Ubiquitination and Deubiquitination of c-Myc in Glioblastoma

总结 胶质母细胞瘤（GBM）是最常见和致命的原发性脑肿瘤， 预后胶质母细胞瘤与神经胶质瘤的细胞异质性 干细胞（GSC）在分化层次的顶点。因为GSC促进 肿瘤血管生成、癌症侵袭、治疗抗性和肿瘤复发， 清除GSC或诱导其分化可有效改善GBM 治疗GSC的干细胞样特性由一组核心细胞维持， 包括c-Myc的转录调节因子。Myc在促进GBM中起关键作用 恶性生长和辐射抗性。C-Myc不仅在转录水平受到调控， 水平，但也严格控制翻译后修饰。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 在非干胶质瘤细胞中的降解。在GSC中，c-Myc蛋白通过 由USP 13（泛素特异性蛋白酶13）介导的去泛素化。重要的是， USP13相对于非干胶质瘤细胞和神经胶质瘤细胞优先在GSC中表达。 祖细胞通过shRNA靶向USP13显著降低了c-Myc蛋白，促进了c-Myc蛋白的表达。 GSC分化，破坏GSC维持，并有效抑制GSC 肿瘤球形成。这些数据表明，USP13在以下方面起着至关重要的作用： 通过Myc稳定化维持GSC自我更新和致瘤潜力。我们 假设USP 13拮抗FBXL 14以稳定c-Myc并促进 维持GSC，并且USP 13的功能抑制破坏GSC， 抑制GBM肿瘤生长。我们将通过追踪三个具体的 目标：1.确定USP13在调节c-Myc以维持GSC致瘤性中的作用 潜力; 2.确定FBXL14在c-Myc降解和肿瘤抑制中的作用， 胶质瘤细胞; 3.评价靶向USP13在GBM治疗中的治疗获益。的 该提案的目的是评估通过以下方式破坏GSC的治疗潜力： 临床前环境中的USP 13抑制。由于c-Myc癌蛋白是一种转录因子， 并且是正常细胞增殖所必需的，因此很难将c-Myc作为治疗靶点。 然而，靶向其上游调节子USP13以选择性地破坏GSC中的c-Myc， 可以提供一个实用的方法。我们将确定是否靶向去泛素化酶 USP 13可以作为改善GBM治疗的有效治疗策略。

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.