Posttranslational Regulation of FOXA1 in Breast Cancer

项目摘要 乳腺癌是女性癌症死亡的第二大原因，占所有乳腺癌的近75%。 肿瘤在诊断时表达雌激素受体α(ER)。尽管在治疗上取得了成功 以ER功能为靶点的内分泌治疗，约30%-40%的肿瘤对内分泌产生抗药性 治疗，无论是通过从头开始还是后天抵抗，仍然保留了ER的表达。在此，我们建议 为了研究FOXA1的调控，FOXA1是一种使ER与染色质结合的先驱转录因子，其 理论上的抑制将绕过内分泌治疗抵抗的已知机制。在乳腺癌方面， FOXA1负责基因组中几乎所有的ER结合事件，其上调与 通过内分泌抵抗中的增强子重新编程。然而，关于如何做到这一点的信息很少。 FOXA1本身是受调控的，以及癌细胞如何重新利用其开创性活动来推动肿瘤形成。 为此，我们的实验室一直在研究内分泌和免疫系统之间的串扰 乳腺癌。我们已经发现，FOXA1在对促炎细胞因子的反应中，被驱动到非 跨越基因组的典型位置，促进雌激素连接的内质网染色质的可及性。这些新的 在基因组的致密/潜伏区发现了形成的增强子，并促进了 可以预测患者不良临床结果的新基因集。与此同时，我们发现FOXA1 翻译后修饰(PTM)对两个进化保守的促炎细胞因子的反应 氨基酸。FOXA1对外界刺激的翻译后修饰尚未显示 之前，并提出了一个重要的机制，FOXA1的调节和功能。因此， 该项目的总体目标是确定允许促炎信号改变的分子事件 通过调节FOXA1功能的内分泌信号和这种串扰的生物学后果。 我们假设雌激素和肿瘤坏死因子α指导的FOXA1的PTM决定结合部位的选择，驱动ERα 到整个基因组中的非规范增强子，导致肿瘤发生的基础表达程序 乳腺癌的风险。为了系统地检验这一假设，将使用一套完整的分子、基因组和 蛋白质组学方法：(目标1)确定FOXA1 PTMS在其先锋功能和染色质中的作用 占有率，(目标2)确定FOXA1 PTM的作者和读者，(目标3)了解炎症- 基于独立于PTMS的FOXA1调制。我们将在乳腺癌细胞中进行这些实验 细胞系，ER+患者来源的异种移植物(PDX)，以及从患者肿瘤分离的ER+成熟腔细胞。这个 对FOXA1激素受体信号的依赖使其成为一个有吸引力的治疗靶点。虽然有 目前还没有已知的FOXA1抑制剂及其蛋白质结构使其难以靶向治疗，我们的 理解基本分子机制的能力与我们更好地发育的能力直接相关 治疗性干预。定义FOXA1是如何监管的成为这一努力的关键。

Project Summary Breast cancer is the second leading cause of cancer mortality in women and nearly 75% of all breast tumors express estrogen receptor alpha (ER) at the time of diagnosis. Despite the therapeutic successes of endocrine therapies designed to target ER function, about 30-40% of tumors become resistant to endocrine therapy, either through de novo or acquired resistance, and still retain the expression of ER. Herein we propose to study the regulation of FOXA1, a pioneer transcription factor that enables ER binding to chromatin, whose theoretical inhibition would circumvent known mechanisms of endocrine therapy resistance. In breast cancer, FOXA1 is responsible for almost all of the ER binding events in the genome and its upregulation is associated with enhancer reprograming in endocrine resistance. However, there is a paucity of information about how FOXA1 itself is regulated and how cancer cells repurpose its pioneering activities to drive oncogenesis. To this end, our lab has been studying the crosstalk between the endocrine and immune systems in breast cancer. We have discovered that FOXA1, in response to the proinflammatory cytokines, is driven to non- canonical sites across the genome to promote chromatin accessibility for estrogen-liganded ER. These newly formed enhancers were found in compacted/latent regions of the genome and promoted the expression of a novel gene set that was predictive of poor clinical outcomes in patients. Concurrently, we discovered that FOXA1 is post-translationally modified (PTM) in response to proinflammatory cytokines at two evolutionarily conserved amino acids. The post-translational modification of FOXA1 in response to external stimuli has not been shown before and suggests an important mechanism that underlies FOXA1 regulation and function. Therefore, the overall goal of this project is to determine the molecular events that allow proinflammatory signaling to alter endocrine signaling through modulation of FOXA1 function and the biological consequences of this crosstalk. We hypothesize that estrogen- and TNFα-directed PTMs of FOXA1 dictate binding site selection, driving ERα to non-canonical enhancers across the genome, leading to expression programs that underlie the tumorigenesis of breast cancer. To systematically test this hypothesis, will use an integrated set of molecular, genomic, and proteomic approaches to: (Aim 1) define the role of FOXA1 PTMs on its pioneering function and chromatin occupancy, (Aim 2) identify the writers and readers of FOXA1 PTMs, and (Aim 3) understand inflammation- based modulation of FOXA1 independent of PTMs. We will perform these experiments in breast cancer cell lines, ER+ patient-derived xenografts (PDX), and in ER+ mature luminal cells isolated from patient tumors. The dependence on FOXA1 for hormone receptor signaling makes it an attractive therapeutic target. While there are currently no known inhibitors of FOXA1 and its protein structure makes it difficult to target therapeutically, our ability to understand basic molecular mechanisms is directly correlated with our ability to develop better therapeutic interventions. Defining how FOXA1 is regulated becomes key to this endeavor.