Enzymatic transfer of acetate on histones from lysine reservoir sites to lysine activating sites (RNA-Seq)

Histone acetylation, a post-translational modification associated with transcriptional activation, is governed by nuclear acetyl-CoA pools that can vary depending on the metabolic state of the cell. The metabolic enzyme acetyl-CoA synthetase 2 (ACSS2) is proposed to regulate nuclear acetyl-CoA levels, using local acetate to produce acetyl-CoA that is utilized for histone acetylation. We hypothesize that during gene activation, a local transfer of intact acetate occurs between histones to upregulate transcription via sequential action of epigenetic and metabolic enzymes. Here we present converging lines of evidence in support of this acetate transfer to serve rapid gene induction. Using stable isotope labeling, we detect local transfer of intact acetate between histone acetylation sites both in vitro using purified mammalian enzymes and in vivo using quiescence exit in Saccharomyces cerevisiae as a change-of-state model. We delineate the enzymatic components required for this transfer mechanism, finding that ACSS2, histone deacetylase and histone acetyltransferase enzymes are necessary for efficient acetyl-group transfer in vitro. We show that Acs2, the yeast orthologue of ACSS2, is recruited to the genome during quiescence exit, and observe dynamic changes of histone acetylation in the vicinity of Acs2 peaks in vivo. Strikingly, we find that Acs2 is preferentially associated with the most upregulated growth genes, suggesting that acetyl-group transfer might play an important role in increased gene expression. Overall, our data reveal direct transfer of acetate between histone lysine residues to facilitate rapid transcriptional induction, an exchange that may be critical during metabolic alterations and changes in nutrient availability.组蛋白乙酰化（histone acetylation）是一类与转录激活相关的翻译后修饰，其调控有赖于细胞核内的乙酰辅酶A（acetyl-CoA）库，而该库的水平会随细胞代谢状态发生变化。乙酰辅酶A合成酶2（ACSS2）作为一种代谢酶，被认为可通过利用局部乙酸盐生成乙酰辅酶A，进而调控细胞核内乙酰辅酶A水平以用于组蛋白乙酰化。我们提出假说：在基因激活过程中，完整乙酸盐会在组蛋白间发生局部转移，通过表观遗传酶与代谢酶的依次作用上调转录。本研究提供了多维度证据，支持该乙酸盐转移机制可介导快速基因诱导。借助稳定同位素标记技术，我们分别在体外（使用纯化的哺乳动物酶体系）与体内（以酿酒酵母（Saccharomyces cerevisiae）静止退出作为状态转换模型）中，检测到组蛋白乙酰化位点之间存在完整乙酸盐的局部转移。我们阐明了该转移机制所需的酶促组分，发现ACSS2、组蛋白去乙酰化酶（histone deacetylase）与组蛋白乙酰转移酶（histone acetyltransferase）对于体外高效的乙酰基转移是必需的。我们证实，酿酒酵母中ACSS2的同源物Acs2会在静止退出过程中被招募至基因组，并在体内观察到Acs2结合峰附近的组蛋白乙酰化水平发生动态变化。值得注意的是，我们发现Acs2优先结合上调幅度最高的生长相关基因，这提示乙酰基转移可能在基因表达增强过程中发挥重要作用。综上，我们的数据揭示了组蛋白赖氨酸残基之间可直接发生乙酸盐转移，以促进快速转录激活；这种交换过程或许在代谢改变与营养可获得性变化期间发挥关键作用。