(A) mRNA expression level of p27kip1 was measured in a panel of breast cancer cell lines. Data are displayed as fold changes normalized to the expression level in normal breast tissue. (B) TNBC lines, MDA-MB-231, BT-20, and MDA-MB-468 cells were established to stably express anti-miR-221 (miR-221-ZIP) or a control scramble miRNA (Scramble-ZIP). miR-221 expression level was measured and is displayed as fold changes normalized to the expression level of parental cell lines. (C) Transcript expression level of p27kip1 was measured and is displayed as fold changes normalized to the expression level of parental cell lines. (D) Western blot analysis of MDA-MB-231, BT-20, and MDA-MB-468 cells stably expressing anti-miR-221 or scramble miR-ZIP depicting changes in p27 protein level. GAPDH was used as loading control. (E) MDA-MB-231, BT-20, and MDA-MB-468 cells stably expressing anti-miR-221 or scramble miR-ZIP were cultured for 72 hours to reach 80–90% confluency before harvesting and cell cycle analysis was performed and displayed as percentages of each cell cycle stage. These experiments were repeated at least three times, and representative data is shown.