CircRNA_0040705 promotes the progression of hepatocellular carcinoma

Circular RNAs (circRNAs) are involved in cancer progression. Nonetheless, the role and mechanism of circ_0040705 in hepatocellular carcinoma (HCC) are unclear. The aberrantly expressed circRNAs and microRNAs (miRNAs) in HCC tissues were screened by bioinformatics. Circ_0040705, miR-557, SRY-box transcription factor 2 (SOX2), E-cadherin, and N-cadherin expressions were determined using quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot. Cell counting kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), and Transwell experiments were utilized to examine the changes in HCC cell growth, migration, and invasion after circ_0040475 was overexpressed or knocked down. Lung metastasis assay was used to validate the effects of circRNA_0040705 on the lung metastasis of HCC cells in vivo. Binding sequences between circ_0040705 and miR-557 and between miR-557 and SOX2 were verified using dual-luciferase reporter gene experiments. The expression levels of circ_0040705 and SOX2 mRNA were markedly increased in HCC tissues, but miR-557 expression was down-regulated. Circ_0040705 overexpression enhanced the growth, migration, invasion, and the expressions of E-cadherin and N-cadherin of HCC cells and promoted lung metastasis in vivo, whereas circ_0040705 knockdown exerted the opposite effects in HCC cells. Circ_0040705 worked as a sponge for miR-557 to down-modulate miR-557 expression, and miR-557 could specifically down-modulate SOX2 expression. Circ_0040705 facilitates HCC cell growth, migration, and invasion by down-modulating miR-557 expression and up-modulating SOX2 expression.