Interactions between BRD4S, LOXL2, and MED1 drive cell cycle transcription in triple-negative breast cancer. Interactions between BRD4S, LOXL2, and MED1 drive cell cycle transcription in triple-negative breast cancer

Triple-negative breast cancer (TNBC) often develops resistance to single-agent treatment, which can be circumvented using targeted combinatorial approaches. Here, we demonstrate that the simultaneous inhibition of LOXL2 and BRD4 synergistically limits TNBC proliferation in vitro and in vivo. Mechanistically, LOXL2 interacts in the nucleus with the short isoform of BRD4 (BRD4S), MED1, and the cell cycle transcriptional regulator B-MyB. These interactions sustain the formation of BRD4 and MED1 nuclear transcriptional foci and control cell cycle progression at the gene expression level. The pharmacological co-inhibition of LOXL2 and BRD4 reduces BRD4 nuclear foci, BRD4-MED1 colocalization, and the transcription of cell cycle genes, thus supressing TNBC cell proliferation. Finding novel strategies to disrupt BRD4S-LOXL2 interaction holds potential for developing successful TNBC therapies. Overall design: mRNA (triplicates), ATAC-seq (triplicates) and ChIP-seq of BRD4L/S (AB antibody) (duplicates) and BRD4L (BB antibody) (single replicate) in control and LOXL2 downregulated conditions in MDA-MB-231 cells.

三阴性乳腺癌（Triple-negative breast cancer, TNBC）常对单药治疗产生耐药性，而靶向联合治疗策略可规避该耐药问题。本研究证实，同时抑制LOXL2与BRD4可在体外及体内协同限制三阴性乳腺癌的增殖。机制上，LOXL2可在细胞核内与BRD4短亚型（BRD4S）、MED1以及细胞周期转录调控因子B-MyB发生相互作用。此类相互作用可维持BRD4与MED1的细胞核转录灶形成，并在基因表达层面调控细胞周期进程。对LOXL2与BRD4进行药物联合抑制，可减少BRD4细胞核转录灶、BRD4-MED1共定位以及细胞周期基因的转录，从而抑制三阴性乳腺癌细胞增殖。开发靶向破坏BRD4S-LOXL2相互作用的新型策略，有望助力开发有效的三阴性乳腺癌治疗方案。实验整体设计：在MDA-MB-231细胞的对照及LOXL2敲低条件下，分别开展mRNA测序（生物学重复3次）、ATAC-seq（生物学重复3次），以及针对BRD4L/S（使用AB抗体，生物学重复2次）与BRD4L（使用BB抗体，生物学重复1次）的ChIP-seq。