Submitted to: Cancer Research
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2008
Publication Date: 1/15/2009
Citation: Su, Y., Shankar, K., Simmen, F.A., Simmen, R.C. 2009. Regulation of adipocyte lipid homeostasis by genistein alters mammary epithelial cell differentiation: A paracrine mechanism for mammary tumor protection [abstract]. Cancer Research. 69(2):5082.
Interpretive Summary: The linkage between nutrition and cancer prevention has been widely studied. In our lab, we have shown lifetime consumption of soy diet is protective in the rat carcinogen-induced breast cancer model. In the current study, we found that lifetime soy-feeding female rats have lower body weight and higher mammary gland differentiation status. Global gene profiles from soy- and control-diet-feeding animals showed that dietary soy regulates fat synthesis in the mammary gland. We further used the cell culture system showing that genistein changed fat cells secretion, which indirectly increased the differentiation of mammary epithelial cells. This may be a potential mechanism of dietary soy and genistein protection against breast cancer.
Technical Abstract: Epidemiological and animal studies have shown a negative correlation between breast cancer incidence and intake of soy rich foods. Our laboratory has studied soy protein isolate (SPI), the primary component of soy infant formula, as a paradigm to evaluate diet as a risk factor in mammary cancer. We previously demonstrated that lifetime exposure to dietary SPI reduced the incidence of N-methyl-N-nitrosourea-induced mammary tumors in young adult rats relative to those fed the control Casein diet (CAS). This protection was associated with increased differentiation status of mammary epithelial cells prior to carcinogen insult, suggesting increased differentiation as a mechanism for mammary tumor protection. To identify early events contributing to increased mammary differentiation by diet, we used Affymetrix RAE230A GeneChips containing 14280 probe sets and GeneSpring Gx software to analyze genomic profiles of mammary glands of prepubertal (postnatal day (PND) 21) rats that were lifetime exposed to dietary SPI or CAS. Of the 8 genes down-regulated by SPI, 4 are involved in lipid homeostasis: malic enzyme 1, fatty acid synthase (Fasn), stearoyl CoA desaturase-1 (Scd1), and insulin-induced gene 1. One of five SPI-induced genes is 11beta-hydroxysteroid dehydrogenase 1 (Hsd1), which converts 11beta-dehydrocorticosterone to corticosterone. Quantitative RT-PCR confirmed that Fasn and Scd1 transcript levels were down-regulated and Hsd1 was up-regulated, in PND21 mammary tissues of SPI vs CAS group. To provide mechanistic insights into potential paracrine effects of soy-mediated altered adipocyte lipid metabolism on mammary epithelial cell phenotype, we used the clonal mouse fibroblast 3T3-L1 cell line treated with the bioactive soy isoflavone genistein (GEN) and mouse mammary epithelial cell line HC11 as in vitro systems to recapitulate in vivo stromal/epithelial interactions. GEN (0.5 µM) regulated lipid homeostasis in fully differentiated 3T3-L1 adipocytes. GEN decreased Fasn and Scd1and increased Hsd1, transcript levels in the absence of effects on leptin and PPAR'2 gene expression. To evaluate whether factors produced by GEN-treated adipocytes regulate mammary epithelial differentiation, mature adipocytes were incubated in medium without or with added GEN (0.5 µM) for 48 h. Cells were refreshed with maintenance medium, and 24 h later conditioned medium (CM) was harvested, supplemented with prolactin (5 ng/ml), and added full-strength to HC11 cells. Cells incubated for 72 h in CM from GEN-exposed adipocytes had higher differentiation-associated beta-casein transcript levels than those grown in non-GEN-treated CM. Studies are in progress to identify adipocyte-secreted factors regulated by GEN. Our data provide support to the hypothesis that GEN modulation of mammary adipose tissue metabolism and secretion constitutes one mechanism by which mammary epithelial differentiation is enhanced by diet to confer increased resistance to breast cancer.