SMC4 enhances the chemoresistance of hepatoma cells by promoting autophagy

BACKGROUND: Drug resistance is a major contributing factor to chemotherapy failure in hepatocellular carcinoma (HCC) patients. However, the exact mechanism underlying the chemoresistance of HCC remains unknown. METHODS: HepG2 cells were incubated with different concentrations of 5-fluorouracil (5-FU), and the Cell Counting Kit-8 assay was used to test the cell survival rate. The expression level of structural maintenance of chromosome 4 (SMC4) in drug-resistant cells was analyzed by real-time quantitative polymerase chain reaction (PCR) and western blotting. To assess autophagy, immunofluorescence was applied to detect the light chain 3 beta (LC3B) level in HepG2/5-FU cells. To further study the upstream regulation of miR (microRNA)-219/SMC4, a gene chip assay was performed. A luciferase reporter assay was used to determine whether long non-coding RNA-XIST (lncRNA-XIST) functions as a competitive endogenous RNA (ceRNA) for miR-219. Cellular proliferation was evaluated using MTT [3-(4,5)-dimethylthiahiazo (-z-y1)-2,5-di-phenytetrazoliumromide] and colony formation assays, wound healing and invasion assays were performed to study the invasion and migration ability of the cells, and flow cytometry assays were carried out to evaluate cell apoptosis. RESULTS: In the present study, we established a drug-resistant hepatoma cell line named HepG2/5-FU. We confirmed that SMC4 may play an important role in hepatoma cell autophagy and could promote autophagy to increase the drug resistance of hepatoma cells. We also demonstrated that lncRNA-XIST may competitively bind to miR-219 by acting as a miRNA sponge, thereby preventing miR-219 from effectively reducing the expression of SMC4 and further affecting the autophagy and drug resistance of hepatoma cells via the adenosine 5'-monophosphate (AMP)-activated protein kinase/mechanistic target of rapamycin (AMPK/mTOR) pathway. CONCLUSIONS: Our study suggests that SMC4 may be a potential marker of a poor HCC response to chemotherapy and a novel therapeutic target for HCC chemotherapy.