miR-638-mediated regulation of BRCA1 in breast cancer cell lines. (A) The top part shows the predicted location of the miR-638 binding site of the 3’-UTR of BRCA1. The bottom part indicates the binding site in the CDS of BRCA1 (BRCA1 CDS) as well as the mutant BRCA1 sequence (BRCA1 CDS mut) corresponding to miR-638 sequence, along with the pGL-3 vector. (B) Relative luciferase activity was measured in breast cell lines co-transfected with either 200 ng of miR-638 mimic (dark bars) or a scrambled control (white bar), 100 ng of either pGL3-BRCA1-CDS (BRCA1-wt) or pGL3-BRCA1-CDS mut (BRCA1-mu) by Lipofectamine 2000 (Life Technologies) for 48 h. The data was reported as mean ± SE for three independent experiments. The luciferase activity was significantly decreased in MDA-MB-231 and Hs578T cells when co-transfected with miR-638 mimic and BRCA1-wt (*P <0.05), while either increased in MCF-7 or not changed in T47D and MCF-10A cells. (C) The expression of BRCA1 protein in breast cancer cells when transfected with miR-638 mimic (OV) compared to the mock (Mock). BRCA1 expression was significantly downregulated by miR-638 in TNBC cells, MDA-MB-231 and Hs578T compared to non-TNBC cells, MCF-7 and T47D. The experiments were repeated three times. Band intensities were quantified using the ImageJ software, and the relative expression level was shown in a bar graph. BRCA1, breast cancer susceptibility gene 1; CDS, coding sequence; TNBC, triple-negative breast cancer; UTR, untranslated region.