Roles of the BRD4 short isoform in phase separation and active gene transcription

• Published in: Nature structural & molecular biology Vol. 27; no. 4; pp. 333 - 341
• Main Authors: Han, Xinye, Yu, Di, Gu, Ruirui, Jia, Yanjie, Wang, Qi, Jaganathan, Anbalagan, Yang, Xuelan, Yu, Miaomiao, Babault, Nicolas, Zhao, Chengcheng, Yi, Huanfa, Zhang, Qiang, Zhou, Ming-Ming, Zeng, Lei
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.04.2020; Nature Publishing Group
• Subjects: 101/6; 14/63; 631/337/100/101; 631/337/572/2102; 631/80/458/1275; A549 Cells; Acetylation; Biochemistry; Biological Microscopy; Biomedical and Life Sciences; Cancer; Cell Cycle Proteins - chemistry; Cell Cycle Proteins - genetics; Cell proliferation; Cell Proliferation - genetics; Chemical properties; Chromatin; Chromatin - chemistry; Chromatin - genetics; Cofactors; Composition; Condensation; Deoxyribonucleic acid; DNA; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; Ectopic expression; Gene expression; Gene Expression Regulation, Neoplastic - genetics; Genetic transcription; Histone H3; Histones - chemistry; Histones - genetics; Humans; Isoforms; Kinases; Life Sciences; Lysine; Mediator Complex Subunit 1 - chemistry; Mediator Complex Subunit 1 - genetics; Membrane Biology; Neoplasms - genetics; Neoplasms - pathology; Nuclei (cytology); Phase separation; Phase transformations (Statistical physics); Phosphorylation; Protein Isoforms - genetics; Protein research; Protein Structure; Transcription factors; Transcription Factors - chemistry; Transcription Factors - genetics; China
• ISSN: 1545-9993; 1545-9985; 1545-9985
• DOI: 10.1038/s41594-020-0394-8

BRD4, a major tandem-bromodomain-containing transcription regulator, has two isoforms. The long isoform (BRD4L) has an extended C terminus that binds transcription cofactors, while the short isoform (BRD4S) lacks this C-terminal extension. Unlike BRD4L, the role of BRD4S in gene transcription remains unclear. Here, we report that, in human cancer cells, BRD4S forms nuclear puncta that possess liquid-like properties and that colocalize with BRD4L, MED1 and sites of histone H3 lysine 27 acetylation. BRD4 puncta are correlated with BRD4S but not BRD4L expression levels. BRD4S knockdown reduces BRD4S condensation, and ectopic expression promotes puncta formation and target gene transcription. BRD4S nuclear condensation is mediated by its intrinsically disordered regions and binding of its bromodomains to DNA and acetylated chromatin, respectively, and BRD4S phosphorylation diminishes BRD4 condensation. Our study illuminates a previously unappreciated role of BRD4S in organizing chromatin and transcription factors through phase separation to sustain gene transcription in chromatin for cancer cell proliferation. A combination of cellular, in vitro phase separation and functional assays shows that the intrinsically disordered regions and bromodomains of the BRD4 short isoform induce formation of liquid-like condensates in cancer cell nuclei and enhance transcriptional activity.