The role of FOXO transcriptional factors in TSC-mediated tumorigenesis

描述（由申请人提供）：恶性硬化症（TSC）是由TSC 1或TSC 2基因突变引起的，其特征是在多种器官中形成错构瘤。然而，恶性肿瘤的发展是非常罕见的TSC。TSC 1-TSC 2复合物是哺乳动物雷帕霉素靶蛋白（mTOR）的重要负调节因子。已经表明，mTOR介导的负反馈环导致TSC相关肿瘤中Akt信号传导的减弱和TSC缺陷细胞中细胞存活的受损，这可能解释TSC中罕见的恶性进展。然而，关于（i）介导TSC的促存活功能的Akt的潜在机制和关键下游效应物和（ii）TSC相关肿瘤的减弱的癌症表型的基础仍然存在不确定性。最近对小鼠模型和人类癌症的遗传学研究强烈表明，FoxO转录因子代表PI 3 K-AKT信号网络的关键下游效应臂，并在癌症发展中发挥关键作用。事实上，内皮细胞的肿瘤转化是TSC或FoxO缺失后的突出表型，表明上位关系。此外，FoxOs定位于细胞核中，并在TSC缺陷细胞和肿瘤中具有活性，表明FoxOs可能在TSC病理生理学中起关键作用。因此，清楚地了解TSC和FoxO之间的遗传和功能相互作用对于理解TSC发病机制和最终管理至关重要。该提案旨在阐明TSC相关肿瘤中罕见恶性肿瘤的潜在机制。我们推测TSC的抗凋亡功能主要是通过促进Akt介导的FoxO磷酸化而抑制FoxO的转录活性。TSC缺失后FoxOs的重新激活可能有助于降低TSC相关肿瘤的严重程度，因此TSC和FoxOs两者的复合缺失将导致更恶性的表型。具体目的是（1）检查小鼠中FoxO和TSC的复合失活是否会加剧在TSC单突变体中观察到的肿瘤表型，（2）研究FoxO对原代细胞中TSC介导的细胞生物学活性的影响，以及（3）鉴定可能介导TSC细胞生物学功能的直接FoxO转录靶标。这一建议将提供重要的生物化学和生物学见解的作用和必要性FoxO转录因子在TSC的发展。TSC-mTOR信号传导对Akt信号传导的负反馈调节表明雷帕霉素类似物与PI 3 K-Akt信号传导抑制剂的联合治疗应用于TSC临床试验。鉴于FoxO在PI 3 K-Akt信号传导中的关键作用，我们鉴定参与TSC调节的直接FoxO转录靶点的努力可能会扩大TSC的药物开发机会，或者至少鉴定FoxO生物标志物，其可以提供用于监测抗PI 3 K药物在临床试验中的影响的药效学标志物。公共卫生相关性：该提案旨在通过结合遗传学、基因组学和细胞生物学方法来研究FoxO转录因子在TSC介导的负反馈调节中的作用，FoxO转录因子是癌症发展中PI 3 K-AKT信号传导的关键下游替代物。鉴定具有致癌活性的经验证的FoxO靶点在TSC的调节中发挥重要作用，可能会扩大这种疾病的药物靶点机会。1

DESCRIPTION (provided by applicant): Tuberous Sclerosis (TSC) is caused by mutation in either TSC1 or TSC2 gene and is characterized by the formation of hamartomas in a variety of organs. However, the development of malignancy is very rare in TSC. TSC1-TSC2 complex is a critical negative regulator of the mammalian target of rapamycin (mTOR). It has been showed that an mTOR-mediated negative feedback loop leads to attenuation of Akt signaling in TSC-related tumors and compromised cell survival in TSC deficient cells, which might explain the rare progression to malignancy in TSC. However, uncertainties remain as to (i) the underlying mechanisms and key downstream effector(s) of Akt that mediate the pro-survival function of TSC and (ii) the basis for the attenuated cancer phenotype of the TSC-related tumors. Recent genetic studies from both mouse models and human cancers strongly suggest that the FoxO transcription factors represent key downstream effector arms of PI3K-AKT signaling network and play critical roles in cancer development. Indeed, neoplastic conversion of endothelial cells is a prominent phenotype upon loss of either TSC or FoxO, suggesting an epistatic relationship. Furthermore, FoxOs were shown to localize in the nucleus and active in TSC deficient cells and tumors, suggesting that FoxOs might play a critical role in TSC pathophysiology. Thus, a clear understanding the genetic and functional interactions between TSC and FoxO appears to be critical to understand TSC pathogenesis and ultimate management. This proposal aims to elucidate the underlying mechanisms of rare malignancy in TSC-related tumors. We hypothesize that the anti-apoptotic function of TSC is mainly mediated by suppression of FoxOs transcriptional activity through promoting Akt-mediated FoxO phosphorylation. Reactivation of FoxOs upon loss of TSC might contribute to the less severity of TSC-related tumors and thus compound deletion of both TSC and FoxOs would lead more malignant phenotypes. The specific aims are (1) to examine whether compound inactivation of FoxOs and TSC in the mouse would exacerbate the tumor phenotypes observed in TSC single mutants, (2) to study the impact of FoxOs on TSC-mediated cell biological activity in primary cells, and (3) to identify direct FoxO transcriptional targets which might mediate the cell biological functions of TSC. This proposal will provide important biochemical and biological insights into the role and essentiality of FoxO transcriptional factors in TSC development. The negative feedback regulation of Akt signaling by TSC-mTOR signaling suggests combined treatment of rapamycin analogues with inhibitors of PI3K-Akt signaling should be used in TSC clinical trials. Given the critical role of FoxO in PI3K-Akt signaling, our efforts to identify direct FoxO transcriptional targets involved in the regulation of TSC might expand drug development opportunities for TSC or, minimally, identify a FoxO biomarker which may provide a pharmacodynamic marker for monitoring the impact of anti-PI3K drugs in clinical trials. PUBLIC HEALTH RELEVANCE: This proposal aims to examine the role of FoxO transcriptional factors, a key downstream surrogate of PI3K-AKT signaling in cancer development, in TSC-mediated negative feedback regulation through combined genetic, genomics and cell biological approaches. The identification of validated FoxO targets with oncogenic activities playing essential roles in the regulation of TSC may expand drug target opportunities for this disease. 1