The pure estrogen receptor antagonist ICI 182,780 promotes a novel interaction of estrogen receptor-alpha with the 3',5'-cyclic adenosine monophosphate response element-binding protein-binding protein/p300 coactivators

HNRNPA2B1 regulates tamoxifen- and fulvestrant-sensitivity and hallmarks of endocrine resistance in breast cancer cells

Despite new combination therapies improving survival of breast cancer patients with estrogen receptor α (ER+) tumors, the molecular mechanisms for endocrine-resistant disease remain unresolved. Previously we demonstrated that expression of the RNA binding protein and N6-methyladenosine (m6A) reader HNRNPA2B1 (A2B1) is higher in LCC9 and LY2 tamoxifen (TAM)-resistant ERα breast cancer cells relative to parental TAM-sensitive MCF-7 cells. Here we report that A2B1 protein expression is higher in breast tumors than paired normal breast tissue. Modest stable overexpression of A2B1 in MCF-7 cells (MCF-7-A2B1 cells) resulted in TAM- and fulvestrant- resistance whereas knockdown of A2B1 in LCC9 and LY2 cells restored TAM and fulvestrant, endocrine-sensitivity. MCF-7-A2B1 cells gained hallmarks of TAM-resistant metastatic behavior: increased migration and invasion, clonogenicity, and soft agar colony size, which were attenuated by A2B1 knockdown in MCF-7-A2B1 and the TAM-resistant LCC9 and LY2 cells. MCF-7-A2B1, LCC9, and LY2 cells have a higher proportion of CD44+/CD24-/low cancer stem cells (CSC) compared to MCF-7 cells. MCF-7-A2B1 cells have increased ERα and reduced miR-222-3p that targets ERα. Like LCC9 cells, MCF-7-A2B1 have activated AKT and MAPK that depend on A2B1 expression and are growth inhibited by inhibitors of these pathways. These data support that targeting A2B1 could provide a complimentary therapeutic approach to reduce acquired endocrine resistance.

Bazedoxifene Ameliorates Homocysteine-Induced Apoptosis via NADPH Oxidase-Interleukin 1β and 6 Pathway in Osteocyte-like Cells

Homocysteine (Hcy) increases oxidation and inflammation; however, the mechanism of Hcy-induced bone fragility remains unclear. Because selective estrogen modulators (SERMs) have an anti-oxidative effect, SERMs may rescue the Hcy-induced bone fragility. We aimed to examine whether oxidative stress and pro-inflammatory cytokines such as interleukin (IL)-1β and IL-6 are involved in the Hcy-induced apoptosis of osteocytes and whether bazedoxifene (BZA) inhibits the detrimental effects of Hcy. We used mouse osteocyte-like cell lines MLO-Y4-A2 and Ocy454. Apoptosis was examined by DNA fragmentation ELISA and TUNEL staining, and gene expression was evaluated by real-time PCR. Hcy 5 mM significantly increased expressions of NADPH oxidase (Nox)1, Nox2, IL-1β, and IL-6 as well as apoptosis in MLO-Y4-A2 cells. Nox inhibitors, diphenyleneiodonium chloride and apocynin, significantly suppressed Hcy-induced IL-1β and IL-6 expressions. In contrast, an IL-1β receptor antagonist and an IL-6 receptor monoclonal antibody had no effects on Hcy-induced Nox1 and Nox2 expressions, but significantly rescued Hcy-induced apoptosis. BZA (1 nM-1 μM) and 17β estradiol 100 nM significantly rescued Hcy-induced apoptosis, while an estrogen receptor blocker ICI 182,780 reversed the effects of BZA and 17β estradiol. BZA also rescued Hcy-induced apoptosis of Ocy454 cell, and ICI canceled the effect of BZD. Moreover, BZA significantly ameliorated Hcy-induced expressions of Nox1, Nox2, IL-1β, and IL-6, and ICI canceled the effects of BZA on their expressions. Hcy increases apoptosis through stimulating Nox 1 and Nox 2-IL-1β and IL-6 expressions in osteocyte-like cells. BZA inhibits the detrimental effects of Hcy on osteocytes via estrogen receptor.

Tumor-Associated Macrophages Induce Endocrine Therapy Resistance in ER+ Breast Cancer Cells

Antiestrogenic adjuvant treatments are first-line therapies in patients with breast cancer positive for estrogen receptor (ER+). Improvement of their treatment strategies is needed because most patients eventually acquire endocrine resistance and many others are initially refractory to anti-estrogen treatments. The tumor microenvironment plays essential roles in cancer development and progress; however, the molecular mechanisms underlying such effects remain poorly understood. Breast cancer cell lines co-cultured with TNF-α-conditioned macrophages were used as pro-inflammatory tumor microenvironment models. Proliferation, migration, and colony formation assays were performed to evaluate tamoxifen and ICI 182,780 resistance and confirmed in a mouse-xenograft model. Molecular mechanisms were investigated using cytokine antibody arrays, WB, ELISA, ChIP, siRNA, and qPCR-assays. In our simulated pro-inflammatory tumor microenvironment, tumor-associated macrophages promoted proliferation, migration, invasiveness, and breast tumor growth of ER+ cells, rendering these estrogen-dependent breast cancer cells resistant to estrogen withdrawal and tamoxifen or ICI 182,780 treatment. Crosstalk between breast cancer cells and conditioned macrophages induced sustained release of pro-inflammatory cytokines from both cell types, activation of NF-κB/STAT3/ERK in the cancer cells and hyperphosphorylation of ERα, which resulted constitutively active. Our simulated tumor microenvironment strongly altered endocrine and inflammatory signaling pathways in breast cancer cells, leading to endocrine resistance in these cells.

17β-Estradiol and ICI182,780 Differentially Regulate STAT5 Isoforms in Female Mammary Epithelium, With Distinct Outcomes

Prolactin (PRL) and estrogen cooperate in lobuloalveolar development of the mammary gland and jointly regulate gene expression in breast cancer cells in vitro. Canonical PRL signaling activates STAT5A/B, homologous proteins that have different target genes and functions. Although STAT5A/B are important for physiological mammary function and tumor pathophysiology, little is known about regulation of their expression, particularly of STAT5B, and the consequences for hormone action. In this study, we examined the effect of two estrogenic ligands, 17β-estradiol (E2) and the clinical antiestrogen, ICI182,780 (ICI, fulvestrant) on expression of STAT5 isoforms and resulting crosstalk with PRL in normal and tumor murine mammary epithelial cell lines. In all cell lines, E2 and ICI significantly increased protein and corresponding nascent and mature transcripts for STAT5A and STAT5B, respectively. Transcriptional regulation of STAT5A and STAT5B by E2 and ICI, respectively, is associated with recruitment of estrogen receptor alpha and increased H3K27Ac at a common intronic enhancer 10 kb downstream of the Stat5a transcription start site. Further, E2 and ICI induced different transcripts associated with differentiation and tumor behavior. In tumor cells, E2 also significantly increased proliferation, invasion, and stem cell-like activity, whereas ICI had no effect. To evaluate the role of STAT5B in these responses, we reduced STAT5B expression using short hairpin (sh) RNA. shSTAT5B blocked ICI-induced transcripts associated with metastasis and the epithelial mesenchymal transition in both cell types. shSTAT5B also blocked E2-induced invasion of tumor epithelium without altering E2-induced transcripts. Together, these studies indicate that STAT5B mediates a subset of protumorigenic responses to both E2 and ICI, underscoring the need to understand regulation of its expression and suggesting exploration as a possible therapeutic target in breast cancer.

Fenofibrate induced PPAR alpha expression was attenuated by oestrogen receptor alpha overexpression in Hep3B cells

The physiological regulation of Oestrogen receptor α (ERα) and peroxisome proliferator-activated receptor alpha (PPARα) in Hepatocellular carcinoma (HCC) remains unknown. The present study we first treat the cells with fenofibrate and further investigated the possible mechanisms of 17β-estradiol (E₂ ) and/or ERα on regulating PPARα expression. We also found higher PPARα expression in the tumor area than adjacent areas and subsequently compared PPARα expression in four different hepatic cancer cell lines. Hep3B cells were found to express more PPARα than the other cell lines. Using the PPARα agonist fenofibrate, we found that fenofibrate increased Hep3B cell proliferation efficiency by increasing cell cycle proteins, such as cyclin D1 and PCNA, and inhibiting p27 and caspase 3 expressions. Next, we performed transient transfections and immuno-precipitation studies using the pTRE2/ERα plasmid to evaluate the interaction between ERα and PPARα. ERα interacted directly with PPARα and negatively regulated its function. Moreover, in Tet-on ERα over-expressed Hep3B cells, E₂ treatment inhibited PPARα, its downstream gene acyl-CoA oxidase (ACO), cyclin D1 and PCNA expression and further increased p27 and caspase 3 expressions. However, over-expressed ERα plus 17-β-estradiol (10^-8 M) reversed the fenofibrate effect and induced apoptosis, which was blocked in ICI/melatonin/fenofibrate-treated cells. This study illustrates that PPARα expression and function were negatively regulated by ERα expression in Hep3B cells.

The estrogen receptor alpha nuclear localization sequence is critical for fulvestrant-induced degradation of the receptor

Fulvestrant, a selective estrogen receptor down-regulator (SERD) is a pure competitive antagonist of estrogen receptor alpha (ERα). Fulvestrant binds ERα and reduces the receptor's half-life by increasing protein turnover, however, its mechanism of action is not fully understood. In this study, we show that removal of the ERα nuclear localization sequence (ERΔNLS) resulted in a predominantly cytoplasmic ERα that was degraded in response to 17-β-estradiol (E2) but was resistant to degradation by fulvestrant. ERΔNLS bound the ligands and exhibited receptor interaction similar to ERα, indicating that the lack of degradation was not due to disruption of these processes. Forcing ERΔNLS into the nucleus with a heterologous SV40-NLS did not restore degradation, suggesting that the NLS domain itself, and not merely receptor localization, is critical for fulvestrant-induced ERα degradation. Indeed, cloning of the endogenous ERα NLS onto the N-terminus of ERΔNLS significantly restored both its nuclear localization and turnover in response to fulvestrant. Moreover, mutation of the sumoylation targets K266 and K268 within the NLS impaired fulvestrant-induced ERα degradation. In conclusion, our study provides evidence for the unique role of the ERα NLS in fulvestrant-induced degradation of the receptor.

Synthesis of novel estrogen receptor antagonists using metal-catalyzed coupling reactions and characterization of their biological activity

Estrogen receptor (ER) antagonists are valuable in the treatment of ER-positive human breast cancer. In this study, we designed and synthesized nine new derivatives of 17β-estradiol (E2) with a bulky side chain attached to its C-7α position, and determined their ER antagonistic activity using in vitro bioassays. Four of the derivatives showed a strong inhibition of ERα transactivation activity in a luciferase reporter assay and blocked ERα interactions with coactivators. Similarly, these derivatives also strongly inhibited the growth of the ERα-positive human breast cancer cells. Computational docking analysis was conducted to model the interaction of these antagonists with the human ERα and showed that they could tightly bind to the ERα in a manner similar to that of ICI-182,780, a pure ER antagonist. These results provide an example that attachment of a bulky side chain to the C-7α position of E2 can produce ER antagonists with ER affinity comparable to that of ICI-182,780.

The terminal substituents of 7α, 6-hexanyl derivatives of estradiol determine their selective estrogen receptor modulator versus agonist activities

Pure antiestrogens were clinically developed as alternative therapies for estrogen receptor (ER) positive breast cancers. Unlike the selective estrogen receptor modulators (SERMs), these antiestrogens are devoid of tissue-specific ER agonist activity. Many of these compounds are steroidal in nature, containing an estradiol (E2) structural core with long alkyl side chains at the C-7α position. Two novel 7α-substituted E2 derivatives were evaluated that retain high binding affinity for ER. Compared to known pure antiestrogens, these compounds, referred to as compound 13 (C13) and C14, contain shorter 7α alkyl side chains and differ only in their terminal substituent: a hydroxyl moiety versus a benzyloxy group, respectively. Herein we assessed the effects of these compounds on ER transcriptional activity and report that despite their similar overall structure, C13 and C14 produce distinct cell type-specific responses. Of note, C13 functions as a mixed agonist/antagonist in Hela cells, inducing only weak ER transcriptional activity while preventing coactivator recruitment and stabilizing ER expression. However, this compound effectively stimulates ER activity in MCF-7 cells, does not increase ER levels and promotes cell proliferation on par with E2. Conversely, C14 stimulates transcriptional activity in both cell types and enhances ER-coactivator interactions. The activities of both compounds were inhibited by the pure antiestrogen ICI 182,780. Taken together, these results reveal that C13 is a SERM while C14 is an ER agonist, and indicate that the terminal modification of the C-7α hexanyl side chain of these estradiol derivatives is an important determinant of the biocharacter of these ER ligands.

Estrogen and TCDD influence RLN2 gene activity in estrogen receptor-positive human breast cancer cells

Expression of relaxin is increased in human breast cancer, and relaxin was shown to increase in vitro invasiveness through increased production and secretion of matrix metalloproteinases in human breast cancer cells. The role of estrogen in the promotion of breast cancer is well-known. The environmental toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a known carcinogen but has been shown to have antiestrogenic effects in human breast cancer cells. In this study, we have employed real-time PCR and chromatin immunoprecipitation (ChIP) assays to investigate the influence of estrogen and TCDD on relaxin-1 (RLN1) and relaxin-2 (RLN2) gene expression in MCF-7 and T47D human breast cancer cells. Estrogen increased RLN2 transcripts in T47D and MCF-7 cells after just 4 h of exposure, whereas TCDD did not. RLN1 transcripts were only induced after 24 h of estrogen exposure. TCDD did have antiestrogenic activity and reduced the estrogen-mediated increase in RLN2 and RLN1 mRNA. The estrogen-mediated increase in RLN2 mRNA levels was not caused by changes in the mRNA stability. ChIP analysis revealed binding of estrogen receptor-alpha (ERalpha) to promoter sequences of the RLN2 gene. Thus, we provide evidence that RLN2 gene activity is directly regulated by activated ERalpha in human breast cancer cells and we show that activation of the arylhydrocarbon receptor by TCDD inhibits this regulation by estrogen.

Estradiol downregulation of the tumor suppressor gene BTG2 requires estrogen receptor-alpha and the REA corepressor

B-cell Translocation Gene 2 (BTG2/TIS21/PC3) is an anti-proliferative tumor suppressor gene whose expression is significantly reduced in breast carcinomas, and in MCF-7 and T-47D breast cancer cell lines treated with estradiol (E2). In this study the mechanisms involved in E2 down regulation of BTG2 gene expression were examined. Depletion of ERalpha by siRNA indicated that the receptor is required for E2 down regulation of BTG2 mRNA levels, and cycloheximide experiments indicated that the effect of E2 on BTG2 expression was independent of intermediary protein synthesis. Chromatin immunoprecipitation analyses revealed that ERalpha interacts with the BTG2 promoter in a ligand-independent fashion whereas transfection experiments indicated that ERalpha's DNA and ligand binding domains are required for E2 repression of BTG promoter activity. Surprisingly, histone deacetylase (HDACs) activity is essential for basal expression as evidenced by trichostatin A inhibition of BTG2 mRNA levels. Estradiol treatment did not alter histone H3 acetylation although it did induce displacement of RNA polymerase II from the BTG2 gene. Depletion of the ER specific corepressor REA (Repressor of Estrogen Receptor Activity) significantly abrogated E2-mediated BTG2 repression. Taken together, our results reveal a requirement of HDAC activity for basal BTG2 expression and the ERalpha-REA interaction for estrogen repression of the BTG2 gene. The ability of E2-bound ERalpha and REA to suppress BTG2 expression indicates a positive role for this corepressor in regulation of breast cancer cell proliferation.

Ligand-selective transactivation and transrepression via the glucocorticoid receptor: role of cofactor interaction

The mechanisms that determine ligand-selective transcriptional responses by the glucocorticoid receptor (GR) are not fully understood. Using a wide panel of GR ligands, we investigated the relationships between the potency and maximal response for transactivation via a glucocorticoid response element (GRE) and transrepression via both nuclear factor small ka, CyrillicB (NFsmall ka, CyrillicB) and activator protein-1 (AP-1) sites, relative binding affinity for the GR, as well as interaction with both coactivators and corepressors. The results showed ligand-selective differences in potency and efficacy for each promoter, as well as for a particular ligand between the three promoters. Ligand potency correlated with relative affinity for the GR for agonists and partial agonists in transactivation but not for transrepression. Maximal response was unrelated to relative affinity of ligand for GR for both transactivation and transrepression. A good and significant correlation between full length coactivator binding in two-hybrid assays and efficacy as well as potency of different receptor-steroid complexes for both transactivation and transrepression supports a major role for coactivator recruitment in determination of ligand-selective transcriptional activity. Furthermore, ligand-selective GR binding to GRIP-1, as determined by both two-hybrid and DNA pull down assays, correlated positively with ligand-selective efficacy for transactivation of both a synthetic GRE reporter with expressed GR as well as of an endogenous gene via endogenous GR. The receptor interacting domain of the corepressor SMRT exhibited strong interaction with both agonists and partial agonists, similar to the results for coactivators, suggesting a possible role for SMRT in activation of transcription. However, there was no correlation between ligand affinity for the GR and cofactor interaction. These results provide strong quantitative biochemical support for a model in which GR-mediated ligand-selective differential interaction with GRIP-1, SRC-1A, NCoR and SMRT is a major determinant of ligand-selective and promoter-specific differences in potency and efficacy, for both transactivation and transrepression.

Topical fulvestrant solution has no effect on male and postmenopausal female androgenetic alopecia: results from two randomized, proof-of-concept studies

BACKGROUND

Androgenetic alopecia (pattern baldness) affects approximately half of all white-skinned men and women over the age of 40 years. Based on preclinical studies in mice in which topical fulvestrant (ICI182,780, an anti-oestrogen) caused telogen hair follicles to enter anagen, thereby causing hair growth, a topical formulation of fulvestrant was developed for the potential treatment of androgenetic alopecia.

OBJECTIVES

To evaluate the efficacy of fulvestrant solution in stimulating hair growth in men and postmenopausal women with androgenetic alopecia in two randomized, phase II, minoxidil- and/or vehicle-controlled studies.

METHODS

One hundred and two white-skinned men aged 18-50 years with Norwood/Hamilton grades III, IIIv, IV, V or Va androgenetic alopecia received topical fulvestrant 70 mg mL(-1) solution, vehicle or minoxidil 2% solution twice daily for 16 weeks. Seventy postmenopausal women with Ludwig grade 1 or 2 androgenetic alopecia received topical fulvestrant 70 mg mL(-1) solution or vehicle twice daily for 16 weeks. The endpoints in both studies were hair density, cumulative hair thickness and hair growth rate, measured by TrichoScan analysis of digital images.

RESULTS

There were no statistically significant differences favouring fulvestrant over vehicle at study end (day 113) for any of the efficacy parameters in men or women. Statistically significant differences in favour of minoxidil over fulvestrant were seen from day 57 onwards for hair density, cumulative hair thickness and hair growth rate in men.

CONCLUSIONS

These results indicate a lack of effect of topical fulvestrant in the treatment of subjects with androgenetic alopecia. The reasons for this lack of effect remain unclear.

The silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor is required for full estrogen receptor alpha transcriptional activity

Multiple factors influence estrogen receptor alpha (ERalpha) transcriptional activity. Current models suggest that the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor functions within a histone deactylase-containing protein complex that binds to antiestrogen-bound ERalpha and contributes to negative regulation of gene expression. In this report, we demonstrate that SMRT is required for full agonist-dependent ERalpha activation. Chromatin immunoprecipitation assays demonstrate that SMRT, like ERalpha and the SRC-3 coactivator, is recruited to an estrogen-responsive promoter in estrogen-treated MCF-7 cells. Depletion of SMRT, but not histone deacetylases 1 or 3, negatively impacts estradiol-stimulated ERalpha transcriptional activity, while exogenous expression of SMRT's receptor interaction domains blocks ERalpha activity, indicating a functional interaction between this corepressor and agonist-bound ERalpha. Stimulation of estradiol-induced ERalpha activity by SMRT overexpression occurred in HeLa and MCF-7 cells, but not HepG2 cells, indicating that these positive effects are cell type specific. Similarly, the ability of SMRT depletion to promote the agonist activity of tamoxifen was observed for HeLa but not MCF-7 cells. Furthermore, impairment of agonist-stimulated activity by SMRT depletion is specific to ERalpha and not observed for receptors for vitamin D, androgen, or thyroid hormone. Nuclear receptor corepressor (N-CoR) depletion increased the transcriptional activity of all four tested receptors. SMRT is required for full expression of the ERalpha target genes cyclin D1, BCL-2, and progesterone receptor but not pS2, and its depletion significantly attenuated estrogen-dependent proliferation of MCF-7 cells. Taken together, these data indicate that SMRT, in conjunction with gene-specific and cell-dependent factors, is required for positively regulating agonist-dependent ERalpha transcriptional activity.

The Hormonal Response of Estrogen Receptor β Is Decreased by the Phosphatidylinositol 3-Kinase/Akt Pathway via a Phosphorylation-dependent Release of CREB-binding Protein

The hormonal response of estrogen receptors (ER) alpha and ERbeta is controlled by a number of cofactors, including the general transcriptional coactivator CREB-binding protein (CBP). Growing evidence suggests that specific kinase signaling events also modulate the formation and activity of the ER coactivation complex. Here we show that ERbeta activity and target gene expression are decreased upon activation of ErbB2/ErbB3 receptors despite the presence of CBP. This inhibition of ERbeta involved activation of the phosphatidylinositol 3-kinase/Akt pathway, abrogating the potential of CBP to facilitate ERbeta response to estrogen. Such reduced activity was associated with an impaired ability of ERbeta to recruit CBP upon activation of Akt. Mutation of serine 255, an Akt consensus site contained in the hinge region of ERbeta, prevented the release of CBP and rendered ERbeta transcriptionally more responsive to CBP coactivation, suggesting that Ser-255 may serve as a regulatory site to restrain ERbeta activity in Akt-activated cells. In contrast, we found that CBP intrinsic activity was increased by Akt through threonine 1872, a consensus site for Akt in the cysteine- and histidine-rich 3 domain of CBP, indicating that such enhanced transcriptional potential of CBP did not serve to activate ERbeta. Interestingly, nuclear receptors sharing a conserved Akt consensus site with ERbeta also exhibit a reduced ability to be coactivated by CBP, whereas others missing that site were able to benefit from the activation of CBP by Akt. These results therefore outline a regulatory mechanism by which the phosphatidylinositol 3-kinase/Akt pathway may discriminate nuclear receptor response through coactivator transcriptional competence.

ICI 182,780 has agonistic effects and synergizes with estradiol-17 beta in fish liver, but not in testis

BACKGROUND

ICI 182,780 (ICI) belongs to a new class of antiestrogens developed to be pure estrogen antagonists and, in addition to its therapeutic use, it has been used to knock-out estrogen and estrogen receptor (ER) actions in several mammalian species. In the present study, the effects and mechanism of action of ICI were investigated in the teleost fish, sea bream (Sparus auratus).

METHODS

Three independent in vivo experiments were performed in which mature male tilapia (Oreochromis mossambicus) or sea bream received intra-peritoneal implants containing estradiol-17 beta (E2), ICI or a combination of both compounds. The effects of E2 and ICI on plasma calcium levels were measured and hepatic and testicular gene expression of the three ER subtypes, ER alpha, ER beta a and ER beta b, and the estrogen-responsive genes, vitellogenin II and choriogenin L, were analyzed by semi-quantitative RT-PCR in sea bream.

RESULTS

E2 treatment caused an increase in calcium levels in tilapia, while ICI alone had no noticeable effect, as expected. However, pretreatment with ICI synergistically potentiated the effect of E2 on plasma calcium in both species. ICI mimicked some E2 actions in gene expression in sea bream liver upregulating ER alpha, vitellogenin II and choriogenin L, although, unlike E2, it did not downregulate ER beta a and ER beta b. In contrast, no effects of E2 or ICI alone were detected in the expression of ERs in testis, while vitellogenin II and choriogenin L were upregulated by E2 but not ICI. Finally, pretreatment with ICI had a synergistic effect on the hepatic E2 down-regulation of ER beta b, but apparently blocked the ER alpha up-regulation by E2.

CONCLUSION

These results demonstrate that ICI has agonistic effects on several typical estrogenic responses in fish, but its actions are tissue-specific. The mechanisms for the ICI agonistic activity are still unknown; although the ICI induced up-regulation of ER alpha mRNA could be one of the factors contributing to the cellular response.