ERβ1 Sensitizes and ERβ2 Desensitizes ERα-Positive Breast Cancer Cells to the Inhibitory Effects of Tamoxifen, Fulvestrant and Their Combination with All-Trans Retinoic Acid

Abstract

Adjuvant endocrine therapy (AET) is the treatment of choice for early-stage estrogen receptor alpha (ERα)-positive breast cancer (BC). However, almost 40% of tamoxifen-treated cases display no response or a partial response to AET, thus increasing the need for new treatment options and strong predictors of the therapeutic response of patients at high risk of relapse. In addition to ERα, BC research has focused on ERβ1 and ERβ2 (isoforms of ERβ), the second ER isotype. At present, the impact of ERβ isoforms on ERα-positive BC prognosis and treatment remains elusive. In the present study, we established clones of MCF7 cells constitutively expressing human ERβ1 or ERβ2 and investigated their role in the response of MCF7 cells to antiestrogens [4-hydroxytamoxifen (ΟΗΤ) and fulvestrant (ICI182,780)] and retinoids [all-trans retinoic acid (ATRA)]. We show that, compared to MCF7 cells, MCF7-ERβ1 and MCF7-ERβ2 cells were sensitized and desensitized, respectively, to the antiproliferative effect of the antiestrogens, ATRA and their combination and to the cytocidal effect of the combination of OHT and ATRA. Analysis of the global transcriptional changes upon OHT–ATRA combinatorial treatment revealed uniquely regulated genes associated with anticancer effects in MCF7-ERβ1 cells and cancer-promoting effects in MCF7-ERβ2 cells. Our data are favorable to ERβ1 being a marker of responsiveness and ERβ2 being a marker of resistance of MCF7 cells to antiestrogens alone and in combination with ATRA.

Recent Advances in Breast Cancer Research

“…Moreover, this SI covers several in vitro studies that investigated different human cell types [13][14][15][16][17][18][19]. Two such publications used data sourced from animal experiments [15,19].…”

“…Meligova et al [16] conducted a pharmacological study that investigated MCF-7 BC cells and their responses to antiestrogens and retinoids [16]. The authors showed that ERβ1 is a marker of responsiveness; in contrast, ERβ2 was shown to be an indicator of MCF7 cells' resistance to antiestrogens alone and in combination with all-trans retinoic acid (ATRA) [16].…”

“…Meligova et al [16] conducted a pharmacological study that investigated MCF-7 BC cells and their responses to antiestrogens and retinoids [16]. The authors showed that ERβ1 is a marker of responsiveness; in contrast, ERβ2 was shown to be an indicator of MCF7 cells' resistance to antiestrogens alone and in combination with all-trans retinoic acid (ATRA) [16]. The authors concluded that the five unique hub genes (PPARG, HIPK2, ZFP36L1, HMGB2, and ALDH1A3) create a gene expression signature that specified the therapeutic response of ERβ1-expressing and ERα-positive BC cells to 4-hydroxytamoxifen and ATRA therapy [16].…”