Roles of Tuberin (TSC2), Hamartin (TSC1), and Rheb in Renal Cyst Pathogenesis

描述（由申请人提供）：多发性硬化症（TSC）是由分别编码错构瘤蛋白（TSC 1）和块茎蛋白（TSC 2）的TSC 1或TSC 2基因中的种系失活突变引起的。TSC 1或TSC 2突变的人类和小鼠都可能患上囊性肾病。TSC 1和TSC 2蛋白作为异二聚体发挥作用以抑制Rheb，Rheb是块茎素的GT3激活结构域的靶标。Rheb激活哺乳动物雷帕霉素靶蛋白（mTOR）复合物1（TORC 1）。我们和其他人已经观察到常染色体显性遗传性多囊肾病（ADPKD）患者囊肿中mTOR通路过度活化的证据，表明TSC/Rheb/mTOR通路参与ADPKD发病机制。除了ADPKD囊肿和Pkd 1失活小鼠囊肿中的mTOR激活外，另外两条证据表明TSC蛋白和Rheb与ADPKD的发病机制密切相关：已发现TSC 2蛋白调节多囊蛋白1（PC 1）的膜定位，并且已发现PC 1的过表达羧基末端与TSC 2共免疫沉淀。这些数据导致了这样的假设，即PC 1的失活足以激活mTOR。然而，我们发现Pkd 1-/- MEFs没有mTOR激活的证据，并且mTOR仅在ADPKD囊肿的一个子集中过度活跃。阐明mTOR在ADPKD囊肿亚组中被激活的不完全理解的机制，这是Aim 1的焦点，具有特别的临床重要性，因为雷帕霉素和其他TORC 1抑制剂目前正在ADPKD患者的临床试验中。在未发表的工作中，我们已经发现，错构瘤蛋白（TSC 1）定位于初级纤毛的基体，并且Tsc 1-null和Tsc 2-null小鼠胚胎成纤维细胞（MEFs）比对照MEFs具有更高比例的纤毛细胞。这些数据为Aim 2提供了基础，首次将TSC途径与纤毛联系起来，并表明Rheb可能通过多种机制影响囊肿发病机制。我们的中心假设是Rheb的激活与PKD 1的突变失活协同作用，促进ADPKD中的囊肿发病机制。为了验证这一点，我们提出了以下目的：目的1：定义mTOR在ADPKD中被激活的机制。目的2：探讨TSC蛋白调控纤毛形成的机制。目的3：确定Rheb激活是否增强Pkd 1诱导的囊肿发病机制。 公共卫生相关性：确定ADPKD中mTOR激活的机制以及TSC蛋白和Rheb在纤毛形成中的作用可能对全球估计的400 - 600万ADPKD患者具有关键的治疗意义，特别是因为mTOR抑制剂已经在PKD的临床试验中。

DESCRIPTION (provided by applicant): Tuberous sclerosis complex (TSC) is caused by germline inactivating mutations in the TSC1 or TSC2 genes, which encode hamartin (TSC1) and tuberin (TSC2), respectively. Both humans and mice with mutations in TSC1 or TSC2 can develop cystic kidney disease. The TSC1 and TSC2 proteins function as a heterodimer to inhibit Rheb, which is the target of tuberin's GTPase activating domain. Rheb activates the mammalian target of rapamycin (mTOR) complex 1 (TORC1). We and others have observed evidence of mTOR pathway hyperactivation in cysts from autosomal dominant polycystic kidney disease (ADPKD) patients, suggesting that the TSC/Rheb/mTOR pathway is involved in ADPKD pathogenesis. In addition to the mTOR activation in ADPKD cysts and in cysts from mice with Pkd1 inactivation, two other lines of evidence suggest that the TSC proteins and Rheb are closely linked with the pathogenesis of ADPKD: the TSC2 protein has been found to regulate membrane localization of Polycystin 1 (PC1), and the overexpressed carboxyl-terminus of PC1 has been found to co-immunoprecipitate with TSC2. These data have led to the hypothesis that inactivation of PC1 is sufficient to activate mTOR. However, we have found that Pkd1-/- MEFs do not have evidence of mTOR activation and that mTOR is hyperactive in only a subset of ADPKD cysts. Elucidating the incompletely understood mechanisms through which mTOR is activated in a subset of ADPKD cysts, which is the focus of Aim 1, has particular clinical importance since rapamycin and other TORC1 inhibitors are now in clinical trials for patients with ADPKD. In unpublished work, we have found that hamartin (TSC1) localizes to the basal body of the primary cilium, and that Tsc1-null and Tsc2-null mouse embryonic fibroblasts (MEFs) have a higher fraction of ciliated cells than control MEFs. These data, which provide the foundation for Aim 2, link the TSC pathway with the cilium for the first time and suggest that Rheb may impact cyst pathogenesis through multiple mechanisms Our central hypothesis is that activation of Rheb cooperates with mutational inactivation of PKD1 to promote cyst pathogenesis in ADPKD. To test this, we propose the following Aims: Aim 1: To define the mechanisms through which mTOR is activated in ADPKD. Aim 2: To identify the mechanisms through which the TSC proteins regulate ciliary formation. Aim 3: To determine whether Rheb activation potentiates Pkd1-induced cyst pathogenesis. PUBLIC HEALTH RELEVANCE: Determining the mechanisms of mTOR activation in ADPKD and the role of the TSC proteins and Rheb in ciliary formation may have key therapeutic implications for the estimated 4-6 million ADPKD patients worldwide, particularly since mTOR inhibitors are already in clinical trials for PKD.