Updated publication reference for PubMed record(s): 26153859. Immuno-precipitation followed by MS was performed using the RIME protocol in this study. Estrogen Receptor (ER) and Progestorone Receptor (PR) were targetted using antibodies. The experiments were performed in a quantitative manner using SILAC labelling. Cells grown in complete serum (estrogenic) conditions were compared against an cells in similar complete media, however supplemented with Progesterone (PG) or R5020 for 4 hours. Experiments were performed in MCF7 and T47D cell lines