Pathologic and therapeutic implications of Akt attenuation in TSC cells and tumor

描述(申请人提供)：结节性硬化症(TSC)是一种肿瘤综合征，大约每6,000人中就有一人患病，最常发生在儿童早期。这种临床上严重的疾病是由两个肿瘤抑制基因TSC1和TSC2中的一个突变引起的，这两个基因的产物形成了一个复合体。我们实验室和其他实验室最近的研究发现，这种复合体是哺乳动物雷帕霉素靶标(MTOR)的关键负调控因子。缺乏TSC基因功能的细胞和肿瘤表现出结构性的mTOR信号，这有助于TSC小鼠模型的肿瘤形成。此外，这种升高的mTOR活性在TSC缺陷细胞中触发了一个负反馈循环，使PI3K-Akt通路对特定的生长因子没有反应。PI3K-Akt通路是一条关键的细胞生存和增殖通路，在很大比例的人类癌症中被异常激活。利用小鼠遗传学，我们最近发现，该途径的反馈抑制限制了TSC肿瘤的生长。我们的中心假设是，TSC基因功能丧失时Akt的衰减显著影响TSC细胞和肿瘤的生存和增殖特性。此外，由于目前正在对TSC进行临床试验的mTOR抑制剂雷帕霉素可以恢复这些细胞中的Akt信号，我们预测这种药物也将提高TSC的存活率。这项提案中描述的研究将确定这些缺陷对Akt信号的影响，重点是确定治疗TSC的新的治疗机会。其具体目的是：1)鉴定TSC缺陷细胞和肿瘤中Akt介导的细胞生存信号的缺陷以及对缺乏TSC基因的细胞的凋亡潜能的影响；2)比较联合抑制mTOR和PI3K-Akt通路与单独抑制mTOR在TSC细胞培养和小鼠模型中诱导凋亡的有效性；3)确定GSK3在TSC缺陷细胞中的调控机制及其对这些细胞生长因子非依赖性增殖特性的影响；4)确定Akt信号缺陷是否延伸到TSC缺陷神经元。对TSC1/2复合体功能失活所触发的信号缺陷的详细分子理解对于设计适当的TSC治疗方法以及我们了解广泛的人类疾病是至关重要的，例如散发性癌症和糖尿病，这一通路参与其中。

DESCRIPTION (provided by applicant): Tuberous sclerosis complex (TSC) is a tumor syndrome affecting approximately one in 6,000 individuals, most often in early childhood. This clinically severe disease is caused by mutations in one of two tumor suppressor genes, TSC1 and TSC2, whose gene products form a complex. Recent studies by our laboratory and others have found that this complex is a critical negative regulator of the mammalian target of rapamycin (mTOR). Cells and tumors lacking TSC gene function exhibit constitutive mTOR signaling, and this contributes to tumor formation in mouse models of TSC. In addition, this elevated mTOR activity triggers a negative feedback loop in TSC-deficient cells that renders the PI3K-Akt pathway unresponsive to specific growth factors. The PI3K-Akt pathway is a critical cell survival and proliferation pathway that is aberrantly activated in a large percentage of human cancers. Using mouse genetics, we have recently found that feedback inhibition of this pathway limits the growth of TSC tumors. Our central hypothesis is that Akt attenuation upon loss of TSC gene function significantly affects the survival and proliferation properties of TSC cells and tumors. Additionally, as treatment with the mTOR inhibitor rapamycin, which is currently in clinical trials for TSC, can restore Akt signaling in these cells, we predict that this drug will also enhance the survival of TSC cells. The studies described in this proposal will determine the implications of these defects in Akt signaling with an emphasis on identifying novel therapeutic opportunities for the treatment of TSC. The specific aims are: 1) characterize defects in Akt-mediated cell survival signaling in Tsc-deficient cells and tumors and the effects on the apoptotic potential of cells lacking the TSC genes; 2) compare the effectiveness of combination therapy inhibiting both mTOR and the PI3K-Akt pathway to mTOR inhibition alone toward inducing apoptosis in TSC cell culture and mouse models; 3) determine the mechanism of regulation of GSK3 in Tsc-deficient cells and its effects on the growth factor-independent proliferation property of these cells; 4) determine if the defects in Akt signaling extend to Tsc-deficient neurons. A detailed molecular understanding of the signaling defects triggered by functional inactivation of the TSC1/2 complex is critical to the design of proper treatments for TSC and to our knowledge of the wide variety of human diseases, such as sporadic cancers and diabetes, in which this pathway is involved.