The effects of the unfolded protein response on medulloblastoma

描述（申请人提供）：髓母细胞瘤是一种高度恶性的小儿脑肿瘤，5年生存率约为60%。sonic hedgehog （SHH）通路在成神经管细胞瘤的发展中起关键作用。在小鼠中，SHH受体PTCH1的杂合性缺失导致成神经管细胞瘤的发生率约为14%。另一方面，我们已经证明异位表达免疫细胞因子干扰素- ？（IFN-?）在中枢神经系统发育期间表现为小脑发育不良或成神经管细胞瘤。内质网（ER）应激由未折叠或错误折叠蛋白的积累引发，激活未折叠蛋白反应（UPR）。UPR激活胰内质网激酶（PERK），该激酶通过磷酸化翻译起始因子2a （eIF2a）来协调一个适应性程序。eIF2a的磷酸化通过蛋白生物合成的全局衰减和诱导许多应激诱导的细胞保护基因来促进应激抵抗状态。生长停滞和DNA损伤34 （GADD34）失活，是一种胁迫诱导的磷酸酶复合物的调控亚基，可使eIF2a去磷酸化，增加应激细胞中磷酸化的eIF2a水平，并使细胞适应各种应激。在肿瘤细胞积累克服细胞周期和凋亡检查点的突变后，对肿瘤微环境的适应被认为是恶性肿瘤的关键驱动因素。有证据表明，普遍定期审议可能在这一适应进程中发挥作用。有趣的是，我们的初步观察表明，在IFN- ？-表达转基因小鼠和PTCH1杂合缺陷小鼠。因此，我们的广泛假设是，UPR通过使肿瘤细胞适应肿瘤微环境中的各种应激（如缺氧和营养缺乏），从而促进成神经管细胞瘤的发展，并使细胞对化疗产生耐药性。本项目的具体目的如下：(1)确定GADD34失活是否增强PERK- eIF2a通路的活性并与IFN-协同作用？诱导成神经管细胞瘤；(2)确定PERK- eIF2a通路的激活是否促进PTCH1杂合缺陷小鼠成神经管细胞瘤的发展；(3)确定PERK通路是否能使人髓母细胞瘤细胞适应缺氧和营养缺乏，并使细胞对化疗药物产生耐药性。这项工作的意义在于，它将揭示UPR在成神经管细胞瘤的发展和化疗耐药性中的作用。这些信息对于开发治疗这种疾病的新治疗策略至关重要。

DESCRIPTION (provided by applicant): Medulloblastoma is a highly malignant pediatric brain tumor with a 5-year survival rate of ~ 60%. The sonic hedgehog (SHH) pathway plays a critical role in medulloblastoma development. Heterozygous deficiency of patched1 (PTCH1), a SHH receptor, in mice results in ~ 14% incidence of medulloblastoma. On the other hand, we have shown that transgenic mice that ectopically express immune cytokine interferon- ? (IFN-?) in the central nervous system during development display cerebellar dysplasia or medulloblastoma. Endoplasmic reticulum (ER) stress, initiated by the accumulation of unfolded or misfolded proteins, activates the unfolded protein response (UPR). The UPR activates pancreatic ER kinase (PERK), which coordinates an adaptive program by phosphorylating translation initiation factor 2a (eIF2a). Phosphorylation of eIF2a promotes a stress-resistant state through global attenuation of protein biosynthesis and induction of numerous stress- induced cytoprotective genes. Inactivation of growth arrest and DNA damage 34 (GADD34), a stress-inducible regulatory subunit of a phosphatase complex that dephosphorylates eIF2a, increases the level of phosphorylated eIF2a in stressed cells and adapts cells to various stresses. Adaptation to the tumor microenvironment is thought to be a key driver of malignancy after tumor cells accumulate mutations that overcome cell cycle and apoptotic checkpoints. Evidence is emerging that the UPR may play a role in this adaptation process. Interestingly, our preliminary observations suggest that the PERK pathway is activated in medulloblastoma in both IFN- ? -expressing transgenic mice and PTCH1 heterozygous deficient mice. Thus, our broad hypothesis is that the UPR promotes medulloblastoma development by adapting the tumor cells to various stresses in the tumor microenvironment such as hypoxia and nutrition deficiency, and renders the cells resistant to chemotherapy. The specific aims of this project are as follows: (1) to determine whether GADD34 inactivation enhances the activity of the PERK- eIF2a pathway and acts in synergy with IFN-? to induce medulloblastoma; (2) to determine whether activation of the PERK- eIF2a pathway promotes medulloblastoma development in PTCH1 heterozygous deficient mice; and (3) to determine whether the PERK pathway adapts human medulloblastoma cells to hypoxia and nutrition deficiency, and renders the cells resistant to chemotherapy agents. The significance of this proposed work is that it will shed light on the role of the UPR in medulloblastoma development and chemotherapy resistance. Such information is critical to developing novel therapeutic strategies for treating this disease.