Prenylated chalcone xanthohumol associates with histones in breast cancer cells--a novel target identified by a monoclonal antibody.

The intracellular fate of xanthohumol (XN) from hops is an underexplored field in the research for the molecular mechanisms causing its wide range of effects in chemoprevention and gene expression involved in hepatic metabolism. We aimed to elucidate possible targets for binding of XN in a human mammary carcinoma cell line (MCF-7/6), using a mAB. We investigated the overall solubility and stability of XN in growth medium and the cellular uptake and distribution of XN in MCF-7/6 cells using an optimized immunocytochemistry technique. After incubation of MCF-7/6 cells, with 10 μM XN for 0.5 h up to 6 h, we observed primarily a granular nuclear staining, which intensified with increasing exposure times. Immunoprecipitation of cell lysates (treated with 10 μM XN for 2 h) revealed binding of XN to a fraction of proteins with a molecular weight below 20 kDa. Further analysis of the protein mixture via LC-MS/MS (Q-TOF) resulted in the identification of specific members of the histone family, i.e. histone H2A, H2B, and H4. The identity of histone H2A was confirmed using immunodetection with a specific anti-histone H2A antibody. In summary, we did successfully apply a mAB against XN in immunocytochemistry and precipitation with highly unexpected results.