The role of ATRX mutation in the epigenetic dysregulation of cell cycle in pediatric high-grade glioma

项目总结/摘要 背景和长期目标：小儿高级别胶质瘤（pHGG）是最致命的小儿胶质瘤之一， 癌症和新的靶向治疗是迫切需要的。批准的pHGG治疗仍然没有 目标和2年生存率低于20%。染色质重塑中的功能缺失突变 在30%的pHGG和DIPG中发现蛋白ATRX，通常在组蛋白变体中同时发生突变 H3F3A（H3.3）。我们以前开发了一种ATRX缺陷GBM的小鼠模型，并表明ATRX的缺失 导致对放射治疗的敏感性增加。我们最近发现具有同基因ATRX的HGG细胞 丢失表明照射和放射增敏后G1/S和G2/M检查点的不适当释放 与主细胞周期调节剂ATM的抑制剂。然而，驱动这种表型的机制还没有 已经建立，并且没有利用pHGG突变背景（例如H3.3）的模型被用于 研究ATRX损失。因此，迫切需要确定ATRX损失如何去调节细胞周期检查点， 并阐明H3F3A突变对细胞周期调控和放射增敏治疗的影响。 在缺乏这些知识的情况下，将靶向细胞周期检查点缺陷的疗法转化为治疗的能力 在ATRX缺陷型pHGG中仍然不太可能。 我们的总体目标是确定ATRX中细胞周期功能障碍的表观遗传机制 突变的pHGG和并发H3F3A突变的影响/靶向性。我们的中心假设是ATRX pHGG突变导致H3.3启动子结合和细胞周期检查点调节因子表达减少 检查点激酶1（CHK1），导致DNA损伤后允许的细胞周期检查点。我们建议 H3K27M突变的共同出现将增强这种缺陷，并增加ATM抑制的放射增敏作用。 这是基于我们的初步数据，表明（i）ATRX/H3.3沉积在CHEK1启动子位点，（ii） 在ATRX缺陷模型中照射后Chk1表达和检查点维持减少，和（iii） 与对照相比，在H3K27M细胞中ATM抑制增加细胞周期释放。 具体目的1：确定ATRX缺陷型pHGG细胞周期时相功能障碍的机制。我们 将通过整合多种人类和小鼠预处理的互补实验方法来实现这一目标。 pHGG中ATRX损失的临床模型，包括表观遗传、细胞周期和DNA损伤修复实验。 具体目的2：确定共发生的H3F3A突变对ATRX靶向性的影响- pHGG缺陷。我们将通过整合多种人类和小鼠临床前模型来实现这一目标。 pHGG中的ATRX损失，包括具有H3F3A的同基因控制的新型基因工程小鼠模型 和ATRX，以分离每种驱动因子对细胞周期缺陷和靶向性的贡献。 我们的综合实验方法将建立我们最近发现的表型背后的机制。 发现并为靶向ATRX缺陷型pHGG的独特特征的疗法打开了新的窗口。

PROJECT SUMMARY / ABSTRACT Background and long-term objectives: Pediatric high-grade glioma (pHGG) is among the most lethal pediatric cancers, and new targeted therapies are desperately needed. Approved therapies for pHGG remain non- targeted and 2-year survival rates are less than 20%. Loss of function mutations in the chromatin remodeling protein ATRX are found in 30% of pHGG and DIPG, usually with concurrent mutation in the histone variant H3F3A (H3.3). We previously developed a mouse model of ATRX-deficient GBM and showed that loss of ATRX results in increased sensitivity to radiation treatment. We recently discovered that HGG cells with isogenic ATRX loss demonstrate inappropriate release of G1/S and G2/M checkpoint after irradiation and radio-sensitization with inhibitors of the master cell cycle regulator ATM. However, the mechanism driving this phenotype has not been established, and no models utilizing a background of pHGG mutations (e.g. H3.3) have been employed to study ATRX loss. Thus, there is a critical need to determine how ATRX loss deregulates cell cycle checkpoints, and to clarify the impact of concurrent H3F3A mutation on cell cycle regulation and radiation sensitizing therapy. In the absence of such knowledge, the ability to translate therapies targeted to the cell cycle checkpoint deficit in ATRX-deficient pHGG will remain unlikely. Our overall objective in this proposal is to determine the epigenetic mechanism of cell cycle dysfunction in ATRX mutated-pHGG and the impact/targetability of concurrent H3F3A mutation. Our central hypothesis is that ATRX mutation in pHGG results in reduced H3.3-promotor binding and expression of the cell cycle checkpoint regulator Checkpoint Kinase 1 (CHK1), leading to permissive cell cycle checkpoints after DNA damage. We propose that co-occurrence of H3K27M mutation will enhance this deficit and increase radio-sensitization with ATM inhibition. This is based on our preliminary data demonstrating (i) ATRX/H3.3 deposition at CHEK1 promoter sites, (ii) reduction in Chk1 expression and checkpoint maintenance after irradiation in ATRX deficient models, and (iii) increased cell cycle release with ATM inhibition in H3K27M cells compared to controls. Specific Aim 1: Determine the mechanism of cell-cycle phase dysfunction in ATRX-deficient pHGG. We will accomplish this by integrating complementary experimental approaches of multiple human and mouse pre- clinical models of ATRX loss in pHGG, including epigenetic, cell cycle and DNA-damage repair experiments. Specific Aim 2: Determine the impact of co-occurring H3F3A mutation on the targetability of ATRX- deficient pHGG. We will accomplish this Aim by integrating multiple human and mouse pre-clinical models of ATRX loss in pHGG, including a novel genetically engineered mouse model with isogenic control of H3F3A and ATRX, to isolate contribution of each driver on cell-cycle deficit and targetability. Our integrative experimental approach will establish the mechanism behind the phenotypes we have recently discovered and open new windows for therapies targeted to the unique features of ATRX-deficient pHGG.