ETS1-dependent combinatorial control of oncogenic transcription in Notch-activated T-ALL

发现NOTCH 1是T细胞急性淋巴细胞白血病（T-ALL）中最常见的癌基因 病人们对这种癌症的靶向治疗寄予了希望。不幸的是，在临床试验中，泛Notch抑制剂 由于Notch功能的废除，GSI引起剂量限制性毒性，特别是肠毒性。我们见面的想法 这一挑战来自果蝇研究，表明Notch需要共结合转录因子 在其反应元件上的伙伴，以产生细胞类型特异性基因表达程序。如果这些“缺口”- 协作”转录因子被劫持，以帮助驱动Notch诱导的T-ALL，然后抑制它们可能会 对抗Notch信号并规避GSI毒性。因此，我们的长期目标是确定Notch协作 转录因子，并确定其作为安全的治疗靶点的潜力。在我们的初步数据中，我们显示 ETS 1是T细胞中排名第一的Notch相关转录因子，但不是肠细胞。 与GSI相比，Ets 1失活的影响对T-ALL细胞同样有害，但要温和得多 对小鼠模型的肠道稳态和整体健康的影响。从机制上讲，我们表明，CDC 73， 聚合酶相关因子复合物（PAF 1C）的支架组分结合ETS 1并被募集以 激活ETS 1反应元件。其中一个元件是以前未被识别但高度保守的 我们暂时将其标记为“E-Me”，表示“ETS 1依赖性MYB增强子”。我们的目标 目的是确定Ets 1依赖的反式因子和顺式元件对肿瘤细胞的调控作用， Notch激活的T-ALL中的转录程序。我们假设，破坏ETS 1依赖的 通过靶向CDC 73或E-Me的转录元件的组合控制将安全地抑制Notch， 诱导T-ALL。为了验证这一点，我们将确定抑制Ets 1依赖性因子如Cdc 73对 小鼠和人T-ALL模型中的白血病维持。我们还将确定抑制 ets 1依赖因子对致癌转录程序及顺式元件活化的影响。最后我们将 确定E-Me元件的作用，其中反式作用因子被ETS 1募集以共同驱动E-Me元件。 致癌MYB效应子通路。我们的工作提高了靶向共结合Notch协作的可能性。 转录调节因子如Ets 1，其产生指导Notch功能的染色质背景。这里我们将 建立Cdc 73作为连接Ets 1与转录机制和染色质修饰剂的桥梁， 激活启动子和增强子元件，并强调E-Me作为一个重要的例子。如果成功， 我们的项目意义重大，因为我们针对癌症中排名第一的Notch相关辅因子来禁用Notch， 驱动致癌信号，而没有在临床试验中观察到的泛Notch抑制剂的毒性。这个项目是 创新，因为据我们所知，除了ETS 1之外，没有其他Notch辅因子被证明在物理上 招募Notch染色质全基因组具有强大的统计和正交严谨性，并具有惊人的高 Notch辅因子和Notch结合基序的会聚，这通过染色质谱分析验证。

The discovery of NOTCH1 as the most prevalent oncogene in T-cell acute lymphoblastic leukemia (T-ALL) patients raised hopes for targeted therapy in this cancer. Unfortunately, in clinical trials, the pan-Notch inhibitor GSI caused dose-limiting toxicities, particularly intestinal, due to abrogation of Notch functions. Our idea to meet this challenge stems from Drosophila studies showing that Notch requires co-binding transcriptional factor partners at its response elements to generate cell-type specific gene expression programs. If these “Notch- collaborating” transcription factors are hijacked to help drive Notch-induced T-ALL, then inhibiting them might oppose Notch signals and circumvent GSI toxicities. Thus, our long-term goal is to identify Notch-collaborating transcription factors and determine their potential as safe, therapeutic targets. In our preliminary data, we show that ETS1 is the top-ranked Notch-associated transcription factor in the context of T cells, but not intestinal cells. Compared to GSI, the effects of Ets1 inactivation were just as deleterious to T-ALL cells but were much milder on intestinal homeostasis and overall health in mouse models. Mechanistically, we show that CDC73, the scaffold component of the polymerase-associated factor complex (PAF1C), binds ETS1 and is recruited to activate ETS1 response elements. One of these elements is a previously unrecognized but highly conserved superenhancer, which we have tentatively labeled “E-Me” for “ETS1-dependent MYB enhancer”. Our objective is to determine the effects of Ets1-dependent trans-factors and cis-elements on the control of oncogenic transcriptional programs in Notch-activated T-ALL. We hypothesize that disrupting the ETS1-dependent combinatorial control of transcriptional elements by targeting CDC73 or the E-Me will safely repress Notch- induced T-ALL. To test this, we will determine the effects of inhibiting Ets1-dependent factors like Cdc73 on leukemia maintenance in mouse and human models of T-ALL. We will also determine the effects of inhibiting Ets1-dependent factors on oncogenic transcriptional programs and cis-element activation. Finally, we will determine the role of the E-Me element where trans-acting factors are recruited by ETS1 to collectively drive the oncogenic MYB effector pathway. Our work raises the possibility of targeting co-binding Notch-collaborating transcriptional regulators like Ets1 that create the chromatin context that directs Notch functions. Here we will establish Cdc73 as the bridge that connects Ets1 to transcriptional machinery and chromatin modifiers that activate promoters and enhancer elements and highlight E-Me as an important example. Therefore, if successful, our project is significant because we target the #1 ranked Notch-associated cofactor in a cancer to disable Notch- driven oncogenic signals without the toxicities of pan-Notch inhibitors seen in clinical trials. This project is innovative because, to our knowledge, no other Notch cofactor besides ETS1 has been shown to physically recruit Notch to chromatin genome-wide with strong statistical and orthogonal rigor and with a strikingly high convergence of Notch cofactor and Notch binding motifs that was validated by chromatin profiling.