MiR-21 Upregulation Induced by Promoter Zone Histone Acetylation is Associated with Chemoresistance to Gemcitabine and Enhanced Malignancy of Pancreatic Cancer Cells

Background and Aims: MicroRNA-21 (miR-21) is reported to be overexpressed and to contribute toproliferation, apoptosis and gemcitabine resistance in pancreatic ductal adenocarcinomas (PDACs). The aims ofthis study were to explore regulation of miR-21 expression by epigenetic change and its impact on chemoresistanceand malignant properties of of pancreatic cancer. Materials and methods: We retrospectively collected 41 cases ofadvanced pancreatic cancer patients who were sensitive or resistant to gemcitabine and assessed levels of serumcirculating miR-21 for correlation with cytotoxic activity. Histone acetylation in the miR-21 promoter was alsostudied in gemcitabine-sensitive and gemcitabine-resistant PDAC cells. Gemcitabine-resistant HPAC and PANC-1cells were transfected with pre-miR-21 precursors (pre-miR-21) and antisense oligonucleotides (anti-miR-21), andwere treated with TSA. Finally, invasion and metastasis assays were performed and alteration in mir-21, PTEN,AKT and pAKT level was evaluated in these cells.
Results: Serum miR-21 levels were increased in gemcitabineresistantPDAC patients compared with gemcitabine-sensitive subjects. The miR-21 levels were increased in 6PDAC cells treated with gemcitabine significantly, associated with 50% inhibitory concentrations (IC50s). Histoneacetylation levels at miR-21 promoter were increased in PDAC cells after treatment with gemcitabine. Enhancedinvasion and metastasis, increased miR-21 expression, decreased PTEN, elevated pAKT level were demonstratedin gemcitabine-resistant HPAC and PANC-1 cells. Pre-miR-21 transfection or TSA treatment further increasedinvasion and metastasis ability, decreased PTEN, and elevated pAKT levels in these two lines. In contrast,anti-miR-21 transfection could reverse invasion and metastasis, and PTEN and pAKT expressions induced bygemcitabine.
Conclusions: MiR-21 upregulation induced by histone acetylation in the promoter zone is associatedwith chemoresistance to gemcitabine and enhanced malignant potential in pancreatic cancer cells.