Akt/mTOR Signaling in Energy Balance Modulation of Epithelial Carcinogenesis

描述(由申请人提供)：卡路里限制(CR)预防成人肥胖症并抑制多种物种的实验性致癌作用。不幸的是，这些CR效应背后的机制还知之甚少。鉴于肥胖发病率的上升，肥胖是许多类型癌症的既定危险因素，迫切需要对CR的影响进行机械性的洞察，以开发新的癌症预防策略。我们最近使用A-ZIP/F1和Akt转基因小鼠的研究表明，Akt和mTOR信号在小鼠皮肤上皮癌发生中起着重要作用。此外，我们已经证明：i)CR降低Akt和mTOR的活性，包括减少包括表皮在内的几个组织中IGF-1受体(IGF-1R)和表皮生长因子(EGF)-R的磷酸化；以及ii)肝脏特异性IGF-1缺陷(LID，导致循环中IGF-1水平降低)通过抑制皮肤肿瘤的促进作用以及通过IGF-1R/EGFR和随后的下游信号通路(包括Akt和mTOR)来模拟CR。此外，我们还发现CR降低了细胞周期蛋白D1，增加了表皮中p27的水平。这些发现表明，CR通过IGF-1R和EGF-R减少信号，通过多个信号通路(包括Akt和mTOR)减少下游信号，最终通过调节细胞周期调节蛋白导致细胞增殖减少。我们将具体研究Akt和mTOR通路在CR的这些效应中的重要性。我们建议使用上皮癌形成的两阶段皮肤模型，结合饮食、遗传和药理学方法来验证这一假说。其具体目的是：1)确定饮食能量平衡操作对佛波酯(TPA)诱导的野生型和肝脏IGF-1缺陷小鼠皮肤肿瘤促进作用的影响；2)检测饮食能量平衡操作引起的细胞信号通路和表皮基因表达的变化；3)研究CR促进皮肤肿瘤作用的机制；4)研究雷帕霉素(mTOR选择性抑制剂)、API-2(选择性Akt抑制剂)和NVP-AE451(IGF-1受体选择性抑制剂)对随机饲养或CR小鼠皮肤肿瘤的预防作用。在上皮癌变中，CR的抗癌作用与IGF-1R/Akt/mTOR通路之间的因果联系的成功建立，将为翻译研究提供可靠的基础，以确定以该通路为靶点是否为预防人类上皮癌的策略。公共卫生相关性：卡路里限制(CR)在多种模型中预防成人肥胖症和抑制上皮癌变。鉴于肥胖(许多人类癌症的既定危险因素)在世界各地的流行程度不断上升，迫切需要对CR的影响进行机械性的洞察，以制定预防上皮癌的新目标和战略。我们建议的研究旨在建立CR和胰岛素样生长因子-1途径之间的直接联系，包括IGF-1受体下游的Akt和mTOR，以抑制上皮癌变。这些研究的完成将有助于更好地了解特定的生长因子信号通路在上皮细胞癌变中所起的作用，以及它们作为癌症预防靶点(如IGF-1受体、Akt、mTOR)的潜力。此外，拟议的研究将建立CR抗癌作用的分子机制，特别是在假定的癌症发展靶细胞(即干细胞)中。

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.