Increased expression of histone proteins during estrogen-mediated cell proliferation.

Background: There is concern about the potential risk posed by compounds with estrogen-like activity present in the environment. As previous studies have shown that combined exposure to such compounds results in dose additivity, it should be possible to assess estrogen exposure with suitable biomarkers of effect. Objectives: Our goal was to identify candidate protein biomarkers of effect for estrogenic compounds. Methods: In the search for biomarkers, we assessed the effect of several estrogenic compounds on the expression profile of proteins in breast-derived cell lines varying in their estrogen receptor (ER) phenotype using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. We identified responsive proteins, after separating them by SDS-polyacrylamide gel electrophoresis, and analyzing the trypsin-digested proteins by tandem mass spectrometry. Results: The estrogenic compounds 17β-estradiol, genistein, bisphenol A, and endosulfan produced similar protein profile changes in MCF-7 cells (phenotype: ERα⁺/ERß⁺), but had no effect on MDA-MB-231 (ERα^-/ ERß⁺), MCF-10F (ERα^-/ ERß⁺), or MCF-10A (ERα^-/ ERß^-) cells. The most responsive proteins in MCF-7 cells were identified as histones H2A, H2B, H3, and H4. Histone levels were not increased in cell lines that showed no proliferative response to estrogens despite their rapid intrinsic growth rate in culture. Conclusion: Our results indicate that ER-mediated cell proliferation results in up-regulation of core histone proteins.