Abstract 966: Dietary energy balance modulates IGF-1R and EGFR signaling and crosstalk during tumor promotion
Authors: Moore Tricia , Beltran Linda , Carbajal Steve , Jiang Guiyu , Bhatt Tarlochan , Hursting Stephen , DiGiovanni John 
Published: February 2011

Abstract
Negative energy balance (calorie restriction, CR) inhibits, while positive energy balance enhances tumor promotion during two-stage skin carcinogenesis. Biochemical studies have demonstrated that CR reduced, while diet-induced obesity (DIO) increased activation of the insulin-like growth factor-1 receptor (IGF-1R) and the epidermal growth factor receptor (EGFR), as well as downstream signaling (e.g., Akt and mTOR) during tumor promotion. Additional studies performed using the liver IGF-1 deficient (LID) mouse model demonstrated that a 75% reduction in circulating IGF-1 attenuated growth factor signaling through the IGF-1R and the EGFR similar to mice on CR diets. These findings suggest that dietary energy balance, primarily through its effects on levels of circulating IGF-1, modulates epithelial carcinogenesis and tumor promotion through diet-induced changes in signaling and crosstalk between the IGF-1R and the EGFR, which subsequently alters signaling to downstream effectors. To determine the impact of IGF-1 on IGF-1R and EGFR signaling and crosstalk, Western blot analyses, immunoprecipiation and qPCR analyses were performed on C50 cells (nontumorigenic keratincyte cell line) stimulated with IGF-1. IGF-1 increased activation of the IGF-1R and the EGFR, as well as signaling to downstream effectors (i.e., Akt and mTOR). Immunoprecipitation experiments demonstrated an increase in association between the IGF-1R and the EGFR following IGF-1 stimulation. Furthermore, IGF-1 induced changes in expression levels of the EGFR, as well as EGFR ligands (i.e., HB-EGF, amphiregulin, TGF-α). Additional experiments performed using C50 cells stably transfected with EGFR shRNA or cells pretreated with PD153035 (EGFR inhibitor) demonstrated reduced IGF-1 mediated activation of the EGFR as well as reduced downstream signaling to Akt and mTOR. In vivo studies were performed to evaluate the effect of dietary energy balance on IGF-1R and EGFR crosstalk. For these experiments, ICR mice were maintained on a CR and DIO regimen for 15 weeks, after which they were treated with a single application of 3.4 nmol TPA. CR reduced, while DIO increased the interaction between the IGF-1R and the EGFR in the epidermis of TPA treated mice. Furthermore, dietary energy balance modulated EGFR and EGFR ligand expression levels. Taken together, these data suggest that levels of IGF-1 can modulate signaling through both the IGF-1R and the EGFR. Furthermore, diet-induced changes in IGF-1R/EGFR crosstalk subsequently modulate activation of downstream signaling to Akt and mTOR, thus contributing, at least in part, to the effect of dietary energy balance on skin tumor promotion. Supported by NIH grants CA37111 and CA129409.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 966.