Overexpression of miR-181a in chronic myeloid leukemia K562 cells inhibits the proliferation of these cells by repressing the transition from the G 1 to S phase of the cell cycle. (A) miR-181a inhibited the growth of the K562 cells overexpressing miR-181a compared with the control K562-EGFP cells. (B) miR-181a prevented the K562 cells from undergoing the G 1 /S phase transition of the cell cycle. Compared with the control cells, a larger number of K562-miR-181a cells were arrested at the G 1 phase of the cell cycle, whereas the opposite was observed for the number of cells arrested at the S phase of the cell cycle. miR-181a, microRNA-181a; EGFP, enhanced green fluorescent protein.