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RNA sequencing of mammary tumors induced in MTB-IGFIR transgenic mice fed 20% ISP, 1% ISP, or 20% Casein

ABSTRACT: Epidemiologic studies demonstrate that women from cultures that consume high levels of dietary soy have reduced breast cancer rates compared to women from cultures where soy consumption is typically much lower. The types of soy products consumed can also differ with Asian cultures consuming primarily minimally refined soy products while Western cultures often consume more highly refined soy products such as isolated soy protein (ISP). Our previous work showed that lifetime exposure to a diet containing 20% ISP promoted mammary tumor development in MTB-IGFIR transgenic mice. In this study, lifetime exposure to lower levels of ISP were evaluated (5% ISP and 1% ISP) to determine whether more moderate levels of ISP could protect against mammary tumorigenesis. A standard rodent diet, Teklad 2018 was also included in this study and Teklad 2018 contains a less refined form of soy, namely soybean meal. MTB-IGFIR mice fed ISP diets, independent of the concentration, displayed increased mammary tumor incidence and reduced tumor latency compared to MTB-IGFIR mice fed a 20% casein diet. Unexpectedly, MTB-IGFIR mice fed Teklad 2018 were completely protected against mammary tumor development. Although RNA sequencing of mammary tumors from ISP or casein fed mice did not identified gene expression patterns associated with the ISP diets, the ISP diets consistently promoted the expression of contractile related proteins in pubertal mammary glands. Therefore, lifetime exposure to ISP may alter gene expression in pubertal mammary glands rendering them more susceptible to transformation. Based on these findings women may want to avoid highly refined soy products such as ISP and switch to less refined forms of dietary soy until additional studies can be performed.

ORGANISM(S): Mus musculus

PROVIDER: GSE122294 | GEO | 2020/07/15

REPOSITORIES: GEO

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Project description:The role of diet in the prevention of breast cancer is widely accepted, yet little is known on how early dietary effects mitigate adult cancer risk. Soy consumption is associated with reduced breast cancer risk in women, an effect largely attributed to the soy isoflavone genistein (GEN). We previously showed lower chemically-induced mammary tumor incidence in young adult rats with lifetime dietary intake of soy protein isolate (SPI), a highly refined soy product in infant formula, than in those fed the control diet Casein (CAS). To gain insight into signaling pathways underlying dietary tumor protection, we performed genome-wide expression profiling of mammary epithelial cells from young adult rats lifetime fed CAS, SPI, or supplemental GEN-based diets. We identified mammary epithelial genes regulated by SPI (79 total) and GEN (99 total) using Affymetrix rat 230A GeneChip arrays and found minimal overlap in gene expression patterns. We showed that the regulated transcripts functionally cluster in biochemical pathways involving metabolism, immune response, signal transduction, and ion transport. We confirmed the differential expression of Wnt (Wnt5a, Sfrp2) and Notch (Notch2, Hes1) signaling components by SPI and/or GEN using QPCR. Wnt pathway inhibition by GEN was supported by lower Cyclin D1 immunoreactivity in mammary ductal epithelium of GEN relative to CAS and SPI, despite their comparable levels of membrane-localized E-cadherin and Î²-catenin. Identification of distinct GEN and SPI responsive genes in mammary epithelial cells may define early events contributing to tumor protection by diet relevant to the prevention of breast and other types of cancer. Experiment Overall Design: Female Sprague-Dawley rats, fed one of the three purified diets, were studied at postnatal day50. Total RNA( each RNA samples were extracted from #4 mammary gland from two animals under the same diet group) purified from non-tumor tissue within the proximal half of each colon, was used to prepare biotinylated probes, which were hybridized to Affymetrix RAE230 rat microarrays.