Methylation-directed glycosylation of chromatin factors represses retrotransposon promoters
Methylation-directed glycosylation of chromatin factors represses retrotransposon promoters
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DOI：
10.1073/pnas.1912074117
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发表时间：
2020-06-23
影响因子：
11.1
通讯作者：
Bestor, Timothy H.
中科院分区：
文献类型：
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作者：
Boulard, Mathieu;Rucli, Sofia;Bestor, Timothy H.
即使在其表达所需的所有因子存在的情况下，甲基化哺乳动物启动子转录沉默的机制长期以来一直是表观遗传学领域未解决的主要问题。抑制需要组装甲基化依赖性沉默复合物，该复合物包含 TRIM28 蛋白（也称为 KAP1 和 TIF1 beta），这是一种没有内在抑制或 DNA 结合特性的支架蛋白。该复合物中抑制转录的关键效应子的身份尚不清楚。我们开发了甲基化敏感的相互作用筛选，结果表明 TRIM28 仅在具有正常基因组甲基化模式的细胞中与 O-连接 β-N-乙酰氨基葡萄糖转移酶 (OGT) 复合。 OGT 是唯一一种通过将 N-乙酰氨基葡萄糖 (O-GlcNAc) 转移至丝氨酸和苏氨酸羟基来修饰细胞质和核蛋白的糖基转移酶。全基因组分析表明，O-糖基化蛋白和 TRIM28 与活性逆转录转座子的启动子和印记控制区（受 DNA 甲基化控制的两个主要调控序列）特异性结合。此外，全基因组 DNA 甲基化缺失导致与 TRIM28 相关的多个转录抑制蛋白中 O-GlcNAc 缺失。一种新开发的基于 Cas9 的编辑方法，用于靶向去除 O-GlcNAc，该方法针对反转录转座子启动子。局部染色质脱 GlcNAc 特异性地重新激活目标逆转录转座子家族的表达，而不会丢失 DNA 甲基化。这些数据表明染色质因子的 O 连接糖基化对于甲基化逆转录转座子的转录抑制至关重要。
The mechanisms by which methylated mammalian promoters are transcriptionally silenced even in the presence of all of the factors required for their expression have long been a major unresolved issue in the field of epigenetics. Repression requires the assembly of a methylation-dependent silencing complex that contains the TRIM28 protein (also known as KAP1 and TIF1 beta), a scaffolding protein without intrinsic repressive or DNA-binding properties. The identity of the key effector within this complex that represses transcription is unknown. We developed a methylation-sensitized interaction screen which revealed that TRIM28 was complexed with O-linked beta-N-acetylglucosamine transferase (OGT) only in cells that had normal genomic methylation patterns. OGT is the only glycosyltransferase that modifies cytoplasmic and nuclear protein by transfer of N-acetylglucosamine (O-GlcNAc) to serine and threonine hydroxyls. Whole-genome analysis showed that O-glycosylated proteins and TRIM28 were specifically bound to promoters of active retrotransposons and to imprinting control regions, the two major regulatory sequences controlled by DNA methylation. Furthermore, genome-wide loss of DNA methylation caused a loss of O-GlcNAc from multiple transcriptional repressor proteins associated with TRIM28. A newly developed Cas9-based editing method for targeted removal of O-GlcNAc was directed against retrotransposon promoters. Local chromatin de-GlcNAcylation specifically reactivated the expression of the targeted retrotransposon family without loss of DNA methylation. These data revealed that O-linked glycosylation of chromatin factors is essential for the transcriptional repression of methylated retrotransposons.