The role of the Ras effector Nore1a in tumor suppression

描述（由申请人提供）：Nore1a是肿瘤抑制因子RASSF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。Nore1a过表达可促进细胞凋亡、细胞周期阻滞和衰老。Nore1a表达恢复到生理水平可阻断致瘤表型，shRNA介导的Nore1a失活可增强转化表型。因此，Nore1a是一个重要的人类肿瘤抑制因子的证据是强有力的。Nore1a也直接结合Ras癌蛋白，并似乎作为一种新的效应物，介导致癌Ras的一些促凋亡和促衰老作用。因此，Nore1a的功能缺失可能对Ras依赖性肿瘤特别重要，允许致癌Ras规避其凋亡和衰老功能。然而，Nore1a控制的信号通路尚未明确，也没有研究过Nore1a功能的动物模型。此外，Nore1a功能缺失对致癌Ras转化作用的影响尚未被表征。Nore1a缺乏明显的酶活性，其作用机制尚不清楚。然而，它可能作为一种支架蛋白来调节肿瘤抑制复合物的形成。我们现在已经在内源性Nore1a复合物中发现了两种肿瘤抑制因子：同源结构域相互作用蛋白激酶2 （HIPK2）蛋白和Von Hippel-Lindau蛋白（VHL），这是一种臭名昭著的肿瘤抑制因子，在大多数肾细胞癌（RCC）的发展中起着关键作用。HIPK2和VHL在一定程度上都是通过直接调节主肿瘤抑制因子p53来起作用的。在大约50%的人类肿瘤中发现了p53的缺陷，可以认为p53是目前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之间众所周知但尚未被充分描述的联系的一部分。我们提出了一系列旨在确定Nore1a功能丧失在致瘤表型发展和Ras介导转化中的确切作用的实验目标。这包括使用一种新的Nore1a敲除小鼠模型来确定Nore1a/Ras在体内相互作用的建议。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是否整合它们对p53的作用。我们预计这些实验将确定Nore1a作为癌症诊断和治疗的重要新靶点。

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.