Circ_RPPH1 regulates glioma cell malignancy by binding to miR-627-5p/miR-663a to induce SDC1 expression.

Background: Recent studies revealed the key role of circular RNA (circRNA) in glioma progression. However, the effect of circ_0000520, also named as circRNA ribonuclease P RNA component H1 (circ_RPPH1), in glioma development was unknown. The study aimed to reveal the role of circ_RPPH1 in glioma cell malignancy.

Methods: Human astrocytes (NHA) and glioma cell lines (A172 and U251) were employed in this study. Quantitative real-time polymerase chain reaction and western blot were used to check the expression of circ_RPPH1, microRNA-627-5p (miR-627-5p), miR-663a and syndecan 1 (SDC1). Immunohistochemistry assay was conducted to assess the protein expression of nuclear proliferation marker ki67 and matrix metalloprotein 9 (MMP9). Cell viability was assessed by 3-(4,5-Dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell proliferation and apoptosis were investigated by flow cytometry analysis, 5-Ethynyl-29-deoxyuridine, or cell colony formation assay. Cell migration and invasion were evaluated by transwell assays. The interaction between miRNAs (miR-627-5p and miR-663a) and circ_RPPH1 or SDC1 was identified by a dual-luciferase reporter assay. A mouse model assay was performed to reveal the impact of circ_RPPH1 knockdown on glioma cell malignancy in vivo by analyzing neoplasm volume and weight.

Results: Circ_RPPH1 and SDC1 expression were significantly increased, whereas miR-627-5p and miR-663a expression were decreased in glioma tissues and cells in comparison with healthy brain tissues or human astrocytes. Circ_RPPH1 depletion led to the decreased cell proliferation, migration and invasion, and the increased cell apoptosis. Additionally, circ_RPPH1 bound to miR-627-5p/miR-663a and mediated glioma cell processes by interacting with them. SDC1 overexpression attenuated miR-627-5p/miR-663a-mediated actions. Moreover, circ_RPPH1 regulated SDC1 expression through interaction with miR-627-5p and/or miR-663a. Furthermore, circ_RPPH1 knockdown inhibited glioma cell malignancy in vivo, accompanied by the decreases of ki67 and MMP9 expression.

Conclusion: Circ_RPPH1 knockdown inhibited glioma tumorigenesis by downregulating SDC1 by binding to miR-627-5p/miR-663a, showing that circ_RPPH1 might be an effective therapeutic target for glioma.