Molecular Analysis and Role of RGS6 as a Novel Growth Suppressor

描述（由申请人提供）：RGS （G蛋白信号调节因子）蛋白是一种新的蛋白家族，被认为是异质三聚体G蛋白1亚基的gtpase激活蛋白（gap），从而负向调节G蛋白信号传导的持续时间和强度。除了少数RGS蛋白外，我们对它们的确切生理作用知之甚少，为什么存在近30种不同的哺乳动物RGS蛋白，如果这些蛋白仅作为GAP起作用，或者在RGS蛋白的标志结构域（RGD）之外的结构多样性负责RGS蛋白的GAP活性。gpcr和G蛋白的异常激活已被认为是多种人类癌症的原因之一。因此，令人惊讶的是，RGS蛋白以前没有被认为是生长或肿瘤抑制蛋白。在这里，我们提供了新的证据，表明RGS蛋白家族的成员RGS6具有这样的作用，RGS6存在于36种剪接形式中，具有相同的RGDs，但在其他蛋白结构域存在结构差异。RGS6多态性增加mRNA翻译的人患膀胱癌的风险显著降低，RGS6转录物在多种人类癌症中下调。我们的初步数据显示，相对于正常组织，RGS6蛋白在人胶质瘤和乳腺癌中表达缺失或显著降低，并在人胶质母细胞瘤细胞中鉴定出两种RGS6突变体。在缺乏或表达异常分子形式RGS6的癌细胞系中，RGS6的表达会导致生长抑制、细胞周期阻滞、DNA损伤过程中信号通路的激活，从而阻止异常细胞的增殖，抑制肿瘤异种移植物的生长。我们假设RGS6在保护细胞免受异常增殖方面起着重要作用，其缺失或突变有助于肿瘤的形成。目的1将确定RGS6作为肿瘤抑制因子和DNA损伤反应调节剂的作用。我们将确定RGS6基因如何在人类癌症中表达失调，以及其抑制肿瘤生长能力所需的结构特征和蛋白质相互作用。目的2将确定RGS6促进生长阻滞和调节细胞DNA损伤信号的分子机制。我们将确定RGS6的结构特征，以及RGS6参与生长抑制、细胞周期阻滞和DNA损伤反应调节的信号通路，我们将测试RGS6在不存在G蛋白的细胞核中的新功能作用。目的3将确定RGS6的整体缺失或乳腺组织或小鼠胶质细胞中的缺失如何调节肿瘤发生。本研究将为RGS6作为生长抑制因子的作用及其在体内的生物学表现提供新的结构和机制见解。该项目可能暗示RGS6和其他RGS蛋白是g蛋白依赖性肿瘤发生的守门人，或确定RGS6在这一过程中的新作用。这些研究可能有助于癌症治疗的新方法。项目描述：该项目将研究一种名为RGS6的蛋白质的作用，这种蛋白质可能具有预防人类癌症的功能。我们的初步结果使我们假设RGS6在保护细胞免受异常增殖方面起着重要作用，其缺失或突变有助于人类肿瘤的发生。这项工作将确定RGS6如何起作用，并将确定人类癌症中RGS6表达缺失的基础。这些研究可能有助于癌症治疗的新方法。

DESCRIPTION (provided by applicant): RGS (Regulator of G protein Signaling) proteins represent a novel protein family believed to function as GTPase-activating proteins (GAPs) for heterotrimeric G protein 1 subunits, thereby negatively regulating the duration and intensity of G protein signaling. Little is known concerning the precise physiological roles of all but a few RGS proteins, why nearly thirty different mammalian RGS proteins exist if these proteins function only as GAPs, or the role of structural diversity outside of the hallmark RGS domain (RGD) responsible for RGS protein GAP activity. Abberant activation of GPCRs and G proteins has been implicated as a cause of a variety of human cancers. Therefore, it is surprising that RGS proteins have not been considered previously as growth or tumor suppressor proteins. Here we provide new evidence suggesting such a role for a member of the RGS protein family, RGS6, which exists in thirty-six splice forms possessing identical RGDs but structural variations in other protein domains. Humans with an RGS6 polymorphism that increases mRNA translation have a significant reduction in the risk of bladder cancer, and transcripts of RGS6 are down- regulated in various human cancers. Our preliminary data show that RGS6 protein expression is absent or greatly reduced in human glioma and breast cancer relative to normal tissue, and have identified two RGS6 mutants in human glioblastoma cells. Expression of RGS6 in cancer cell lines, which either lack or express aberrant molecular forms RGS6, leads to growth suppression, cell cycle arrest, activation of signaling pathways during DNA damage that prevent proliferation of abnormal cells, and inhibition of growth of tumor xenografts. We hypothesize that RGS6 plays an important role in protecting cells against abnormal proliferation and that its loss or mutation contributes to tumor formation. Aim 1 will ascertain the role of RGS6 as a tumor suppressor and modulator of DNA damage responses. We will identify how RGS6 gene expression is dysregulated in human cancers and the structural features and protein interactions required for its ability to suppress tumor growth. Aim 2 will determine the molecular mechanisms by which RGS6 promotes growth arrest and modulates DNA damage signaling in cells. We will identify the structural features of RGS6 and signaling pathways involved in growth suppression, cell cycle arrest and modulation of DNA damage responses by RGS6 and we will test novel functional roles of RGS6 in the nucleus where G proteins are not present. Aim 3 will determine how global deletion of RGS6 or deletion in mammary tissue or glial cells of mice modulates tumorigenesis. The proposed research would provide new structural and mechanistic insights into the role of RGS6 as a growth suppressor and the biological manifestations of its actions in vivo. This project may implicate RGS6 and other other RGS proteins as gatekeepers to G-protein-dependent tumorigenesis or define novel roles of RGS6 in this process. These studies could contribute to novel approaches in cancer therapy. PROJECT NARRATIVE: This project will study the role of a protein called RGS6 that may function to prevent cancer in humans. Our preliminary results lead us to hypothesize that RGS6 plays an important role in protecting cells against abnormal proliferation and that its loss or mutation contributes to tumors in humans. This work will determine how RGS6 works and will determine the basis for loss of RGS6 expression in human cancers. These studies could contribute to novel approaches in cancer therapy.