Background: microRNAs (miRNAs) are a class of non-coding, single-stranded RNA molecules that regulate gene expression at the posttranscriptional level. Methyl-CpG-binding domain proteins (MBPs) are transcription repressors through binding to methylated gene promoters. Recent studies have shown that the effect of miRNAs on DNA methylation by targeting DNA methyltransferase (DNMTs) and/or MBPs plays an important role in various human cancers.
Aims: This study focuses on the regulation of MBPs by miR-373 and its downstream effect in hilar cholangiocarcinoma.
Methods: miR-373 was investigated by TaqMan miRNA Assay; mRNA and protein of MBD1, MBD2, and Mecp2 were determined by QuantiTect(®) Primer Assays and Western blotting, respectively; RASSF1A mRNA was measured by SYBR-Green real-time PCR; The targeting at MBD2-3'UTR by miR-373 was evaluated by dual-luciferase reporter gene assay.
Results: miR-373 decreased and closely associated with poor cell differentiation, advanced clinical stage, and shorter survival in hilar cholangiocarcinoma; MBD2 exclusively over-expressed and reciprocally related to miR-373; precursor miR-373 inhibited the luciferase activity of MBD2-3'UTR construct; exogenous miR-373 suppressed the expression of MBD2 and enhanced RASSF1A mRNA in QBC(939) cells; anti-miR-373 inhibitor up-regulated the expression of MBD2 and reduced RASSF1A mRNA in HIBEpic cells.
Conclusions: miR-373 is one negative regulator of MBD2. In hilar cholangiocarcinoma, down-expression of miR-373 leads to increase of MBD2, which in turn suppresses the methylation-mediated gene such as RASSF1A.