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

描述（由申请人提供）：结节性硬化症（TSC）是一种肿瘤综合征，影响大约6000人中有1人，最常见于幼儿期。这种临床上严重的疾病是由两种肿瘤抑制基因TSC1和TSC2中的一种突变引起的，其基因产物形成复合物。我们实验室和其他实验室最近的研究发现，该复合物是哺乳动物雷帕霉素靶蛋白（mTOR）的关键负调节因子。缺乏TSC基因功能的细胞和肿瘤表现出组成性mTOR信号，这有助于TSC小鼠模型中的肿瘤形成。此外，mTOR活性升高在tsc缺陷细胞中引发负反馈回路，使PI3K-Akt通路对特定生长因子无反应。PI3K-Akt通路是一个关键的细胞存活和增殖通路，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基因功能丧失后Akt的衰减显著影响TSC细胞和肿瘤的存活和增殖特性。此外，由于mTOR抑制剂雷帕霉素（目前正在进行TSC的临床试验）可以恢复这些细胞中的Akt信号，我们预测该药物也可以提高TSC细胞的存活率。本提案中描述的研究将确定Akt信号中这些缺陷的含义，重点是确定治疗TSC的新治疗机会。具体目的是：1)表征TSC缺陷细胞和肿瘤中akt介导的细胞存活信号缺陷及其对缺乏TSC基因的细胞凋亡电位的影响；2)在TSC细胞培养和小鼠模型中，比较联合抑制mTOR和PI3K-Akt通路与单独抑制mTOR诱导凋亡的效果；3)确定GSK3在tsc缺陷细胞中的调控机制及其对tsc缺陷细胞不依赖生长因子增殖特性的影响；4)确定Akt信号的缺陷是否延伸到tsc缺陷神经元。对TSC1/2复合体功能失活引发的信号缺陷的详细分子理解对于设计适当的TSC治疗方法以及我们对各种人类疾病（如散发性癌症和糖尿病）的了解至关重要，这些疾病都涉及该途径。

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.