New Vulnerabilities in MYC-Driven Breast Cancer

三阴性乳腺癌（TNBC）是一种侵袭性乳腺癌亚型， 每年新增20万例诊断。癌基因Myc是TNBC的常见驱动因素。但尽管 尽管对Myc的生物学和分子功能进行了重要的研究，但还没有出现易于治疗的疗法， 抑制这种致癌转录因子。TNBC和其他Myc驱动的癌症仍然不符合当前的 靶向治疗，强调迫切需要确定这些恶性肿瘤的新的脆弱性。 除了促进肿瘤发生外，Myc等癌基因还在肿瘤细胞中产生独特的应激。 癌细胞，统称为致癌应激。使用平行的全基因组RNAi筛选，我们发现 Myc对TNBC施加了一种新的致癌应激，我们称之为RNA剪接应激，或RSS （Kessler，Science 2012; Hsu，Nature 2015）。在许多癌症类型中，Myc（或其他致癌损伤）在全球范围内 放大转录，导致剪接体上的前mRNA负荷增加。因此，Myc驱动 TNBC对剪接体中的适度扰动非常敏感（通过增强RSS）。重要的是， 剪接体的药理学或遗传抑制剂损害TNBC的原发性和转移性进展， 在动物临床前模型中耐受良好。虽然剪接体抑制剂已进入临床试验， RSS和剪接体抑制剂选择性杀死癌细胞的机制尚不清楚。在此我们 我们建议发现RNA剪接应激的感知和响应途径，并描绘RNA剪接应激的分子机制。 RSS触发癌细胞死亡的机制。 目的1：描述RSS在体内Myc + TNBC中刺激的dsRNA敏感通路（DSP）。我们 初步数据表明，RSS通过触发先天免疫途径诱导TNBC凋亡， 并对双链RNA有反应通过利用具有新的遗传和蛋白质组学平台的TNBC PDX队列，我们将 确定DSP和其他应激反应途径是如何被激活以响应剪接体抑制的。 目标2：探索RSS如何触发TNBC中的dsRNA传感途径。许多病毒病原体编码 由先天免疫系统的dsRNA传感器检测的dsRNA基因组。我们的研究表明 RSS导致内含子保留mRNA的细胞质积累，这是dsRNA的潜在来源。使用新 测序和单分子显微镜的方法，我们将研究的机制，RSS的形状 TNBC转录组的二级结构和亚细胞定位并刺激dsRNA传感器。 目标3：描述DSP和其他应激反应途径如何控制TNBC对 剪接体抑制剂。我们假设，有一个协调的细胞反应RSS平行 被充分研究的稳态应激反应，如未折叠蛋白质反应。通过利用前沿遗传学 并确定RSS的新调节因子，我们建议揭示这种新型细胞的遗传框架。 并提供利用这种癌症脆弱性的新的治疗方法。

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with more than 200,000 new diagnoses each year. The oncogene Myc is a common driver of TNBC. However, despite important research into the biologic and molecular functions of Myc, no tractable therapies have emerged to inhibit this oncogenic transcription factor. TNBC and other Myc-driven cancers remain recalcitrant to current targeted therapies, underlining the urgent need to identify new vulnerabilities in these malignancies. In addition to promoting tumorigenesis, oncogenes such as Myc also produce unique stresses in cancer cells, collectively termed oncogenic stress. Using parallel whole-genome RNAi screens, we discovered that Myc imposes a new type of oncogenic stress on TNBCs that we term RNA splicing stress, or RSS (Kessler, Science 2012; Hsu, Nature 2015). In many cancer types, Myc (or other oncogenic insults) globally amplifies transcription leading to increased pre-mRNA burden on the spliceosome. Consequently, Myc-driven TNBCs are exquisitely sensitive to modest perturbations in the spliceosome (by enhancing RSS). Importantly, pharmacologic or genetic inhibitors of the spliceosome impair primary and metastatic progression of TNBC and are well tolerated in animal pre-clinical models. While spliceosome inhibitors have entered clinical trials, the mechanisms by which RSS and spliceosome inhibitors selectively kill cancer cells are unknown. Herein, we propose to discover the pathway(s) sensing and responding to RNA splicing stress and to delineate the mechanisms by which RSS triggers cancer cell death. Aim 1: Delineate the dsRNA-sensing pathways (DSP’s) stimulated by RSS in Myc+ TNBCs in vivo. Our preliminary data suggest that RSS induces TNBC apoptosis by triggering innate immune pathways that detect and respond to dsRNAs. By leveraging a TNBC PDX cohort with new genetic and proteomic platforms, we will determine how DSP’s and other stress response pathways are activated in response to spliceosome inhibition. Aim 2: Discover how RSS triggers dsRNA-sensing pathways in TNBCs. Many viral pathogens encode dsRNA genomes that are detected by dsRNA-sensors of the innate immune system. Our studies indicate RSS leads to cytoplasmic accumulation of intron-retained mRNAs, a potential source of dsRNAs. Using new sequencing and single-molecule microscopy methods, we will study the mechanisms by which RSS shapes the secondary structure and subcellular localization of TNBC transcriptomes and stimulates dsRNA-sensors. Aim 3: Delineate how DSPs and other stress response pathways govern TNBC response to spliceosome inhibitors. We hypothesize that there is a coordinated cellular response to RSS that parallels well-studied homeostatic stress responses like the unfolded protein response. By leveraging forward genetics and identifying new regulators of RSS, we propose to unveil a genetic framework for this novel type of cellular stress and provide new therapeutic inroads that exploit this cancer vulnerability.