The histone deacetylase inhibitor trichostatin A sensitizes estrogen receptor α-negative breast cancer cells to tamoxifen

Abstract

Many cases of breast cancer show loss of estrogen receptor (ER) expression, which leads to unresponsiveness to antihormonal treatment even though there is no loss of the structurally and biochemically similar ER . ER activity is positively and negatively regulated by transcriptional regulators such as histone deacetylase (HDAC), which is known to be a negative ER regulator. Here, we evaluated using ER as an alternative target for tamoxifen therapy by treating ER -negative, -positive breast cancer cells with the HDAC inhibitor trichostatin A (TSA), and testing whether tamoxifen responsiveness increased following upregulation of ER . TSA enhanced the overall ER transcriptional activity in these cells, as visualized by estrogen response element-regulated reporter and the expression of progesterone receptor, a known ER target, without ER restoration. Additionally, TSA induced the expression and nuclear translocation of ER but not , suggesting that these actions leading to increase of ER transcriptional activity are mediated through ER rather than . Furthermore, following treatment with TSA, the formerly unresponsive MDA-MB-231 and Hs578T breast cancer cells became responsive to tamoxifen. However, reduction of ER expression by short interfering RNA abrogated this TSA-induced sensitization effect in these cells. Together, these results show that the HDAC inhibitor TSA sensitized ER -negative, antihormone-unresponsive breast cancer cells to tamoxifen treatment possibly by upregulating ER activity.