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Background: It is known that the biology and clinical features of breast cancers were very different according to hormone receptor expression. Recent gene expression profiling studies identified estrogen receptor (ER) expression as a fundamental classifier of breast cancers. Our purpose is to compare the proteomic profiles of hormone receptor positive vs. negative breast cancer cells and tissues, respectively.

Material and Methods: MCF-7 and MDA-MB-231 harvested with scrapper. After sonication and centrifuge, urea lysis buffer were used. Three pairs of ER+ and ER- snap frozen human breast cancer tissue samples were obtained during operation. ER+ and ER- patients were matched by age and tumor stage. Tissue samples were homogenized and sonicated and then membrane fraction was isolated from the supernatant. 2-D difference in gel electrophoresis (2-D DIGE) and tandem mass spectrometry were used to investigate differentially expressed proteins.

Results: A total of57 identified proteins showed significantly different level of expression between MCF-7 and MDA-MB-231 cells. In MDA-MB-231, 33 proteins such as, tropomyosin 4, Glyoxalase I, Brevin, Stratifin, and annexin A5, were increased and 24 proteins such as, Cytokeratin 8, 18, and 19, G6PD, and Peroxiredoxin 2 were decreased compared with MCF-7 more than two-fold. In tissues, a total of 12 significant proteins were identified. Among membrane fraction, 6 proteins showed increased and 6 proteins showed decreased expression in ER- cancers compared to ER+ cancers. In cytosol fraction, another 12 proteins different between ER- and + cancers were identified. A total of 55 proteins in whole proteome samples were identified to show significantly different level of expression between normal and cancer. 41 proteins, such as Alpha enolase, malate dehydrogenase, and heat shock 27 kDa protein, were increased, and 14 proteins, such as serotransferrin precursor, fatty acid-binding protein, and retinal dehydrogenase 1, were decreased in cancer samples compared to normal samples. In the analysis of fraction samples, 8 and 12 differentially expressed proteins were identified in membrane fraction and cytosolic fraction, respectively. A total of 55 proteins in whole proteome samples were identified to show significantly different level of expression between normal and cancer. In the analysis of fraction samples, 8 and 12 differentially expressed proteins were identified in membrane fraction and cytosolic fraction, respectively. Conclusion: We found several novel protein markers that can differentiate ER+ and ER- breast cancer cells and tissues. It could be due to the narrow pH range of our experiment and posttranscriptional change. The proteins are under validation with conventional methods.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA