Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore.
Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore.
Nat Commun. 2024 Sep 2;15(1):7646. doi: 10.1038/s41467-024-52040-y.
Despite their prevalent cancer implications, the in vivo dynamics of SWI/SNF chromatin remodelers and how misregulation of such dynamics underpins cancer remain poorly understood. Using live-cell single-molecule tracking, we quantify the intranuclear diffusion and chromatin-binding of three key subunits common to all major human SWI/SNF remodeler complexes (BAF57, BAF155 and BRG1), and resolve two temporally distinct stable binding modes for the fully assembled complex. Super-resolved density mapping reveals heterogeneous, nanoscale remodeler binding "hotspots" across the nucleoplasm where multiple binding events (especially longer-lived ones) preferentially cluster. Importantly, we uncover distinct roles of the bromodomain in modulating chromatin binding/targeting in a DNA-accessibility-dependent manner, pointing to a model where successive longer-lived binding within "hotspots" leads to sustained productive remodeling. Finally, systematic comparison of six common BRG1 mutants implicated in various cancers unveils alterations in chromatin-binding dynamics unique to each mutant, shedding insight into a multi-modal landscape regulating the spatio-temporal organizational dynamics of SWI/SNF remodelers.
尽管 SWI/SNF 染色质重塑因子普遍与癌症有关，但它们在体内的动态变化以及这种动态变化的失调如何导致癌症仍知之甚少。本研究采用活细胞单分子追踪技术，定量分析了三种常见的全人源 SWI/SNF 重塑因子复合物（BAF57、BAF155 和 BRG1）的关键亚基的核内扩散和染色质结合情况，并解析了完整复合物的两种具有时间区分的稳定结合模式。超分辨密度映射揭示了核质中异质的、纳米级的重塑因子结合“热点”，其中多个结合事件（尤其是寿命较长的事件）优先聚集。重要的是，我们发现溴结构域在以依赖于 DNA 可及性的方式调节染色质结合/靶向方面具有不同的作用，这表明在“热点”内的连续更长寿命的结合会导致持续的有效重塑。最后，对六种常见的 BRG1 突变体进行系统比较，揭示了每种突变体特有的染色质结合动力学改变，深入了解了调节 SWI/SNF 重塑因子时空组织动力学的多模态景观。
