Circ_ORC2 enhances the regulatory effect of miR-19a on its target gene PTEN to affect osteosarcoma cell growth.

Osteosarcoma is a highly malignant and aggressive bone tumor. Its occurrence and development involve many factors and multiple signaling pathways. Some studies have shown that circular RNAs (circRNAs) play important roles in the development of various tumors. This research showed that circ_ORC2 was generally up-regulated in various osteosarcoma cell lines, and mainly distributed in the cytoplasm. Circ_ORC2 had the binding site of miR-19a, and its expression was positively correlated with miR-19a expression. RIP experiments showed that circ_ORC2 could bind to Ago2 protein. RNA pull-down using biotinylated circ_ORC2 or miR-19a showed that circ_ORC2 could directly interact with miR-19a, and dual luciferase reporter gene assay also confirmed that miR-19a could bind to circ_ORC2. After circ_ORC2 knockdown, miR-19a expression was down-regulated, but the downstream target gene PTEN expression was up-regulated, and the phosphorylation level of Akt was reduced, which indicated that circ_ORC2 enhanced the inhibition of miR-19a on PTEN expression by combining miR-19a. Further functional experiments showed that after circ_ORC2 knockdown, cell proliferation and invasion decreased, while the apoptosis level increased. When co-transfected with circ_ORC2 siRNA and miR-19a mimics or PTEN siRNA, the above cell biological behaviors did not change significantly. Therefore, circ_ORC2 binds with miR-19a and enhances its expression, thereby inhibiting downstream PTEN expression and activating Akt pathway to promote osteosarcoma cell growth and invasion. These findings enrich the circRNA molecular regulation mechanism, and provide more reference ideas for the research and application of circRNAs in tumors and other diseases.