Ubiquitination and Deubiquitination of c-Myc in Glioblastoma

摘要 摘要脑胶质母细胞瘤(GBM)是最常见、最致命的原发脑肿瘤。 预后。基底膜在胶质瘤群体中表现出显著的细胞异质性 位于分化层次顶端的干细胞(GSCs)。因为GSC促进了 肿瘤血管生成、肿瘤侵袭、治疗抵抗和肿瘤复发 消除GSC或诱导其分化可能有效改善GBM 治疗。GSCs干细胞样属性由一组核心维持 转录调控因子包括c-Myc。MYC在促进GBM方面发挥着关键作用 恶性生长和辐射抵抗。C-Myc不仅在转录水平上受到调控 但也受到翻译后修改的严格控制。我们的初步数据 表明c-Myc被E3泛素连接酶FBXL14泛素化，并靶向于 非干细胞胶质瘤细胞的降解。在GSCs中，c-Myc蛋白通过 USP13(泛素特异性蛋白水解酶13)介导的去泛素化。重要的是 相对于非干细胞胶质瘤细胞和神经细胞，USP13在神经干细胞中优先表达 祖细胞。靶向USP13的shRNA显著降低c-Myc蛋白，促进 GSC分化，破坏GSC维持，并有效抑制GSC 肿瘤球的形成。这些数据表明，USP13在 通过稳定Myc来维持GSC的自我更新和致瘤潜能。我们 假设USP13拮抗FBXL14稳定c-Myc和促进c-Myc GSCs的维持，而USP13的功能抑制扰乱GSCs 抑制基底膜肿瘤生长。我们将通过追求三个具体的例子来验证我们的假设 目的：1.确定USP13在调节c-Myc维持GSC致瘤性中的作用 确定FBXL14在c-Myc降解和肿瘤抑制中的作用 3.评价靶向USP13在GBM治疗中的疗效。这个 该提案的目标是评估通过以下途径干扰GSCs的治疗潜力 临床前环境中的USP13抑制。因为c-Myc癌蛋白是一种转录因子 而c-Myc是正常细胞增殖所必需的，因此很难靶向治疗c-Myc。 然而，靶向其上游调控因子USP13选择性地干扰GSC中的c-Myc 可以提供一种实用的方法。我们将确定靶向脱泛素酶 USP13可以作为一种有效的治疗策略来提高GBM的治疗水平。

Summary Glioblastoma (GBM) is the most common and lethal primary brain tumor with dismal prognosis. GBM displays remarkable cellular heterogeneity with a population of glioma stem cells (GSCs) at the apex of the differentiation hierarchy. Because GSCs promote tumor angiogenesis, cancer invasion, therapeutic resistance and tumor recurrence, eliminating GSCs or inducing their differentiation may effectively improve GBM treatment. The stem cell-like property of GSCs is maintained by a set of core transcriptional regulators including c-Myc. Myc plays a critical role in promoting GBM malignant growth and radioresistance. C-Myc is not only regulated at the transcriptional level but also tightly controlled by post-translational modifications. Our preliminary data indicate that c-Myc is ubiquitinated by the E3 ubiquitin ligase, FBXL14, and targeted for degradation in non-stem glioma cells. In GSCs, c-Myc protein is stabilized through the deubiquitination mediated by USP13 (Ubiquitin-Specific Protease 13). Importantly, USP13 is preferentially expressed in GSCs relative to non-stem glioma cells and neural progenitor cells. Targeting USP13 by shRNA markedly reduced c-Myc protein, promoted GSC differentiation, disrupted GSC maintenance, and potently inhibited GSC tumorsphere formation. These data indicated that USP13 plays a crucial role in maintaining GSC self-renewal and tumorigenic potential through Myc stabilization. We hypothesize that USP13 antagonizes FBXL14 to stabilize c-Myc and promote the maintenance of GSCs, and that functional inhibition of USP13 disrupts GSCs to suppress GBM tumor growth. We will test our hypothesis by pursuing three specific aims: 1. Determine the role of USP13 in regulating c-Myc to maintain GSC tumorigenic potential; 2. Define the role of FBXL14 in c-Myc degradation and tumor suppression of glioma cells; 3. Evaluate the therapeutic benefit of targeting USP13 in GBM therapy. The goal of this proposal is to evaluate the therapeutic potential of disrupting GSCs through USP13 inhibition in a preclinical setting. As c-Myc oncoprotein is a transcription factor and is required for normal cell proliferation, therapeutic targeting of c-Myc is difficult. However, targeting its upstream regulator USP13 to selectively disrupt c-Myc in GSCs could provide a practical approach. We will determine whether targeting deubiquitinase USP13 can serve as an effective therapeutic strategy to improve GBM treatment.