Proteomic evaluation of mammary glands of rats prepubertally exposed to Bisphenol A

4463 Bisphenol A (BPA), is an industrial compound commonly used in the production of polycarbonate plastic, epoxy resins, and dental sealants. BPA has been shown to advance puberty and disrupt estrous cyclicity, identifying it as an endocrine disruptor. It has previously been reported that rats treated with BPA during the prepubertal period were susceptible to irregular estrous cycles demonstrating that endocrine disruption during this critical developmental period can result in permanent reproductive alterations. The goal of this research was to identify differentially expressed proteins in mammary glands of rats that were treated early in postnatal life with BPA. For this study, lactating dams were gavaged with 250 μg BPA/kg body weight or an equivalent volume of sesame oil on days 1–20 postpartum. On day 21, the female offspring were euthanized and the 4 th abdominal mammary glands were dissected and frozen in liquid nitrogen for later use. These mammary glands were homogenized and subjected to 2-D gel electrophoresis. The gels were analyzed using Progenesis Discovery . Protein spots that were common to all gels were statistically evaluated in order to identify significantly regulated spots. Using MALDI-TOF mass spectrometry, we have determined that crystallin β-B2 and heat shock 70kD protein 5 (GRP78) were down regulated and RAD51 homolog 2 was up-regulated in mammary glands of BPA rats compared to control rats. Immuno-blot analysis confirmed the differential regulation and identity of these proteins. Crystallin-β B2, a lens protein, is thought to directly interact with various components of programmed cell death machinery and has previously been found to be a marker of lymph node involvement in breast carcinoma. RAD51 homolog 2 functions in DNA maintenance, participating in a common DNA damage response pathway associated with double-strand break repair, and hence up regulated in cancerous tissue. GRP78, a chaperone protein involved in the folding and assembly of proteins, displays increased expression during times of glucose starvation. Our future interests in this study include measuring glucose concentrations in mammary tissue from the animals treated with BPA in order to establish a correlation between glucose levels and down regulation of GRP78. Furthermore, analysis of differentially regulated biomarkers from 50 day animals and comparison with the 21 day data can yield useful information on developmental changes and protein-protein interaction in detailed biochemical pathways related to BPA exposure. The application of proteomics to mammary carcinogenesis studies should aid in identifying key biomarkers that predetermine mammary cancer susceptibility. Specifically, we should be able to compare proteins that are differentially expressed during mammary gland differentiation (day 21) and at time of sexual maturity (day 50). Supported by NIH/NIEHS 1 U01 ES012771.