A causal role for asymmetric cell division defects in glioma initiation

描述(申请人提供)：胶质瘤是成人中最常见和最致命的脑肿瘤，可由突变的少突胶质细胞前体细胞以一种基本未知的机制发生。消除这些恶性OPC的具体治疗方法尚未开发出来，主要是因为与其恶变相关的潜在机制尚未很好地了解。这项建议的目的是通过调查不对称细胞分裂中的缺陷来寻找OPC恶性转化的潜在原因，并测试特定的药理学药物，以重新存储这些缺陷的能力，以影响肿瘤生长。我们最近首次提供了少突胶质前体细胞不对称分裂自我更新和产生成熟少突胶质细胞的分子证据，表明跨膜蛋白多糖NG2在有丝分裂过程中不对称分布，从而促进表皮受体生长因子的激活和自我更新，并阻止NG2+后代的分化。NG2不对称的少突胶质细胞前体细胞异常地自我更新，不能分化并转变为胶质瘤起始细胞。我们假设，失去细胞的不对称性会通过破坏自我更新和分化来转化少突胶质前体细胞。我们的初步结果确实表明，通过移除保守的不对称调节因子致死性巨型幼虫LGL1在少突胶质前体细胞中的表达来实施不对称细胞分裂会导致肿瘤的形成。此外，药物抑制Plk1，一种保守的不对称细胞分裂调节因子，在恶性的胶质瘤启动细胞中恢复NG2的不对称性。在如此强大的初步数据的指导下，我们有三个具体的目标：在第一个目标中，我们确定LGL1的少突胶质祖细胞特异性缺失是否导致NG2依赖的肿瘤启动。为了实现这一目标，我们建议使用CRE-LOX方法在小鼠模型中产生单独缺乏LGL1而共同缺乏LGL1和NG2的少突胶质前体细胞和少突胶质前体细胞。对这些模型中肿瘤形成的分析将使我们能够区分LGL1在肿瘤启动中的NG2依赖和非独立功能。在第二个目标中，我们将确定OPC中LGL1缺失、NG2不对称性中断和肿瘤启动的因果联系。我们将测试LGL1-/-少突胶质前体细胞在NG2不对称、自我更新和分化方面的缺陷。为了将LGL1和NG2不对称缺失与恶性转化联系起来，我们将评估LGL1-/-的恶性潜能，并测试NG2的共同缺失是否改善肿瘤的形成，以及对称、异位NG2的重新表达是否增强了LGL1-/-OPC的缺陷。在第三个目标中，我们将研究不对称细胞分裂对肿瘤生长的影响的药理学调节。我们的目标是证明不对称细胞分裂的丧失是肿瘤发生的原因，从而评估将不对称细胞分裂重新存储到恶性前体细胞的新的治疗方法及其对肿瘤生长的影响。

DESCRIPTION (provided by applicant): Gliomas are the most common and deadly brain tumors in adults and can arise from mutant oligodendrocyte progenitors by a largely unknown mechanism. Specific treatments to eliminate these malignant OPC have not been developed, primarily because the underlying mechanisms associated with their malignant transformation are not well understood. The goal of this proposal is to find the underlying causes for malignant transformation of OPC by investigating defects in asymmetric cell division and to test specific pharmacological agents targeted to re-store these defects for their ability to impact tumor growth. We have recently provided first molecular evidence that oligodendrocyte progenitors divide asymmetrically to self-renew and generate mature oligodendrocytes by showing that the transmembrane proteoglycan NG2 distributes asymmetrically during mitosis and thereby promotes activation of epidermal receptor growth factor and self-renewal and prevents differentiation of the NG2+ progeny. Oligodendrocyte progenitors with defective NG2 asymmetry aberrantly self-renew, fail to differentiate and turn into glioma - initiating cells. We hypothesize that losing cellular asymmetry transforms oligodendrocyte progenitor cells, by disrupting self-renewal and differentiation. Our preliminary results indeed show that enforcing a block of asymmetric cell division by removing expression of conserved asymmetry regulator Lethal giant larvae, LGL1, in oligodendrocyte progenitors causes tumor formation. Moreover, pharmacological inhibition of Plk1, a conserved regulator of asymmetric cell division, re-stores NG2 asymmetry in malignant, glioma- initiating cells. Guided by such strong preliminary data, we have three specific aims: In the first aim, we determine whether oligodendrocyte progenitor-specific loss of LGL1 causes NG2-dependent tumor- initiation. To fulfill this aim, we propose to generate oligodendrocyte progenitors and oligodendrocyte progenitor precursor deficient for LGL1 alone and co-deficient for LGL1 and NG2, in mouse models using a CRE-LOX approach. The analysis of tumor formation in these models will enable us to distinguish between NG2-dependent and - independent functions of LGL1 in tumor initiation. In the second aim, we will determine a causal link of loss of LGL1, disrupted NG2 asymmetry and tumor initiation in OPC. We will test LGL1-/- oligodendrocyte progenitors for defects in NG2 asymmetry, self-renewal and differentiation. To link losing LGL1 and NG2 asymmetry to malignant transformation, we will evaluate the malignant potential of LGL1-/- and test whether co-deletion of NG2 ameliorates tumor formation and re-expression of symmetric, ectopic NG2 enhances defects in LGL1-/- OPC. In the third aim, we will investigate the pharmacological modulation of asymmetric cell division for its impact on tumor growth. Our goal is to prove that loss of asymmetric cell division is causal to tumor initiation and thereby evaluate novel therapeutic approaches that re-store asymmetric cell division to malignant progenitors and for their potential to impact tumor growth.