Hedgehog:YAP:IGF2/mTOR axis in cerebellar precursor division and medulloblastoma

描述（申请人提供）：髓母细胞瘤是最常见的儿童实体恶性肿瘤。这些肿瘤在幼儿中由小脑的祖细胞分裂而产生。目前治疗髓母细胞瘤的方法，手术，颅脊髓放射和化疗，给幸存者留下了终生的，毁灭性的副作用。此外，髓母细胞瘤的复发和转移是致命的。由于缺乏对导致肿瘤和促进其复发和转移的分子和细胞生物学事件的理解，新的髓母细胞瘤治疗方法的发展受到了阻碍。更深入地了解基因和蛋白质如何调节小脑祖细胞的增殖，以及它们的调节失调如何促进肿瘤发生，将确定新疗法的目标，这些新疗法可以特异性地影响肿瘤生长，而不会损害仍在发育的大脑。髓母细胞瘤可分为4-6个遗传亚类。大约30%的成神经管细胞瘤与Sonic hedgehog （SHH）通路的遗传特征相关，在基因工程小鼠模型中，该通路的异常激活可促进成神经管细胞瘤的发生。小脑颗粒神经元前体（CGNPs）被认为是SHH成神经管细胞瘤的起源细胞，它们在发育过程中依赖于SHH进行增殖。在体外，这些细胞（来自新生小鼠）的分裂和分化与在体内一样多，因此它们对于研究正常大脑发育和成神经管细胞瘤期间信号通路如何调节增殖是有用的。使用这种培养和小鼠模型，我们发现Shh促进致癌基因YAP的活性，进而驱动IGF2的表达，促进增殖并允许肿瘤细胞在辐射中存活，这可能导致肿瘤复发和基因组不稳定。重要的是，我们已经证明YAP和IGF2在人类SHH髓母细胞瘤中高度表达。“Hedgehog:YAP:IGF2/mTOR轴在小脑前体分裂和成神经管细胞瘤中的作用”提案中描述的研究侧重于表征这些途径如何相互作用以促进成神经管细胞瘤的生长和转移。这些研究使用原代CGNP培养、野生型和Shh髓母细胞瘤小鼠的分析以及匿名的人类患者样本来研究YAP如何调节IGF2， IGF2抑制是否可能是一种可行的治疗方式，确定YAP在Shh髓母细胞瘤生长、复发和转移中的需求。并验证缺氧诱导因子（HIF）位于Shh/ igf介导的mTOR激活的下游，并在Shh有丝分裂和致癌信号传导中发挥关键作用的假设。这些研究的长期目标是确定如何调节Shh和IGF下游效应物（如YAP和HIF）的功能，可能是治疗成神经管细胞瘤和其他这些途径活跃的癌症的有用治疗方法。

DESCRIPTION (provided by applicant): Medulloblastomas are the most common solid pediatric malignant tumors. These tumors arise in young children from dividing progenitor cells in the cerebellum. Current treatments for medulloblastoma, surgery, cranio-spinal radiation, and chemotherapy, leave survivors with life-long, devastating side effects. Moreover, medulloblastoma recurrence and metastasis are lethal. Development of new medulloblastoma therapies that are less debilitating and more effective has been hampered by poor understanding of the molecular and cell biological events causing the tumors and promoting their recurrence and metastasis. Greater insight into how genes and proteins regulate proliferation in cerebellar progenitor cells, and how their dys-regulation contributes to tumorigenesis, will identify targets for new therapies that can specifically affect tumor growth without damaging the still-developing brain. Medulloblastomas are divided into 4-6 genetic subclasses. Approximately 30% of medulloblastomas are associated with a Sonic hedgehog (SHH) pathway genetic signature, and aberrant activation of this pathway promotes medulloblastoma in genetically engineered mouse models. Cerebellar granule neuron precursors (CGNPs) have been proposed as cells of origin for SHH medulloblastomas, and they depend on SHH for proliferation during development. In vitro, these cells (derived from neonatal mice) divide and differentiate much as they do in vivo, hence they are useful for studying how signaling pathways regulate proliferation during normal brain development and in medulloblastomas. Using such cultures and mouse models, we have found that Shh promotes activity of the oncogene YAP, which in turn drives expression of IGF2, contributing to enhanced proliferation and permitting tumor cells to survive radiation, which can lead to tumor recurrence and genomic instability. Importantly, we have shown that YAP and IGF2 are highly expressed in human SHH medulloblastomas. The studies described in the proposal "Hedgehog:YAP:IGF2/mTOR axis in cerebellar precursor division and medulloblastoma" focus on characterizing how these pathways interact to promote medulloblastoma growth and metastasis. These studies use primary CGNP cultures, analysis of wild-type and Shh medulloblastoma-bearing mice, and anonymized human patient samples to investigate how YAP regulates IGF2, whether IGF2 inhibition may be a viable therapeutic modality, determine the requirement for YAP in Shh medulloblastoma growth, recurrence, and metastasis, and test the hypothesis that hypoxia-inducible factor (HIF) lies downstream of Shh/IGF-mediated mTOR activation and plays critical roles in Shh mitogenic and oncogenic signaling. The long-term goal of these studies is to determine how modulating the function of Shh and IGF downstream effectors such as YAP and HIF might be a useful therapeutic approach to treat medulloblastomas and other cancers where these pathways are active.