INTEGRATION OF ONCOGENIC SIGNALS BY THE NUCLEOLAR ARF-NPM NETWORK

描述(申请人提供)：最初被描述为包含在特定染色体区域内的细胞器，核仁在过去的一个世纪中取得了进展，在此过程中传授了许多细胞和癌症生物学的知识。曾经被认为是核糖体生物发生的静态中心的标签阻碍了人们对这种可见细胞器的新的欣赏，近年来已经建立起来。哺乳动物核仁中最活跃的成分之一是ARF肿瘤抑制蛋白。自发现以来，ARF的肿瘤抑制作用背后的机制一直处于紧张的研究之中。最初被吹捧为P53负调控因子MDM2的真正抑制剂，最近的研究发现ARF在抑制小鼠和人类肿瘤形成方面具有P53非依赖性作用。最近的许多工作都集中在ARF在核仁中的新定位上，核仁是一种看似良性的细胞器，就转化特性而言。ARF生物学最鲜为人知的方面之一是ARF在核仁中的作用。许多实验室，包括我们的实验室，已经确定核磷蛋白(NPM)原癌基因是ARF的核仁结合伙伴。我们的初步数据表明，由于失去TSC1抑癌基因而产生的过度生长信号刺激了NPM和ARF的蛋白表达，从而努力影响核糖体的合成速率。此外，基础核仁ARF蛋白与核仁中的NPM池相互作用，这些基础ARF分子的急性丢失导致NPM功能失调和核糖体生物合成增加。核仁ARF的丢失改变了核仁的形态，使蛋白质，如p68RNA解旋酶，更容易与NPM相互作用，潜在地促进核糖体的生物发生和细胞转化。我们假设ARF存在于核仁中，通过感应过度生长信号来严格调控核糖体的生物发生，并停止不必要的NPM-p68活动。基于我们的初步数据和我们提出的假设，我们提出了三个具体的目标：1)确定核仁ARF-NPM复合体如何解释致癌生长信号；2)建立p68RNA解旋酶与NPM的物理和功能相互作用；以及3)确定ARF在体外和体内作为核仁检查点蛋白的能力。公共卫生简介：ARF肿瘤抑制基因是人类癌症中第二大最常见的突变基因，仅次于p53。我们刚刚开始了解这种关键的肿瘤抑制因子如何发挥作用，防止细胞过度生长和增殖。我们试图了解ARF在体内调节P53非依赖性生长停滞的能力背后的机制，并将这些发现转移到更临床的环境中，在那里，新的ARF靶向疗法可能会影响广泛的癌症患者。因此，鉴于ARF在人类癌症中的突变流行，对ARF生物学的基础研究是适当的。

DESCRIPTION (provided by applicant): Initially described as an organelle contained within specific chromosomal regions, the nucleolus has advanced through the past century imparting much knowledge about cell and cancer biology along the way. Once hindered with the label as being the static center of ribosome biogenesis, a newfound appreciation for this visible organelle has been established in recent years. One of the most dynamic occupants of the mammalian nucleolus is the ARF tumor suppressor protein. Since its discovery, the mechanism behind ARF's tumor suppressive function has been under intense investigation. Initially touted as a bona fide inhibitor of the p53 negative regulator, Mdm2, more recent studies have identified a p53-independent role for ARF in suppressing tumor formation in mice and humans. Much of the more recent work has focused on the novel localization of ARF in the nucleolus, a seemingly benign organelle in terms of transformation properties. One of the least understood aspects of ARF biology is what is ARF doing in the nucleolus. Numerous labs, including ours, have identified the nucleophosmin (NPM) proto-oncogene as a nucleolar binding partner of ARF. Our preliminary data demonstrates that hypergrowth signals emanating from the loss of the Tsc1 tumor suppressor stimulate the protein expression of both NPM and ARF in an effort to influence ribosome synthesis rates. Additionally, basal nucleolar ARF proteins interact with a pool of NPM in the nucleolus and acute loss of these basal ARF molecules results in dysregulated NPM function and increased ribosome biogenesis. Loss of nucleolar ARF alters the landscape of the nucleolus, allowing for proteins, such as the p68 RNA helicase, to interact more readily with NPM to potentially promote ribosome biogenesis and cell transformation. We hypothesize that ARF resides in the nucleolus to tightly regulate ribosome biogenesis through the sensing of hypergrowth signals and to halt unwarranted NPM-p68 activities. Based on our preliminary data and our stated hypothesis, three specific aims are proposed: 1) Determine how oncogenic growth signals are interpreted by the nucleolar ARF-NPM complex, 2) Establish the physical and functional interaction of the p68 RNA helicase with NPM, and 3) Determine the in vitro and in vivo ability of ARF to act as a nucleolar checkpoint protein. PUBLIC HEALTH NARRATIVE: The ARF tumor suppressor is the second most commonly mutated gene in human cancers, second only to p53. We are just beginning to appreciate how this critical tumor suppressor functions to prevent unwarranted cell growth and proliferation. We seek to understand the mechanism behind ARF's ability to regulate p53-independent growth arrest in vivo and to move these findings into a more clinical setting where novel ARF-targeted therapeutics might affect a broad spectrum of cancer patients. Thus, basic research into ARF biology is appropriate given its mutational prevalence in human cancers.