Verification of the five target microRNAs of hsa_circ_0006220 by RT-PCR in MDA-MB-231. The expression of miR-197-5p (A), miR-302b-3p (B), miR-302c-3p (C), miR-302d-3p (D), and miR-520d-3p (E) were measured when overexpressing hsa_circ_0006220. 2−∆CT values were used to calculate the expression; values were means ± SD; ****, P<0.0001.