Abstract 57: Adipocyte oxidative stress promotes epithelial-mesenchymal transition (EMT) related gene expression and estrogen receptor (ER) negative phenotype in breast cancer cells

Abstract

Abstract Epidemiological studies have linked obesity with basal-like breast cancer risk in both premenopausal and postmenopausal women, suggesting that obesity may affect tumor phenotype by skewing the microenvironment toward support of more aggressive tumor cell phenotypes (typically ER/PR−, HER-2−). In order to study the interactions between adipocytes and breast tumor cells, we developed an adipocyte-breast cancer cell co-culture system. The adipocytes SGBS (Simpson-Golabi-Behmel Syndrome) and human ER positive breast cancer MCF7 cells were co-cultured for 24 hours. Following co-culture, the cells from the inserts (MCF7 cells) and wells (SGBS cells) were collected separately and total RNA was then isolated. The mRNA levels of the NADPH oxidase subunit NOX4 and hypoxia-inducible factor 1α (HIF1α) were determined by RT-PCR and normalized to 18S RNA levels. When SGBS cells were co-cultured with MCF7 cells, SGBS NOX4 and HIF1α mRNA levels increased more than 10 fold and 3 fold, respectively, while there were no changes in NOX4 and HIF1α expression detected in co-cultured MCF7 cells. We also compared several epithelial-mesenchymal transition (EMT) process-related gene expression levels. Expression in MCF7 cells of the EMT-inducing transcription factors FOXC2 and Twist1 were increased more than 8 fold and 5 fold respectively, after co-culture with SGBS. E-cadherin mRNA level was decreased 2 fold, while N-cadherin mRNA level was increased more than 6 fold in co-cultured MCF7. We also found that mRNA levels of ER-α were significantly (p<0.05) repressed in MCF7 cells co-cultured with SGBS cells. To explore the mechanism of the effect of adipocyte co-culture on ER expression in breast cancer cells, SGBS cells were transfected with 30nM of siHIF1α for 48 hours before co-culture with MCF7 cells. ER gene expression level did not change in MCF7 cells co-cultured with SGBS cells that had been transfected with siHIF1α. In summary, we have shown that adipocytes and breast tumor cells interact with each other: MCF7 cells increased hypoxia and oxidative stress in SGBS cells, while SGBS increased the expression of EMT-inducing factor genes in MCF7 cells, as well as repressing ER expression. This repression was controlled, at least in part, by HIF1α. These results suggest that hypoxia and oxidative stress from adipocytes can modify ER gene expression and promote EMT processes in breast cancer cells, supporting an important role of obesity in aggressive breast cancer development. 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 57. doi:1538-7445.AM2012-57