MicroRNA-21 is a potential link between non-alcoholic fatty liver disease and hepatocellular carcinoma via modulation of the HBP1-p53-Srebp1c pathway.

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a major risk factor for hepatocellular carcinoma (HCC). However, the mechanistic pathways that link both disorders are essentially unknown. Our study was designed to investigate the role of microRNA-21 in the pathogenesis of NAFLD and its potential involvement in HCC. Wildtype mice maintained on a high fat diet (HFD) received tail vein injections of microRNA-21-anti-sense oligonucleotide (ASO) or miR-21 mismatched ASO for 4 or 8 weeks. Livers were collected after that time period for lipid content and gene expression analysis. Human hepatoma HepG2 cells incubated with oleate were used to study the role of miR-21 in lipogenesis and analysed with Nile-Red staining. microRNA-21 function in carcinogenesis was determined by soft-agar colony formation, cell cycle analysis and xenograft tumour assay using HepG2 cells. The expression of microRNA-21 was increased in the livers of HFD-treated mice and human HepG2 cells incubated with fatty acid. MicroRNA-21 knockdown in those mice and HepG2 cells impaired lipid accumulation and growth of xenograft tumour. Further studies revealed that <i>Hbp1</i> was a novel target of microRNA-21 and a transcriptional activator of <i>p53</i>. It is well established that p53 is a tumour suppressor and an inhibitor of lipogenesis by inhibiting <i>Srebp1c</i>. As expected, microRNA-21 knockdown led to increased <i>HBP1</i> and <i>p53</i> and subsequently reduced lipogenesis and delayed G1/S transition, and the additional treatment of <i>HBP1</i>-siRNA antagonised the effect of microRNA-21-ASO, suggesting that <i>HBP1</i> mediated the inhibitory effects of microRNA-21-ASO on both hepatic lipid accumulation and hepatocarcinogenesis. Mechanistically, microRNA-21 knockdown induced <i>p53</i> transcription, which subsequently reduced expression of genes controlling lipogenesis and cell cycle transition. In contrast, the opposite result was observed with overexpression of microRNA-21, which prevented <i>p53</i> transcription. Our findings reveal a novel mechanism by which microRNA-21, in part, promotes hepatic lipid accumulation and cancer progression by interacting with the <i>Hbp1</i>-<i>p53</i>-<i>Srebp1c</i> pathway and suggest the potential therapeutic value of microRNA-21-ASO for both disorders.