Project 4: The BRCA Network in Medulloblastoma Responses to Replication Stress

髓母细胞瘤对复制应激反应中的BRCA网络(方案4) 摘要： BRCA1和BRCA2是DNA链断裂修复的关键基因 重组(HR)。PALB2的功能是将BRCA1与BRCA2连接起来。由于两人之间的亲密关系 BRCA1、PALB2和BRCA2，这些基因及其编码的蛋白质被认为是 网络。“带有BRCA突变的癌症表现出独特的“BRCAness”分子特征，包括 对复制应激药过敏。除了核心BRCA蛋白外，其他BRCA1/2- 相关基因通常具有“BRCAness”特征。 脑瘤是儿童癌症相关死亡的主要原因，髓母细胞瘤(MBS)占 治疗超过60%的儿科肿瘤。目前MBS的治疗主要依靠局部放射治疗。 与普通化疗相结合。针对MBS的靶向治疗还没有被积极考虑。 最近，人们认识到BRCA2和PALB2这两个核心基因的种系突变是人类致病的主要原因之一。 “BRCA网络”是MBS的主要原因之一。此外，广泛的DNA碱基激活 损伤信号和过度复制应激在不同的MBS组中普遍存在。基于 20%-30%的零星MB，包括MB组2、3和4的基因组特征可能带有HR 缺陷(HRD)。这些最新的发展提出了一个重要的问题，即DNA损伤是否可以修复 缺陷和复制应激是MBS对新的治疗发展的共同脆弱性 目标是人力资源部。如果是这样的话，如何有效地识别患有HRD的个别病例仍然是一个问题。 在初步研究中，我们在胚胎中建立了BRCA1、PALB2和BRCA2的条件性敲除 利用胶质纤维酸性蛋白(GFAP)启动子驱动的Cre诱导多潜能干/祖细胞 表情。我们首次证明了PALB2和BRCA1的条件缺失是有效的诱导剂 与BRCA2损失的效力相似。这些MBS的初步基因组特征显示 “BRCAness”确定了可用来定义人力资源开发状况的几个独特的结构特征。通过 用一种正在开发的拓扑异构酶1抑制剂治疗新生MBS，我们发现它对 延长MBS小鼠的存活时间。因此，我们假设起源于BRCA缺陷的MBS具有 独特的基因组特征来确定患有HRD的MBS，并将更多地靶向治疗MBS伴HRD 比目前的治疗方案更有效。在Project-4中，我们利用了我们最近在 建立BRCA相关的小鼠MB模型，并努力鉴定与 并验证MB“BRCAness”对复制应激药物的反应。目标1将确定结构 以及染色体上下文签名，准确地反映了表现为“BRCAness”的MBS中的HDR状态。 目标2将在实验中针对MBS中HRD的脆弱性，并研究其潜在机制 治疗后肿瘤复发。这项研究的成功将有效地建立一种新的治疗方法 MB处理。

The BRCA Network in Medulloblastoma Responses to Replication Stress (Project-4) Abstract: BRCA1 and BRCA2 are critical genes for the repair of DNA strand breaks (DSB) via homologous recombination (HR). PALB2 functions to bridge BRCA1 with BRCA2. Due to the intimate relationship between BRCA1, PALB2, and BRCA2, these genes and their coded proteins are considered the core of a “BRCA network.” Cancers with BRCA mutations display unique molecular features of “BRCAness,” including hypersensitivity to replication stress drugs. In addition to the core BRCA proteins, defects of other BRCA1/2- associated genes often share the “BRCAness” characteristics. Brain tumors are the leading cause of childhood cancer-related deaths, and medulloblastomas (MBs) account for more than 60% of pediatric tumors. Current treatments of MBs mainly rely on local control by radiation in combination with generic chemotherapy. Targeted therapy has not been vigorously considered for MBs. Recently, it has been recognized that germline mutations in BRCA2 and PALB2, two of the core genes in the “BRCA Network,” are among the top causes of MBs. Furthermore, widespread basal activation of DNA damage signaling and excessive replication stress were common among different groups of MBs. Based on genomic signatures, 20-30% of sporadic MBs, including those from MB groups 2, 3, and 4, likely bear HR defects (HRD). These recent developments raise an important question of whether DNA damage repair defects and replication stress represent common vulnerabilities of MBs to new therapeutic developments targeting HRD. If so, how to efficiently identify the individual cases with HRD remains an issue. In the preliminary studies, we established conditional knockouts of Brca1, Palb2, and Brca2 in embryonic multi-potential stem and progenitor cells using the glial fibrillary acidic protein (GFAP) promoter-driven Cre expression. For the first time, we demonstrated that conditional loss of Palb2 and Brca1 are effective inducers of MBs, with a similar potency as that of Brca2 loss. An initial genomic characterization of these MBs exhibiting “BRCAness” had identified several unique structural features that can be used to define the HRD status. By treating the de novo MBs with a developing topoisomerase 1 inhibitor, we found it to be very effective to extend the survival of mice with MBs. Thus, we hypothesize that MBs originated from BRCA defects have unique genomic signatures to define the MBs with HRD, and targeted therapy of MBs with HRD will be more effective than the current treatment regimens. In Project-4, we take advantage of our recent success in establishing BRCA-related mouse MB models and strive to identify the genomic signatures associated with HRD and to validate the MB “BRCAness” response to replication stress drugs. Aim 1 will identify the structural and chromosome-context signatures that accurately reflect the HDR status in MBs exhibiting “BRCAness”. Aim 2 will experimentally target the vulnerability of HRD in MBs and investigate the potential mechanism of tumor recurrence after the treatment. The success of this study would effectively establish a new remedy for MB treatment.