Tristetraprolin Represses Estrogen Receptor α Transactivation in Breast Cancer Cells

Estrogen receptor (ER) mediates the effects of 17-estradiol (E2) in normal mammary gland, and it is a key participant in breast cancer tumor development. ER transactivation activity is mediated by the synergistic interaction of two domains designated AF1 and AF2. The function of AF2 is to recruit coactivator and corepressor proteins that allow ER to oscillate between the roles of transcriptional activator and repressor. In contrast, the mechanism responsible for AF-1 transcriptional activity is not completely understood. In this study, we identified tristetraproline (TTP) as a novel ER-associated protein. TTP expression in MCF7 cells repressed ER transactivation and reduced MCF7 cell proliferation and the ability of the cells to form tumors in a mouse model. We show that TTP transcriptional activity is mediated through its recruitment to the promoter region of ER target genes and its interaction with histone deacetylases, in particular with HDAC1. TTP expression attenuates the coactivating activity of SRC-1, suggesting that exchange between TTP and other coactivators may play an important role in fine-tuning ER transactivation. These results indicate that TTP acts as a bona fide ER corepressor and suggest that this protein may be a contributing factor in the development of E2-dependent tumors in breast cancer.