The Tamoxifen-responsive Estrogen Receptor α Mutant D351Y Shows Reduced Tamoxifen-dependent Interaction with Corepressor Complexes

Abstract

The effects of estrogen and anti-estrogen are mediated through the estrogen receptors ERα and β, which function as ligand-induced transcriptional factors. The non-steroidal anti-estrogen tamoxifen is the most commonly used endocrine in the treatment of all stages of breast cancer in both pre- and postmenopausal women. Several lines of evidence have indicated that tamoxifen promotes association between ERα and corepressors N-CoR or silencing mediator for retinoid and thyroid hormone receptor (SMRT). Our results indicate that N-CoR/SMRT recognize and interact with helices H3 and H5 of the ERα ligand-binding domain in a 4-hydroxy tamoxifen-dependent manner. The mutant ERα(D351Y), derived from a tamoxifen-stimulated tumor and containing an amino acid substitution at position 351 within H3, showed reduced interaction with N-CoR/SMRT and high tamoxifen-induced activation function-1 (AF-1) activity. While the estradiol-dependent transcriptional activity of ERα(D351Y) was almost equal to that of wild-type ERα, the mutant exhibited higher levels of transcriptional activity in the presence of both E2 and 4-hydroxy tamoxifen compared with wild-type ERα. These results may explain the observation that the growth of tumor cells expressing ERα(D351Y) can be stimulated by tamoxifen, E2, or both.