Preferential Estrogen Receptor β Ligands Reduce Bcl-2 Expression in Hormone-Resistant Breast Cancer Cells to Increase Autophagy

Abstract

Acquired resistance to selective estrogen receptor (ER) modulators (SERM) and downregulators (SERD) is a significant clinical problem in the treatment of estrogen (E2) receptor-positive (ER þ ) breast cancers. There are two ER subtypes, ERa and ERb, which promote and inhibit breast cancer cell proliferation, respectively. Although ER þ breast cancers typically express a high ratio of ERa to ERb, the acquisition of SERM resistance in vitro and in vivo is associated with increased relative expression of the ERb. On some gene enhancers, ERb has been shown to function in opposition to the ERa in the presence of E2. Here, we demonstrate that two different ERb agonists, WAY-20070 and a novel "A-CD" estrogen called L17, produce a marked reduction in G 2 -M phase correlated with effects on cyclin D1 and cyclin E expression in a SERM/SERD-resistant breast cancer cell line. ERb agonists recruited both the ERa and ERb to the Bcl-2 E2-response element strongly reducing Bcl-2 mRNA and protein in an ERb-dependent manner. L17 recruited RIP140 to the Bcl-2 promoter in cells overexpressing ERb. Exposure to the ERb ligands also resulted in increased processing of LC3-I to LC3-II, indicative of enhanced autophagic flux. The coaddition of ERb agonist and the autophagy inhibitor chloroquine resulted in a significant accumulation of sub-G 1 DNA which was completely prevented by the addition of the caspase inhibitor Z-VAD-FMK. We propose that combined therapies with an ERb agonist and an inhibitor of autophagy may provide the basis for a novel approach to the treatment of SERM/SERD-resistant breast cancers. Mol Cancer Ther; 13(7); 1882-93. Ó2014 AACR.

Novel Ligands Balance Estrogen Receptor β and α Agonism for Safe and Effective Suppression of the Vasomotor Response in the Ovariectomized Female Rat Model of Menopause

“…These results contrast with those obtained after E2 treatment, which resulted in a profound and significant increase in proliferation involving more than 50% of cells within the mammary ducts ( Figure 3D). Consistent with these results, in other work, we have shown that L17 reduces the expression of E2-responsive genes involved in proliferation (cyclin D1) and antiapoptosis (Bcl-2) in breast cancer cells expressing a reduced level of ER␣ relative to ER␤ (36).…”

Comprehensive assessment of estrogen receptor beta antibodies in cancer cell line models and tissue reveals critical limitations in reagent specificity

“…Despite a large body of literature, the function of ERβ in these two cancers remains unclear (Haldosen et al., 2014, Nelson et al., 2014). Most authors agree that ERβ has a predominantly antiproliferative, pro-apoptotic and tumor-suppressive role (Attia and Ederveen, 2012, Bottner et al., 2014, Chang and Prins, 1999, Ellem and Risbridger, 2007, Horvath et al., 2001, Madak-Erdogan et al., 2013, McPherson et al., 2010, Muthusamy et al., 2011, Nakajima et al., 2011, Rizza et al., 2014, Ruddy et al., 2014, Zhu et al., 2004), however ERβ has also been implicated as an oncogene. This is particularly in the context of Castrate Resistant Prostate Cancer (CRPC) where it has been proposed as a driver of androgen receptor (AR)-dependent gene transcription (Yang et al., 2012, Yang et al., 2015), along with a potential role in mediating the transition from hormone-sensitive to CRPC (Zellweger et al., 2013).…”

Estrogen receptor β ligation inhibits Hodgkin lymphoma growth by inducing autophagy

“…Because ERβ ligation was reported to induce autophagy in different transformed human cells [13, 14], we evaluated whether DPN could modulate autophagy in HL cells. To this aim, we analyzed the expression level of the autophagic markers microtubule-associated protein 1 light chain 3 (LC3)-II and (sequestosome 1) SQSTM1 by western blot.…”

“…A key role for ERβ in the inhibition of tumor growth in different forms of cancers has been hypothesized [10, 12, 25, 26]. In particular, a recent study carried out in breast cancer suggested that ERβ activation could inhibit cancer cell proliferation through a mechanism that bring into play a marked reduction of G2/M phase as well as triggering autophagy [14]. Interestingly, also in a male tumor such as seminoma, a testicular germ cell tumor, ERβ ligation was capable of impairing tumor growth enhancing the expression of autophagy-related markers [13].…”

“…However, the precise molecular mechanisms of ERβ-activated pathways underlying these effects still remain unidentified. Interestingly, recent studies suggest that ERβ ligation could also trigger the lysosome-mediated pathway named autophagy [13, 14]. This is a selective catabolic process involved both in basal turnover of altered cellular components and in counteracting stressful dysmetabolic conditions.…”