Circular RNA circ_UBAP2 facilitates the progression of osteosarcoma by regulating microRNA miR-637/high-mobility group box (HMGB) 2 axis.

Circular RNA circ_UBAP2 has been reported to be closely associated with various tumors. The present work focused on exploring the roles of circ_UBAP2 and its molecular mechanism in osteosarcoma (OS). Circ_UBAP2, miR-637, and high-mobility group box (HMGB) 2 levels in OS cells and tissues were detected by quantitative real-time polymerase chain reaction. The relationship between miR-637 and circ_UBAP2, as well as between miR-637 and HMGB2, was predicted and examined through bioinformatics analysis and luciferase reporter gene experiments. Moreover, OS cell growth, invasion, migration, and apoptosis were detected using the cell counting kit-8 (CCK-8), Transwell and flow cytometry assays, respectively. HMGB2 protein levels were measured using Western blotting. Xenograft tumor formation assay was also performed. Circ_UBAP2 showed high expression levels in OS tissues and cells, which was directly proportional to metastasis and clinical stage of OS. The overexpression of circ_UBAP2 enhanced the growth, invasion, and migration of OS cells, but suppressed their apoptosis. In contrast, circ_UBAP2 silencing had opposite effects. Furthermore, miR-637 served as a downstream target of circ_UBAP2, which played opposite roles to circ_UBAP2 in OS. More importantly, HMGB2 served as miR-637's downstream target. The xenograft experiments in nude mice also proved that knockdown of circ_UBAP2 could increase miR-637 expression, but decrease HMGB2 expression, thus alleviating OS progression. Mechanistically, circ_UBAP2 exerts a cancer-promoting effect on OS by downregulating miR-637 and upregulating the expression of HMGB2. Circ_UBAP2 plays a promoting role in OS, and the circ_UBAP2/miR-637/HMGB2 axis is involved in OS progression.