miR-505 enhances doxorubicin-induced cytotoxicity in hepatocellular carcinoma through repressing the Akt pathway by directly targeting HMGB1

Compelling evidence has suggested the relevance of miRNAs in resistance to chemotherapeutic agents in HCC. miR-505 was reported to be downregulated and function as a tumor suppressor in HCC cells by binding to high-mobility group box 1 (HMGB1). Whether miR-505/HMGB1 axis was involved in ADM cytotoxicity in HCC remains to be addressed. The aim of this study was to explore the effect of miR-505/HMGB1 axis on ADM cytotoxicity in HCC cells. MTT, flow cytometry analysis, and caspase-3 activity assays were conducted to assess ADM-induced cytotoxicity. The protein level of phosphorylation of histone H2 AX at Ser139 (γH2AX) was detected to evaluate DNA damage. The effects of miR-505 and HMGB1 on the protein kinase B (Akt) pathway were determined by examining the protein levels of phosphorylated Akt (p-Akt), Akt, phosphorylated glycogen synthase kinase-3β (p-GSK-3β), and GSK-3β. We found that HMGB1 knockdown and miR-505 overexpression exacerbated ADM-induced cell viability inhibition, enhanced ADM-induced apoptosis, and increased caspase-3 activity in ADM-treated HCC cells. However, HMGB1 overexpression reversed the effects of miR-505 on ADM-induced cytotoxicity in HCC cells. HMGB1 knockdown and miR-505 overexpression promoted ADM-induced DNA damage in HCC cells, which was abated by HMGB1 overexpression. On a molecular mechanism level, HMGB1 silencing and miR-505 overexpression inactivated the Akt pathway in HCC cells, while exogenous HMGB1 resisted miR-505-induced Akt pathway inactivation. In conclusion, miR-505 overexpression enhanced ADM-induced cytotoxicity in HCC cells, at least partly by targeting HMGB1 and inactivating the Akt pathway.