Circular RNA circ-FOXP1 induced by SOX9 promotes hepatocellular carcinoma progression via sponging miR-875-3p and miR-421

Circular RNA (circRNA) is a special type of endogenous non-coding RNA that plays an important role in carcinogenesis. However, its biological relevance in hepatocellular carcinoma (HCC) is still largely uncharacterized. Here, we aimed to explore the function and clinical implication of circ-FOXP1 in HCC. We found that circ-FOXP1 was significantly upregulated in HCC tissues, serum and cell lines., which was attributed to the upregulation of oncogenic transcription factor SOX9. Depletion of circ-FOXP1 significantly inhibited HCC cell proliferation, invasion and induced apoptosis. Nevertheless, overexpression of circ-FOXP1 displayed the opposite trend. Further mechanismic study revealed that circ-FOXP1 was preferentially located in the cytoplasm and could concurrently sponge miR-875-3p and miR-421, resulting in increasing levels of a cohort of their target oncogenes, including SOX9. Moreover, knockdown of circ-FOXP1 evidently retarded tumor growth in vivo, but this effect was significantly abolished after silencing of miR-875-3p or miR-421. Clinically, high circ-FOXP1 was closely correlated with larger tumor size, microvascular invasion, advanced TNM stage, and predicted poor prognosis. In addition, serum circ-FOXP1 level could effectively discriminate HCC patients from healthy controls. Collectively, our data clearly suggest that circ-FOXP1 is a novel driver for the tumorigenesis and aggressive progression of HCC, which provides a potential therapeutic target for patients with HCC.