Fig. 5: BRD4 inhibits ferroptosis and regulates SLC7A11 expression in ER+ breast cancer cells.

A, B BRD4 inhibition decreased the growth of ER+ breast cancer cells. MCF-7 and ZR-75-1 cells treated with BRD4 inhibitor (+)-JQ-1 (5 μM) (A) for 3 d and expressing BRD4-shRNAs (B) were subjected to the colony formation assay (n = 4). C (+)-JQ-1 increased lipid peroxidation in ER+ breast cancer cells. MCF-7 and ZR-75-1 cells were treated with (+)-JQ-1 (5 μM) for 24 h and stained with 5 μM C11-BODIPY before being subjected to flow cytometry analysis (n = 3). D BRD4 mRNA level was positively correlated with SLC7A11 mRNA level in ER+ breast cancer. Analysis of breast cancer data in TCGA showed that BRD4 mRNA level was positively associated with SLC7A11 mRNA level in luminal A and B subtypes of breast cancer. E, F (+)-JQ-1 or knockdown of BRD4 decreased SLC7A11 mRNA level. MCF-7 and ZR-75-1 cells were treated with (+)-JQ-1 (5 μM) (E) for the indicated times, or knocked down with BRD4-shRNAs (sh#28 and sh#76) (F), and subjected to quantitative RT-PCR (n = 4). G, H BRD4 inhibition decreased SLC7A11 protein level. Cells treated with (+)-JQ-1 or with BRD4 knockdown were subjected to western blot analysis (n = 3). I BRD4 overexpression increased SLC7A11 level. MCF-7 and ZR-75-1 cells with vector alone and BRD4 overexpression were subjected to western blot analysis. BRD4 and SLC7A11 levels were quantified and normalized to corresponding β-actin levels, which were presented as fold changes relative to the controls that were set to 1 (n = 3). All experiments were performed at least three times. A Mann–Whitney test, (C) unpaired t test. Data are shown as Mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.