Interactions Between MYC and BRD4 Result in Their Reciprocal Regulation

MYC 和 BRD4 之间的相互作用导致它们的相互调节

• 批准号: 10702727
• 负责人: Dinah S. Singer
• 金额: $ 39.12万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10702727
• 关键词: Affect; Binding Proteins; C-terminal; Cell physiology; Chromatin; DNA Polymerase II; DNA Repair; Disease; Gene Activation; Genetic Transcription; Goals; Hematopoietic Neoplasms; Histone H3; Inflammation; JUN gene; Lead; Lysine; MAP Kinase Gene; MAPK8 gene; Malignant Neoplasms; Mediating; Mitosis; Mitotic; N-terminal; Nature; Nucleosomes; Phosphorylation; Phosphotransferases; Play; Protamine Kinase; Protein Family; RNA; Regulation; Reporting; Role; Signal Transduction; Site; Solid Neoplasm; Stress; Superhelical DNA; Therapeutic Studies; Topoisomerase; Transcription Coactivator; Transcriptional Activation; Transcriptional Elongation Factors; Ubiquitination; Work; base; c-myc Genes; chromatin remodeling; histone acetyltransferase; member; recruit; therapeutic target; transcription factor; transcription factor S-II; Affect; Binding Proteins; C-terminal; Cell physiology; Chromatin; DNA Polymerase II; DNA Repair; Disease; Gene Activation; Genetic Transcription; Goals; Hematopoietic Neoplasms; Histone H3; Inflammation; JUN gene; Lead; Lysine; MAP Kinase Gene; MAPK8 gene; Malignant Neoplasms; Mediating; Mitosis; Mitotic; N-terminal; Nature; Nucleosomes; Phosphorylation; Phosphotransferases; Play; Protamine Kinase; Protein Family; RNA; Regulation; Reporting; Role; Signal Transduction; Site; Solid Neoplasm; Stress; Superhelical DNA; Therapeutic Studies; Topoisomerase; Transcription Coactivator; Transcriptional Activation; Transcriptional Elongation Factors; Ubiquitination; Work; base; c-myc Genes; chromatin remodeling; histone acetyltransferase; member; recruit; therapeutic target; transcription factor; transcription factor S-II

BRD4, a member of the BET family of proteins, has been identified as a key factor controlling multiple cancers and is being investigated as a therapeutic target in cancer as well as many other diseases. BRD4 is a chromatin bound protein primarily with dual enzymatic activities that plays critical roles as a chromatin remodeler and transcriptional activator. The chromatin remodeling function of BRD4 depends on its intrinsic HAT activity while its transcriptional activation function depends on its kinase activity. It is well documented that BRD4 is released from the chromatin during periods of increased transcription such as immediate early transcription at the end of mitosis or during stress. The chromatin free BRD4 recruits and activates PTEFb, a transcription elongation factor, and directly phosphorylates the RNA Pol II to activate transcription. Work from our lab has shown that the enzymatic activities of BRD4, and thereby its chromatin remodeling and transcription activation functions, are tightly cross-regulated by the substrates it interacts with. These results suggest that the chromatin remodeling and transcriptional functions of BRD4 are distinctly delineated and do not overlap temporally, leading to the conclusion that the dual-function BRD4 transitions from being a chromatin remodeler to a transcriptional activator. The central goal of this project is to define the signals and mechanism that trigger the release of BRD4 from chromatin, allowing its transition from a chromatin remodeler to a transcriptional regulator. While attempting to delineate the chromatin remodeling/HAT and transcriptional activation/kinase activities of BRD4 we recently discovered that the kinase and HAT activities of BRD4 are regulated by its interacting partners. When BRD4 is bound to the chromatin and interacting with nucleosomes its kinase activity is repressed. On the other hand, when BRD4 is interacting with its transcriptional partners such as MYC or the Pol II CTD, its HAT activity is suppressed. These findings suggest that the HAT and kinase activities of BRD4 are tightly cross-regulated and dependent on its interactions and function. BRD4 transcription/kinase functions are kept suppressed when it is functioning as a chromatin remodeler/ HAT and conversely, its chromatin remodeling/ HAT functions are repressed when it is functioning as a transcription factor/ kinase. The release of BRD4 from chromatin immediately after mitosis during early G1 gene activation is well documented and consistent with our hypothesis that BRD4 transitions from a chromatin remodeler to become a transcriptional activator upon its release from chromatin. We have exploited the observation of chromatin release at the M/G1 interface to further characterize the mechanisms underlying cross-regulation of BRD4. The primary objective of our ongoing studies is to characterize the JNK-BRD4 interaction and its effects on the functions of BRD4. We hypothesized, based on earlier reports, that the Jun-C N-terminal kinase (JNK), a key member of the MAPK signaling cascade might be involved in releasing BRD4 from chromatin during mitotic stress. Our results show that JNK interacts with BRD4 directly and causes its release from the chromatin. Preliminary results also indicate that JNK phosphorylates BRD4 at multiple sites. JNK phosphorylation of BRD4 affects both its HAT and kinase activities. We are currently further characterizing the nature of the JNK-BRD4 interaction and its functional effects. In summary, our findings suggest that the cross-regulation of BRD4 enzymatic activities lead to its transition from being a chromatin remodeler to a transcriptional activator and that the JNK kinase may play a critical role in this transition.

BRD4是BET蛋白质家族的成员，已被确定为控制多种癌症的关键因素，并正在研究为癌症以及许多其他疾病的治疗靶点。 BRD4是一种染色质蛋白，主要与双重酶促活性，其作为染色质重塑剂和转录激活剂起着关键作用。 BRD4的染色质重塑函数取决于其内在的HAT活性，而其转录激活函数取决于其激酶活性。有充分的文献证明，在增加转录期间，BRD4是从染色质中释放出来的，例如有丝分裂结束时的立即早期转录。染色质brd4募集并激活PTEFB，这是一种转录伸长因子，并直接磷酸化RNA POL II以激活转录。我们实验室的工作表明，BRD4的酶促活性及其染色质重塑和转录激活函数，与与之相互作用的底物紧密地交叉调节。这些结果表明，BRD4的染色质重塑和转录功能是明确描述的，并且不会在时间上重叠，得出的结论是，双功能BRD4从染色质重塑剂转变为转录激活剂。该项目的核心目标是定义触发从染色质释放BRD4的信号和机制，从而使其从染色质重塑到转录调节器的过渡。在尝试描述BRD4的染色质重塑/HAT和转录激活/激酶活动时，我们最近发现BRD4的激酶和HAT活动受其相互作用的伙伴的调节。当BRD4与染色质结合并与核小体相互作用时，其激酶活性被抑制。另一方面，当BRD4与MYC或Pol II CTD等转录伙伴进行交互时，其帽子活动就会被抑制。这些发现表明，BRD4的HAT和激酶活性紧密地交叉调节，并取决于其相互作用和功能。当BRD4转录/激酶功能作为染色质重塑器/ HAT起作用时，将保持抑制作用，相反，当其染色质重塑/ HAT功能充当转录因子/激酶时，其染色质重塑/ HAT功能会受到抑制。在G1早期激活期间有丝分裂后立即从染色质中释放BRD4的释放是充分的，并且与我们的假设一致，即BRD4从染色质重塑剂转变后，从染色质释放后成为转录激活剂。我们已经利用了M/G1界面上染色质释放的观察，以进一步表征BRD4的交叉调节的机制。我们正在进行的研究的主要目的是表征JNK-BRD4相互作用及其对BRD4功能的影响。我们根据较早的报道假设Jun-C N末端激酶（JNK），MAPK信号级联的关键成员可能参与有丝分裂应激期间从染色质中释放BRD4。我们的结果表明，JNK直接与BRD4相互作用，并导致其从染色质释放。初步结果还表明JNK在多个位点磷酸化BRD4。 BRD4的JNK磷酸化会影响其HAT和激酶活性。目前，我们正在进一步表征JNK-BRD4相互作用及其功能效应的性质。总而言之，我们的发现表明，BRD4酶促活性的交叉调节导致其从染色质重塑剂过渡到转录激活剂，并且JNK激酶在此过渡中可能起关键作用。