The role of USP27X-Cyclin D1 axis in HER2 Therapy Resistant Breast Cancer

项目摘要/摘要 细胞周期蛋白D_1(CCND_1)的过表达是HER2靶向耐药的主要机制 探员们。CCND1扩增的患者对曲妥珠单抗治疗的反应最差，并且 CCND1的过度表达足以使癌细胞对HER2失活不敏感。此外，肿瘤 通过减少HER2表达来逃避HER2靶向治疗依赖于CCND1过表达 对它的消融极为敏感。因此，靶向CCND1是克服抗药性的一个有前途的策略 乳腺癌患者中的HER2靶向药物。尽管CCND1本身不是一个可用药的靶点，但这个蛋白质 具有快速的周转，其在细胞中的稳定水平受到泛素介导的降解的严格调控。 CCND1去泛素化的扰动加速了它的降解。我们最近发现了一部小说， 先前未知的去泛素化酶-USP27X，其高表达显著相关 HER2阳性乳腺癌患者存活率低。重要的是，我们的研究发现USP27X是一个关键的 HER2耐药乳腺癌细胞中CCND1蛋白稳定性的调节。USP27X严重烧蚀 减少异种移植瘤生长，显著提高细胞对HER2和CDK4/6抑制剂的敏感性。我们 假设USP27X可作为HER2耐药或复发乳腺癌的关键治疗靶点 通过对CCND1的降解。本项目的重点是了解USP27X在CCND1中的功能 调节和阐明这种脱泛素化酶在癌症发生和发展中的作用。我们 将利用几个工程细胞系以及一种新的和临床相关的小鼠模型，该模型携带 条件Usp27X等位基因至1)阐明CCND1稳态降低的分子机制 USP27X消融细胞中的水平决定了USP27X的缺失将如何影响肿瘤的发展和 体内进展，以及3)确定USP27X活性的取消如何改变HER2的治疗反应 耐药细胞对HER2的抑制作用。USP27X是一个可用药的靶点，我们的研究将照亮新的 HER2耐药和CCND1依赖型癌症的治疗干预途径。尽管在那里 目前还没有USP27X特异性抑制剂，该项目中提出的研究对于 建立这种脱泛素酶作为药物靶点将为开发USP27X提供理论基础 特定的抑制剂。

PROJECT SUMMARY/ABSTRACT Overexpression of Cyclin D1 (CCND1) is recognized as a major resistance mechanism to HER2 targeting agents. Patients with CCND1 amplification have the worst response to trastuzumab-containing therapy, and CCND1 overexpression is enough to render cancer cells insensitive to HER2 inactivation. Furthermore, tumors that evade HER2 targeted therapy by reducing HER2 expression rely on CCND1 overexpression and are extremely sensitive to its ablation. Thus, targeting CCND1 is a promising strategy for overcoming resistance to HER2-targeting agents in breast cancer patients. Although CCND1 itself is not a druggable target, this protein has a rapid turnover, and its steady-state level in cells is tightly regulated by ubiquitin-mediated degradation. Perturbation of CCND1 deubiquitination accelerates its degradation. We have recently discovered a novel, previously uncharacterized deubiquitinating enzyme – USP27X, whose higher expression significantly correlates with poor survival of HER2 positive breast cancer patients. Importantly, our studies identify USP27X as a critical regulator of CCND1 protein stability in HER2 therapy-resistant breast cancer cells. Ablation of USP27X severely reduces xenograft tumor growth and significantly increases cell sensitivity to HER2 and CDK4/6 inhibitors. We hypothesize that USP27X can be a key therapeutic target in HER2 therapy-resistant or recurrent breast cancer through CCND1 degradation. This project focuses on understanding the functions of USP27X in CCND1 regulation and elucidating the roles of this deubiquitinating enzyme in cancer development and progression. We will utilize several engineered cell lines as well as a novel and clinically relevant mouse model carrying a conditional Usp27X allele to 1) Elucidate the molecular mechanism underlying the reduced CCND1 steady-state levels in USP27X ablated cells 2) Determine how the loss of USP27X will affect tumor development and progression in vivo, and 3) Define how abrogation of USP27X activity alters the therapeutic response of HER2 therapy-resistant cells to HER2 inhibition. USP27X is a druggable target, and our studies will illuminate new avenues for therapeutic intervention in HER2 therapy-resistant and CCND1 dependent cancers. Although there are no USP27X specific inhibitors currently available, the studies proposed in this project are essential for establishing this deubiquitinating enzyme as a drug target as they will provide a rationale for developing USP27X specific inhibitors.