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

发现NOTCH1是T细胞急性淋巴细胞白血病最常见的癌基因 患者提高了对这种癌症进行靶向治疗的希望。不幸的是，在临床试验中，PAN-Notch抑制剂 由于Notch功能的丧失，GSI引起了剂量限制性毒性，特别是肠道毒性。我们相遇的想法 这一挑战源于果蝇的研究表明Notch需要共同结合的转录因子 与其反应元件合作，生成细胞类型特定的基因表达程序。如果这些“诺奇- 协同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 反对Notch信号，规避GSI毒性。因此，我们的长期目标是确定与Notch合作 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 ETS1是T细胞中排名最高的Notch相关转录因子，但不是肠道细胞。 与GSI相比，Ets1失活对T-ALL细胞的影响同样有害，但要温和得多 对小鼠模型的肠道内稳态和整体健康的影响。从机制上讲，我们证明了CDC73、 聚合酶相关因子复合体(PAF1C)的支架成分，与ETS1结合，并被招募到 激活ETS1响应元素。其中一个元素是以前未被发现但高度保守的 超级增强子，我们暂时将其标记为“E-Me”，即“ETS1依赖的MYB增强子”。我们的目标 目的是确定Ets1依赖的反式因子和顺式元件对肿瘤发生的控制作用 Notch激活的T-ALL的转录程序。我们假设，扰乱依赖ETS1的 靶向CDC73或E-Me的转录元件的组合控制将安全地抑制Notch- 诱导T-ALL。为了测试这一点，我们将确定抑制Ets1依赖因子(如CDC73)对 T-ALL小鼠和人模型的白血病维持。我们还将确定抑制的效果 Ets1依赖因子对致癌转录程序和顺式元件激活的影响。最后，我们会 确定电子邮件元素的作用，其中反式作用因子由ETS1招募，以共同推动 致癌MYB效应通路。我们的工作提高了靶向共同结合Notch-Collaborating的可能性 转录调节因子，如Ets1，创造了指导Notch功能的染色质上下文。在这里，我们将 将CDC73建立为连接Ets1与转录机制和染色质修饰物的桥梁 激活推动者和增强者元素，并强调E-Me是一个重要的例子。因此，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相关辅助因子来禁用Notch- 驱动致癌信号，没有临床试验中看到的PAN-Notch抑制剂的毒性。这个项目是 创新是因为，据我们所知，除了ETS1，还没有其他Notch辅助因子被证明是物理上的 Recruit Notch到染色质全基因组，具有很强的统计和正交严谨性，并具有惊人的高 通过染色质图谱验证了Notch辅因子和Notch结合基序的收敛。

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.