INTRODUCTION: Epidemiological studies show an association between increased calorie intake and breast cancer risk, mainly in industrialized countries; experimental studies also support this association. Calorie restriction (CR) dramatically reduces the incidence of spontaneous and chemically induced mammary tumors in rodents and other models. Exercise (EX) increases energy expenditure and reduces body weight gain, yet there is conflicting data on exercise effects and mammary cancer in humans and in animal models. Increased physical activity has been reported to inhibit, stimulate, or have no effect on mammary carcinogenesis both in humans and animal models. The mechanisms by which CR and EX influence mammary development and tumorigenesis remain unknown. AIMS: To evaluate the effects of CR and/or EX on mammary gland gene expression in C57BL/6 mice. MATERIALS AND METHODS: Forty-eight 6wks old female C57BL/6 mice were randomized into 4 experimental groups: 1) ad libitum (AL)-fed (Control); 2) AL-fed with access to running wheels (EX); 3) 30% CR; and 4) 30% CR with access to running wheels (CR+EX). Mice in the AL treatment groups received AIN-76A diet; CR mice were pair-fed 30% less with an AIN-76A formula modified to provide 70% of calories but 100% of all other nutrients. After 6 wks of treatment animals were necropsied. The Affymetrix oligo microarray platform was used to determine global gene expression patterns in mammary gland total RNA. The genes altered by 2-fold or more from Control (p<0.05) were selected for the analysis. RESULTS: The treatments had significant effects on body composition and levels of physical activity: 1) CR were significantly lighter than AL fed animals; and 2) EX AL-fed animals ran 1.7 miles/day compared to CR+EX which ran 0.5 miles/day. The global expression patterns of Control, CR, EX, CR+EX were clearly distinct. Preliminary data indicated that 356 genes were differentially expressed. The main functional category altered by CR was morphogenesis. Leptin expression was down-regulated in all treated groups. Differentiation genes including β-catenin and transcription factors like N-myc 1 and T-box 15 were over expressed in the CR and CR+EX groups, suggesting the possible involvement of the Wnt/β-catenin pathway in response to CR. In addition to its well-documented role in human breast cancer, recent data strongly implicate this pathway, both in vitro and in transgenic mouse models, in the development of mammary rudiments, and in the ductal branching and alveolar morphogenesis during pregnancy. Wnt/β-catenin signaling also acts in the upstream of N-myc regulation during proximal-distal differentiation in airway epithelium in mice. These data may contribute to better understanding of mechanisms involved in the breast cancer prevention and risk as it relates to energy balance.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]