Akt/mTOR Signaling in Energy Balance Modulation of Epithelial Carcinogenesis

描述（由申请人提供）：热量限制（CR）可预防成年肥胖症并抑制多个物种的实验性致癌作用。不幸的是，这些CR效应背后的机制知之甚少。鉴于肥胖的患病率不断上升，这是许多类型癌症的既定风险因素，迫切需要对CR影响的机制见解，以制定新的癌症预防策略。我们最近使用A-ZIP/F1和Akt转基因小鼠的研究已经证明了Akt和mTOR信号在小鼠皮肤上皮癌发生中的重要作用。此外，我们已经表明i）CR降低Akt和mTOR的活性，包括在包括表皮的几种组织中IGF-1受体（IGF-1 R）和表皮生长因子（EGF）-R的磷酸化降低;和ii）肝特异性IGF-1缺乏（盖子，导致循环IGF-1水平降低）通过抑制皮肤肿瘤促进和经由IGF-1 R/IGF-1受体的信号传导来模拟CR。EGFR和随后的下游信号通路，包括小鼠中的Akt和mTOR。此外，我们发现CR降低表皮细胞周期蛋白D1和增加p27水平。这些发现表明，CR减少了通过IGF-1 R和EGF-R的信号传导，减少了通过多种信号传导途径（包括Akt和mTOR）的下游信号传导，最终通过调节细胞周期调节蛋白导致增殖减少。我们将专门研究Akt和mTOR通路在CR的这些作用中的重要性。我们建议使用特征良好的两阶段皮肤上皮癌模型，结合饮食，遗传和药理学的方法，以测试这一假设。具体目的是：1）确定操纵膳食能量平衡对野生型和肝脏IGF-1缺陷小鼠中佛波酯（TPA）诱导的皮肤肿瘤促进的影响; 2）检查由膳食能量平衡操纵引起的表皮中细胞信号传导途径和基因表达的改变; 3）检查CR对皮肤肿瘤促进作用的潜在机制;和4）表征雷帕霉素（mTOR的选择性抑制剂）、API-2（Akt的选择性抑制剂）和NVP-AE 451（IGF-1受体的选择性抑制剂）对自由进食或CR小鼠中皮肤肿瘤促进的预防作用。成功建立CR的抗癌作用和IGF-1 R/Akt/mTOR通路在上皮癌发生之间的因果关系将为翻译研究提供良好的基础，以确定靶向该通路是否是预防人类上皮癌的策略。公共卫生相关性：在多种模型中，热量限制（CR）可预防成人型肥胖并抑制上皮癌发生。鉴于肥胖（许多人类癌症的既定风险因素）在世界各地的流行率不断上升，迫切需要对CR影响的机制见解，以开发预防上皮癌的新靶点和策略。我们提出的研究旨在建立CR和胰岛素样生长因子-1通路之间的直接联系，包括IGF-1受体下游的Akt和mTOR，以抑制上皮癌发生。完成拟议的研究将导致更好地理解特定生长因子信号通路在上皮癌发生中的作用及其作为靶点的潜力（例如，IGF-1受体，Akt，mTOR）用于癌症预防。此外，提出的研究将建立CR抗癌作用的分子机制，特别是在假定的靶细胞中（即，干细胞）的癌症发展。

DESCRIPTION (provided by applicant): Calorie restriction (CR) prevents adult-onset obesity and suppresses experimental carcinogenesis in multiple species. Unfortunately, the mechanisms underlying these CR effects are poorly understood. Given the rising prevalence of obesity, an established risk factor for many types of cancer, mechanistic insights into the effects of CR are urgently needed to develop new cancer prevention strategies. Our recent studies using A-ZIP/F1 and Akt transgenic mice have demonstrated an important role for Akt and mTOR signaling in epithelial carcinogenesis in mouse skin. Furthermore, we have shown that i) CR decreases activity of Akt and mTOR, including reduced phosphorylation of the IGF-1 receptor (IGF-1R) and epidermal growth factor (EGF)-R, in several tissues including the epidermis; and ii) liver-specific IGF-1 deficiency (LID, resulting in reduced circulating IGF-1 levels) mimics CR by inhibiting skin tumor promotion and signaling through the IGF-1R/EGFR and subsequent downstream signaling pathways, including Akt and mTOR in mice. Furthermore, we have found that CR reduces cyclin D1 and increases p27 levels in epidermis. These findings suggest the hypothesis that CR reduces signaling through the IGF-1R and EGF-R, decreasing downstream signaling through multiple signaling pathways (including Akt and mTOR), ultimately leading to decreased proliferation through modulation of cell cycle regulatory proteins. We will specifically examine the importance of the Akt and mTOR pathways in these effects of CR. We propose to use the well-characterized two-stage skin model of epithelial carcinogenesis, in combination with dietary, genetic, and pharmacologic approaches, to test this hypothesis. The specific aims are to The specific aims are to: 1) Determine the impact of manipulation of dietary energy balance on phorbol ester (TPA)-induced skin tumor promotion in wild-type and liver IGF-1-deficient mice; 2) Examine cell signaling pathways and alterations in gene expression in epidermis resulting from dietary energy balance manipulations; 3) Examine mechanisms underlying the effects of CR on skin tumor promotion; and 4) Characterize the preventive effects of rapamycin (a selective inhibitor of mTOR), API-2 (a selective Akt inhibitor) and NVP-AE451 (a selective inhibitor of the IGF-1 receptor) on skin tumor promotion in ad libitum-fed or CR mice. The successful establishment of a causal link between the anticancer effects of CR and the IGF- 1R/Akt/mTOR pathway in epithelial carcinogenesis will provide a sound basis for translational studies to determine if targeting this pathway is a strategy for preventing epithelial cancers in humans. PUBLIC HEALTH RELEVANCE: Calorie restriction (CR) prevents adult-onset obesity and inhibits epithelial carcinogenesis in multiple models. Given the rising prevalence of obesity (an established risk factor for many human cancers) throughout the world, mechanistic insights into the effects of CR are urgently needed to develop new targets and strategies for preventing epithelial cancers. Our proposed studies aim to establish a direct link between CR and the insulin-like growth factor-1 pathway, including Akt and mTOR downstream of the IGF-1 receptor, in inhibiting epithelial carcinogenesis. Completion of the proposed studies will lead to a greater understanding of the role specific growth factor signaling pathways play in epithelial carcinogenesis and their potential as targets (e.g., IGF-1 receptor, Akt, mTOR) for cancer prevention. Furthermore, the proposed studies will establish molecular mechanisms underlying the anticancer effects of CR, especially in the putative target cells (i.e., stem cells) for cancer development.