The role of the Ras effector Nore1a in tumor suppression

描述(申请人提供)：Nore1a是RASSF肿瘤抑制因子家族的成员。它在人类原发肿瘤中经常下调，并在基因上与家族性人类癌症综合征有关。Nore1a过表达可促进细胞凋亡、细胞周期停滞和衰老。将Nore1a的表达恢复到生理水平可阻断致瘤表型，shRNA介导的Nore1a失活可增强转化的表型。因此，Nore1a是一种重要的人类肿瘤抑制因子的证据是强有力的。Nore1a还直接与RAS癌蛋白结合，似乎是一种新的效应器，介导了致癌RAS的一些促凋亡和促衰老作用。因此，Nore1a功能的丧失可能对RAS依赖的肿瘤特别重要，使致癌的RAS能够绕过其凋亡和衰老功能。然而，Nore1a调控的信号通路尚未确定，也没有研究Nore1a功能的动物模型。此外，Nore1a功能缺失对致癌RAS转化效应的影响还没有被表征。Nore1a缺乏明显的酶活性，对其作用机制知之甚少。然而，它被假设为可能作为支架蛋白来调节肿瘤抑制复合体的形成。我们现在已经在与Nore1a的内源性复合体中发现了两种肿瘤抑制因子：同源结构域相互作用蛋白Kinase 2(HIPK2)蛋白和Von Hippel-Lindau蛋白(VHL)，后者是一种臭名昭著的肿瘤抑制因子，在大多数肾细胞癌(RCC)的发生发展中起着关键作用。HIPK2和VHL的作用部分是通过直接调节主要的肿瘤抑制因子P53来实现的。在大约50%的人类肿瘤中发现了P53的缺陷，有人可能会认为P53是迄今发现的最关键的肿瘤抑制因子。因此，Nore1a可能通过双途径调节P53发挥作用，并可能作为RAS和P53之间众所周知但特征不佳的联系的一部分。我们提出了一系列实验目标，旨在确定Nore1a功能丧失在肿瘤形成表型的发展和RAS介导的转化中的确切作用。这包括一项利用一种新的Nore1a基因敲除小鼠模型来确定Nore1a/RAS相互作用在体内的作用的建议。然后我们将确定Nore1a的作用机制是否涉及HIPK2或VHL肿瘤抑制因子的调节，以及Nore1a是否整合了它们对p53的影响。我们预计，这些实验将确认NORE1a是一种重要的癌症新诊断和治疗靶点。

DESCRIPTION (provided by applicant): Nore1a is a member of the RASSF family of tumor suppressors. It is frequently down- regulated in primary human tumors and is genetically linked to a familial human cancer syndrome. Over-expression of Nore1a can promote apoptosis, cell cycle arrest and senescence. Restoration of Nore1a expression to physiological levels blocks the tumorigenic phenotype and shRNA mediated inactivation of Nore1a enhances the transformed phenotype. Thus, the evidence that Nore1a is an important human tumor suppressor is strong. Nore1a also directly binds the Ras oncoprotein and appears to serve as a novel effector, mediating some of the pro-apoptotic and pro-senescent effects of oncogenic Ras. Thus, loss of function of Nore1a may be particularly important to Ras dependent tumors, allowing oncogenic Ras to circumvent its apoptotic and senescent functions. However, the signaling pathways controlled by Nore1a have not been defined, and no animal model for Nore1a function has been investigated. Furthermore, the effects of loss of Nore1a function on the transforming effects of oncogenic Ras have not been characterized. Nore1a lacks obvious enzymatic activity, and little is known about its mechanism of action. However, it has been hypothesized that it may serve as a scaffolding protein to modulate the formation of tumor suppressor complexes. We have now identified two tumor suppressors in endogenous complex with Nore1a: the Homeodomain Interacting Protein Kinase 2 (HIPK2) protein and the Von Hippel-Lindau protein (VHL), a notorious tumor suppressor which plays a critical role in the development of the majority of Renal Cell Carcinomas (RCC). Both HIPK2 and VHL act, in part, by directly modulating the master tumor suppressor p53. Defects in p53 have been detected in approximately 50% of human tumors, and it may be argued that p53 is the most critical tumor suppressor yet identified. Thus, Nore1a may function by modulating p53 by dual pathways and could serve as part of the well known, but poorly characterized, link between Ras and p53. We propose a series of experimental aims designed to determine the precise role of Nore1a loss of function in the development of the tumorigenic phenotype and in Ras mediated transformation. This includes a proposal to determine the role of the Nore1a/Ras interaction in vivo, using a novel Nore1a knockout mouse model. We will then determine if the mechanism of action of Nore1a involves the modulation of the HIPK2 or VHL tumor suppressors, and whether Nore1a acts to integrate their effects upon p53. We anticipate that these experiments will identify Nore1a as an important novel diagnostic and therapeutic target for cancer.