Focus on Dicer inhibition as a novel treatment for brain tumors

 描述(由申请人提供)：我们建议的重点是评估DICER抑制是否是选择性靶向髓母细胞瘤细胞的有效策略 神经元。虽然DICER的microRNA依赖功能是众所周知的，但最近的研究发现了DICER在DNA损伤修复中的一种新的、不依赖于MicroRNA的功能。由于保持基因组的完整性对于经历结构性复制应激诱导的DNA损伤的细胞的快速分裂至关重要，我们评估了在小脑发育的背景下，在体内解决这种DNA损伤的关键因素是否是DICER。在没有DICER的情况下，快速分裂的小脑颗粒神经元前体(CGNPs)积累了DNA损伤，导致了它们的退化。值得注意的是，这种退化被P53缺乏症挽救，这表明Dird缺乏症触发了P53介导的DNA损伤途径的激活。与增殖中的CGNPs高表达相比，我们发现在小脑颗粒神经元中几乎检测不到DICER。这些结果表明，与增殖的CGNPs不同，DICER可能不是有丝分裂后神经元存活所必需的--我们将在小鼠模型中检验这一假设，在小鼠模型中，我们可以有条件地选择性地删除有丝分裂后小脑神经元中的DICER。重要的是，我们还将评估Dier的失活是否会引发髓母细胞瘤的细胞死亡。髓母细胞瘤是一种儿童小脑肿瘤，发生于发育期后CGNPs的异常和持续增殖。髓母细胞瘤细胞表达DICER，我们预测，就像在发育过程中看到的增殖的CGNPs一样，增殖期的髓母细胞瘤细胞也依赖DICER来解决内源性DNA损伤。我们将在两种髓母细胞瘤小鼠模型中测试这一假设，在这两种模型中，我们可以很容易地评估Dier缺失对肿瘤生长和肿瘤消退的影响。总之，这些实验关键地评估了Dier作为髓母细胞瘤治疗靶点的意想不到的潜力，神经毒性最小。

 DESCRIPTION (provided by applicant): The focus of our proposal is to evaluate whether Dicer inhibition is an effective strategy to selectively target medulloblastoma cells while sparing neurons. While the microRNA-dependent functions of Dicer are well known, recent studies have identified a novel, microRNA-independent function of Dicer in DNA damage repair. As maintenance of genomic integrity is critical for rapidly dividing cells that experience constitutiv replicative stress-induced DNA damage, we evaluated whether Dicer was essential for resolving such DNA damage in vivo in the context of developing cerebellum. In the absence of Dicer, the rapidly dividing cerebellar granule neuron precursors (CGNPs) accumulated DNA damage, which resulted in their degeneration. Remarkably, this degeneration was rescued by p53 deficiency, indicating that Dicer deficiency triggered the activation of the p53-mediated DNA damage pathway. In contrast to the high expression of Dicer in proliferating CGNPs, we found that Dicer is virtually undetectable in cerebellar granule neurons. These results suggest that unlike the proliferating CGNPs, Dicer may not be essential for survival in postmitotic neurons - a hypothesis we will test in a mouse model where we can conditionally delete Dicer selectively in the postmitotic cerebellar neurons. Importantly, we will also evaluate whether inactivation of Dicer could trigger cell death in medulloblastomas. Medulloblastomas are pediatric cerebellar tumors that arise from the aberrant and sustained proliferation of CGNPs beyond the developmental period. Medulloblastoma cells express Dicer, and we predict that, just as seen with the proliferating CGNPs during development, the proliferating medulloblastoma tumor cells also depend on Dicer for resolving endogenous DNA damage. We will test this hypothesis in two mouse models of medulloblastoma where we can readily assess the outcome of Dicer deletion on tumor growth as well as tumor regression. Together, these experiments critically evaluate the unexpected potential of Dicer as a therapeutic target for medulloblastoma with minimal neurotoxicity.