miR-638 modulates proliferation in breast cancer cells and inhibits invasive ability in TNBC cells. (A) Effects of miR-638 on cell proliferation were determined by MTT assay. The proliferation rate decreased after transfection of miR-638 mimic (gray bars) in TNBC cell lines MDA-MB-231 and Hs578T as well as in MCF-10A, and increased in MCF-7 cells, and had no effect in T47D cells, compared to the mock control (white bars). Transfection of miR-638 inhibitor (dark bars) promoted proliferation in TNBC cell lines, MDA-MB-231 and Hs578T, but inhibited proliferation in MCF-7 cells compared to the mock. There were no obvious changes in T47D cells in either mimic or inhibitor transfection, while MCF10A exhibited similar pattern as TNBC cells. Values represent the mean ± SE for three independent experiments. (*P <0.05). (B) Transwell assays with matrigel were performed for the invasion activity of breast cancer cells transfected with either miR-638 mimic or the mock control. Overexpression of miR-638 reduces cell invasion in TNBC cell lines, MDA-MB-231 and Hs578T, but not in ER-positive cells, MCF-7 and T47D. (C) Invasion ability of the cells was displayed as a percentage of the absolute cell numbers. Results are displayed as mean data ± SE. (*P <0.05 and **P <0.001). Five fields of unit area on each membrane or whole membrane were counted for cell numbers, and the experiments were repeated three times in triplicate. ER, estrogen receptor; TNBC, triple-negative breast cancer.