Knockdown of circHIPK3 suppresses proliferation, migration and invasion in OS cells. Expression levels of circHIPK3 and HIPK3 mRNA in (A) HOS and (B) U2OS cells after transfection of specific circHIPK3 siRNAs were measured by reverse transcription-quantitative PCR. A Cell Counting Kit 8 assay was performed to investigate the proliferation ability of (C) HOS and (D) U2OS cells. (E) A Transwell assay was used to evaluate the metastatic ability of HOS and U2OS cells. Magnification, ×20; scale bar, 200 µm. (F) A wound healing assay was performed to determine the migration ability of HOS and U2OS cells. Magnification, ×4; scale bar, 500 µm. *P<0.05 and **P<0.01 vs. NC siRNA group. All data are presented as the mean ± SD of three independent experiments. circ, circular RNA; HIPK3, homeodomain interacting protein kinase 3; NC, negative control; n.s, not significant (P>0.05); OD, optical density; siRNA, small interfering RNA.