The Tumor Suppression Potential of NF-kappaB2 p100

描述(申请人提供)：该项目的长期目标是了解核因子-(B2)基因的基因改变如何导致肿瘤发生。核因子-kappaBeta2基因编码一个约100 kDa的蛋白(P100)，可通过其C端死亡结构域和/或lkappaB活性促进细胞凋亡。响应于某些信号，P100被处理以产生对应于P100的N末端一半的52 kDa转录因子(P52)。在乳腺癌中已经观察到p52的异常激活。此外，核因子-kappaB2基因的C末端缺失和重排在各种B细胞和T细胞淋巴瘤中反复发生。这些基因改变的一个基本特征是产生具有致癌潜力的C末端截短的NF-kappaB2突变体，并使作为凋亡蛋白的P100失活。我们最近的工作表明，P100是肿瘤坏死因子-α和激活诱导的胸腺细胞凋亡的关键调节因子，也是肿瘤来源的核因子-kappaB2突变体p80HT在细胞和动物中的致癌活性的抑制因子。这些发现使我们假设P100是一种促进细胞凋亡的肿瘤抑制因子，并作为一种内在防御机制，对抗核因子-kappaB2的致癌突变和p52的异常激活。我们将在基于细胞和动物的系统中测试这一假设。在以动物为基础的研究中(目标1)，我们将在靶向表达p80HT或p52的转基因小鼠中建立P100作为肿瘤抑制因子，以抑制淋巴癌的发生；我们将检查在这些小鼠模型中NF-kappaB2 P100基因对于肿瘤抑制的半不足的可能性；将在E/MU-myc转基因小鼠中评估P100作为一般肿瘤抑制因子的潜力。在以细胞为基础的研究中(目标2)，我们将以骨髓细胞转化为读数，确定P100抗肿瘤功能所必需的生化活性以及P100抑制肿瘤转化的凋亡途径；我们将表征存在明确的NF-kappaB2突变的动物的淋巴细胞和淋巴瘤细胞的凋亡反应，以从分子水平识别与淋巴癌发生相关的凋亡调控缺陷；我们将以胸腺激活诱导的细胞凋亡为模型，描述P100作为一种凋亡蛋白的分子机制。这些研究可能定义一类新的肿瘤抑制基因，作为对自身基因致癌突变的监测机制。

DESCRIPTION (provided by applicant): The long-term goal of this project is to understand how genetic alterations of the NF-(B2 gene may lead to tumorigenesis. The NF-kappaBeta2 gene encodes a protein of approximately 100-kDa (p100) that can promote apoptosis via its C-terminal death domain and/or lkappaB activity. In response to certain signals, p100 is processed to generate a 52-kDa transcriptional factor (p52) corresponding to the N-terminal half of p100. Aberrant activation of p52 has been observed in breast cancers. Also, C-terminal deletions and rearrangements of the NF-kappaB2 gene occur recurrently in a variety of B- and T-cell lymphomas. A fundamental feature of these genetic alterations is the generation of C-terminally truncated NF-kappaB2 mutants with oncogenic potential and the inactivation of p100 as an apoptotic protein. Our recent work suggests that p100 is a crucial regulator of TNF-alpha- and activation-induced apoptosis in thymocytes, and an inhibitor of the oncogenic activity of the tumor-derived NF-kappaB2 mutant p80HT in cells and in animals. These findings lead us to hypothesize that p100 is a tumor suppressor that promotes apoptosis and acts as a built-in defense against oncogenic mutations of NF-kappaB2 and aberrant activation of p52. We will test this hypothesis in both cell- and animal-based systems. In animal-based studies (Aim 1), we will establish p100 as a tumor suppressor against lymphomagenesis in transgenic mice with targeted expression of p80HT or p52 in lymphocytes; we will examine the possibility that the NF-kappaB2 p100 gene is haplo-insufficient for tumor suppression in these mouse models; the potential of p100 as a general tumor suppressor will be assessed in E/mu-myc transgenic mice. In cell-based studies (Aim 2), we will use bone marrow cell transformation as readout to define the biochemical activity of p100 essential for its anti-oncogenic function and the apoptotic pathway through which p100 suppresses oncogenic transformation; we will characterize apoptotic responses in lymphocytes and lymphoma cells from the animals with defined NF-kappaB2 mutations to identify at molecular levels the defects in apoptosis regulation that are linked to lymphomagenesis; we will use thymic activation-induced apoptosis as a model to delineate the molecular mechanism for p100 as an apoptotic protein. These studies may define a new class of tumor suppressors that act as a surveillance mechanism against oncogenic mutations of their own genes.