Determining and targeting mechanisms controlling cancer cell division

总体总结 Cyclin D-CDK4/6-Rb-E2F途径整合外部和内部信号控制细胞周期进程 在细胞周期的G1/S过渡期。细胞周期蛋白D-CDK4/6-Rb-E2F通路的改变广泛存在于 大多数人类癌症。这些变化被认为增加了癌细胞的增殖潜力。 例如，视网膜母细胞瘤(RB1)肿瘤抑制因子的功能失活或 细胞周期蛋白D基因在多种人类癌症的发生发展过程中是一个反复发生的事件。在简单的 共识模型，视网膜母细胞瘤蛋白Rb在细胞周期的G1/S过渡期抑制细胞增殖 通过结合和抑制E2F转录因子。在对细胞生长和增殖信号的反应中，Rb 正常细胞中一系列细胞周期蛋白依赖性激酶复合体(第一周期蛋白)的磷酸化和失活 D-CDK4/6和Cyclin E/A-CDK2)。Rb的磷酸化导致Rb从E2F解离 转录因子从而导致对DNA合成和其他关键方面至关重要的基因的转录 对细胞周期进程的影响。因此，具有结构性不活跃的Rb的癌细胞被认为获得了增加的 增殖潜力。对正常细胞和癌细胞中Cyclin D-CDK4/6-Rb-E2F通路的了解导致了 已被批准用于乳腺癌和乳腺癌治疗的特异性CDK4/6抑制剂的开发 正在对其他几种癌症进行临床试验。在这个范例中，抑制CDK4/6会导致Rb降低 磷酸化，激活RB的细胞周期抑制功能。然而，许多肿瘤对 这些抑制剂只能暂时起作用。最近在患者和临床前模型中的观察表明 我们对RB途径的理解并不像我们之前认为的那样完整。这可能解释了变量 CDK4/6抑制剂的临床应用结果。这项提议的总体目标是获得更深层次的结构，分子， 以及细胞对Rb通路的理解，最终目标是帮助设计新的和改进的治疗方法 在广泛的癌症患者中针对这一途径的策略。我们的第一个目标是确定核心 细胞周期蛋白D-CDK4/6-Rb-E2F通路的调控机制，包括细胞周期蛋白D-CDK4/6如何磷酸化 RB以及以前未知的翻译后修饰如何调节RB和E2F活动。我们的第二个 目的是确定和研究Rb通路组件的新功能，包括Cyclin D的新靶点。 CDK4/6激酶、Rb及其家族成员p107和p130的新功能和新的调控机制 控制E2F转录因子的浓度和活性。我们的第三个目标是启动发展 以创新的方式针对Rb途径的策略，包括抑制Cyclin D-Rb的分子 联合，刺激p107和p130的抑癌活性，并操纵E2F的稳定性。这些目标 将通过综合、协同和多学科办法在三个相互关联的项目中实现。 最终，从这些研究中获得的信息可能会为靶向Cyclin D-CDK4/6-Rb- E2F途径，提高癌症治疗水平。

OVERALL SUMMARY The Cyclin D-Cdk4/6-Rb-E2F pathway integrates external and internal signals to control cell cycle progression at the G1/S transition of the cell cycle. Alterations in the Cyclin D-Cdk4/6-Rb-E2F pathway are found in the vast majority of human cancers. These alterations are thought to increase the proliferative potential of cancer cells. For example, the functional inactivation of the retinoblastoma (RB1) tumor suppressor or the amplification of Cyclin D genes is a recurrent event in the development of a wide range of human cancers. In the simple consensus model, the retinoblastoma protein Rb inhibits cell proliferation at the G1/S transition of the cell cycle by binding and inhibiting E2F transcription factors. In response to cell growth and proliferative signals, Rb is phosphorylated and inactivated in normal cells by a series of Cyclin-dependent kinase complexes (first Cyclin D-Cdk4/6 and then Cyclin E/A-Cdk2). Phosphorylation of Rb results in the dissociation of Rb from E2F transcription factors thereby causing transcription of genes important for DNA synthesis and other key aspects of cell cycle progression. Thus, cancer cells with constitutively inactive Rb are thought to acquire an increased proliferative potential. Knowledge of the Cyclin D-Cdk4/6-Rb-E2F pathway in normal and cancer cells has led to the development of specific Cdk4/6 inhibitors that have been approved for the treatment of breast cancer and are in clinical trials for several other cancer types. In this paradigm, inhibition of Cdk4/6 results in decreased Rb phosphorylation, which activates Rb’s cell cycle inhibitory function. However, many tumors do not respond to these inhibitors or do so only transiently. Recent observations in patients and pre-clinical models indicate that our understanding of the Rb pathway is not as complete as we previously thought. This may explain the variable results of Cdk4/6 inhibitors in the clinic. The overall goal of this proposal is to gain a deeper structural, molecular, and cellular understanding of the Rb pathway with the ultimate goal to help design new and improved therapeutic strategies targeting this pathway in a broad range of cancer patients. Our first goal is to determine the core mechanisms regulating the Cyclin D-Cdk4/6-Rb-E2F pathway, including how Cyclin D-Cdk4/6 phosphorylates Rb and how previously unknown post-translational modifications regulate Rb and E2F activities. Our second goal is to identify and investigate new functions of Rb pathway components, including new targets of Cyclin D- Cdk4/6 kinases, new functions for Rb and its family members p107 and p130, and new regulatory mechanisms controlling the concentration and activity of E2F transcription factors. Our third goal is to initiate the development of strategies that target the Rb pathway in innovative ways, including molecules that inhibit Cyclin D-Rb association, stimulate the tumor suppressor activity of p107 and p130, and manipulate E2F stability. These goals will be achieved in three inter-related Projects via a comprehensive, synergistic and multi-disciplinary approach. Ultimately, the information gained from these studies may provide new ways to target the Cyclin D-Cdk4/6-Rb- E2F pathway to improve cancer therapy.