Altered target gene regulation controlled by estrogen receptor-alpha concentration

A review of prognostic and predictive biomarkers in breast cancer

Breast cancer (BC) is a common cancer all over the world that affects women. BC is one of the leading causes of cancer mortality in women, which today has decreased with the advancement of technology and new diagnostic and therapeutic methods. BCs are histologically divided into in situ and invasive carcinoma, and both of them can be divided into ductal and lobular. The main function after the diagnosis of invasive breast cancer is which patient should use chemotherapy, which patient should receive adjuvant therapy, and which should not. If the decision is for adjuvant therapy, the next challenge is to identify the most appropriate treatment or combination of treatments for a particular patient. Addressing the first challenge can be helped by prognostic biomarkers, while addressing the second challenge can be done by predictive biomarkers. Among the molecular markers related to BC, ER, PR, HER2, and the Mib1/Ki-67 proliferation index are the most significant ones and are tightly confirmed in the standard care of all primary, recurrent, and metastatic BC patients. CEA and CA-15-3 antigens are the most valuable markers of serum tumors in BC patients. Determining the series of these markers helps monitor response to the treatment and early detection of recurrence or metastasis. miRNAs have been demonstrated to be intricate in mammary gland growth, proliferation, and formation of BC known to be incriminated in BC biology. By combining established prognostic factors with valid prognostic/predicted biomarkers, we can start the journey to personalized treatment for every recently diagnosed BC patient.

Forskolin Stimulates Estrogen Receptor (ER) α Transcriptional Activity and Protects ER from Degradation by Distinct Mechanisms

Estradiol action is mediated by estrogen receptors (ERs), a and ß. Estradiol binding initiates ER-mediated transcription and ER degradation, the latter of which occurs via the ubiquitin-proteasome pathway. Inhibition of proteasome activity prevents estradiol-induced ERα degradation and transactivation. In ER-positive GH3 cells (a rat pituitary prolactinoma cell line), forskolin, acting via protein kinase A (PKA), stimulates ERα transcriptional activity without causing degradation, and proteasome inhibition does not block forskolin-stimulated transcription. Forskolin also protects liganded ERα from degradation. In the current study, we first examined ERα and ERβ transcriptional activity in ER-negative HT22 cells and found that forskolin stimulated ERα-, but not ERβ-dependent transcription, through the ligand-binding domain (LBD). We also identified four mutations (L396R, D431Y, Y542F, and K534E/M548V) on the ERα LBD that selectively obliterated the response to forskolin. In GH3 cells, transfected ERα mutants and ERβ were protected from degradation by forskolin. Ubiquitination of ERα and ERβ was increased by forskolin or estradiol. ERα ubiquitination was diminished by a mutated ubiquitin (K48R) that prevents elongation of polyubiquitin chains for targeting the proteasome. Increased ERα ubiquitination was not affected by the deletion of the A/B domain but significantly diminished in the F domain deletion mutant. Our results indicate distinct and novel mechanisms for forskolin stimulation of ERα transcriptional activity and protection from ligand-induced degradation. It also suggests a unique mechanism by which forskolin increases unliganded and liganded ERα and ERβ ubiquitination but uncouples them from proteasome-mediated degradation regardless of their transcriptional responses to forskolin.

Decoding the Therapeutic Implications of the ERα Stability and Subcellular Distribution in Breast Cancer

Approximately 70% of all breast cancer cases are estrogen receptor-alpha positive (ERα+) and any ERα signaling pathways deregulation is critical for the progression of malignant mammary neoplasia. ERα acts as a transcription factor that promotes the expression of estrogen target genes associated with pro-tumor activity in breast cancer cells. Furthermore, ERα is also part of extranuclear signaling pathways related to endocrine resistance. The regulation of ERα subcellular distribution and protein stability is critical to regulate its functions and, consequently, influence the response to endocrine therapies and progression of this pathology. This minireview highlights studies that have deciphered the molecular mechanisms implicated in controlling ERα stability and nucleo-cytoplasmic transport. These mechanisms offer information about novel biomarkers, therapeutic targets, and promising strategies for breast cancer treatment.

TRIMming Down Hormone-Driven Cancers: The Biological Impact of TRIM Proteins on Tumor Development, Progression and Prognostication

The tripartite motif (TRIM) protein family is attracting increasing interest in oncology. As a protein family based on structure rather than function, a plethora of biological activities are described for TRIM proteins, which are implicated in multiple diseases including cancer. With hormone-driven cancers being among the leading causes of cancer-related death, TRIM proteins have been described to portrait tumor suppressive or oncogenic activities in these tumor types. This review describes the biological impact of TRIM proteins in relation to hormone receptor biology, as well as hormone-independent mechanisms that contribute to tumor cell biology in prostate, breast, ovarian and endometrial cancer. Furthermore, we point out common functions of TRIM proteins throughout the group of hormone-driven cancers. An improved understanding of the biological impact of TRIM proteins in cancer may pave the way for improved prognostication and novel therapeutics, ultimately improving cancer care for patients with hormone-driven cancers.

Differential Regulation and Targeting of Estrogen Receptor α Turnover in Invasive Lobular Breast Carcinoma

Invasive lobular breast carcinoma (ILC) accounts for 10% to 15% of breast cancers diagnosed annually. Evidence suggests that some aspects of endocrine treatment response might differ between invasive ductal carcinoma (IDC) and ILC, and that patients with ILC have worse long-term survival. We analyzed The Cancer Genome Atlas dataset and observed lower levels of ESR1 mRNA (P = 0.002) and ERα protein (P = 0.038) in ER+ ILC (n = 137) compared to IDC (n = 554), and further confirmed the mRNA difference in a local UPMC cohort (ILC, n = 143; IDC, n = 877; P < 0.005). In both datasets, the correlation between ESR1 mRNA and ERα protein was weaker in ILC, suggesting differential post-transcriptional regulation of ERα. In vitro, 17β-estradiol (E2) decreased the rate of degradation and increased the half-life of ERα in ILC cell lines, whereas the opposite was observed in IDC cell lines. Further, E2 failed to induce robust ubiquitination of ERα in ILC cells. To determine the potential clinical relevance of these findings, we evaluated the effect of 2 selective estrogen receptor downregulators (SERDs), ICI 182,780 and AZD9496, on ERα turnover and cell growth. While ICI 182,780 and AZD9496 showed similar effects in IDC cells, in ILC cell lines, AZD9496 was not as effective as ICI 182,780 in decreasing ERα stability and E2-induced proliferation. Furthermore, AZD9496 exhibited partial agonist activity in growth assays in ILC cell lines. Our study provides evidence for a distinct ERα regulation by SERDs in ILC cell lines, and therefore it is important to include ILC models into preclinical and clinical testing of novel SERDs.

Intrinsic and Extrinsic Factors Governing the Transcriptional Regulation of ESR1

Transcriptional regulation of ESR1, the gene that encodes for estrogen receptor α (ER), is critical for regulating the downstream effects of the estrogen signaling pathway in breast cancer such as cell growth. ESR1 is a large and complex gene that is regulated by multiple regulatory elements, which has complicated our understanding of how ESR1 expression is controlled in the context of breast cancer. Early studies characterized the genomic structure of ESR1 with subsequent studies focused on identifying intrinsic (chromatin environment, transcription factors, signaling pathways) and extrinsic (tumor microenvironment, secreted factors) mechanisms that impact ESR1 gene expression. Currently, the introduction of genomic sequencing platforms and additional genome-wide technologies has provided additional insight on how chromatin structures may coordinate with these intrinsic and extrinsic mechanisms to regulate ESR1 expression. Understanding these interactions will allow us to have a clearer understanding of how ESR1 expression is regulated and eventually provide clues on how to influence its regulation with potential treatments. In this review, we highlight key studies concerning the genomic structure of ESR1, mechanisms that affect the dynamics of ESR1 expression, and considerations towards affecting ESR1 expression and hormone responsiveness in breast cancer.

The Phosphorylated Estrogen Receptor α (ER) Cistrome Identifies a Subset of Active Enhancers Enriched for Direct ER-DNA Binding and the Transcription Factor GRHL2

Posttranslational modifications are key regulators of protein function, providing cues that can alter protein interactions and cellular location. Phosphorylation of estrogen receptor α (ER) at serine 118 (pS118-ER) occurs in response to multiple stimuli and is involved in modulating ER-dependent gene transcription. While the cistrome of ER is well established, surprisingly little is understood about how phosphorylation impacts ER-DNA binding activity. To define the pS118-ER cistrome, chromatin immunoprecipitation sequencing was performed on pS118-ER and ER in MCF-7 cells treated with estrogen. pS118-ER occupied a subset of ER binding sites which were associated with an active enhancer mark, acetylated H3K27. Unlike ER, pS118-ER sites were enriched in GRHL2 DNA binding motifs, and estrogen treatment increased GRHL2 recruitment to sites occupied by pS118-ER. Additionally, pS118-ER occupancy sites showed greater enrichment of full-length estrogen response elements relative to ER sites. In an in vitro DNA binding array of genomic binding sites, pS118-ER was more commonly associated with direct DNA binding events than indirect binding events. These results indicate that phosphorylation of ER at serine 118 promotes direct DNA binding at active enhancers and is a distinguishing mark for associated transcription factor complexes on chromatin.

Polyubiquitination inhibition of estrogen receptor alpha and its implications in breast cancer

Estrogen receptor alpha (ERα) is detected in more than 70% of the cases of breast cancer. Nuclear activity of ERα, a transcriptional regulator, is linked to the development of mammary tumors, whereas the extranuclear activity of ERα is related to endocrine therapy resistance. ERα polyubiquitination is induced by the estradiol hormone, and also by selective estrogen receptor degraders, resulting in ERα degradation via the ubiquitin proteasome system. Moreover, polyubiquitination is related to the ERα transcription cycle, and some E3-ubiquitin ligases also function as coactivators for ERα. Several studies have demonstrated that ERα polyubiquitination is inhibited by multiple mechanisms that include posttranslational modifications, interactions with coregulators, and formation of specific protein complexes with ERα. These events are responsible for an increase in ERα protein levels and deregulation of its signaling in breast cancers. Thus, ERα polyubiquitination inhibition may be a key factor in the progression of breast cancer and resistance to endocrine therapy.

18F-16α-17β-Fluoroestradiol Binding Specificity in Estrogen Receptor-Positive Breast Cancer

Purpose To determine the binding specificity of ¹⁸F-16α-17β-fluoroestradiol (FES) in estrogen receptor (ER) α-positive breast cancer cells and tumor xenografts. Materials and Methods Protocols were approved by the office of biologic safety and institutional animal care and use committee. By using ER-negative MDA-MB-231 breast cancer cells, clonal lines were created that expressed either wild-type (WT; 231 WT ER) or G521R mutant ERα (231 G521R ER), which is defective in estradiol binding. ERα protein levels, subcellular localization, and transcriptional function were confirmed. FES binding was measured by using an in vitro cell uptake assay. In vivo FES uptake was measured in tumor xenografts by using small-animal positron emission tomographic/computed tomographic imaging of 24 mice (17 WT ER tumors, nine mutant G521R ER tumors, eight MDA-MB-231 tumors, and four MCF-7 ER-positive tumors). Statistical significance was determined by using Mann-Whitney (Wilcoxon rank sum) test. Results ERα transcriptional function was abolished in the mutated 231 G521R ER cells despite appropriate receptor protein expression and nuclear localization. In vitro FES binding in the 231 G521R ER cells was reduced to that observed in the parental cells. Similarly, there was no significant FES uptake in the 231 G521R ER xenografts (percent injected dose [ID] per gram, 0.49 ± 0.042), which was similar to the negative control MDA-MB-231 xenografts (percent ID per gram, 0.42 ± 0.051; P = .20) and nonspecific muscle uptake (percent ID per gram, 0.41 ± 0.0095; P = .06). Conclusion This study showed that FES retention in ER-positive breast cancer is strictly dependent on an intact receptor ligand-binding pocket and that FES binds to ERα with high specificity. These results support the utility of FES imaging for assessing tumor heterogeneity by localizing immunohistochemically ER-positive metastases that lack receptor-binding functionality. ^© RSNA, 2017 Online supplemental material is available for this article.

Antiestrogen Resistant Cell Lines Expressing Estrogen Receptor α Mutations Upregulate the Unfolded Protein Response and are Killed by BHPI

Outgrowth of metastases expressing ERα mutations Y537S and D538G is common after endocrine therapy for estrogen receptor α (ERα) positive breast cancer. The effect of replacing wild type ERα in breast cancer cells with these mutations was unclear. We used the CRISPR-Cas9 genome editing system and homology directed repair to isolate and characterize 14 T47D cell lines in which ERαY537S or ERαD538G replace one or both wild-type ERα genes. In 2-dimensional, and in quantitative anchorage-independent 3-dimensional cell culture, ERαY537S and ERαD538G cells exhibited estrogen-independent growth. A progestin further increased their already substantial proliferation in micromolar 4-hydroxytamoxifen and fulvestrant/ICI 182,780 (ICI). Our recently described ERα biomodulator, BHPI, which hyperactivates the unfolded protein response (UPR), completely blocked proliferation. In ERαY537S and ERαD538G cells, estrogen-ERα target genes were constitutively active and partially antiestrogen resistant. The UPR marker sp-XBP1 was constitutively activated in ERαY537S cells and further induced by progesterone in both cell lines. UPR-regulated genes associated with tamoxifen resistance, including the oncogenic chaperone BiP/GRP78, were upregulated. ICI displayed a greater than 2 fold reduction in its ability to induce ERαY537S and ERαD538G degradation. Progestins, UPR activation and perhaps reduced ICI-stimulated ERα degradation likely contribute to antiestrogen resistance seen in ERαY537S and ERαD538G cells.

Mechanisms that Increase Stability of Estrogen Receptor Alpha in Breast Cancer

Estrogen receptor alpha (ER) is a transcriptional regulator that controls the expression of genes related to cellular proliferation and differentiation in normal mammary tissue. However, the expression, abundance, and activity of this receptor are increased in 70% of breast cancers. The ER upregulation is facilitated by several molecular mechanisms, including protein stability, which represents an important strategy to maintain an active and functional repertoire of ER. Several proteins interact and protect ER from degradation by the ubiquitin-proteasome system. Through diverse mechanisms, these proteins prevent polyubiquitination and degradation of ER, leading to an increase in ER protein levels; consequently, estrogen signaling and its physiologic effects are enhanced in breast cancer cells. Thus, increased protein stability seems to be one of the main reasons that ER is upregulated in breast cancer. Here, we highlight findings on the proteins and mechanisms that participate directly or indirectly in ER stability and their relevance to breast cancer.

Estrogen Receptor α Is Required for Maintaining Baseline Renin Expression

Enzymatic cleavage of angiotensinogen by renin represents the critical rate-limiting step in the production of angiotensin II, but the mechanisms regulating the initial expression of the renin gene remain incomplete. The purpose of this study is to unravel the molecular mechanism controlling renin expression. We identified a subset of nuclear receptors that exhibited an expression pattern similar to renin by reanalyzing a publicly available microarray data set. Expression of some of these nuclear receptors was similarly regulated as renin in response to physiological cues, which are known to regulate renin. Among these, only estrogen receptor α (ERα) and hepatic nuclear factor α have no known function in regulating renin expression. We determined that ERα is essential for the maintenance of renin expression by transfection of small interfering RNAs targeting Esr1, the gene encoding ERα, in renin-expressing As4.1 cells. We also observed that previously characterized negative regulators of renin expression, Nr2f2 and vitamin D receptor, exhibited elevated expression in response to ERα inhibition. Therefore, we tested whether ERα regulates renin expression through an interaction with Nr2f2 and vitamin D receptor. Renin expression did not return to baseline when we concurrently suppressed both Esr1 and Nr2f2 or Esr1 and vitamin D receptor mRNAs, strongly suggesting that Esr1 regulates renin expression independent of Nr2f2 and vitamin D receptor. ERα directly binds to the hormone response element within the renin enhancer region. We conclude that ERα is a previously unknown regulator of renin that directly binds to the renin enhancer hormone response element sequence and is critical in maintaining renin expression in renin-expressing As4.1 cells.

Estrogen receptor α inhibitor activates the unfolded protein response, blocks protein synthesis, and induces tumor regression

Recurrent estrogen receptor α (ERα)-positive breast and ovarian cancers are often therapy resistant. Using screening and functional validation, we identified BHPI, a potent noncompetitive small molecule ERα biomodulator that selectively blocks proliferation of drug-resistant ERα-positive breast and ovarian cancer cells. In a mouse xenograft model of breast cancer, BHPI induced rapid and substantial tumor regression. Whereas BHPI potently inhibits nuclear estrogen-ERα-regulated gene expression, BHPI is effective because it elicits sustained ERα-dependent activation of the endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR), and persistent inhibition of protein synthesis. BHPI distorts a newly described action of estrogen-ERα: mild and transient UPR activation. In contrast, BHPI elicits massive and sustained UPR activation, converting the UPR from protective to toxic. In ERα(+) cancer cells, BHPI rapidly hyperactivates plasma membrane PLCγ, generating inositol 1,4,5-triphosphate (IP3), which opens EnR IP3R calcium channels, rapidly depleting EnR Ca(2+) stores. This leads to activation of all three arms of the UPR. Activation of the PERK arm stimulates phosphorylation of eukaryotic initiation factor 2α (eIF2α), resulting in rapid inhibition of protein synthesis. The cell attempts to restore EnR Ca(2+) levels, but the open EnR IP3R calcium channel leads to an ATP-depleting futile cycle, resulting in activation of the energy sensor AMP-activated protein kinase and phosphorylation of eukaryotic elongation factor 2 (eEF2). eEF2 phosphorylation inhibits protein synthesis at a second site. BHPI's novel mode of action, high potency, and effectiveness in therapy-resistant tumor cells make it an exceptional candidate for further mechanistic and therapeutic exploration.

Pin1 modulates ERα levels in breast cancer through inhibition of phosphorylation-dependent ubiquitination and degradation

Estrogen receptor-alpha (ERα) is an important biomarker used to classify and direct therapy decisions in breast cancer (BC). Both ERα protein and its transcript, ESR1, are used to predict response to tamoxifen therapy, yet certain tumors have discordant levels of ERα protein and ESR1, which is currently unexplained. Cellular ERα protein levels can be controlled post-translationally by the ubiquitin-proteasome pathway through a mechanism that depends on phosphorylation at residue S118. Phospho-S118 (pS118-ERα) is a substrate for the peptidyl prolyl isomerase, Pin1, which mediates cis-trans isomerization of the pS118-P119 bond to enhance ERα transcriptional function. Here, we demonstrate that Pin1 can increase ERα protein without affecting ESR1 transcript levels by inhibiting proteasome-dependent receptor degradation. Pin1 disrupts ERα ubiquitination by interfering with receptor interactions with the E3 ligase, E6AP, which also is shown to bind pS118-ERα. Quantitative in situ assessments of ERα protein, ESR1, and Pin1 in human tumors from a retrospective cohort show that Pin1 levels correlate with ERα protein but not to ESR1 levels. These data show that ERα protein is post-translationally regulated by Pin1 in a proportion of breast carcinomas. As Pin1 impacts both ERα protein levels and transactivation function, these data implicate Pin1 as a potential surrogate marker for predicting outcome of ERα-positive BC.

Transcriptional activity of human brain estrogen receptor-α splice variants: evidence for cell type-specific regulation

Estrogen receptor α (ERα) isoforms with complex types of alternative splicing are naturally present in the human brain and may affect canonical receptor signaling. In the present study we investigated transcriptional activity of common ERα splice variants from this group with different molecular defects: MB1 (intron retention), TADDI (small deletion between exons 3 and 4 with an insert), the Δ (deletion) 3(⁎)-7(*)/819 (complete skipping of exons 4, 5 and 6 and partial deletion of exons 3 and 7) and the Δ3-6 (lacking exons 3, 4, 5 and 6) in HeLa and M17 cells upon stimulation with (17β)estradiol or insulin-like growth factor 1 (IGF-1). In HeLa cells, all these splice variants showed the dominant negative function that was more pronounced for the TADDI. In M17 cells the dominant negative variants appeared to be the MB1 and the Δ3-6, whereas TADDI turned out to be a clearly dominant positive variant. In M17 cells mRNA levels of Δ3-6 and Δ3(*)-7(*)/819 variants increased following (17β)estradiol administration. In Hela cells (17β)estradiol up-regulated the IGF-1 receptor mRNA levels in cultures transfected with MB1, TADDI and Δ3(*)-7(*)/819. Our data demonstrate that ERα splice variants show differential levels of the transcriptional activity in a cell type-specific way and that IGF-1 signaling pathways are differentially employed in a cell-type specific manner depending on the level of the discrete ERα splice variants expressed. Functional properties of various ERα splice variants and their cell type-specificity should, thus, be considered as potential confounders of estrogen therapy effects on the brain.

A model of estrogen-related gene expression reveals non-linear effects in transcriptional response to tamoxifen

BACKGROUND

Estrogen receptors alpha (ER) are implicated in many types of female cancers, and are the common target for anti-cancer therapy using selective estrogen receptor modulators (SERMs, such as tamoxifen). However, cell-type specific and patient-to-patient variability in response to SERMs (from suppression to stimulation of cancer growth), as well as frequent emergence of drug resistance, represents a serious problem. The molecular processes behind mixed effects of SERMs remain poorly understood, and this strongly motivates application of systems approaches. In this work, we aimed to establish a mathematical model of ER-dependent gene expression to explore potential mechanisms underlying the variable actions of SERMs.

RESULTS

We developed an equilibrium model of ER binding with 17β-estradiol, tamoxifen and DNA, and linked it to a simple ODE model of ER-induced gene expression. The model was parameterised on the broad range of literature available experimental data, and provided a plausible mechanistic explanation for the dual agonism/antagonism action of tamoxifen in the reference cell line used for model calibration. To extend our conclusions to other cell types we ran global sensitivity analysis and explored model behaviour in the wide range of biologically plausible parameter values, including those found in cancer cells. Our findings suggest that transcriptional response to tamoxifen is controlled in a complex non-linear way by several key parameters, including ER expression level, hormone concentration, amount of ER-responsive genes and the capacity of ER-tamoxifen complexes to stimulate transcription (e.g. by recruiting co-regulators of transcription). The model revealed non-monotonic dependence of ER-induced transcriptional response on the expression level of ER, that was confirmed experimentally in four variants of the MCF-7 breast cancer cell line.

CONCLUSIONS

We established a minimal mechanistic model of ER-dependent gene expression, that predicts complex non-linear effects in transcriptional response to tamoxifen in the broad range of biologically plausible parameter values. Our findings suggest that the outcome of a SERM's action is defined by several key components of cellular micro-environment, that may contribute to cell-type-specific effects of SERMs and justify the need for the development of combinatorial biomarkers for more accurate prediction of the efficacy of SERMs in specific cell types.

Ligand-free estrogen receptor activity complements IGF1R to induce the proliferation of the MCF-7 breast cancer cells

Background

Ligand-dependent activation of the estrogen receptor (ER) as well as of the insulin-like growth factor type 1 (IGF1R) induces the proliferation of luminal breast cancer cells. These two pathways cooperate and are interdependent. We addressed the question of the mechanisms of crosstalk between the ER and IGF1R.

Methods

We evaluated the mitogenic effects of estradiol (E2; agonist ligand of ER) and of insulin (a ligand of IGF1R) in the MCF-7 cells by flow cytometry and by analyzing the cell levels of cell cycle-related proteins (immunoblotting) and mRNA (RT-QPCR). To verify the requirement for the kinase activity of Akt (a downstream target of IGF1R) in the mitogenic action of estradiol, we used shRNA strategy and shRNA-resistant expression vectors.

Results

The activation of the ER by E2 is unable to induce the cell cycle progression when the phosphatidyl inositol-3 kinase (PI3K)/Akt signaling is blocked by a chemical inhibitor (LY 294002) or by shRNA targeting Akt1 and Akt2. shRNA-resistant Akt wild-type constructs efficiently complemented the mitogenic signaling activity of E2 whereas constructs with inactivated kinase function did not. In growth factor-starved cells, the residual PI3K/Akt activity is sufficient to complement the mitogenic action of E2. Conversely, when ER function is blocked by the antiestrogen ICI 182780, IGF1R signaling is intact but does not lead to efficient reinitiation of the cell cycle in quiescent, growth factor-starved MCF-7 cells. The basal transcription-promoting activity of ligand-free ER in growth factor-starved cells is sufficient to complement the mitogenic action of the IGF1R-dependent signaling.

Conclusions

The basal ER activity in the absence of ligand is sufficient to allow efficient mitogenic action of IGF1R agonists and needs to be blocked to prevent the cell cycle progression.

Research resource: enhanced genome-wide occupancy of estrogen receptor α by the cochaperone p23 in breast cancer cells

p23 is a chaperone with multiple heat shock protein 90 dependent and independent cellular functions, including stabilizing unliganded steroid receptors and modulating receptor-DNA dynamics. p23 protein is also up-regulated in several cancers, notably breast cancer. We previously demonstrated that higher expression of p23 in the estrogen-dependent breast cancer line MCF-7 (MCF-7+p23) selectively increased estrogen receptor (ER) target gene transcription and ER recruitment to regulatory elements, promoted cell invasion, and predicted a poor prognosis in breast cancer patients. To probe the impact of p23 on ER binding throughout the human genome, we compared ER occupancy in MCF-7+p23 cells relative to MCF-7-control cells by using chromatin immunoprecipitation followed by ultrahigh-throughput DNA sequencing in the absence and presence of 17β-estradiol (E2) treatment. We found that increased expression of p23 resulted in a 230% increase in the number of E2-induced ER-binding sites throughout the genome compared with control cells and also increased ER binding under basal conditions. Motif analysis indicated that ER binds to a similar DNA sequence regardless of p23 status. We also observed that ER tends to bind closer to genes that were induced, rather than repressed by either E2 treatment or p23 overexpression. Interestingly, we also found that the increased invasion of MCF-7+p23 cells was not only p23 dependent but also ER dependent. Thus, a small increase in the expression of p23 amplifies ER-binding genome wide and, in combination with ER, elicits an invasive phenotype. This makes p23 an attractive target for combating tumor cell metastasis in breast cancer patients.

Small molecule inhibitors as probes for estrogen and androgen receptor action

Because activated estrogen (ER) and androgen (AR) receptors stimulate cell proliferation in breast and prostate cancer, inhibiting their actions represents a major therapeutic goal. Most efforts to modulate ER and AR activity have focused on inhibiting the synthesis of estrogens or androgens or on the identification of small molecules that act by competing with agonist hormones for binding in the ligand-binding pocket of the receptor. An alternative approach is to implement screens for small molecule inhibitors that target other sites in the pathway of steroid receptor action. Many of these second-site inhibitors directly target ER or AR; others have still unknown sites of action. Small molecule inhibitors that target second sites represent new leads with clinical potential; they serve as novel modulators of receptor action; and they can reveal new and as yet unidentified interactions and pathways that modulate ER and AR action.

Estrogen receptors similarly mediate the effects of 17β-estradiol on cellular responses but differ in their potencies

17β-estradiol (E2), as the main circulating estrogen hormone, plays critical roles in the physiology and pathophysiology of various tissues. The E2 information is primarily conveyed by the transcription factors, estrogen receptors (ERs) α and β. ERs share similar structural and functional features. Experimental studies indicate that upon binding to E2, ERs directly or indirectly interact with DNA and regulate gene expressions with ERα being more potent transregulator than ERβ. However, studies also showed that ERβ induces alterations in phenotypic features of cancer cell lines independent of E2. These observations suggested that the manner in which the unliganded ERβ induces phenotypic alterations in cancer cell models differs from that of ERα. Studies demonstrated that while requiring E2 for function at low levels of synthesis, the unliganded ERα at augmented concentrations modulates gene expressions and cellular growth. We, therefore, anticipated that heightened levels of ERβ synthesis could similarly circumvent the dependency on E2 leading to gene transcriptions and cellular proliferation. To test this prediction, we used adenovirus-infected cancer cell lines in which ERs were shown to induce genomic and cellular responses. We found that while ERβ at low levels of synthesis was dependent upon E2 for function, the receptor at high levels regulated gene expression and cellular proliferation independent of E2. We then addressed whether ERs at comparable levels that require E2 for function differentially alter gene expressions and cellular responses. We found that ERs mediate the effects of E2 on gene expression, cellular proliferation, apoptosis, and motility with an overlapping pattern. However, ERα was more potent regulator than ERβ in inducing cellular responses. Our results suggest that differences in potencies to regulate the expression of genes are a critical feature of the ER subtypes in mediating E2 signaling in cancer cell lines.

A noncompetitive small molecule inhibitor of estrogen-regulated gene expression and breast cancer cell growth that enhances proteasome-dependent degradation of estrogen receptor {alpha}

The mechanisms responsible for 17β-estradiol (E(2))-stimulated breast cancer growth and development of resistance to tamoxifen and other estrogen receptor α (ERα) antagonists are not fully understood. We describe a new tool for dissecting ERα action in breast cancer, p-fluoro-4-(1,2,3,6,-tetrahydro-1,3-dimethyl-2-oxo-6-thionpurin-8-ylthio) (TPSF), a potent small-molecule inhibitor of estrogen receptor α that does not compete with estrogen for binding to ERα. TPSF noncompetitively inhibits estrogen-dependent ERα-mediated gene expression with little inhibition of transcriptional activity by NF-κB or the androgen or glucocorticoid receptor. TPSF inhibits E(2)-ERα-mediated induction of the proteinase inhibitor 9 gene, which is activated by ERα binding to estrogen response element DNA, and the cyclin D1 gene, which is induced by tethering ERα to other DNA-bound proteins. TPSF inhibits anchorage-dependent and anchorage-independent E(2)-ERα-stimulated growth of MCF-7 cells but does not inhibit growth of ER-negative MDA-MB-231 breast cancer cells. TPSF also inhibits ERα-dependent growth in three cellular models for tamoxifen resistance; that is, 4-hydroxytamoxifen-stimulated MCF7ERαHA cells that overexpress ERα, fully tamoxifen-resistant BT474 cells that have amplified HER-2 and AIB1, and partially tamoxifen-resistant ZR-75 cells. TPSF reduces ERα protein levels in MCF-7 cells and several other cell lines without altering ERα mRNA levels. The proteasome inhibitor MG132 abolished down-regulation of ERα by TPSF. Thus, TPSF affects receptor levels at least in part due to its ability to enhance proteasome-dependent degradation of ERα. TPSF represents a novel class of ER inhibitor with significant clinical potential.

Proteasome inhibition represses ERalpha gene expression in ER+ cells: a new link between proteasome activity and estrogen signaling in breast cancer

Estrogen receptor-alpha (ERα) is a major therapeutic target of hormonal therapies in breast cancer and its expression in tumors is predictive of clinical response. Protein levels of ERα are tightly controlled by the 26S proteasome, yet how the clinical proteasome inhibitor, bortezomib, impacts ERα regulation has not been studied. Bortezomib selectively inhibits the chymotrypsin-like activity of the proteasome. Unlike other laboratory proteasome inhibitors, bortezomib failed to stabilize ERα protein at a dose exceeding 90% inhibition of the chymotrypsin-like activity. Unexpectedly, however, chronic bortezomib exposure caused a reduction of ERα levels in multiple ER+ breast cancer cell lines. This response can be explained by the fact that bortezomib induced a dramatic decrease in ERα mRNA due to direct transcriptional inhibition and loss of RNA polymerase II recruitment on the ERα gene promoter. Bortezomib treatment resulted in promoter-specific changes in estrogen-induced gene transcription that related to occupancy of ERα and RNA PolII on endogenous promoters. In addition, bortezomib inhibited estrogen-dependent growth in soft agar. These results reveal a novel link between proteasome activity and expression of ERα in breast cancer and uncover distinct roles of the chymotrypsin-like activity of the proteasome in the regulation of the ERα pathway.

New stably transfected bioluminescent cells expressing FLAG epitope-tagged estrogen receptors to study their chromatin recruitment

BACKGROUND

Biological actions of estrogens are mediated by the two specific estrogen receptors ERalpha and ERbeta. However, due to the absence of adequate cellular models, their respective transcriptional activities are still poorly understood. For instance, the evaluation of such differing properties on the transcription of responsive genes using ChIP experiments was hindered by the deficiency of cells exhibiting the same genotypic background and properties but expressing only one of the ERs. We describe here the generation of such cells, using an estrogen receptor negative HELN cell line that was derived from HeLa cells stably transfected with an ERE-driven luciferase plasmid. These HELN-Falpha and HELN-Fbeta cell lines stably express either the alpha or beta (full length) estrogen receptor tagged with the FLAG epitope. The use of antibodies directed against the FLAG epitope allowed a direct comparative evaluation of the respective actions of both ERs using ChIP.

RESULTS

HELN-Falpha and HELN-Fbeta cell lines were found to express comparable levels of their corresponding tagged receptors with a Kd for estradiol binding of 0.03 and 0.27 nM respectively. The presence of a stably transfected ERE-driven luciferase plasmid in these cells allowed the direct evaluation of the transcriptional activity of both tagged receptors, using natural or synthetic estrogens. FLAG-ERalpha and FLAG-ERbeta were found to exhibit similar transcriptional activity, as indicated by a kinetic evaluation of the transcriptional activation of the luciferase gene during 10 hrs of treatment with estradiol. The validity of these model cells was further confirmed by the predictable transcriptional regulations measured upon treatments with ERalpha or ERbeta specific ligands. The similar immunoprecipitation efficiency of both tagged receptors by an anti-FLAG antibody allowed the assessment of their kinetic recruitment on the synthetic luciferase promoter (containing an estrogen response element) by ChIP assays during 8 hours. A biphasic curve was obtained for both FLAG-ERalpha and FLAG-ERbeta, with a peak occurring either at 2 hr or at 1 hr, respectively, and a second one following 4 hr of E2 stimulation in both cases. In MCF-7 cells, the recruitment of ERalpha also exhibited a biphasic behaviour; with the second peak however not so important than in the HeLa cell lines.

CONCLUSION

In HELN derived cell lines, no fundamental differences between kinetics were observed during 8 hours for FLAG-ERalpha and FLAG-ERbeta, as well as for polymerase II recruitment. However, the relative importance of recruitment between 1 hr and 4 hr was found to be different in HeLa cell line expressing exogenous tagged ERalpha and in MCF-7 cell line expressing endogenous ER.

Effects of environmental relevant doses of pollutants from offshore oil production on Atlantic cod (Gadus morhua)

The release of produced water (PW), a by-product of offshore oil production, has increased in Norwegian waters in recent years. Alkylphenols (AP), a major component of PW, have been shown to have endocrine disrupting effects on several fish species. In the present study, four groups of female Atlantic cod (Gadus morhua) were orally exposed for 20 weeks to two different concentrations of a mixture of C4-C7 APs, PW or 17beta-estradiol. The transcriptional responses in the liver of Atlantic female cod were studied using a custom-made cDNA microarray. The largest transcriptional effects were seen in cod exposed to the lowest dose of APs. Several biological processes such as glycolysis, apoptosis and the general stress response were affected by exposure to APs. In addition, genes coding for the detoxification enzymes CYP1A and sulfotransferase 2 were up-regulated in the low exposure group. Significant reduction in gonadosomatic index (GSI) and the concentration of plasma vitellogenin were seen in both AP and 17beta-estradiol exposed cod. Exposure to PW had little effect on GSI and the regulation of stress responsive genes. The findings indicate that chronic exposure to low levels of APs may cause a stress response and delayed maturation in female cod.

Repression of ESR1 through actions of estrogen receptor alpha and Sin3A at the proximal promoter

Gene expression results from the coordinated actions of transcription factor proteins and coregulators. Estrogen receptor alpha (ERalpha) is a ligand-activated transcription factor that can both activate and repress the expression of genes. Activation of transcription by estrogen-bound ERalpha has been studied in detail, as has antagonist-induced repression, such as that which occurs by tamoxifen. How estrogen-bound ERalpha represses gene transcription remains unclear. In this report, we identify a new mechanism of estrogen-induced transcriptional repression by using the ERalpha gene, ESR1. Upon estrogen treatment, ERalpha is recruited to two sites on ESR1, one distal (ENH1) and the other at the proximal (A) promoter. Coactivator proteins, namely, p300 and AIB1, are found at both ERalpha-binding sites. However, recruitment of the Sin3A repressor, loss of RNA polymerase II, and changes in histone modifications occur only at the A promoter. Reduction of Sin3A expression by RNA interference specifically inhibits estrogen-induced repression of ESR1. Furthermore, an estrogen-responsive interaction between Sin3A and ERalpha is identified. These data support a model of repression wherein actions of ERalpha and Sin3A at the proximal promoter can overcome activating signals at distal or proximal sites and ultimately decrease gene expression.

Low concentrations of the soy phytoestrogen genistein induce proteinase inhibitor 9 and block killing of breast cancer cells by immune cells

The risks and benefits of diets and supplements containing the estrogenic soy isoflavone genistein are not well established. We report that 10 nm genistein potently induces the granzyme B inhibitor, proteinase inhibitor 9 (PI-9) in MCF-7 human breast cancer cells. By inducing PI-9, genistein inhibits the ability of human natural killer (NK) cells to lyse the target breast cancer cells. In ERalphaHA cells, stably transfected MCF-7 cells, which contain elevated levels of estrogen receptor-alpha (ERalpha), 100 pm genistein or 17beta-estradiol potently induce PI-9 and prevent NK cells from killing the target breast cancer cells. The concentrations of genistein that fully induce PI-9 in MCF-7 cells, and in ERalphaHA cells, are far lower than those previously reported to elicit estrogenic responses through ERalpha. Because 4-hydroxytamoxifen, raloxifene, and ICI 182,780/Faslodex all block genistein induction of PI-9 and elevated levels of ERalpha enhance induction of PI-9, genistein acts via ERalpha to induce PI-9. Increasing levels of ERalpha in breast cancer cells results in a progressive increase in induction of PI-9 by genistein and in the cell's ability to evade killing by NK cells. Moderate levels of dietary genistein and soy flour effectively induce PI-9 in human breast cancers grown in ovariectomized athymic mice. A significant population consumes levels of genistein in soy products that may be high enough to induce PI-9, perhaps potentiating the survival of some preexisting breast cancers by enabling them to evade immunosurveillance.

Glucocorticoid receptor phosphorylation differentially affects target gene expression

The glucocorticoid receptor (GR) is phosphorylated at multiple sites within its N terminus (S203, S211, S226), yet the role of phosphorylation in receptor function is not understood. Using a range of agonists and GR phosphorylation site-specific antibodies, we demonstrated that GR transcriptional activation is greatest when the relative phosphorylation of S211 exceeds that of S226. Consistent with this finding, a replacement of S226 with an alanine enhances GR transcriptional response. Using a battery of compounds that perturb different signaling pathways, we found that BAPTA-AM, a chelator of intracellular divalent cations, and curcumin, a natural product with antiinflammatory properties, reduced hormone-dependent phosphorylation at S211. This change in GR phosphorylation was associated with its decreased nuclear retention and transcriptional activation. Molecular modeling suggests that GR S211 phosphorylation promotes a conformational change, which exposes a novel surface potentially facilitating cofactor interaction. Indeed, S211 phosphorylation enhances GR interaction with MED14 (vitamin D receptor interacting protein 150). Interestingly, in U2OS cells expressing a nonphosphorylated GR mutant S211A, the expression of IGF-binding protein 1 and interferon regulatory factor 8, both MED14-dependent GR target genes, was reduced relative to cells expressing wild-type receptor across a broad range of hormone concentrations. In contrast, the induction of glucocorticoid-induced leucine zipper, a MED14-independent GR target, was similar in S211A- and wild-type GR-expressing cells at high hormone levels, but was reduced in S211A cells at low hormone concentrations, suggesting a link between GR phosphorylation, MED14 involvement, and receptor occupancy. Phosphorylation also affected the magnitude of repression by GR in a gene-selective manner. Thus, GR phosphorylation at S211 and S226 determines GR transcriptional response by modifying cofactor interaction. Furthermore, the effect of GR S211 phosphorylation is gene specific and, in some cases, dependent upon the amount of activated receptor.

A new small molecule inhibitor of estrogen receptor alpha binding to estrogen response elements blocks estrogen-dependent growth of cancer cells

Estrogen receptor alpha (ERalpha) plays an important role in several human cancers. Most current ERalpha antagonists bind in the receptor ligand binding pocket and compete for binding with estrogenic ligands. Instead of the traditional approach of targeting estrogen binding to ER, we describe a strategy using a high throughput fluorescence anisotropy microplate assay to identify small molecule inhibitors of ERalpha binding to consensus estrogen response element (cERE) DNA. We identified small molecule inhibitors of ERalpha binding to the fluorescein-labeled (fl)cERE and evaluated their specificity, potency, and efficacy. One small molecule, theophylline, 8-[(benzylthio)methyl]-(7CI,8CI) (TPBM), inhibited ERalpha binding to the flcERE (IC(50) approximately 3 microm) and inhibited ERalpha-mediated transcription of a stably transfected ERE-containing reporter gene. Inhibition by TPBM was ER-specific, because progesterone and glucocorticoid receptor transcriptional activity were not significantly inhibited. In tamoxifen-resistant breast cancer cells that overexpress ERalpha, TPBM inhibited 17beta-estradiol (E(2))-ERalpha (IC(50) 9 microm) and 4-hydroxytamoxifen-ERalpha-mediated gene expression. Chromatin immunoprecipitation showed TPBM reduced E(2).ERalpha recruitment to an endogenous estrogen-responsive gene. TPBM inhibited E(2)-dependent growth of ERalpha-positive cancer cells (IC(50) of 5 microm). TPBM is not toxic to cells and does not affect estrogen-independent cell growth. TPBM acts outside of the ER ligand binding pocket, does not act by chelating the zinc in ER zinc fingers, and differs from known ERalpha inhibitors. Using a simple high throughput screen for inhibitors of ERalpha binding to the cERE, a small molecule inhibitor has been identified that selectively inhibits ERalpha-mediated gene expression and estrogen-dependent growth of cancer cells.

Gene expression profiling reveals that the regulation of estrogen-responsive element-independent genes by 17 beta-estradiol-estrogen receptor beta is uncoupled from the induction of phenotypic changes in cell models

Estrogen hormone 17beta-estradiol (E(2)) is involved in the physiology and pathology of many tissues. E(2) information is conveyed by the transcription factors estrogen receptors (ER) alpha and beta that mediate a complex array of nuclear and non-nuclear events. The interaction of ER with specific DNA sequences, estrogen-responsive elements (EREs), constitutes a critical nuclear signaling pathway. In addition, E(2)-ER regulates transcription through interactions with transfactors bound to their cognate regulatory elements on DNA, hence the ERE-independent signaling pathway. However, the relative importance of the ERE-independent pathway in E(2)-ERbeta signaling is unclear. To address this issue, we engineered an ERE-binding defective ERbeta mutant (ERbeta(EBD)) by changing critical residues in the DNA-binding domain required for ERE binding. Biochemical and functional studies revealed that ERbeta(EBD) signaled exclusively through the ERE-independent pathway. Using the adenovirus infected ER-negative cancer cell models, we found that although E(2)-ERbeta(EBD) regulated the expression of a number of genes identified by microarrays, it was ineffective in altering cellular proliferation, motility, and death in contrast to E(2)-ERbeta. Our results indicate that genomic responses from the ERE-independent pathway to E(2)-ERbeta are not sufficient to alter the cellular phenotype. These findings suggest that the ERE-dependent pathway is a required signaling route for E(2)-ERbeta to induce cellular responses.

Akt stabilizes estrogen receptor alpha with the concomitant reduction in its transcriptional activity

We have investigated the effect of Akt on estrogen receptor (ER) alpha protein level and its transcriptional activity. Transient transfection studies revealed that constitutively active Akt1 up-regulated ERalpha at the post-transcriptional level. Studies using Akt inhibitor and dominant-negative Akt1 showed that Akt1 kinase activity is required for the up-regulation of ERalpha. Cycloheximide decay assays and studies with proteasome inhibitor indicated that Akt1-mediated up-regulation of ERalpha was maintained by inhibiting proteasome-mediated degradation of ERalpha. When Akt consensus phosphorylation site mutant, ERalphaS167A was tested for Akt1-mediated up-regulation, increase of ERalphaS167A by Akt1 was significantly impaired as compared to wild type ERalpha. In addition, dominant-negative glycogen synthase kinase (GSK) 3beta and LiCl could also partially up-regulate ERalpha protein level, suggesting that concerted action of Akt1-mediated phosphorylation on S167 and kinase activity of Akt-downstream GSK3beta could affect ERalpha protein level. Paradoxically, co-expression of Akt1 could down-regulate transcriptional activity of ERalpha. The inhibitory effect of Akt1 on ERalpha transcriptional activity was not attributable to changes in subcellular distribution of ERalpha. Transfection studies using increasing amount of Akt1 and ERalpha indicated that the transcriptional activity of ERalpha was negatively regulated by ERalpha protein quantities at higher ERalpha concentrations. Chromatin immunoprecipitation assays revealed that at Akt1 concentration high enough to induce up-regulation of ERalpha, association of ERalpha to promoter region of ERalpha target pS2 gene was impaired. Taken together, these data suggest that Akt1 could increase ERalpha protein level with simultaneous reduction in its transcriptional activity, possibly by modulating association of ERalpha to the target gene promoters.

Amping up estrogen receptors in breast cancer

This article highlights a recent study by Holst et al. in Nature Genetics that finds estrogen receptor-alpha (ER-α) amplification in early benign lesions and more advanced invasive carcinomas of the breast, and discusses the potential implications to our present understanding of the role of ER-α in breast tumorigenesis.

Human prolactin gene promoter regulation by estrogen: convergence with tumor necrosis factor-alpha signaling

Estrogens have been implicated in the regulation of prolactin gene expression in man, although previous studies have not defined the molecular mechanism whereby estradiol activates the human prolactin gene promoter (hPrl). We found that estradiol induced a reproducible 1.8-fold activation of the hPrl gene promoter, using pituitary GH3 cells stably transfected with a 5000-bp hPrl promoter fragment linked to luciferase reporter gene. This activation was blocked by treatment with estrogen receptor (ER) antagonists 4-hydroxytamoxifen and ICI-182,780. Promoter deletion and mutagenesis experiments identified a functional estrogen response element (ERE) sequence 1189 bp upstream of the transcription start site that was responsible for estrogen-mediated promoter activation. This site differed from the consensus ERE sequence by two base pairs, one in each half-site. This ERE was identified to be functional through binding ERalpha in EMSAs. Chromatin immunoprecipitation assays confirmed ERalpha binding to this sequence in vivo in the absence of ligand, with increased recruitment when cells were cultured in the presence of estradiol. When cells were treated with both estradiol and TNFalpha, we observed synergistic activation of the hPrl promoter, which was mediated by the -1189-bp ERE. Mutagenesis of this ERE abolished the promoter-activating effect not only of estradiol but also of TNFalpha. These data suggest a novel, promoter-specific signaling interaction between estrogen and TNFalpha signaling, which is likely to be important for prolactin regulation in vivo.

Expression of high levels of human proteinase inhibitor 9 blocks both perforin/granzyme and Fas/Fas ligand-mediated cytotoxicity

Proteinase inhibitor 9 (PI-9, SerpinB9) is the only known human intracellular granzyme B inhibitor. Whether expression of PI-9 is sufficient to block cytolysis induced by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells remains controversial. To evaluate the roles of PI-9, we isolated and tested three lines of stably transfected HeLa cells expressing wild-type PI-9 and one line expressing an inactive mutant PI-9. Expressions of wild-type PI-9, but not the inactive mutant PI-9, inhibited cytolysis induced by human NK92 and NKL natural killer cells. Expression of high levels of PI-9 is therefore sufficient to protect human cells against NK cell-mediated cell death. Using two assays, we show that expressing wild-type PI-9, but not the inactive mutant PI-9, blocks Fas/Fas ligand (Fas/FasL)-mediated apoptosis. PI-9 expression has no effect on etoposide-induced apoptosis. HeLa cells exhibiting substantial resistance to Fas/FasL-mediated apoptosis contain 2- to 3-fold higher PI-9 levels than HCT116 human colon cancer cells and 2- to 3-fold lower PI-9 levels than MCF7/ERHA breast cancer cells, in which PI-9 is strongly induced by estrogens, and by tamoxifen. Expression of increasing levels of PI-9 in target cells may progressively inhibit immune surveillance by blocking NK and CTL-induced cytotoxicity through the perforin/granzyme pathway and then through the Fas/FasL pathway.

Intestinal resistance to 1,25 dihydroxyvitamin D in mice heterozygous for the vitamin D receptor knockout allele

We tested the hypothesis that low vitamin D receptor (VDR) level causes intestinal vitamin D resistance and intestinal calcium (Ca) malabsorption. To do so, we examined vitamin D regulated duodenal Ca absorption and gene expression [transient receptor potential channel, vallinoid subfamily member 6 (TRPV6), 24-hydroxylase, calbindin D(9k) (CaBP) mRNA, and CaBP protein] in wild-type mice and mice with reduced tissue VDR levels [i.e. heterozygotes for the VDR gene knockout (HT)]. Induction of 24-hydroxylase mRNA levels by 1,25 dihydroxyvitamin D(3) [1,25(OH)(2) D(3)] injection was significantly reduced in the duodenum and kidney of HT mice in both time-course and dose-response experiments. TRPV6 and CaBP mRNA levels in duodenum were significantly induced after 1,25(OH)(2) D(3) injection, but there was no difference in response between wild-type and HT mice. Feeding a low-calcium diet for 1 wk increased plasma PTH, renal 1alpha-hydroxylase (CYP27B1) mRNA level, and plasma 1,25(OH)(2) D(3), and this response was greater in HT mice (by 88, 55, and 37% higher, respectively). In contrast, duodenal TRPV6 and CaBP mRNA were not higher in HT mice fed the low-calcium diet. However, the response of duodenal Ca absorption and CaBP protein to increasing 1,25(OH)(2) D(3) levels was blunted by 40% in HT mice. Our data show that low VDR levels lead to resistance of intestinal Ca absorption to 1,25(OH)(2) D(3), and this resistance may be due to a role for the VDR (and VDR level) in the translation of CaBP.

Interplay between the levels of estrogen and estrogen receptor controls the level of the granzyme inhibitor, proteinase inhibitor 9 and susceptibility to immune surveillance by natural killer cells

Estrogens promote cell proliferation and metastases in several human cancers. Here, we describe a different action of estrogens likely to contribute to tumor development-blocking immunosurveillance. In breast cancer cells, increasing concentrations of estrogen induce increasing levels of the granzyme B inhibitor, SerpinB9/proteinase inhibitor 9 (PI-9) and progressively block cell death induced by NK92 natural killer (NK) cells, but do not block killing by a second NK cell line, NKL cells. RNA interference knockdown of PI-9 abolishes estrogen's ability to block NK92 cell-induced cytotoxicity. Expressing elevated levels of estrogen receptor alpha (ERalpha) increases the induced level of PI-9, and makes tamoxifen (TAM), but not raloxifene or ICI 182,780, a potent inducer of PI-9. At elevated levels of ERalpha, induction of PI-9 by estradiol or TAM blocks killing by both NK92 and NKL cells. When the Erk pathway is activated with epidermal growth factor, the concentration of estrogen required to induce a protective level of PI-9 is reduced to 10 pM. Elevated concentrations of estrogen and ER may provide a dual selective advantage to breast cancer cells by controlling PI-9 levels and thereby blocking immunosurveillance. Expressing elevated levels of ERalpha reveals a potentially important difference in the effects of TAM, raloxifene and ICI 182,780 on immunosurveillance in breast cancer.