Mechanistic Analysis of the Role of Bromodomain-containing Protein 4 (BRD4) in BRD4-NUT Oncoprotein-induced Transcriptional Activation
Mechanistic Analysis of the Role of Bromodomain-containing Protein 4 (BRD4) in BRD4-NUT Oncoprotein-induced Transcriptional Activation
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DOI：
10.1074/jbc.m114.600759
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发表时间：
2015-01-30
影响因子：
4.8
通讯作者：
You, Jianxin
中科院分区：
文献类型：
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作者：
Wang, Ranran;You, Jianxin
背景：NUT 中线癌是一种侵袭性癌症，通常由 BRD4-NUT 融合癌蛋白的形成引起。结果：BRD4-NUT 刺激的组蛋白高度乙酰化会招募 BRD4 和相关转录因子来激活基因表达。结论：BRD4-NUT 扰乱正常基因表达，引发 NMC 致癌事件。意义：打破 BRD4-NUT 与组蛋白乙酰转移酶的相互作用是消除 BRD4-NUT 致癌活性的绝佳策略。NUT 中线癌 (NMC) 是一种罕见但高度侵袭性的癌症，通常由 t(15;19) 易位引起，导致 BRD4-NUT 融合癌蛋白的形成。先前的研究表明，NUT 蛋白与 BRD4 双溴结构域的融合可能会显着改变细胞基因表达谱，从而促进 NMC 肿瘤发生。然而，人们对 BRD4-NUT 功能的机制细节仍然知之甚少。在这项研究中，我们通过将 NUT 靶向整合到 U2OS 2-6-3 细胞中的 LacO 转基因阵列来检查 NUT 在转录调控中的功能，这使我们能够直观地了解 NUT 如何改变原位基因转录动态。使用该系统，我们证明了与 LacO 位点相连的 NUT 蛋白招募 p300/CREB 结合蛋白 (CBP)，诱导组蛋白高度乙酰化，并将 BRD4 富集到转基因阵列染色质焦点。我们还发现，在 NMC 细胞中表达的 BRD4-NUT 中，通过双溴结构域锚定到染色质的融合蛋白的 NUT 部分也会刺激组蛋白过度乙酰化，从而导致 BRD4 与染色质结合更紧密。因此，多个 BRD4 相互作用因子被招募到 NUT 相关染色质位点以激活原位转基因表达。 p300-NUT 相互作用的显性失活抑制剂的表达或 (+)-JQ1 处理（使 BRD4 从 LacO 染色质位点解离）会抑制该基因转录功能。我们的数据支持一个模型，其中 BRD4-NUT 刺激的组蛋白高度乙酰化招募额外的 BRD4 和相互作用伙伴来支持转录激活，这是 NMC 中 BRD4-NUT 致癌机制的基础。
Background: NUT midline carcinoma is an aggressive cancer typically caused by the formation of the BRD4-NUT fusion oncoprotein. Results: BRD4-NUT-stimulated histone hyperacetylation recruits BRD4 and associated transcription factors to activate gene expression. Conclusion:BRD4-NUT perturbs normal gene expression to trigger oncogenic events in NMC. Significance: Breaking BRD4-NUT interaction with histone acetyltransferases is an excellent strategy to abrogate the BRD4-NUT oncogenic activities.NUT midline carcinoma (NMC) is a rare but highly aggressive cancer typically caused by the translocation t(15;19), which results in the formation of the BRD4-NUT fusion oncoprotein. Previous studies have demonstrated that fusion of the NUT protein with the double bromodomains of BRD4 may significantly alter the cellular gene expression profile to contribute to NMC tumorigenesis. However, the mechanistic details of this BRD4-NUT function remain poorly understood. In this study, we examined the NUT function in transcriptional regulation by targeting it to a LacO transgene array integrated in U2OS 2-6-3 cells, which allow us to visualize how NUT alters the in situ gene transcription dynamic. Using this system, we demonstrated that the NUT protein tethered to the LacO locus recruits p300/CREB-binding protein (CBP), induces histone hyperacetylation, and enriches BRD4 to the transgene array chromatin foci. We also discovered that, in BRD4-NUT expressed in NMC cells, the NUT moiety of the fusion protein anchored to chromatin by the double bromodomains also stimulates histone hyperacetylation, which causes BRD4 to bind tighter to chromatin. Consequently, multiple BRD4-interacting factors are recruited to the NUT-associated chromatin locus to activate in situ transgene expression. This gene transcription function was repressed by either expression of a dominant negative inhibitor of the p300-NUT interaction or treatment with (+)-JQ1, which dissociates BRD4 from the LacO chromatin locus. Our data support a model in which BRD4-NUT-stimulated histone hyperacetylation recruits additional BRD4 and interacting partners to support transcriptional activation, which underlies the BRD4-NUT oncogenic mechanism in NMC.