microRNA-526b servers as a prognostic factor and exhibits tumor suppressive property by targeting Sirtuin 7 in hepatocellular carcinoma

Recent studies have reported that microRNA-526b (miR-526b) is implicated in the growth and metastasis of cancer cells. However, the clinical significance of miR-526b and its role as well as underlying mechanisms are largely unknown in hepatocellular carcinoma (HCC). Here, we detected miR-526b expression difference between HCC and matched nontumor tissues with qRT-PCR. We found that miR-526b displayed lower expression in HCC patient tissues and cells. Clinical analysis revealed that low miR-526b expression correlated with large tumor size, venous infiltration, advanced tumor-node-metastasis (TNM) stage. Furthermore, miR-526b underexpression independently predicted poor prognosis of HCC patients. Functionally, we demonstrated that miR-526b inhibited proliferation, migration and invasion of HCC cells in vitro. Moreover, miR-526b overexpression restrained the tumor growth and pulmonary metastasis in vivo. Mechanistically, we proved that miR-526b could directly bind to 3′UTR of sirtuin 7 (SIRT7) mRNA and repressed its expression. miR-526b and SIRT7 showed a negative correlation in HCC tissues. More importantly, up-regulating SIRT7 expression antagonized miR-526b-inhibited proliferation, migration and invasion in SMMC-7721 cells. Furthermore, miR-526b suppressed epithelial-to-mesenchymal transition (EMT) of HCC cells. Immunoblotting analysis indicated that miR-526b reduced the levels of phosphorylated ERK (p-ERK), c-Myc, Cyclin D1, c-Jun, SNAIL and SLUG in HCC cells. SIRT7 restoration promoted phosphorylation of ERK and EMT in miR-526b overexpressing SMMC-7721 cells. Taken together, this is the first time we demonstrated that miR-526b might function as a prognostic biomarker and suppressed SIRT7 expression, and subsequently led to the growth and metastasis of HCC. Our findings provide miR-526b/SIRT7 axis as a promising drug target for HCC.