Molecular Analysis and Role of RGS6 as a Novel Growth Suppressor

描述（由申请人提供）：RGS（G蛋白信号传导调节因子）蛋白代表一种新的蛋白质家族，据信其作为异源三聚体G蛋白1亚基的GTP酶激活蛋白（GAP）发挥作用，从而负调节G蛋白信号传导的持续时间和强度。除了少数RGS蛋白外，关于所有RGS蛋白的精确生理作用知之甚少，如果这些蛋白仅作为GAP起作用，为什么存在近三十种不同的哺乳动物RGS蛋白，或者负责RGS蛋白GAP活性的标志性RGS结构域（RGD）之外的结构多样性的作用。GPCR和G蛋白的异常激活已被认为是多种人类癌症的原因。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这样的作用的RGS蛋白质家族，RGS6，它存在于36个剪接形式拥有相同的RGDs，但在其他蛋白质结构域的结构变化的成员。具有增加mRNA翻译的RGS6多态性的人具有膀胱癌风险的显著降低，并且RGS6的转录物在各种人类癌症中下调。我们的初步数据表明，RGS6蛋白表达是不存在或大大减少，在人类胶质瘤和乳腺癌相对于正常组织，并已确定两个RGS6突变体在人类胶质母细胞瘤细胞。RGS6在缺乏或表达异常分子形式RGS6的癌细胞系中的表达导致生长抑制、细胞周期停滞、DNA损伤期间信号传导途径的激活，其防止异常细胞的增殖，以及肿瘤异种移植物生长的抑制。我们假设RGS6在保护细胞免受异常增殖中起重要作用，并且其缺失或突变有助于肿瘤形成。目的1将确定RGS6作为肿瘤抑制剂和DNA损伤反应调节剂的作用。我们将确定RGS6基因表达在人类癌症中是如何失调的，以及其抑制肿瘤生长的能力所需的结构特征和蛋白质相互作用。目的2将确定RGS6促进细胞生长停滞和调节DNA损伤信号的分子机制。我们将确定RGS6的结构特征和参与生长抑制，细胞周期阻滞和RGS6对DNA损伤反应的调节的信号通路，我们将测试RGS6在G蛋白不存在的细胞核中的新功能作用。目的3将确定RGS6的整体缺失或小鼠乳腺组织或神经胶质细胞中的缺失如何调节肿瘤发生。这项研究将为RGS6作为生长抑制剂的作用及其在体内作用的生物学表现提供新的结构和机制见解。该项目可能涉及RGS6和其他RGS蛋白作为G蛋白依赖性肿瘤发生的守门人或定义RGS6在此过程中的新作用。这些研究可能有助于癌症治疗的新方法。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，并且其丢失或突变有助于人类肿瘤。这项工作将确定RGS6是如何工作的，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.