Delineation of a FOXA1/ERα/AGR2 regulatory loop that is dysregulated in endocrine therapy-resistant breast cancer

Modulation of Protein Disulfide Isomerase Functions by Localization: The Example of the Anterior Gradient Family

Significance: Oxidative folding within the endoplasmic reticulum (ER) introduces disulfide bonds into nascent polypeptides, ensuring proteins' stability and proper functioning. Consequently, this process is critical for maintaining proteome integrity and overall health. The productive folding of thousands of secretory proteins requires stringent quality control measures, such as the unfolded protein response (UPR) and ER-Associated Degradation (ERAD), which contribute significantly to maintaining ER homeostasis. ER-localized protein disulfide isomerases (PDIs) play an essential role in each of these processes, thereby contributing to various aspects of ER homeostasis, including maintaining redox balance, proper protein folding, and signaling from the ER to the nucleus. Recent Advances: Over the years, there have been increasing reports of the (re)localization of PDI family members and other ER-localized proteins to various compartments. A prime example is the anterior gradient (AGR) family of PDI proteins, which have been reported to relocate to the cytosol or the extracellular environment, acquiring gain of functions that intersect with various cellular signaling pathways. Critical Issues: Here, we summarize the functions of PDIs and their gain or loss of functions in non-ER locations. We will focus on the activity, localization, and function of the AGR proteins: AGR1, AGR2, and AGR3. Future Directions: Targeting PDIs in general and AGRs in particular is a promising strategy in different human diseases. Thus, there is a need for innovative strategies and tools aimed at targeting PDIs; those strategies should integrate the specific localization and newly acquired functions of these PDIs rather than solely focusing on their canonical roles.

AGR2 and FOXA1 as prognostic markers in ER-positive breast cancer

BACKGROUND

The prognostic role of either forkhead box A1 (FOXA1) or anterior gradient 2 (AGR2) in breast cancer has been found separately. Considering that there were interplays between them depending on ER status, we aimed to assess the statistical interaction between AGR2 and FOXA1 on breast cancer prognosis and examine the prognostic role of the combination of them by ER status.

METHODS

AGR2 and FOXA1 expression in tumor tissues were evaluated with tissue microarrays by immunohistochemistry in 915 breast cancer patients with follow up data. The expression levels of these two markers were treated as binary variables, and many different cutoff values were tried for each marker. Survival and Cox proportional hazard analyses were used to evaluate the relationship between AGR2, FOXA1 and prognosis, and the statistical interaction between them on the prognosis was assessed on multiplicative scale.

RESULTS

Statistical interaction between AGR2 and FOXA1 on the PFS was significant with all the cutoff points in ER-positive breast cancer patients but not ER-negative ones. Among ER-positive patients, the poor prognostic role of the high level of FOXA1 was significant only in patients with the low level of AGR2, and vice versa. When AGR2 and FOXA1 were considered together, patients with low levels of both markers had significantly longer PFS compared with all other groups.

CONCLUSIONS

There was a statistical interaction between AGR2 and FOXA1 on the prognosis of ER-positive breast cancer. The combination of AGR2 and FOXA1 was a more useful marker for the prognosis of ER-positive breast cancer patients.

FOXA1 Reprogramming Dictates Retinoid X Receptor Response in ESR1-Mutant Breast Cancer

Estrogen receptor alpha (ER/ESR1) mutations occur in 30% to 40% of endocrine resistant ER-positive (ER+) breast cancer. Forkhead box A1 (FOXA1) is a key pioneer factor mediating ER-chromatin interactions and endocrine response in ER+ breast cancer, but its role in ESR1-mutant breast cancer remains unclear. Our previous FOXA1 chromatin immunoprecipitation sequencing (ChIP-seq) identified a large portion of redistributed binding sites in T47D genome-edited Y537S and D538G ESR1-mutant cells. Here, we further integrated FOXA1 genomic binding profile with the isogenic ER cistrome, accessible genome, and transcriptome data of T47D cell model. FOXA1 redistribution was significantly associated with transcriptomic alterations caused by ESR1 mutations. Furthermore, in ESR1-mutant cells, FOXA1-binding sites less frequently overlapped with ER, and differential gene expression was less associated with the canonical FOXA1-ER axis. Motif analysis revealed a unique enrichment of retinoid X receptor (RXR) motifs in FOXA1-binding sites of ESR1-mutant cells. Consistently, ESR1-mutant cells were more sensitive to growth stimulation with the RXR agonist LG268. The mutant-specific response was dependent on two RXR isoforms, RXR-α and RXR-β, with a stronger dependency on the latter. In addition, T3, the agonist of thyroid receptor (TR) also showed a similar growth-promoting effect in ESR1-mutant cells. Importantly, RXR antagonist HX531 blocked growth of ESR1-mutant cells and a patient-derived xenograft (PDX)-derived organoid with an ESR1 D538G mutation. Collectively, our data support the evidence for a stronger RXR response associated with FOXA1 reprograming in ESR1-mutant cells, suggesting development of therapeutic strategies targeting RXR pathways in breast tumors with ESR1 mutation.

IMPLICATIONS

It provides comprehensive characterization of the role of FOXA1 in ESR1-mutant breast cancer and potential therapeutic strategy through blocking RXR activation.

AGR2: a secreted protein worthy of attention in diagnosis and treatment of breast cancer

AGR2 is a secreted protein widely existing in breast. In precancerous lesions, primary tumors and metastatic tumors, the expression of AGR2 is increased, which has aroused our interest. This review introduces the gene and protein structure of AGR2. Its endoplasmic reticulum retention sequence, protein disulfide isomerase active site and multiple protein binding sequences endow AGR2 with diverse functions inside and outside breast cancer cells. This review also enumerates the role of AGR2 in the progress and prognosis of breast cancer, and emphasizes that AGR2 can be a promising biomarker and a target for immunotherapy of breast cancer, providing new ideas for early diagnosis and treatment of breast cancer.

From development to cancer - an ever-increasing role of AGR2

Anterior gradient 2, AGR2, is a small, 20 kDa protein that plays a vital role in oxidative protein folding in the endoplasmic reticulum. AGR2 is involved in several signal transduction pathways that are essential for cell survival. It was initially discovered in the African clawed frog, Xenopus laevis, where it plays an important function in embryonic development. Akin to several other developmental genes, it is also frequently deregulated in cancer, where it plays a decisive role in tumor initiation, progression and metastasis. In this review, we have summarized currently known AGR2 functions, its expression and function in embryonic and cancer development, as well as its potential as a candidate tumor biomarker and promising new target for cancer immunotherapy.

Nuclear Mechanisms Involved in Endocrine Resistance

Endocrine therapy is a standard treatment offered to patients with ERα (estrogen receptor α)-positive breast cancer. In endocrine therapy, ERα is either directly targeted by anti-estrogens or indirectly by aromatase inhibitors which cause estrogen deficiency. Resistance to these drugs (endocrine resistance) compromises the efficiency of this treatment and requires additional measures. Endocrine resistance is often caused by deregulation of the PI3K/AKT/mTOR pathway and/or cyclin-dependent kinase 4 and 6 activities allowing inhibitors of these factors to be used clinically to counteract endocrine resistance. The nuclear mechanisms involved in endocrine resistance are beginning to emerge. Exploring these mechanisms may reveal additional druggable targets, which could help to further improve patients' outcome in an endocrine resistance setting. This review intends to summarize our current knowledge on the nuclear mechanisms linked to endocrine resistance.

A Pipeline for Integrated Theory and Data-Driven Modeling of Biomedical Data

Genome sequencing technologies have the potential to transform clinical decision making and biomedical research by enabling high-throughput measurements of the genome at a granular level. However, to truly understand mechanisms of disease and predict the effects of medical interventions, high-throughput data must be integrated with demographic, phenotypic, environmental, and behavioral data from individuals. Further, effective knowledge discovery methods must infer relationships between these data types. We recently proposed a pipeline (CausalMGM) to achieve this. CausalMGM uses probabilistic graphical models to infer the relationships between variables in the data; however, CausalMGM's graphical structure learning algorithm can only handle small datasets efficiently. We propose a new methodology (piPref-Div) that selects the most informative variables for CausalMGM, enabling it to scale. We validate the efficacy of piPref-Div against other feature selection methods and demonstrate how the use of the full pipeline improves breast cancer outcome prediction and provides biologically interpretable views of gene expression data.

Time-varying effects of FOXA1 on breast cancer prognosis

PURPOSE

Results of previous studies on the associations between Forkhead box A1 (FOXA1) expression in breast cancer tissues and the prognosis varied depending on the follow-up durations. The present study would investigate whether there is a time-varying effect of FOXA1 in breast cancer tissues on the prognosis.

METHODS

FOXA1 expressions were evaluated in 1041 primary invasive breast tumors with tissue microarrays by immunohistochemistry. Cox models with restricted cubic splines and Kaplan-Meier survival analysis were used to examine the associations between FOXA1 and the prognosis. Flexible parametric models were applied to explore the time-varying effect of FOXA1.

RESULTS

Overall, the association between FOXA1 expression and the prognosis was not significant but varied on the time of follow-up. Compared to FOXA1 ≤ 270 of H-score, the hazard ratios (HRs) of death for those with 271-285 of FOXA1 expression increased from 0.35 (95% CI 0.14-0.86) at 6 months after diagnosis to 2.88 (95% CI 1.35-6.15) at 120 months with a crossover at around 36 months. Similar patterns were also observed for FOXA1 > 285 of H-score and for progression free survival (PFS). Moreover, when allowed both FOXA1 and estrogen receptor (ER) to change over time in the model (considering that ER had a similar time-varying effect), these time-varying effects remained for FOXA1 on both overall survival (OS) (P < 0.01) and PFS (P = 0.01) but were attenuated for ER (P = 0.13 for OS).

CONCLUSIONS

This study revealed an independent time-varying effect of FOXA1 on breast cancer prognosis, which would provide an insight into the roles of FOXA1 as a marker of breast cancer prognosis and may help optimize the medication strategies.

ZEB1/miR-200c/AGR2: A New Regulatory Loop Modulating the Epithelial-Mesenchymal Transition in Lung Adenocarcinomas

Epithelial-mesenchymal transition (EMT) is a process involved not only in morphogenesis and embryonic development, but also in cancer progression, whereby tumor cells obtain a more aggressive metastatic phenotype. Anterior gradient protein 2 (AGR2) maintains the epithelial phenotype and blocks the induction of EMT, thus playing an undeniable role in tumor progression. However, the mechanism through which AGR2 expression is regulated, not only during EMT, but also in the early stages of cancer development, remains to be elucidated. In the present study, we show an inverse correlation of AGR2 with ZEB1 (zinc finger enhancer binding protein, δEF1) that was verified by analysis of several independent clinical data sets of lung adenocarcinomas. We also identified the ZEB1 binding site within the AGR2 promoter region and confirmed AGR2 as a novel molecular target of ZEB1. The overexpression of ZEB1 decreased the promoter activity of the AGR2 gene, which resulted in reduced AGR2 protein level and the acquisition of a more invasive phenotype of these lung cancer cells. Conversely, silencing of ZEB1 led not only to increased levels of AGR2 protein, but also attenuated the invasiveness of tumor cells. The AGR2 knockout, vice versa, increased ZEB1 expression, indicating that the ZEB1/AGR2 regulatory axis may function in a double negative feedback loop. In conclusion, we revealed for the first time that ZEB1 regulates AGR2 at the transcriptional level, while AGR2 presence contributes to ZEB1 mRNA degradation. Thus, our data identify a new regulatory mechanism between AGR2 and ZEB1, two rivals in the EMT process, tightly associated with the development of metastasis.

Functionally analyzing the important roles of hepatocyte nuclear factor 3 (FoxA) in tumorigenesis

Transcriptional factors (TFs) play a central role in governing gene expression under physiological conditions including the processes of embryonic development, metabolic homeostasis and response to extracellular stimuli. Conceivably, the aberrant dysregulations of TFs would dominantly result in various human disorders including tumorigenesis, diabetes and neurodegenerative diseases. Serving as the most evolutionarily reserved TFs, Fox family TFs have been explored to exert distinct biological functions in neoplastic development, by manipulating diverse gene expression. Recently, among the Fox family members, the pilot roles of FoxAs attract more attention due to their functions as both pioneer factor and transcriptional factor in human tumorigenesis, particularly in the sex-dimorphism tumors. Therefore, the pathological roles of FoxAs in tumorigenesis have been well-explored in modulating inflammation, immune response and metabolic homeostasis. In this review, we comprehensively summarize the impressive progression of FoxA functional annotation, clinical relevance, upstream regulators and downstream effectors, as well as valuable animal models, and highlight the potential strategies to target FoxAs for cancer therapies.

G1T48, an oral selective estrogen receptor degrader, and the CDK4/6 inhibitor lerociclib inhibit tumor growth in animal models of endocrine-resistant breast cancer

Purpose

The combination of targeting the CDK4/6 and estrogen receptor (ER) signaling pathways with palbociclib and fulvestrant is a proven therapeutic strategy for the treatment of ER-positive breast cancer. However, the poor physicochemical properties of fulvestrant require monthly intramuscular injections to patients, which limit the pharmacokinetic and pharmacodynamic activity of the compound. Therefore, an orally available compound that more rapidly reaches steady state may lead to a better clinical response in patients. Here, we report the identification of G1T48, a novel orally bioavailable, non-steroidal small molecule antagonist of ER.

Methods

The pharmacological effects and the antineoplastic mechanism of action of G1T48 on tumors was evaluated using human breast cancer cells (in vitro) and xenograft efficacy models (in vivo).

Results

G1T48 is a potent and efficacious inhibitor of estrogen-mediated transcription and proliferation in ER-positive breast cancer cells, similar to the pure antiestrogen fulvestrant. In addition, G1T48 can effectively suppress ER activity in multiple models of endocrine therapy resistance including those harboring ER mutations and growth factor activation. In vivo, G1T48 has robust antitumor activity in a model of estrogen-dependent breast cancer (MCF7) and significantly inhibited the growth of tamoxifen-resistant (TamR), long-term estrogen-deprived (LTED) and patient-derived xenograft tumors with an increased response being observed with the combination of G1T48 and the CDK4/6 inhibitor lerociclib.

Conclusions

These data show that G1T48 has the potential to be an efficacious oral antineoplastic agent in ER-positive breast cancer.

Electronic supplementary material

The online version of this article (10.1007/s10549-020-05575-9) contains supplementary material, which is available to authorized users.

Identification of key genes as potential biomarkers for triple‑negative breast cancer using integrating genomics analysis

Triple-negative breast cancer (TNBC) accounts for the worst prognosis of all types of breast cancers due to a high risk of recurrence and a lack of targeted therapeutic options. Extensive effort is required to identify novel targets for TNBC. In the present study, a robust rank aggregation (RRA) analysis based on genome-wide gene expression datasets involving TNBC patients from the Gene Expression Omnibus (GEO) database was performed to identify key genes associated with TNBC. A total of 194 highly ranked differentially expressed genes (DEGs) were identified in TNBC vs. non-TNBC. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) enrichment analysis was utilized to explore the biological functions of the identified genes. These DEGs were mainly involved in the biological processes termed positive regulation of transcription from RNA polymerase II promoter, negative regulation of apoptotic process, response to drug, response to estradiol and negative regulation of cell growth. Genes were mainly involved in the KEGG pathway termed estrogen signaling pathway. The aberrant expression of several randomly selected DEGs were further validated in cell lines, clinical tissues and The Cancer Genome Atlas (TCGA) cohort. Furthermore, all the top-ranked DEGs underwent survival analysis using TCGA database, of which overexpression of 4 genes (FABP7, ART3, CT83, and TTYH1) were positively correlated to the life expectancy (P<0.05) of TNBC patients. In addition, a model consisting of two genes (FABP7 and CT83) was identified to be significantly associated with the overall survival (OS) of TNBC patients by means of Cox regression, Kaplan-Meier, and receiver operating characteristic (ROC) analyses. In conclusion, the present study identified a number of key genes as potential biomarkers involved in TNBC, which provide novel insights into the tumorigenesis of TNBC at the gene level and may serve as independent prognostic factors for TNBC prognosis.

The Lineage Determining Factor GRHL2 Collaborates with FOXA1 to Establish a Targetable Pathway in Endocrine Therapy-Resistant Breast Cancer

Notwithstanding the positive clinical impact of endocrine therapies in estrogen receptor-alpha (ERα)-positive breast cancer, de novo and acquired resistance limits the therapeutic lifespan of existing drugs. Taking the position that resistance is nearly inevitable, we undertook a study to identify and exploit targetable vulnerabilities that were manifest in endocrine therapy-resistant disease. Using cellular and mouse models of endocrine therapy-sensitive and endocrine therapy-resistant breast cancer, together with contemporary discovery platforms, we identified a targetable pathway that is composed of the transcription factors FOXA1 and GRHL2, a coregulated target gene, the membrane receptor LYPD3, and the LYPD3 ligand, AGR2. Inhibition of the activity of this pathway using blocking antibodies directed against LYPD3 or AGR2 inhibits the growth of endocrine therapy-resistant tumors in mice, providing the rationale for near-term clinical development of humanized antibodies directed against these proteins.

Pharmacokinetic and pharmacodynamic analysis of fulvestrant in preclinical models of breast cancer to assess the importance of its estrogen receptor-α degrader activity in antitumor efficacy

Purpose

Fulvestrant is a selective estrogen receptor downregulator (SERD) that is approved for first- or second-line use as a single agent or in combination with cyclin dependent kinase or phosphatidylinositol 3-kinase inhibitors for the treatment of metastatic breast cancer. Fulvestrant exhibits exceptionally effective antitumor activity in preclinical models of breast cancer, a success that has been attributed to its robust SERD activity despite modest receptor downregulation in patient tumors. By modeling human exposures in animal models we probe the absolute need for SERD activity.

Methods

Three xenograft models of endocrine therapy-resistant breast cancer were used to evaluate the efficacy of fulvestrant administered in doses historically used in preclinical studies in the field or by using a dose regimen intended to model clinical exposure levels. Pharmacokinetic and pharmacodynamic analyses were conducted to evaluate plasma exposure and intratumoral ER downregulation.

Results

A clinically relevant 25 mg/kg dose of fulvestrant exhibited antitumor efficacy comparable to the historically used 200 mg/kg dose, but at this lower dose it did not result in robust ER downregulation. Further, the antitumor efficacy of the lower dose of fulvestrant was comparable to that observed for other oral SERDs currently in development.

Conclusion

The use of clinically unachievable exposure levels of fulvestrant as a benchmark in preclinical development of SERDs may negatively impact the selection of those molecules that are advanced for clinical development. Further, these studies suggest that antagonist efficacy, as opposed to SERD activity, is likely to be the primary driver of clinical response.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05454-y) contains supplementary material, which is available to authorized users.

The Central Contributions of Breast Cancer Stem Cells in Developing Resistance to Endocrine Therapy in Estrogen Receptor (ER)-Positive Breast Cancer

Breast cancer stem cells (BCSC) play critical roles in the acquisition of resistance to endocrine therapy in estrogen receptor (ER)-positive (ER + ve) breast cancer (BC). The resistance results from complex alterations involving ER, growth factor receptors, NOTCH, Wnt/β-catenin, hedgehog, YAP/TAZ, and the tumor microenvironment. These mechanisms are likely converged on regulating BCSCs, which then drive the development of endocrine therapy resistance. In this regard, hormone therapies enrich BCSCs in ER + ve BCs under both pre-clinical and clinical settings along with upregulation of the core components of “stemness” transcriptional factors including SOX2, NANOG, and OCT4. SOX2 initiates a set of reactions involving SOX9, Wnt, FXY3D, and Src tyrosine kinase; these reactions stimulate BCSCs and contribute to endocrine resistance. The central contributions of BCSCs to endocrine resistance regulated by complex mechanisms offer a unified strategy to counter the resistance. ER + ve BCs constitute approximately 75% of BCs to which hormone therapy is the major therapeutic approach. Likewise, resistance to endocrine therapy remains the major challenge in the management of patients with ER + ve BC. In this review we will discuss evidence supporting a central role of BCSCs in developing endocrine resistance and outline the strategy of targeting BCSCs to reduce hormone therapy resistance.

Robust identification of target genes and outliers in triple-negative breast cancer data

Correct classification of breast cancer subtypes is of high importance as it directly affects the therapeutic options. We focus on triple-negative breast cancer which has the worst prognosis among breast cancer types. Using cutting edge methods from the field of robust statistics, we analyze Breast Invasive Carcinoma transcriptomic data publicly available from The Cancer Genome Atlas data portal. Our analysis identifies statistical outliers that may correspond to misdiagnosed patients. Furthermore, it is illustrated that classical statistical methods may fail to identify outliers due to their heavy influence, prompting the need for robust statistics. Using robust sparse logistic regression we obtain 36 relevant genes, of which ca. 60% have been previously reported as biologically relevant to triple-negative breast cancer, reinforcing the validity of the method. The remaining 14 genes identified are new potential biomarkers for triple-negative breast cancer. Out of these, JAM3, SFT2D2, and PAPSS1 were previously associated to breast tumors or other types of cancer. The relevance of these genes is confirmed by the new DetectDeviatingCells outlier detection technique. A comparison of gene networks on the selected genes showed significant differences between triple-negative breast cancer and non-triple-negative breast cancer data. The individual role of FOXA1 in triple-negative breast cancer and non-triple-negative breast cancer, and the strong FOXA1-AGR2 connection in triple-negative breast cancer stand out. The goal of our paper is to contribute to the breast cancer/triple-negative breast cancer understanding and management. At the same time it demonstrates that robust regression and outlier detection constitute key strategies to cope with high-dimensional clinical data such as omics data.

Integrated molecular analysis of Tamoxifen-resistant invasive lobular breast cancer cells identifies MAPK and GRM/mGluR signaling as therapeutic vulnerabilities

Invasive lobular breast cancer (ILC) is an understudied malignancy with distinct clinical, pathological, and molecular features that distinguish it from the more common invasive ductal carcinoma (IDC). Mounting evidence suggests that estrogen receptor-alpha positive (ER+) ILC has a poor response to Tamoxifen (TAM), but the mechanistic drivers of this are undefined. In the current work, we comprehensively characterize the SUM44/LCCTam ILC cell model system through integrated analysis of gene expression, copy number, and mutation, with the goal of identifying actionable alterations relevant to clinical ILC that can be co-targeted along with ER to improve treatment outcomes. We show that TAM has several distinct effects on the transcriptome of LCCTam cells, that this resistant cell model has acquired copy number alterations and mutations that impinge on MAPK and metabotropic glutamate receptor (GRM/mGluR) signaling networks, and that pharmacological inhibition of either improves or restores the growth-inhibitory actions of endocrine therapy.

Strong and sustained activation of the anticipatory unfolded protein response induces necrotic cell death

The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor α (ERα) and induces death of ERα⁺ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP₃R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

Association of increased primary breast tumor AGR2 with decreased disease-specific survival

Objective

Tumor expression of Anterior Gradient 2 (AGR2), an endoplasmic reticulum protein disulfide isomerase, was associated with decreased breast cancer survival. We aimed to validate the association of tumor AGR2 mRNA expression with disease-specific survival (DSS) and identify differentially expressed signaling pathways between high and low AGR2 expression tumor groups.

Methods

Primary tumor mRNA expression data from the METABRIC study was used to evaluate AGR2 expression as a prognostic factor for DSS while adjusting for survival-determining confounders using Cox proportional-hazards regression. Differentially expressed genes and signaling pathway differences between high and low AGR2 groups were determined by modular enrichment analyses using DAVID and Ingenuity Pathway Analysis.

Results

Increased tumor AGR2 mRNA expression was associated with decreased DSS among 1,341 women (per each standard deviation increase of AGR2 expression: HR 1.14, 95% CI: 1.01-1.29, P = 0.03). Pathway analyses supported prior experimental studies showing that estrogen receptor 1 (ESR1) regulated AGR2 expression. Canonical signaling pathways significantly differentially represented between high and low AGR2 groups included those involved in inflammation and immunity.

Conclusion

Increased primary tumor AGR2 expression was associated with decreased DSS. Pathway analyses suggested that increased AGR2 was associated with endoplasmic reticular homeostasis, possibly allowing tumor cells to overcome hypoxic stress and meet the increased protein demand of tumorigenesis, thereby preventing unfolded protein response-mediated apoptosis.

Enhancer-Mediated Oncogenic Function of the Menin Tumor Suppressor in Breast Cancer

While the multiple endocrine neoplasia type 1 (MEN1) gene functions as a tumor suppressor in a variety of cancer types, we explored its oncogenic role in breast tumorigenesis. The MEN1 gene product menin is involved in H3K4 trimethylation and co-activates transcription. We integrated ChIP-seq and RNA-seq data to identify menin target genes. Our analysis revealed that menin-dependent target gene promoters display looping to distal enhancers that are bound by menin, FOXA1 and GATA3. In this fashion, MEN1 co-regulates a proliferative breast cancer-specific gene expression program in ER⁺ cells. In primary mammary cells, MEN1 exerts an anti-proliferative function by regulating a distinct expression signature. Our findings clarify the cell-type-specific functions of MEN1 and inform the development of menin-directed treatments for breast cancer.

Suppression of AGR2 in a TGF-β-induced Smad regulatory pathway mediates epithelial-mesenchymal transition

Background

During cancer progression, epithelial cancer cells can be reprogrammed into mesenchymal-like cells with increased migratory potential through the process of epithelial-mesenchymal transition (EMT), representing an essential step of tumor progression towards metastatic state. AGR2 protein was shown to regulate several cancer-associated processes including cellular proliferation, survival and drug resistance.

Methods

The expression of AGR2 was analyzed in cancer cell lines exposed to TGF-β alone or to combined treatment with TGF-β and the Erk1/2 inhibitor PD98059 or the TGF-β receptor specific inhibitor SB431542. The impact of AGR2 silencing by specific siRNAs or CRISPR/Cas9 technology on EMT was investigated by western blot analysis, quantitative PCR, immunofluorescence analysis, real-time invasion assay and adhesion assay.

Results

Induction of EMT was associated with decreased AGR2 along with changes in cellular morphology, actin reorganization, inhibition of E-cadherin and induction of the mesenchymal markers vimentin and N-cadherin in various cancer cell lines. Conversely, induction of AGR2 caused reversion of the mesenchymal phenotype back to the epithelial phenotype and re-acquisition of epithelial markers. Activated Smad and Erk signaling cascades were identified as mutually complementary pathways responsible for TGF-β-mediated inhibition of AGR2.

Conclusion

Taken together our results highlight a crucial role for AGR2 in maintaining the epithelial phenotype by preventing the activation of key factors involved in the process of EMT.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3537-5) contains supplementary material, which is available to authorized users.

Foxa2 and Hif1ab regulate maturation of intestinal goblet cells by modulating agr2 expression in zebrafish embryos

Mammalian anterior gradient 2 (AGR2), an endoplasmic reticulum (ER) protein disulfide-isomerase (PDI), is involved in cancer cell growth and metastasis, asthma and inflammatory bowel disease (IBD). Mice lacking Agr2 exhibit decreased Muc2 protein in intestinal goblet cells, abnormal Paneth cell development, ileitis and colitis. Despite its importance in cancer biology and inflammatory diseases, the mechanisms regulating agr2 expression in the gastrointestinal tract remain unclear. In the present study, we investigated the mechanisms that control agr2 expression in the pharynx and intestine of zebrafish by transient/stable transgenesis, coupled with motif mutation, morpholino knockdown, mRNA rescue and ChIP. A 350 bp DNA sequence with a hypoxia-inducible response element (HRE) and forkhead-response element (FHRE) within a region -4.5 to -4.2 kbp upstream of agr2 directed EGFP expression specifically in the pharynx and intestine. No EGFP expression was detected in the intestinal goblet cells of Tg(HREM:EGFP) or Tg(FHREM:EGFP) embryos with mutated HRE or FHRE, whereas EGFP was expressed in the pharynx of Tg(HREM:EGFP), but not Tg(FHREM:EGFP), embryos. Morpholino knockdown of foxa1 (forkhead box A1) reduced agr2 levels in the pharynx, whereas knockdown of foxa2 or hif1ab decreased intestinal agr2 expression and affected the differentiation and maturation of intestinal goblet cells. These results demonstrate that Foxa1 regulates agr2 expression in the pharynx, whereas both Foxa2 and Hif1ab control agr2 expression in intestinal goblet cells to regulate maturation of these cells.

FOXA1 expression affects the proliferation activity of luminal breast cancer stem cell populations

The expression of estrogen receptor is the key in most breast cancers (BC) and binding of estrogen receptor to the genome correlates to Forkhead protein (FOXA1) expression. We herein assessed the correlation between the cancer stem cell (CSC) population and FOXA1 expression in luminal BC. We established luminal BC cells derived from metastatic pleural effusion and analyzed the potency of CSC and related factors with established luminal BC cell lines. We also confirmed that mammosphere cultures have an increased aldehyde dehydrogenase‐positive population, which is one of the CSC markers, compared with adherent culture cells. Using a quantitative PCR analysis, we found that mammosphere forming cells showed a higher expression of FOXA1 and stemness‐related genes compared with adherent culture cells. Furthermore, the growth activity and colony‐forming activity of 4‐hydroxytamoxifen‐treated BC cells were inhibited in a mammosphere assay. Interestingly, 4‐hydroxytamoxifen‐resistant cells had significantly increased FOXA1 gene expression levels. Finally, we established short hairpin RNA of FOXA1 (shFOXA1) MCF‐7 cells and investigated the relationship between self‐renewal potential and FOXA1 expression. As a result, we found no significant difference in the number of mammospheres but decreased colony formation in shFOXA1 MCF‐7 cells compared with control. These results suggest that the expression of FOXA1 appears to be involved in the proliferation of immature BC cells rather than the induction of stemness‐related genes and self‐renewal potency of CSCs.

FOXO factors and breast cancer: outfoxing endocrine resistance

The majority of metastatic breast cancers cannot be cured and present a major public health problem worldwide. Approximately 70% of breast cancers express the estrogen receptor, and endocrine-based therapies have significantly improved patient outcomes. However, the development of endocrine resistance is extremely common. Understanding the molecular pathways that regulate the hormone sensitivity of breast cancer cells is important to improving the efficacy of endocrine therapy. It is becoming clearer that the PI3K-AKT-forkhead box O (FOXO) signaling axis is a key player in the hormone-independent growth of many breast cancers. Constitutive PI3K-AKT pathway activation, a driver of breast cancer growth, causes down-regulation of FOXO tumor suppressor functions. This review will summarize what is currently known about the role of FOXOs in endocrine-resistance mechanisms. It will also suggest potential therapeutic strategies for the restoration of normal FOXO transcriptional activity.

Detection of Endogenous Selective Estrogen Receptor Modulators such as 27-Hydroxycholesterol

The estrogen receptors (ERs) belong to the nuclear receptor superfamily, and as such act as ligand inducible transcription factors, mediating the effects of estrogens. However, their pharmacology is complex, having the ability to be differentially activated by ligands. Such ligands possess the ability to behave as either ER-agonists or ER-antagonists, depending on the cellular and tissue context, and have been termed Selective Estrogen Receptor Modulators (SERMs). Several SERMs have been identified with clinical relevance such as tamoxifen and raloxifene. Recently, 27-hydroxycholesterol has been characterized as the first identified endogenous SERM leading to the notion that other endogenous SERMs may exist, each having potential pathophysiological functions. This, coupled with the historic pharmaceutical interest as well as growing concern over chemicals in the environment with the ability to behave like SERMs, has increased the demand for assays to detect SERM-like activity. Here, we describe a common, straightforward in vitro assay investigating the induction of classic ER-target genes in MCF7 breast cancer cells, allowing one to identify ligands with SERM-like activity.

Benzyl isothiocyanate inhibits breast cancer cell tumorigenesis via repression of the FoxH1-Mediated Wnt/β-catenin pathway

The mechanisms underlying the growth inhibitory effect of Benzyl isothiocyanate (BITC) against breast cancer are still not fully understood. Therefore, we further investigated the mechanism in BITC triggering breast cancer. In the present study, we found that the overexpression of FOXH1 in breast cancers tissues and cells, and FOXH1 significantly promoted cell proliferation, invasion and tumorigenesis in vitro. FOXH1 significantly increased the expression levels of β-catenin, cyclinD1, and c-myc proteins in breast cancer cells. Furthermore, siβ-catenin reduced FOXH1 promotion of cell proliferation and invasion in breast cancer cells. Taken together, these results suggest that FOXH1 promoted breast cancer cell growth and invasion by potentiating the Wnt/β-catenin pathway, suggesting that FOXH1 may be a potential molecular target for breast cancer prevention and therapy. Furthermore, BITC treatment has remarkable effect on the expression level of FOXH1 and β-catenin mRNA and protein in MCF-7 cells, MDA-MB-231 cells and SUM 159 cells. BITC treatment has an obvious significance on transcriptional activity of FOXH1. Cell growth and invasion inhibition resulting from BITC exposure were significantly augmented by FoxH1 knockdown. In conclusion, the present study provides novel insights into the molecular circuitry of BITC-induced cell death involving FoxH1-mediated tumorigenesis. Thus, the present study provides a novel insight into the underlying mechanism of tumorigenesis in BITC triggering breast cancer, indicating the therapeutic potential of FOXH1 in the treatment of breast cancer.

TFAP2C expression in breast cancer: correlation with overall survival beyond 10 years of initial diagnosis

Recurrence and death in a significant number of patients with ERα-positive breast cancer occurs 10-20 years after diagnosis. Prognostic markers for late events have been more elusive. TFAP2C (AP2γ) regulates the expression of ERα, the ERα pioneer factors FOXA1 and GATA3, and controls ERα-dependent transcription. The purpose of this investigation is to determine the long-term prognostic value of TFAP2C. A tissue microarray (TMA) consisting of breast tumors from 451 patients with median follow-up time of 10.3 years was created and tested for the expression of TFAP2C by immunohistochemistry. Wilcoxon Rank-Sum and Kruskal-Wallis tests were used to determine if TFAP2C H-scores correlate with other tumor markers. Cox proportional hazards regression models were used to determine whether TFAP2C H-scores and other tumor markers were related to overall and disease-free survival in univariate and multivariable models. TFPAC2 overexpression did not impact overall survival during the first 10 years after diagnosis, but was associated with a shorter survival after 10 years (HR 3.40, 95 % CI 1.58, 7.30; p value = 0.002). This late divergence persisted in ER-positive (HR 2.86, 95 % CI 1.29, 6.36; p value = 0.01) and endocrine therapy-positive subgroups (HR 4.19, 95 % CI 1.72, 10.23; p value = 0.002). For the ER+ and endocrine therapy subgroup, the HR was 3.82 (95 % CI 1.53, 9.50; p value = 0.004). TFAP2C H-scores were not correlated with other tumor markers or related to disease-free survival. In this hypothesis-generating study, we show that higher TFAP2C scores correlate with poor overall survival after 10 years of diagnosis in ERα-positive and endocrine therapy-treated subgroups.

Induction of anterior gradient 2 (AGR2) plays a key role in insulin-like growth factor-1 (IGF-1)-induced breast cancer cell proliferation and migration

Anterior gradient 2 (AGR2) is a promising anti-tumor target associated with estrogen receptor expression and metastatic progression of breast cancer. Insulin-like growth factor-1 (IGF-1) is another potent factor that stimulates breast cancer progression and mediates anti-estrogen drug resistance. However, the precise mechanism and connections between these two factors in breast cancer drug resistance have not been fully elucidated. Here, for the first time, we decipher that IGF-1 remarkably induces AGR2 in the MCF7 cell line, through an estrogen response element (ERE) between −802 and −808 bp and a leucine zipper transcription factor-binding site located between −972 and −982 bp on the AGR2 promoter. We also found that the ERK1/2 and AKT pathways mediate estrogen receptor-α at the upstream of ERE and that the JNK pathway activates the leucine zipper site through the c-Jun/c-Fos complex. Additionally, our data suggest that knockdown of AGR2 reduces IGF-1-induced cell proliferation, migration and cell cycle progression. Therefore, we report that AGR2 is a key modulator involved in IGF-1-induced breast cancer development. We propose that the identification of the mechanism linking the IGF-1/insulin signal and AGR2 promoter activation is important, because it provides insights into the development of anti-breast cancer drugs.

Mechanisms of anterior gradient-2 regulation and function in cancer

Proteins targeted to secretory pathway enter the endoplasmic reticulum where they undergo post-translational modification and subsequent quality control executed by exquisite catalysts of protein folding, protein disulphide isomerases (PDIs). These enzymes can often provide strict conformational protein folding solutions to highly cysteine-rich cargo as they facilitate disulphide rearrangement in the endoplasmic reticulum. Under conditions when PDI substrates are not isomerised properly, secreted proteins can accumulate in the endoplasmic reticulum leading to endoplasmic reticulum stress initiation with implications for human disease development. Anterior Gradient-2 (AGR2) is an endoplasmic reticulum-resident PDI superfamily member that has emerged as a dominant effector of basic biological properties in vertebrates including blastoderm formation and limb regeneration. AGR2 perturbation in mammals influences disease processes including cancer progression and drug resistance, asthma, and inflammatory bowel disease. This review will focus on the molecular characteristics, function, and regulation of AGR2, views on its emerging biological functions and misappropriation in disease, and prospects for therapeutic intervention into endoplasmic reticulum-resident protein folding pathways for improving the treatment of human disease.

AGR2 regulates IFITM3 expression to promote hepatocellular carcinoma cell proliferation

AIM: To investigate the effect of anterior gradient homolog 2 (AGR2) expression on the proliferation of hepatocellular carcinoma cells, and to explore the possible mechanism.

METHODS: The expression of AGR2 and interferon-induced transmembrane protein 3 (IFITM3) in hepatocellular carcinoma and adjacent tissues was detected by fluorescence quantitative PCR and Western blot. The expression of AGR2 mRNA and protein was examined by real-time fluorescence quantitative PCR and Western blot after transfection with pcDNA3.1-AGR2. The cellular growth ability was examined by CCK-8 assay, and the colony formation ability was detected by colony formation assay. Flow cytometry assay was used to determine the apoptosis index. The expression level of IFITM3 protein was examined by Western blot.

RESULTS: AGR2 and IFITM3 mRNA and protein expression in hepatocellular carcinoma tissues was significantly higher than that in the corresponding adjacent tissues. The pcDNA3.1-AGR2 was successfully constructed, and HepG2 cells with stable expression of AGR2 were established. The expression levels of AGR2 mRNA and protein in HepG2 cells after transfection with pcDNA3.1-AGR2 were higher than those in the negative control cells, and the cellular growth ability of HepG2 cells after transfection with pcDNA3.1-AGR2 was significantly increased. IFITM3 protein expression was also increased after transfection with pcDNA3.1-AGR2.

CONCLUSION: Raised AGR2 expression can increase the expression of IFITM3 and promote the proliferation of hepatocellular cells.

The role of AGR2 and AGR3 in cancer: similar but not identical

In the past decades, highly related members of the protein disulphide isomerase family, anterior gradient protein AGR2 and AGR3, attracted researchers' attention due to their putative involvement in developmental processes and carcinogenesis. While AGR2 has been widely demonstrated as a metastasis-related protein whose elevated expression predicts worse patient outcome, little is known about AGR3's role in tumour biology. Thus, we aim to confront the issue of AGR3 function in physiology and pathology in the following review by comparing this protein with the better-described homologue AGR2. Relying on available data and in silico analyses, we show that AGR proteins are co-expressed or uncoupled in context-dependent manners in diverse carcinomas and healthy tissues. Further, we discuss plausible roles of both proteins in tumour-associated processes such as differentiation, proliferation, migration, invasion and metastasis. This work brings new hints and stimulates further thoughts on hitherto unresolved conundrum of anterior gradient protein function.