Phase separation of PML/RARα and BRD4 coassembled microspeckles governs transcriptional dysregulation in acute promyelocytic leukemia

• 成果类型: Article
• 署名作者: Zhang, Yi; Lou, Jiacheng; Liu, Yabin; Jin, Peng; Tan, Yun; Song, Huan; Jin, Wen; Wang, Dan; Dong, Fangyi; Wu, Shishuang; Fang, Hai; Chen, Saijuan; Chen, Zhu; Wang, Kankan
• 署名单位: Shanghai Jiao Tong University; Chinese Academy of Sciences; Dalian Medical University; Shanghai Jiao Tong University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-12335
• DOI: 10.1073/pnas.2406519121
• 发表日期: 2024-08-13
• 关键词: dna-damage repair; apl pathogenesis; super-enhancers; rar-alpha; pml; protein; cell; inhibition; mechanisms; h3k4me3

摘要

In acute promyelocytic leukemia (APL), the promyelocytic leukemia- retinoic acid receptor alpha (PML/RAR alpha) fusion protein destroys PML nuclear bodies (NBs), leading to the formation of microspeckles. However, our understanding, largely learned from morphological observations, lacks insight into the mechanisms behind PML/RAR alpha- mediated microspeckle formation and its role in APL leukemogenesis. This study presents evidence uncovering liquid-liquid phase separation (LLPS) as a key mechanism in the formation of PML/RAR alpha- mediated microspeckles. This process is facilitated by the intrinsically disordered region containing a large portion of PML and a smaller segment of RAR alpha. We demonstrate the coassembly of bromodomain- containing protein 4 (BRD4) within PML/RAR alpha- mediated condensates, differing from wild- type PML- formed NBs. In the absence of PML/RAR alpha, PML NBs and BRD4 puncta exist as two independent phases, but the presence of PML/RAR alpha disrupts PML NBs and redistributes PML and BRD4 into a distinct phase, forming PML/RAR alpha- assembled microspeckles. Genome-wide profiling reveals a PML/RAR alpha- induced BRD4 redistribution across the genome, with preferential binding to super- enhancers and broad- promoters (SEBPs). Mechanistically, BRD4 is recruited by PML/RAR alpha into nuclear condensates, facilitating BRD4 chromatin binding to exert transcriptional activation essential for APL survival. Perturbing LLPS through chemical inhibition (1, 6- hexanediol) significantly reduces chromatin co- occupancy of PML/RAR alpha and BRD4, attenuating their target gene activation. Finally, a series of experimental validations in primary APL patient samples confirm that PML/RAR alpha forms microspeckles through condensates, recruits BRD4 to coassemble condensates, and co- occupies SEBP regions. Our findings elucidate the biophysical, pathological, and transcriptional dynamics of PML/RAR alpha- assembled microspeckles, underscoring the importance of BRD4 in mediating transcriptional activation that enables PML/RAR alpha to initiate APL.