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。这些肿瘤是由小脑中的祖细胞分裂而产生的。目前对髓母细胞瘤的治疗、手术、颅脑脊椎放射治疗和化疗，都会给幸存者留下终生的、毁灭性的副作用。此外，髓母细胞瘤的复发和转移是致命的。由于对导致肿瘤并促进其复发和转移的分子和细胞生物学事件缺乏了解，髓母细胞瘤的新治疗方法的开发受到了阻碍，这些治疗方法的衰弱程度较低，且更有效。更深入地了解基因和蛋白质如何调节小脑祖细胞的增殖，以及它们的异常调节如何促进肿瘤的发生，将确定新疗法的靶点，这些新疗法可以在不损害仍在发育中的大脑的情况下专门影响肿瘤的生长。髓母细胞瘤分为4-6个遗传亚类。大约30%的髓母细胞瘤与Sonic hedgehog(SHH)途径的遗传特征有关，该途径的异常激活在基因工程小鼠模型中促进了髓母细胞瘤的发生。小脑颗粒神经元前体(CGNPs)被认为是SHH髓母细胞瘤的起源细胞，它们在发育过程中依赖SHH进行增殖。在体外，这些细胞(来自新生小鼠)像在体内一样分裂和分化，因此它们对于研究信号通路如何调控正常脑发育和髓母细胞瘤的增殖是有用的。利用这样的培养和小鼠模型，我们发现Shh促进癌基因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SHH髓母细胞瘤中高度表达。在“Hedgehog：YAP：IGF2/mTOR轴在小脑前体分裂和髓母细胞瘤中的作用”的提案中描述的研究集中在描述这些通路如何相互作用以促进髓母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髓母细胞瘤荷瘤小鼠的分析，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髓母细胞瘤的生长、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，在Shh有丝分裂和癌基因信号转导中发挥关键作用的假设。这些研究的长期目标是确定调节Shh和IGF下游效应物(如YAP和HIF)的功能如何成为治疗髓母细胞瘤和其他这些途径活跃的癌症的有效治疗方法。

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.