A large set of estrogen receptor beta-interacting proteins identified by tandem affinity purification in hormone-responsive human breast cancer cells nuclei.

Estrogen receptors a (ER-a) and b (ER-b) play distinct biological roles in onset and progression of hormone-responsive breast cancer, with ER-b exerting a modulatory activity on ER-a-mediated estrogen signaling and stimulation of cell proliferation by mechanisms still not fully understood. We stably expressed human ER-b fused to a tandem affinity purification-tag in estrogen-responsive MCF-7 cells and applied tandem affinity purification and nanoLC-MS/MS to identify the ER-b interactome of this cell type. Functional annotation by bioinformatics analyses of the 303 proteins that co-purify with ER-b from nuclear extracts identify several new molecular partners of this receptor subtype that repre- sents nodal points of a large protein network controlling multiple processes and functions in breast cancer cells.