Role of Skp2-cyclin A Interaction in Normal Physiology and Cancer

一旦一种蛋白质与癌症有关，接下来重要的是确定它在癌症中的作用以及它在癌症中的功能。Skp 2是SCF（Skp 2）泛素连接酶复合物的F盒蛋白，靶向p27 Kip 1用于泛素化。在临床癌症样本中，p27的减少和Skp 2的增加是常见的且通常相关的事件。目前的传统观点是Skp 2通过靶向p27进行泛素化和降解而作为癌蛋白发挥作用，因此SCF（Skp 2）使p27泛素化的功能一直是药物开发工作的目标。然而，最近的研究表明，需要更仔细地研究SCF（Skp 2）的p27泛素化在肿瘤发生中的意义。我们最近已经确定，Skp 2结合到细胞周期蛋白A的N-末端，以直接保护其免受p27家族CKIs的抑制;并且Skp 2-细胞周期蛋白A相互作用的阻断肽可以选择性地诱导培养中的癌细胞死亡。这些发现使我们假设与细胞周期蛋白A结合是Skp 2在癌症中的重要功能。在这个项目中，我们建议使用我们最近的发现，Skp 2在Rb缺乏诱导的垂体和甲状腺肿瘤发生中起着至关重要的作用，以确定SCF（Skp 2）介导的p27泛素化和结合细胞周期蛋白A的Skp 2功能在这个肿瘤模型中的作用。ENU诱导的肿瘤发生将用于将这些研究扩展到涉及多个器官的肿瘤模型。此外，我们将使用小鼠胚胎和生物化学研究以及遗传研究来确定Skp 2功能和Rb功能如何整合，以维持Rb缺陷细胞在Skp 2存在下的肿瘤发生，并在Skp 2失活时消除Rb缺陷细胞。这些研究的结果将阐明肿瘤抑制基因Rb、癌基因Skp 2的作用和功能机制，以及它们在正常生理和癌症中的关系，以揭示治疗靶点。

DESCRIPTION: Once a protein is implicated in cancer, it is next important to define its role in cancer and how it functions in cancer. Skp2 is an F-box protein of the SCF(Skp2) ubiquitin ligase complex targeting p27Kip1 for ubiquitination. In clinical cancer samples, reduction of p27 and increase in Skp2 are frequent and generally associated events. The conventional view at present is that Skp2 functions as an oncoprotein by targeting p27 for ubiquitination and degradation and, accordingly, the function of SCF(Skp2) to ubiquitinate p27 has been the target of drug development efforts. More recent studies however have indicated the needs to more carefully study the significance of p27 ubiquitination by SCF(Skp2) in tumorigenesis. We have recently determined that Skp2 binds to the N-terminus of cyclin A to directly protect it from inhibition by p27 family CKIs; and a blocking peptide for Skp2-cyclin A interaction can selectively induce cancer cell death in culture. These findings led us to hypothesize that binding to cyclin A is an important function of Skp2 in cancer. In this project, we propose to use our recent discovery that Skp2 plays an essential role in Rb deficiency-induced pituitary and thyroid tumorigenesis to determine the roles of SCF(Skp2)-mediated p27 ubiquitination and binding to cyclin A in Skp2 function in this tumor model. ENU-induced tumorigenesis will be used to extend these studies to a tumor model involving multiple organs. Further, we will use mouse embryo and biochemical studies as well as genetic studies to determine how Skp2 function and Rb function integrate to sustain Rb-deficient cells for tumorigenesis in the presence of Skp2, and to eliminate Rb-deficient cells when Skp2 is inactivated. Results from these studies will elucidate the roles and functional mechanisms of the tumor suppressor Rb, oncogene Skp2, and their relationship in normal physiology and in cancer to reveal therapeutic targets.