TWIST Represses Estrogen Receptor-alpha Expression by Recruiting the NuRD Protein Complex in Breast Cancer Cells

Loss of estrogen receptor a (ER alpha) expression and gain of TWIST (TWIST1) expression in breast tumors correlate with increased disease recurrence and metastasis and poor disease- free survival. However, the molecular and functional regulatory relationship between TWIST and ER alpha are unclear. In this study, we found TWIST was associated with a chromatin region in intron 7 of the human ESR1 gene coding for ER alpha. This association of TWIST efficiently recruited the nucleosome remodeling and deacetylase (NuRD) repressor complex to this region, which subsequently decreased histone H3K9 acetylation, increased histone H3K9 methylation and repressed ESR1 expression in breast cancer cells. In agreement with these molecular events, TWIST expression was inversely correlated with ER alpha expression in both breast cancer cell lines and human breast ductal carcinomas. Forced expression of TWIST in TWIST-negative and ER alpha-positive breast cancer cells such as T47D and MCF-7 cells reduced ER alpha expression, while knockdown of TWIST in TWIST-positive and ER alpha-negative breast cancer cells such as MDA-MB-435 and 4T1 cells increased ER alpha expression. Furthermore, inhibition of histone deacetylase (HDAC) activity including the one in NuRD complex significantly increased ER. expression in MDA-MB-435 and 4T1 cells. HDAC inhibition together with TWIST knockdown did not further increase ER alpha expression in 4T1 and MDA-MB-435 cells. These results demonstrate that TWIST/NuRD represses ER alpha expression in breast cancer cells. Therefore, TWIST may serve as a potential molecular target for converting ER alpha-negative breast cancers to ER alpha-positive breast cancers, allowing these cancers to restore their sensitivity to endocrine therapy with selective ER alpha antagonists such as tamoxifen and raloxifene.