Akt/mTOR Signaling in Energy Balance Modulation of Epithelial Carcinogenesis

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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.