MicroRNA-302a enhances 5-fluorouracil sensitivity in HepG2 cells by increasing AKT/ULK1-dependent autophagy-mediated apoptosis

MicroRNA-302a (miR-302a) has been implicated in the oncogenic processes, but its role in hepatocellular carcinoma (HCC) chemoresistance and related mechanisms are still unclear. Therefore, the aim of this study was to investigate the role of miR-302a in HCC chemoresistance and elucidate its underlying mechanism. In this study, we detected the level of miR-302a in HCC tissues (including chemoresistant and chemosensitive tissues), non-tumor tissues, liver cancer cell lines, and 5-fluorouracil (5-FU)-resistant cells (HepG2/R). Additionally, we conducted cell viability, apoptosis, and autophagy analyses as well as assessed the levels of cleaved caspase-3, cleaved caspase-9, microtubule-associated protein 1 light chain 3 beta II (LC3B-II), Akt, and UNC-51 like kinase 1 (ULK1) in HepG2 cells transfected with miR-302a mimic or inhibitor prior to 5-FU treatment. Lastly, we predicted the target of miR-302a and verified the relationship between miR-302a and Akt by luciferase reporter and functional repair assays. Our results revealed that miR-302a was down-regulated in HCC tissues (p<0.01), especially in chemoresistant tissues (p<0.01). Consistently, the miR-302a level exhibited a lower expression in HepG2/R cells compared to their parental cells (p<0.01). Furthermore, the 5-FU-induced apoptosis and autophagy of HepG2 cells were promoted by miR-302a over-expression and diminished by miR-302a inhibition (p<0.01). Target analysis revealed that miR-302a could directly target Akt. Moreover, miR-302a inhibited Akt expression and subsequently elevated ULK1 expression (p<0.01). Inhibition of ULK1 could abrogate the sensitization of overexpressed miR-302a to 5-FU in HepG2 cells (p<0.01). Altogether, our results demonstrate that the down-regulation of miR-302a promotes 5-FU resistance in HCC by attenuating the Akt/ULK1 axis-dependent autophagy and apoptosis.