Akt/mTOR Signaling in Energy Balance Modulation of Epithelial Carcinogenesis

描述（由申请人提供）：卡路里限制（CR）可以预防成人发病的肥胖，并抑制多种物种的实验性致癌作用。不幸的是，人们对这些CR效应的机制知之甚少。肥胖是许多类型癌症的危险因素，鉴于肥胖的患病率不断上升，迫切需要深入了解CR的作用机制，以制定新的癌症预防策略。我们最近对A-ZIP/F1和Akt转基因小鼠的研究表明，Akt和mTOR信号通路在小鼠皮肤上皮癌变过程中起重要作用。此外，我们已经证明：1)CR降低Akt和mTOR的活性，包括在包括表皮在内的几种组织中IGF-1受体（IGF-1R）和表皮生长因子(EGF)-R的磷酸化降低；ii)肝脏特异性IGF-1缺乏（LID，导致循环IGF-1水平降低）通过抑制皮肤肿瘤的促进和通过IGF-1R/EGFR及随后的下游信号通路，包括Akt和mTOR，模拟CR。此外，我们发现CR降低了表皮细胞周期蛋白D1并增加了p27的水平。这些发现提示了CR通过IGF-1R和EGF-R减少信号通路，通过多种信号通路（包括Akt和mTOR）减少下游信号通路，最终通过调节细胞周期调节蛋白导致增殖减少的假设。我们将专门研究Akt和mTOR通路在这些CR效应中的重要性。我们建议使用具有良好特征的上皮癌变两阶段皮肤模型，结合饮食、遗传和药理学方法来验证这一假设。具体目的是：1)确定操纵饮食能量平衡对TPA诱导的野生型和肝脏igf -1缺陷小鼠皮肤肿瘤促进的影响；2)研究饮食能量平衡调控对表皮细胞信号通路和基因表达的影响；3)研究CR对皮肤肿瘤促进作用的机制；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-AE451 （IGF-1受体的选择性抑制剂）对自由喂养或CR小鼠皮肤肿瘤促进的预防作用。成功建立了CR与IGF- 1R/Akt/mTOR通路在上皮癌变中的抗癌作用之间的因果关系，将为转化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，卡路里限制（CR）可预防成人发病的肥胖并抑制上皮癌变。鉴于肥胖（许多人类癌症的已知危险因素）在全球范围内的患病率不断上升，迫切需要对CR的作用机制进行深入研究，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与胰岛素样生长因子-1通路（包括IGF-1受体下游的Akt和mTOR）在抑制上皮癌变中的直接联系。这些研究的完成将有助于更好地了解特异性生长因子信号通路在上皮癌变中的作用及其作为癌症预防靶点（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，特别是在癌症发展的假定靶细胞（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.