The role of the Ras effector Nore1a in tumor suppression

描述（由申请人提供）：Nore 1a是RASSF肿瘤抑制因子家族的成员。它在原发性人类肿瘤中经常下调，并与家族性人类癌症综合征有遗传联系。Nore 1a过表达可促进细胞凋亡、细胞周期阻滞和衰老。Nore 1a表达恢复到生理水平可阻断肿瘤发生表型，而shRNA介导的Nore 1a失活可增强转化表型。因此，Nore 1a是重要的人类肿瘤抑制因子的证据是强有力的。Nore 1a还直接结合Ras癌蛋白，似乎是一种新的效应子，介导致癌Ras的一些促凋亡和促衰老作用。因此，Nore 1a功能的丧失可能对Ras依赖性肿瘤特别重要，允许致癌Ras绕过其凋亡和衰老功能。然而，由Nore 1a控制的信号通路尚未确定，也没有研究Nore 1a功能的动物模型。此外，Nore 1a功能丧失对致癌Ras转化作用的影响尚未得到表征。 Nore 1a缺乏明显的酶活性，其作用机制知之甚少。然而，人们假设它可能作为支架蛋白来调节肿瘤抑制复合物的形成。我们现在已经确定了与Nore 1a内源性复合物中的两种肿瘤抑制因子：同源结构域相互作用蛋白激酶2（HIPK 2）蛋白和Von Hippel-Lindau蛋白（VHL），VHL是一种臭名昭着的肿瘤抑制因子，在大多数肾细胞癌（RCC）的发展中起着关键作用。HIPK 2和VHL都部分通过直接调节主肿瘤抑制因子p53起作用。在大约50%的人类肿瘤中已经检测到p53的缺陷，并且可以认为p53是迄今为止鉴定的最关键的肿瘤抑制因子。因此，Nore 1a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明确的联系的一部分。 我们提出了一系列的实验目的，旨在确定Nore 1a功能丧失在致瘤表型的发展和Ras介导的转化中的确切作用。这包括一个建议，以确定在体内的Nore 1a/Ras相互作用的作用，使用一种新的Nore 1a基因敲除小鼠模型。然后，我们将确定Nore 1a的作用机制是否涉及HIPK 2或VHL肿瘤抑制因子的调节，以及Nore 1a是否整合了它们对p53的作用。我们预计，这些实验将确定Nore 1a作为一个重要的新的诊断和治疗癌症的目标。 公共卫生相关性：这些研究将用于确定一种新型潜在肿瘤抑制因子Nore 1a在人类癌症中的作用。他们将确定Nore 1a是否是癌症的重要诊断/预后标志物。他们还将确定Nore 1a是否可能是开发表观遗传疗法以恢复其在肿瘤细胞中的正常功能的合适候选者。

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. PUBLIC HEALTH RELEVANCE: These studies will serve to define the role of a novel potential tumor suppressor, Nore1a, in human cancer. They will determine if Nore1a is an important diagnostic/prognostic marker for cancer. They will also determine if Nore1a may be a suitable candidate for the development of epigenetic therapy to restore its normal function in tumor cells.