Abstract 2070: Obesity, p53 and increased oxidative stress: The role of TXNIP

Abstract

Abstract Background: Although epidemiological studies show a strong association between increased BMI and heightened risk of postmenopausal breast cancer, the underlying mechanisms by which obesity influences breast cancer susceptibility are multivariate and poorly characterized. One potential mechanism by which obesity contributes to breast cancer initiation is through induction of oxidative stress. Oxidative burden is strongly implicated in tumor initiating events through induction of chromosome instability, dysregulation of proapoptotic signaling, and redox modulation of the tumor suppressor gene, TP53. Obesity and p53 mutations are both associated with development of aggressive, ER-negative disease in younger women. Therefore, the goal of this study was to identify genes that link obesity to p53 and oxidative stress. Results: We isolated mRNA from the mammary fat pads of obese p53 +/+ and obese +/− mice. Using a qPCR array, we measured the expression of 85 genes related to oxidative stress and screened for transcripts that were altered by at least 2 fold. Expression of the gene thioredoxin-interacting protein (TXNIP) was increased by almost 30 fold in MFP of sedentary, obese p53 +/− mice compared to sedentary, obese p53 +/+ mice (n=3). We validated this finding using 6 mice from each group and found that Txnip mRNA was significantly increased by almost 3 fold in the MFP of obese p53 +/− mice compared to obese p53 +/+ mice (p<0.001). Interestingly, TXNIP expression is increased in response to high glucose flux, can mediate apoptosis through modulation of ROS, and is lost in many cancers, including breast. To further elucidate the function of TXNIP in breast cancer cells, MCF-7 cells were stably transfected with shRNA targeting TXNIP, p53, or both. Cells were incubated overnight in either serum-free media (SFM), 2% FBS, 2% serum from obese mice, or 2% serum from control mice. Cells were then assayed for ROS production, DNA damage, and apoptosis. Cells transfected with control shRNA exhibited a 7-fold increase in ROS when incubated in obese serum compared to cells incubated in SFM, 2%FBS, or 2% control serum. Increased production of ROS was abrogated by knockdown of TXNIP or p53. However, knockdown of both TXNIP and p53 resulted in a 35-fold increase in ROS levels. The significant increase in ROS production was associated with intense nuclear H2AX immunufluorescent staining. Despite high levels of oxidative stress and DNA damage, there was a 25% reduction in apoptosis. Conclusion: TXNIP expression is increased by obesity and p53-deficiency in the mouse mammary fat pad. In human breast cancer cells, TXNIP regulates ROS levels and reduces chronic oxidative stress associated with obesity by mediating an apoptotic response to excessive DNA damage. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2070. doi:1538-7445.AM2012-2070