Molecular Analysis and Role of RGS6 as a Novel Growth Suppressor

描述（由申请人提供）：膀胱癌是美国第五大最常见的癌症，也是每个患者治疗费用最高的癌症，因为其复发率高，缺乏有效的靶向治疗。预计仅今年美国就将有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高且缺乏治疗，但肿瘤发生和进展的机制在很大程度上是未知的。膀胱癌的最大危险因素是吸烟，吸烟通过涉及DNA损伤和癌基因激活的机制促进膀胱移行上皮细胞的恶性转化。在这里，我们提供了第一个证据，完全新的信号作用的调节G蛋白信号 6（RGS 6）作为基因毒性应激期间p53诱导的重要介质和作为膀胱肿瘤抑制剂。RGS 6是显着诱导的致瘤刺激，包括基因毒性应激和癌基因激活。RGS 6作为ATM-p53-凋亡途径的上游激活剂发挥作用，但也通过p53非依赖性机制诱导凋亡、阻止细胞增殖并阻断细胞的致癌转化。RGS 6的这些作用与其作为异源三聚体G蛋白激活剂的典型功能无关。我们先前描述了RGS 6中的单核苷酸多态性，这导致RGS 6翻译增加，这与人类膀胱癌风险的显着降低有关，特别是在吸烟者中。鉴于这些发现，特别重要的是，我们观察到RGS 6缺失小鼠中响应于BBN治疗的膀胱癌发生和p53诱导的丧失显著加速，BBN是一种来自烟草烟雾的DNA损伤性致癌物，其诱导小鼠膀胱癌发生，与大多数人类患者中观察到的非常相似。我们在膀胱移行上皮细胞中发现的RGS 6的强表达在浸润性膀胱癌患者中显著丧失。我们的中心假设，制定了令人信服的初步数据的基础上，是RGS 6是一种新的主调节器的DNA损伤信号和肿瘤抑制在膀胱。提出了三个具体目标：1）确定RGS 6在膀胱癌发生的小鼠模型中作为肿瘤抑制剂的重要性以及p53和ARF在其肿瘤抑制剂功能中的作用，2）确定RGS 6作为DNA损伤信号传导的上游调节剂和作为膀胱移行上皮细胞中的肿瘤抑制剂的潜在分子机制，和3）确定人膀胱癌中RGS 6缺失的分子基础。这些目的旨在阐明RGS 6在抑制膀胱肿瘤发生中的作用及其相关机制。如在人膀胱肿瘤中观察到的，RGS 6的缺失或其突变失活预期将赋予肿瘤细胞异常生长和增强的存活的倾向，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。他们将为膀胱癌的发病机制提供新的认识，并可能将RGS 6确定为膀胱癌预后或诊断的生物标志物以及治疗膀胱癌的新靶点。

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.