACKGROUND Aberrant expression of miR-378 has been observed in various malignancies including acute myeloid leukemia (AML). However, the mechanism regulating of miR-378 expression remains unknown. This study was aimed to investigate miR-378 methylation and to explore its clinical significance in AML. METHODS Methylation status of miR-378 5'-flanking region was investigated by real-time quantitative methylation-specific PCR (RQ-MSP) and bisulfite-sequencing PCR (BSP). The expression of miR-378 was evaluated by real-time quantitative PCR (RQ-PCR). The correlation between expression of miR-378 and 5'-flanking region methylation was analyzed using 5-aza-2'-deoxycytidine (5-aza-dC) treatment. RESULTS miR-378 5'-flanking region was significantly hypomethylated in AML patients compared to controls (median 0.109 vs. 0.058) (P=0.048). miR-378 expression was correlated with miR-378 5'-flanking region in leukemic cell line treated with 5-aza-dC, but not in AML patients. The level of miR-378 hypomethylation significantly increased in M2 subtype compared to other subtypes. Moreover, patients with t(8;21) harbored the highest level of miR-378 hypomethylation. However, there was no significant difference in overall survival between patients with high and low miR-378 hypomethylation. The association of miR-378 expression with methylation was not observed in AML patients, but miR-378 expression in THP-1 line was increased while methylation status of miR-378 5-flanking region was decreased after 5-aza-dC treatment. CONCLUSIONS Our findings suggest that miR-378 is reactivated by demethylation after 5-aza-dC treatment. 5'-flanking region of miR-378 is hypomethylated in AML especially in those with t(8;21).