Molecular Analysis and Role of RGS6 as a Novel Growth Suppressor

描述(申请人提供)：膀胱癌是美国第五大常见癌症，也是每个患者治疗费用最高的癌症，因为它的复发率很高，而且缺乏有效的、有针对性的治疗方法。预计仅今年美国就会有7万名患者被诊断出患有膀胱癌，1.5万名患者将死于膀胱癌。尽管膀胱癌的发病率很高且缺乏治疗，但肿瘤的发生和发展的机制很大程度上是未知的。膀胱癌的最大危险因素是吸烟，吸烟通过DNA损伤和癌基因激活等机制促进膀胱移行上皮细胞的恶性转化。在这里，我们为G蛋白信号调节因子的全新信号作用提供了第一个证据 6(RGS6)是基因毒性应激过程中P53诱导的重要介质，也是膀胱癌的抑制因子。RGS6被包括基因毒性应激和癌基因激活在内的致癌刺激显著诱导。RGS6作为ATM-P53-凋亡通路的上游激活剂，也通过非P53依赖的机制诱导细胞凋亡、抑制细胞增殖和阻断细胞的致癌转化。RGS6的这些作用不依赖于其作为异三聚体G蛋白在激活剂中的典型功能。我们之前描述了RGS6的单核苷酸多态，它导致RGS6翻译增加，这与显著降低人类，特别是吸烟者患膀胱癌的风险有关。鉴于这些发现，尤其重要的是，我们观察到RGS6基因缺失的小鼠在接受BBN治疗后膀胱癌的发生和p53诱导的丢失，BBN是一种从烟草烟雾中提取的DNA破坏性致癌物质，它在小鼠中诱导膀胱癌的发生与在大多数人类患者中观察到的情况非常相似。在浸润性膀胱癌患者中，我们在膀胱移行上皮细胞中发现的RGS6的强阳性表达显著丢失。我们的中心假设是，基于令人信服的初步数据，RGS6是一种新的DNA损伤信号和膀胱肿瘤抑制的主调节因子。我们提出了三个具体的目标：1)确定RGS6作为肿瘤抑制因子在小鼠膀胱癌发生模型中的重要性以及P53和ARF在其抑癌功能中的作用；2)确定RGS6在膀胱移行上皮细胞中作为DNA损伤信号上游调节器和肿瘤抑制因子发挥作用的潜在分子机制；以及3)确定RGS6在人膀胱癌中缺失的分子基础。这些目的旨在阐明RGS6在抑制膀胱癌发生中的作用及其相关的潜在机制。在人类膀胱肿瘤中观察到的RGS6缺失或其突变失活，有望使肿瘤细胞易于异常生长和提高存活率，这是恶性肿瘤的标志。这些研究对人类健康的意义是巨大的。RGS6可能成为膀胱癌预后或诊断的生物标志物，为膀胱癌的治疗提供新的靶点。

DESCRIPTION (provided by applicant): Urinary bladder cancer is the fifth most common cancer in the U.S. and the most expensive cancer to treat on a per patient basis because of its high incidence of recurrence and the lack of effective, targeted therapeutics. An expected 70,000 patients will be diagnosed with and 15,000 patients will die of urinary bladder cancer in the U.S. this year alone. Despite the high incidence and lack of therapy for bladder cancer, the mechanisms of tumor initiation and progression are largely unknown. The greatest risk factor for bladder cancer is smoking, which promotes malignant transformation of transitional epithelial cells of the bladder by mechanisms involving DNA damage and oncogene activation. Here we provide the first evidence for entirely novel signaling actions of Regulator of G protein Signaling 6 (RGS6) as an essential mediator of p53 induction during genotoxic stress and as a tumor suppressor in bladder. RGS6 is dramatically induced by tumorigenic stimuli including genotoxic stress and oncogene activation. RGS6 functions as an upstream activator of the ATM-p53- apoptosis pathway yet also induces apoptosis, arrests cell proliferation and blocks oncogenic transformation of cells by p53-independent mechanisms. These actions of RGS6 are independent of its canonical function as a heterotrimeric G protein in activator. We previously described a single nucleotide polymorphism in RGS6, which leads to increased RGS6 translation, which is associated with a significant reduction in the risk of bladder cancer in humans, particularly in smokers. Given these findings, it is especially significant that we observed a dramatically accelerated bladder carcinogenesis and loss of p53 induction in RGS6 null mice in response to their treatment with BBN, a DNA-damaging carcinogen derived from tobacco smoke that induces bladder carcinogenesis in mice closely mimicking that observed in the majority of human patients. The robust expression of RGS6 we found in bladder transitional epithelial cells was dramatically lost in patients with invasive bladder cancer. Our central hypothesis, formulated on the basis of compelling preliminary data, is that RGS6 is a novel master regulator of both DNA damage signaling and tumor suppression in bladder. Three specific aims are proposed: 1) Determine the importance of RGS6 as a tumor suppressor in a mouse model of bladder carcinogenesis and the role of p53 and ARF in its tumor suppressor function, 2) Determine the underlying molecular mechanisms by which RGS6 functions as an upstream modulator of DNA damage signaling and as a tumor suppressor in bladder transitional epithelial cells, and 3) Determine the molecular basis for RGS6 loss in human bladder cancer. These aims seek to elucidate the role of RGS6 in suppression of bladder tumorigenesis and the underlying mechanisms involved. Loss of RGS6, as observed in human bladder tumors, or its mutational inactivation would be expected to confer tumor cells with a predisposition to aberrant growth and enhanced survival, hallmarks of malignancy. The significance of these studies to human health is great. They will provide new understanding of the pathogenesis of urinary bladder cancer and potentially identify RGS6 as a biomarker for the prognosis or diagnosis of bladder cancer as well as a new therapeutic target for its treatment.