MicroRNA-26a targets the mdm2/p53 loop directly in response to liver regeneration

Liver regeneration (LR) is the result of a dynamic balance between the increased proliferation and decreased apoptosis of hepatocytes. However, the role of microRNA (miR)-26a in regulating complex signalling networks involving E3 ubiquitin.protein ligase Mdm2 (mdm2), p53, p21 and p27 in the process of LR is currently unclear. In the present study, it was hypothesized that miR-26a may negatively regulate the mdm2/p53 signalling loop in response to LR. In vitro experiments were performed, whereby mouse liver cells were transfected with an miR-26a vector or an anti/miR-26a vector. Cell proliferation was analysed using an MTS assay and cell apoptosis, and cell cycle progression were analysed by flow cytometry. In addition, the expression of mdm2, p53, p21 and p27 were assessed using western blotting and reverse transcription.quantitative polymerase chain reaction analyses. Dual.luciferase reporter assays were also used to examine the association between mdm2 and miR-26a. A 70% partial hepatectomy in C57BL/6J mice was then performed, which was followed by injection with an mdm2-cDNA vector or an mdm2-small interfering RNA vector. The liver-to-body weight ratio and liver function of mice were measured at 72 h following vector administration. The results demonstrated an increase in hepatocyte proliferation accompanied by decreased hepatocyte apoptosis levels. In addition, inhibition of miR-26a expression was associated with a marked increase in mdm2 expression, while the expression of p53, p21 and p27 was decreased when compared with negative controls. The opposite effects were observed when miR-26a was overexpressed. Notably, miR-26a was demonstrated to target the 3'.untranslated region of mdm2 directly. The results of the present study are the first to demonstrate as far as the authors are aware that the mdm2/p53 negative feedback loop may be targeted by miR-26a directly in response to LR, and that mdm2 negatively regulates p53, p21 and p27 but not miR-26a. miR-26a may therefore function as an important factor that regulates the interaction between mdm2 and p53.