Metabolically controlled histone H4K5 acylation/acetylation ratio drives BRD4 genomic distribution VII

In addition to acetylation, histones are modified by a series of competing longer chain acylations. Most of these acylation marks are enriched and co-exist with acetylation on active gene regulatory elements. Their seemingly redundant functions have hindered the understanding of histone acylations' specific roles. Here, by using an acute lymphoblastic leukaemia (ALL) cell model and blasts from B-ALL patients, we demonstrate a role for mitochondrial activity in controlling histone acylation/acetylation ratio, especially at H4K5. An increase of the crotonylation and butyrylation over acetylation on H4K5 weakens BRD4-chromatin interaction and increases BRD4 nuclear mobility and availability for binding transcription start site associated nucleosome free regions of active genes. Our data suggest that, with regard to BRD4 dynamics, histone acylations including acetylation, should be considered collectively. A metabolism dependant control of the histone acetylation/longer chain acylation(s) ratio could constitute a common mechanism regulating bromodomain factors' “reservoir” pool, availability and functional genomic distribution. Overall design: Chromatin immunoprecipitation assays and sequencing (ChIPseq) of REH cells (WT and FASTKD1 ko) with anti-H4K5 butyrylation and anti-BRD4除乙酰化修饰外，组蛋白还会受到一系列竞争性长链酰化修饰。这类酰化标记大多富集于活跃基因调控元件，并与乙酰化共存。其看似冗余的功能阻碍了学界对组蛋白酰化特异性作用的认知。本研究借助急性淋巴细胞白血病（acute lymphoblastic leukaemia, ALL）细胞模型与B-ALL患者的原始细胞，证实线粒体活性可调控组蛋白酰化/乙酰化比值，尤其在H4K5位点。H4K5位点上巴豆酰化与丁酰化相对于乙酰化的水平升高，会削弱BRD4与染色质的结合，并提升BRD4的核迁移能力及其与活跃基因转录起始位点相关核小体游离区域结合的可及性。本研究数据表明，就BRD4动态调控而言，包括乙酰化在内的组蛋白酰化应被综合考量。依赖代谢状态的组蛋白乙酰化/长链酰化比值调控，或可作为调控溴结构域因子“储备池”丰度、可及性及其功能基因组分布的通用机制。整体实验设计：对野生型与FASTKD1敲除的REH细胞开展抗H4K5丁酰化与抗BRD4的染色质免疫共沉淀测序（ChIP-seq）实验。