circ-BIRC6, a circular RNA, promotes hepatocellular carcinoma progression by targeting the miR-3918/Bcl2 axis

Circular (circ)RNA is a special type of endogenous RNA consisting of a covalently closed loop structure without 5' to 3' polarity and a polyadenylated tail. Accumulating evidence suggests that circRNAs play important roles in the development and progression of human cancers. However, the role of circRNAs in the progression of hepatocellular carcinoma (HCC) is largely unknown. This was addressed in the present study using high-throughput sequencing to identify aberrantly expressed circRNAs in HCC patient tissue and cell lines. We found that circ-baculoviral IAP repeat-containing (BIRC)6 was upregulated in HCC tissue samples and cells; this was associated with the overall survival of HCC patients. circ-BIRC6 knockdown reduced HCC cell proliferation, migration, and invasion and enhanced their apoptosis. Additionally, circ-BIRC6 overexpression negatively regulated the expression of microRNA miR-3918, which was identified as an inhibitor of B cell lymphoma (Bcl)2. The tumor-suppressive effect of circ-BIRC6 deletion was abrogated by inhibiting miR-3918. These results indicate that circ-BIRC6 functions as a competing endogenous RNA that regulates Bcl2 expression by sponging miR-3918, and may serve as a prognostic biomarker and therapeutic target for the treatment of HCC.