Acetylation is not mere a consequence of transcription: histones are acetylated without ongoing transcription [ChIP-seq]

In all eukaryotes, acetylation of histones lysine residues correlates with transcription activation. Whether histone acetylation is a cause or consequence of transcription is debated. One model suggests that transcription promotes the recruitment and/or activation of acetyltransferases and histone acetylation occurs as a consequence of ongoing transcription. However, the extent to which transcription shapes the global acetylation landscapes is not known. Here we show that global protein acetylation remains virtually unaltered after acute transcription inhibition. Transcription inhibition ablates the co-transcriptionally occurring ubiquitylation of H2BK120 but does not reduce histone acetylation. The combined inhibition of transcription and CBP/p300 further demonstrates that acetyltransferases remain active and continue to acetylate histones independently of transcription. Together, these results show that histone acetylation is not a mere consequence of transcription; acetyltransferase recruitment and activation is uncoupled from the act of transcription and histone and non-histone protein acetylation are sustained in the absence of ongoing transcription. Overall design: H3K27ac ChIP-seq experiments in ESC with or without actinomycin D or NVP-2 treatment. EU-seq experiments in ESC with triptolide treatment.

在所有真核生物中，组蛋白赖氨酸残基的乙酰化与转录激活呈正相关。组蛋白乙酰化究竟是转录的诱因还是结果，目前仍存在争议。有模型提出，转录会促进乙酰转移酶（acetyltransferase）的招募和/或激活，组蛋白乙酰化作为活跃转录的结果而发生。然而，转录对全基因组乙酰化修饰图谱的塑造程度仍不明确。本研究显示，经急性转录抑制处理后，整体蛋白质乙酰化水平几乎未发生改变。转录抑制会消除共转录过程中发生的H2BK120泛素化修饰，但并不会降低组蛋白乙酰化水平。转录与CBP/p300联合抑制实验进一步证实，乙酰转移酶仍保持活性，且可独立于转录过程继续催化组蛋白乙酰化。综上，本研究结果表明，组蛋白乙酰化并非仅仅是转录的结果；乙酰转移酶的招募与激活与转录过程解偶联，且在缺乏活跃转录的情况下，组蛋白与非组蛋白的乙酰化仍可维持。
实验设计：在胚胎干细胞（Embryonic Stem Cell, ESC）中分别设置放线菌素D（actinomycin D）、NVP-2处理组与空白对照组，开展H3K27ac染色质免疫共沉淀测序（Chromatin Immunoprecipitation sequencing, ChIP-seq）实验；同时在经雷公藤内酯醇（triptolide）处理的胚胎干细胞中开展EU-seq实验。