Targeting oncoprotein stability for cancer therapy

针对癌症治疗的癌蛋白稳定性

• 批准号: 280194129
• 负责人: Professorin Dr. Caroline Kisker
• 金额: --
• 依托单位: Rudolf-Virchow-Zentrum - Center for Integrative and Translational Bioimaging
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/280194129?language=en
• 关键词: Targeting; oncoprotein; stability; cancer; therapy

The ubiquitin proteasome system controls the abundance of most cellular proteins. This system includes a set of enzymes, such as ubiquitin ligases and deubiquitinases, which transfer ubiquitin onto and remove it from protein substrates. Ubiquitinated substrates are degraded by a large proteolytic complex, the proteasome. Proteasome inhibition can be instrumental in suppressing cancer cell survival and has been successfully used in treatment of multiple myeloma. However, the mechanisms of cytotoxicity of proteasome inhibition remain elusive, highlighting the need for more selective therapies. Specific targeting of pathways, which maintain stability of oncoproteins may present an alternative antineoplastic strategy. Oncoproteins drive key biological processes during homeostasis, and often become indispensable for cell viability during tumorigenesis. The abundance of oncoproteins can be non-redundantly controlled by specific ubiquitin-dependent pathways, which include ubiquitin-specific proteases. For example, ablation of the Usp7 deubiquitinase in mouse germline destabilizes the oncogenic ubiquitin ligase Mdm2, hyperactivates p53, and leads to embryonic lethality, demonstrating that maintenance of oncoprotein stability is an essential cellular process. Ubiquitin-specific proteases are amenable to small molecule inhibition and therefore are promising therapeutic targets. Inhibitors of Usp7, which abrogate tumorigenesis in mice but are tolerated by healthy adult tissues, show that targeting oncoprotein stability creates a significant therapeutic window.A critical pathway, which controls degradation of multiple oncoproteins including Myc, Notch and cyclin E, is driven by the SCF(Fbw7) ubiquitin ligase. Fbw7 is essential for tissue homeostasis and its loss-of-function promotes tumorigenesis in mouse models. We have recently shown that Fbw7-mediated substrate degradation is antagonized by the Usp28 deubiquitinase. Depletion of Usp28 in tumor cell lines or genetic ablation of Usp28 in mice destabilizes Fbw7 substrates. Importantly, deletion of Usp28 in the intestine has only subtle effects on tissue homeostasis but strongly attenuates intestinal tumor development, and may thus provide a therapeutic window for solid tumors. Intriguingly, we find that loss of the catalytic activity of Usp28 is more efficient in promoting oncoprotein degradation than the complete gene knockout. Therefore, we speculate that inhibition of the catalytic function of Usp28 by small molecules might be particularly effective in tumor suppression. In this project, we will pursue the following aims: 1) model small molecule inhibition of Usp28 during homeostasis and tumorigenesis via expression of catalytically inactive Usp28 in mouse models, 2) elucidate the structural basis of deubiquitination by Usp28 and design small molecule inhibitors targeting Usp28, and 3) identify signaling events that promote oncoprotein degradation via the Usp28/Fbw7 pathway.

泛素蛋白酶体系统控制大多数细胞蛋白质的丰度。该系统包括一组酶，如泛素连接酶和去泛素酶，其将泛素转移到蛋白质底物上并将其从蛋白质底物上去除。泛素化底物被一个大的蛋白水解复合物蛋白酶体降解。蛋白酶体抑制可有助于抑制癌细胞存活，并已成功用于治疗多发性骨髓瘤。然而，蛋白酶体抑制的细胞毒性机制仍然难以捉摸，突出了对更有选择性的治疗的需要。保持癌蛋白稳定性的通路的特异性靶向可能是一种替代的抑制策略。癌蛋白在体内平衡过程中驱动关键的生物学过程，并且通常在肿瘤发生过程中成为细胞活力不可或缺的。癌蛋白的丰度可以由特定的泛素依赖性途径（包括泛素特异性蛋白酶）非冗余地控制。例如，在小鼠生殖系中的Usp 7去泛素化酶的消融使致癌泛素连接酶Mdm 2不稳定，过度激活p53，并导致胚胎致死，表明癌蛋白稳定性的维持是必要的细胞过程。泛素特异性蛋白酶适合于小分子抑制，因此是有希望的治疗靶点。Usp 7抑制剂能抑制小鼠肿瘤的发生，但对健康成年组织耐受，这表明靶向癌蛋白的稳定性创造了一个重要的治疗窗口。SCF（Fbw 7）泛素连接酶是控制多种癌蛋白（包括Myc、Notch和细胞周期蛋白E）降解的关键途径。fbw 7是组织稳态所必需的，其功能丧失促进小鼠模型中的肿瘤发生。我们最近发现，Fbw 7介导的底物降解被Usp 28去泛素化酶拮抗。肿瘤细胞系中Usp 28的耗尽或小鼠中Usp 28的基因消融使Fbw 7底物不稳定。重要的是，肠中Usp 28的缺失对组织稳态仅具有微妙的影响，但强烈减弱肠肿瘤的发展，因此可能为实体瘤提供治疗窗口。有趣的是，我们发现Usp 28催化活性的丧失在促进癌蛋白降解方面比完全基因敲除更有效。因此，我们推测通过小分子抑制Usp 28的催化功能可能在肿瘤抑制中特别有效。在本项目中，我们将追求以下目标：1）通过在小鼠模型中表达无催化活性的Usp 28来模拟稳态和肿瘤发生期间Usp 28的小分子抑制，2）阐明Usp 28去泛素化的结构基础并设计靶向Usp 28的小分子抑制剂，以及3）鉴定通过Usp 28/Fbw 7途径促进癌蛋白降解的信号传导事件。