Simpson Querrey Institute for Epigenetics and the Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
Simpson Querrey Institute for Epigenetics and the Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
Mol Cell. 2023 Aug 17;83(16):2896-2910.e4. doi: 10.1016/j.molcel.2023.06.032. Epub 2023 Jul 12.
The BET family protein BRD4, which forms the CDK9-containing BRD4-PTEFb complex, is considered to be a master regulator of RNA polymerase II (Pol II) pause release. Because its tandem bromodomains interact with acetylated histone lysine residues, it has long been thought that BRD4 requires these bromodomains for its recruitment to chromatin and transcriptional regulatory function. Here, using rapid depletion and genetic complementation with domain deletion mutants, we demonstrate that BRD4 bromodomains are dispensable for Pol II pause release. A minimal, bromodomain-less C-terminal BRD4 fragment containing the PTEFb-interacting C-terminal motif (CTM) is instead both necessary and sufficient to mediate Pol II pause release in the absence of full-length BRD4. Although BRD4-PTEFb can associate with chromatin through acetyl recognition, our results indicate that a distinct, active BRD4-PTEFb population functions to regulate transcription independently of bromodomain-mediated chromatin association. These findings may enable more effective pharmaceutical modulation of BRD4-PTEFb activity.
BET 家族蛋白 BRD4 形成包含 CDK9 的 BRD4-PTEFb 复合物，被认为是 RNA 聚合酶 II (Pol II) 暂停释放的主要调节剂。由于其串联溴结构域与乙酰化组蛋白赖氨酸残基相互作用，长期以来人们一直认为 BRD4 需要这些溴结构域才能被招募到染色质并发挥转录调节功能。在这里，我们使用快速耗竭和基因互补的方法，用结构域缺失突变体进行研究，证明 BRD4 的溴结构域对于 Pol II 暂停释放不是必需的。一个最小的、无溴结构域的 BRD4 羧基末端片段，包含与 PTEFb 相互作用的羧基末端基序 (CTM)，在没有全长 BRD4 的情况下，对于介导 Pol II 暂停释放是必要且充分的。尽管 BRD4-PTEFb 可以通过乙酰化识别与染色质结合，但我们的结果表明，一个不同的、活跃的 BRD4-PTEFb 群体可以独立于溴结构域介导的染色质结合来调节转录。这些发现可能使 BRD4-PTEFb 活性的药物调节更加有效。
