Deciphering the divergent roles of progestogens in breast cancer

Clinical Characteristics and Outcomes of Single Versus Double Hormone Receptor-Positive Breast Cancer in 2 Large Databases

PURPOSE

To identify biologic and outcome differences between double hormone receptor (HR)-positive (dHR⁺, estrogen receptor (ER)⁺/progesterone receptor [PgR⁺]) and single HR-positive (sHR⁺, either ER⁺/PgR^- or ER^-/PgR⁺) breast cancer; and to explore whether hormone therapy (HT) response in HER2-negative breast cancer correlates with HR status.

PATIENTS AND METHODS

This retrospective study was conducted by using 2 large breast cancer databases: the Surveillance, Epidemiology, and End Results (SEER) database and the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) clinical data set. Cox regression analysis was used to estimate overall survival (OS) and breast cancer-specific survival (BCSS) among sHR⁺ and dHR⁺ patients.

RESULTS

In the SEER database, dHR⁺ patients had significantly longer OS and BCSS than ER⁺/PgR^- patients in short-term follow-up (OS: hazard ratio = 0.620; 95% confidence interval [CI], 0.590, 0.652; P < .001; BCSS: hazard ratio = 0.493; 95% CI, 0.462, 0.526; P < .001). Meanwhile, ER^-/PgR⁺ patients had younger age, larger tumor size, and higher disease grade than dHR⁺ and ER⁺/PgR^- patients. In patients who received HT, dHR⁺ patients had a more favorable OS than ER⁺/PgR^- patients (hazard ratio = 0.789; 95% CI, 0.635, 0.982; P = .034), and ER^-/PgR⁺ patients had a worse OS than ER⁺/PgR^- patients at 10 years' follow-up (hazard ratio = 7.991; 95% CI, 1.053, 60.644; P = .044). However, these groups had similar outcomes over longer periods.

CONCLUSION

In HER2-negative breast cancer, sHR⁺ patients are associated with relatively worse characteristics and worse short-term outcomes than dHR⁺ patients. Additionally, the outcome of patients receiving HT may differ according to the HR status. However, further studies are needed to confirm these conclusions.

The genomic landscape of estrogen receptor α binding sites in mouse mammary gland

Estrogen receptor α (ERα) is the major driving transcription factor in the mammary gland development as well as breast cancer initiation and progression. However, the genomic landscape of ERα binding sites in the normal mouse mammary gland has not been completely elucidated. Here, we mapped genome-wide ERα binding events by chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) in the mouse mammary gland in response to estradiol. We identified 6237 high confidence ERα binding sites in two biological replicates and showed that many of these were located at distal enhancer regions. Furthermore, we discovered 3686 unique genes in the mouse genome that recruit ER in response to estradiol. Interrogation of ER-DNA binding sites in ER-positive luminal epithelial cells showed that the ERE, PAX2, SF1, and AP1 motifs were highly enriched at distal enhancer regions. In addition, comprehensive transcriptome analysis by RNA-seq revealed that 493 genes are differentially regulated by acute treatment with estradiol in the mouse mammary gland in vivo. Through integration of RNA-seq and ERα ChIP-seq data, we uncovered a novel ERα targetome in mouse mammary epithelial cells. Taken together, our study has identified the genomic landscape of ERα binding events in mouse mammary epithelial cells. Furthermore, our study also highlights the cis-regulatory elements and cofactors that are involved in estrogen signaling and may contribute to ductal elongation in the normal mouse mammary gland.

The levonorgestrel-releasing intrauterine device induces endometrial decidualisation in women on tamoxifen

There is conflicting literature on whether the levonorgestrel-releasing intrauterine system (LNG-IUS; Mirena^®) induces decidualisation in the tamoxifen-treated endometrium. The expression of the decidualisation marker IGFBP-1 was measured using immunohistochemistry in endometrial biopsies and in serum (using ELISA) of 20 postmenopausal women at the start of tamoxifen-treatment for breast cancer. Ten women were then fitted with LNG-IUS and the other ten received tamoxifen-treatment only and acted as controls. Samples were taken at baseline and after 12 months. At baseline, all endometrial samples were negative for IGFBP-1 and at 12 months, IGFBP-1 was only expressed in the endometria of women fitted with the LNG-IUS, confirming the observed histological features of decidualisation. By contrast, serum IGFBP-1 concentrations were increased by tamoxifen, but not in the group receiving LNG-IUS. In conclusion, tamoxifen induces a rise in serum IGFBP-1 suggesting a systemic, possibly hepatic effect, whilst LNG abrogates this in both the liver and endometrium. Impact statement What is already known on this subject? Previous reports of the use of LNG-IUS in women on tamoxifen have provided conflicting evidence as to whether the endometrium exhibited decidualisation or not. These reports were however based solely on histological examination and lacked supporting biochemical data. What do the results of this study add? After 12 months of treatment with LNG-IUS, the endometria of women on tamoxifen show histological features of decidualisation and the presence of the decidualisation marker IGFBP-1, suggesting that levonorgestrel protects the tamoxifen-treated uterus from additional pathology by causing decidualisation. Serum levels of IGFBP-1 were expected to be a reflection of uterine production, but contrary to expectations, higher levels were identified in women on tamoxifen alone. These data suggest that an inhibition of tamoxifen-induced serum IGFBP-1 production (possibly from a hepatic source) by LNG-IUS occurred and indicates independent systemic effects of both drugs in post menopausal breast cancer patients. What are the implications of these findings for clinical practice and/or further research? This research demonstrated a mechanism for endometrial protection in women on tamoxifen. It also alerts clinicians to the fact that both tamoxifen and LNG-IUS exert systemic effects in this patient group.

Progesterone Receptor Attenuates STAT1-Mediated IFN Signaling in Breast Cancer

Why some tumors remain indolent and others progress to clinical relevance remains a major unanswered question in cancer biology. IFN signaling in nascent tumors, mediated by STAT1, is a critical step through which the surveilling immune system can recognize and destroy developing tumors. In this study, we have identified an interaction between the progesterone receptor (PR) and STAT1 in breast cancer cells. This interaction inhibited efficient IFN-induced STAT1 phosphorylation, as we observed a decrease in phospho-STAT1 in response to IFN treatment in PR-positive breast cancer cell lines. This phenotype was further potentiated in the presence of PR ligand. In human breast cancer samples, PR-positive tumors exhibited lower levels of phospho-STAT1 as compared with their PR-negative counterparts, indicating that this phenotype translates to human tumors. Breast cancer cells lacking PR exhibited higher levels of IFN-stimulated gene (ISG) RNA, the transcriptional end point of IFN activation, indicating that unliganded PR alone could decrease transcription of ISGs. Moreover, the absence of PR led to increased recruitment of STAT1, STAT2, and IRF9 (key transcription factors necessary for ISG transcription) to ISG promoters. These data indicate that PR, both in the presence and absence of ligand, attenuates IFN-induced STAT1 signaling, culminating in significantly abrogated activation of genes transcribed in response to IFNs. PR-positive tumors may use downregulation of STAT1-mediated IFN signaling to escape immune surveillance, leading to the development of clinically relevant tumors. Selective immune evasion of PR-positive tumors may be one explanation as to why over 65% of breast cancers are PR positive at the time of diagnosis.

Ai-lncRNA EGOT enhancing autophagy sensitizes paclitaxel cytotoxicity via upregulation of ITPR1 expression by RNA-RNA and RNA-protein interactions in human cancer

BACKGROUND

The biology function of antisense intronic long noncoding RNA (Ai-lncRNA) is still unknown. Meanwhile, cancer patients with paclitaxel resistance have limited therapeutic options in the clinic. However, the potential involvement of Ai-lncRNA in paclitaxel sensitivity remains unclear in human cancer.

METHODS

Whole transcriptome sequencing of 33 breast specimens was performed to identify Ai-lncRNA EGOT. Next, the role of EGOT in regulation of paclitaxel sensitivity was investigated. Moreover, the mechanism of EGOT enhancing autophagy sensitizes paclitaxel cytotoxicity via upregulation of ITPR1 expression by RNA-RNA and RNA-protein interactions was investigated in detail. Furthermore, upstream transcriptional regulation of EGOT expression was also investigated by co-immunoprecipitation and chromatin immunoprecipitation. Finally, clinical breast specimens in our cohort, TCGA and ICGC were applied to validate the role of EGOT in enhancing of paclitaxel sensitivity.

RESULTS

EGOT enhances autophagosome accumulation via the up-regulation of ITPR1 expression, thereby sensitizing cells to paclitaxel toxicity. Mechanistically, on one hand, EGOT upregulates ITPR1 levels via formation of a pre-ITPR1/EGOT dsRNA that induces pre-ITPR1 accumulation to increase ITPR1 protein expression in cis. On the other hand, EGOT recruits hnRNPH1 to enhance the alternative splicing of pre-ITPR1 in trans via two binding motifs in EGOT segment 2 (324-645 nucleotides) in exon 1. Moreover, EGOT is transcriptionally regulated by stress conditions. Finally, EGOT expression enhances paclitaxel sensitivity via assessment of cancer specimens.

CONCLUSIONS

These findings broaden comprehensive understanding of the biology function of Ai-lncRNAs. Proper regulation of EGOT may be a novel synergistic strategy for enhancing paclitaxel sensitivity in cancer therapy.

LncRNA SNHG1 correlates with higher T stage and worse overall survival, and promotes cell proliferation while reduces cell apoptosis in breast cancer

Background

The aim of this study was to investigate the correlation of long non-coding RNA (lncRNA) small nucleolar RNA host gene 1 (SNHG1) with the prognosis in breast cancer patients, and its effect on breast cancer cell proliferation and apoptosis.

Methods

A total of 178 breast cancer patients were consecutively recruited, then tumor tissue and the paired adjacent tissue were obtained during surgery for lncRNA SNHG1 determination by quantitative polymerase chain reaction (qPCR). LncRNA SNHG1 expression was also measured in breast cancer cell lines and normal breast epithelial cell line. Subsequently, negative control (NC) overexpression plasmids, lncRNA SNHG1 overexpression plasmids, NC short hairpin RNA (shRNA) plasmids and lncRNA SNHG1 shRNA plasmids were transfected into MDA-MB-453 cells as well as MCF7 cells, and cell proliferation and apoptosis were measured afterward.

Results

LncRNA SNHG1 expression in tumor tissue was increased compared with paired adjacent tissue, and it correlated with higher T stage and worse overall survival (OS) in breast cancer patients. LncRNA SNHG1 expression was also elevated in breast cancer cell lines compared with normal breast epithelial cell line. Cell Counting Kit-8 (CCK8) assay revealed that lncRNA SNHG1 overexpression promoted while lncRNA SNHG1 shRNA reduced cell proliferation, and Annexin V-fluorescein isothiocyanate/propidium iodide staining (AV/PI) assay illustrated that lncRNA SNHG1 overexpression decreased while lncRNA SNHG1 shRNA increased cell apoptosis rate. In addition, Western Blot assay disclosed that lncRNA SNHG1 overexpression downregulated while lncRNA SNHG1 shRNA upregulated pro-apoptotic marker (C-Caspase3) expression, and lncRNA SNHG1 overexpression increased while lncRNA SNHG1 shRNA decreased anti-apoptotic marker (p-P38) expression.

Conclusions

LncRNA SNHG1 is upregulated in tumor tissue and correlates with higher T stage and worse OS, and it promotes cell proliferation but inhibits cell apoptosis in breast cancer.

Estrogen Signaling in Endometrial Cancer: a Key Oncogenic Pathway with Several Open Questions

Endometrial cancer is the most common gynecological cancer in the developed world, and it is one of the few cancer types that is becoming more prevalent and leading to more deaths in the USA each year. The majority of endometrial tumors are considered to be hormonally driven, where estrogen signaling through estrogen receptor α (ER) acts as an oncogenic signal. The major risk factors and some treatment options for endometrial cancer patients emphasize a key role for estrogen signaling in the disease. Despite the strong connections between estrogen signaling and endometrial cancer, important molecular aspects of ER function remain poorly understood; however, progress is being made in our understanding of estrogen signaling in endometrial cancer. Here, we discuss the evidence for the importance of estrogen signaling in endometrial cancer, details of the endometrial cancer-specific actions of ER, and open questions surrounding estrogen signaling in endometrial cancer.

The evolving role of receptors as predictive biomarkers for metastatic breast cancer

INTRODUCTION

In breast cancer, estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) are essential biomarkers to predict response to endocrine and anti-HER2 therapies, respectively. In metastatic breast cancer, the use of these receptors and targeted therapies present additional challenges: temporal heterogeneity, together with limited sampling methodologies, hinders receptor status assessment, and the constant evolution of the disease invariably leads to resistance to treatment. Areas covered: This review summarizes the genomic abnormalities in ER and HER2, such as mutations, amplifications, translocations, and alternative splicing, emerging as novel biomarkers that provide an insight into underlying mechanisms of resistance and hold potential predictive value to inform treatment selection. We also describe how liquid biopsies for sampling of circulating markers and ultrasensitive detection technologies have emerged which complement ongoing efforts for biomarker discovery and analysis. Expert commentary: While evidence suggests that genomic aberrations in ER and HER2 could contribute to meeting the pressing need for better predictive biomarkers, efforts need to be made to standardize assessment methods and better understand the resistance mechanisms these markers denote. Taking advantage of emerging technologies, research in upcoming years should include prospective trials incorporating these predictors into the study design to validate their potential clinical value.

Improved relapse-free survival on aromatase inhibitors in breast cancer is associated with interaction between oestrogen receptor-α and progesterone receptor-b

BACKGROUND

Recent pre-clinical studies indicate that activated progesterone receptor (PR) (particularly the PR-B isoform) binds to oestrogen receptor-α (ER) and reprogrammes transcription toward better breast cancer outcomes. We investigated whether ER and PR-B interactions were present in breast tumours and associated with clinical parameters including response to aromatase inhibitors.

METHODS

We developed a proximity ligation assay to detect ER and PR-B (ER:PR-B) interactions in formalin-fixed paraffin-embedded tissues. The assay was validated in a cell line and patient-derived breast cancer explants and applied to a cohort of 229 patients with ER-positive and HER2-negative breast cancer with axillary nodal disease.

RESULTS

Higher frequency of ER:PR-B interaction correlated with increasing patient age, lower tumour grade and mitotic index. A low frequency of ER:PR-B interaction was associated with higher risk of relapse. In multivariate analysis, ER:PR-B interaction frequency was an independent predictive factor for relapse, whereas PR expression was not. In subset analysis, low frequency of ER:PR-B interaction was predictive of relapse on adjuvant aromatase inhibitor (HR 4.831, p = 0.001), but not on tamoxifen (HR 1.043, p = 0.939).

CONCLUSIONS

This study demonstrates that ER:PR-B interactions have utility in predicting patient response to adjuvant AI therapy.

Hypoxia-Inducible Factor 1α Regulates the Transforming Growth Factor β1/SMAD Family Member 3 Pathway to Promote Breast Cancer Progression

Purpose

The transforming growth factor β1 (TGF-β1)/SMAD family member 3 (SMAD3) pathway, and hypoxia-inducible factor 1α (HIF-1α) are two key players in various types of malignancies including breast cancer. The TGF-β1/SMAD3 pathway can interact with HIF-1α in some diseases; however, their interaction in breast cancer is still unknown. Therefore, our study aimed to investigate the interactions between the TGF-β1/SMAD3 pathway and HIF-1α in breast cancer.

Methods

Expression of HIF-1α in serum of breast cancer patients and healthy controls was detected by quantitative reverse transcription polymerase chain reaction, and the diagnostic value of HIF-1α for breast cancer was evaluated by receiver operating characteristic curve analysis. Breast cancer cell lines overexpressing SMAD3 and HIF-1α were established. Cell apoptosis and proliferation following different treatments were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, and cell counting kit-8, respectively. Expression of related proteins was detected by western blot.

Results

Serum levels of HIF-1α were higher in breast cancer patients than in normal controls. Both SMAD3 and HIF-1α overexpression inhibited cell apoptosis and promoted cell proliferation. Treatment with inhibitors of HIF-1α and SMAD3 promoted apoptosis in breast cancer cells and inhibited their proliferation. Overexpression of HIF-1α promoted the expression of TGF-β1 and SMAD3, while SMAD3 overexpression did not significantly affect expression of HIF-1α or TGF-β1.

Conclusion

HIF-1α serves as an upstream regulator of the TGF-β1/SMAD3 pathway and promotes the growth of breast cancer.

Hypoxia-Inducible Factor 1α Regulates the Transforming Growth Factor β1/SMAD Family Member 3 Pathway to Promote Breast Cancer Progression

Purpose

The transforming growth factor β1 (TGF-β1)/SMAD family member 3 (SMAD3) pathway, and hypoxia-inducible factor 1α (HIF-1α) are two key players in various types of malignancies including breast cancer. The TGF-β1/SMAD3 pathway can interact with HIF-1α in some diseases; however, their interaction in breast cancer is still unknown. Therefore, our study aimed to investigate the interactions between the TGF-β1/SMAD3 pathway and HIF-1α in breast cancer.

Methods

Expression of HIF-1α in serum of breast cancer patients and healthy controls was detected by quantitative reverse transcription polymerase chain reaction, and the diagnostic value of HIF-1α for breast cancer was evaluated by receiver operating characteristic curve analysis. Breast cancer cell lines overexpressing SMAD3 and HIF-1α were established. Cell apoptosis and proliferation following different treatments were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, and cell counting kit-8, respectively. Expression of related proteins was detected by western blot.

Results

Serum levels of HIF-1α were higher in breast cancer patients than in normal controls. Both SMAD3 and HIF-1α overexpression inhibited cell apoptosis and promoted cell proliferation. Treatment with inhibitors of HIF-1α and SMAD3 promoted apoptosis in breast cancer cells and inhibited their proliferation. Overexpression of HIF-1α promoted the expression of TGF-β1 and SMAD3, while SMAD3 overexpression did not significantly affect expression of HIF-1α or TGF-β1.

Conclusion

HIF-1α serves as an upstream regulator of the TGF-β1/SMAD3 pathway and promotes the growth of breast cancer.

Signaling pathways and steroid receptors modulating estrogen receptor α function in breast cancer

Estrogen receptor α (ER) is the major driver of ∼75% of breast cancers, and multiple ER targeting drugs are routinely used clinically to treat patients with ER+ breast cancer. However, many patients relapse on these targeted therapies and ultimately develop metastatic and incurable disease, and understanding the mechanisms leading to drug resistance is consequently of utmost importance. It is now clear that, in addition to estrogens, ER function is modulated by other steroid receptors and multiple signaling pathways (e.g., growth factor and cytokine signaling), and many of these pathways affect drug resistance and patient outcome. Here, we review the mechanisms through which these pathways impact ER function and drug resistance as well as discuss the clinical implications.

Biological and clinical impact of imbalanced progesterone receptor isoform ratios in breast cancer

There is a consensus that progestins and thus their cognate receptor molecules, the progesterone receptors (PR), are essential in the development of the adult mammary gland and regulators of proliferation and lactation. However, a role for natural progestins in breast carcinogenesis remains poorly understood. A hint to that possible role came from studies in which the synthetic progestin medroxyprogesterone acetate was associated with an increased breast cancer risk in women under hormone replacement therapy. However, progestins have been also used for breast cancer treatment and to inhibit the growth of several experimental breast cancer models. More recently, PR have been shown to be regulators of estrogen receptor signaling. With all this information, the question is how can we target PR, and if so, which patients may benefit from such an approach? PR are not single unique molecules. Two main PR isoforms have been characterized, PRA and PRB, that exert different functions and the relative abundance of one isoform respect to the other determines the response of PR agonists and antagonists. Immunohistochemistry with standard antibodies against PR do not discriminate between isoforms. In this review, we summarize the current knowledge on the expression of both PR isoforms in mammary glands, in experimental models of breast cancer and in breast cancer patients, to better understand how the PRA/PRB ratio can be exploited therapeutically to design personalized therapeutic strategies.

BRCA1-associated mammary tumorigenesis is dependent on estrogen rather than progesterone signaling

Hereditary breast cancers in BRCA1 mutation carriers are mostly estrogen receptor α (ERα)-negative and progesterone receptor (PR)-negative; however, hormone depletion via bilateral oophorectomy does result in a marked reduction in breast cancer risk, suggesting that BRCA1-associated breast tumorigenesis is dependent on hormone signaling. We used geneticaly engineered mouse models to determine the individual influences of ERα and PR signaling on the development of BRCA1-deficient breast cancer. In line with the human data, BRCA1-deficient mouse mammary tumors are ERα-negative, and bilateral ovariectomy leads to abrogation of mammary tumor development. Hormonal replacement experiments in ovariectomized mice showed that BRCA1-deficient mammary tumor formation is promoted by estrogen but not by progesterone. In line with these data, mammary tumorigenesis was significantly delayed by the selective ERα downregulator fulvestrant, but not by the selective PR antagonist Org33628. Together, our results illustrate that BRCA1-associated tumorigenesis is dependent on estrogen signaling rather than on progesterone signaling, and call into question the utility of PR antagonists as a tumor prevention strategy for BRCA1 mutation carriers. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Flavonoid Apigenin Is a Progesterone Receptor Modulator with In Vivo Activity in the Uterus

Apigenin is a flavonoid with well-documented anti-cancer properties; however, its mechanisms of action are still unclear. We previously identified apigenin as a potential phytoprogestin, a natural product with a chemical scaffold that interacts with the progesterone receptor (PR). Our objective was to characterize the ability of apigenin to interact with PR through molecular docking studies, in vitro activity assays, and the ability of apigenin to elicit progestin-like effects in vivo. Molecular docking confirmed that apigenin could interact with PR, though with lower affinity than progesterone due to fewer van der Waals interactions. In Ishikawa cells stably expressing PR-B, apigenin significantly increased progesterone response element/luciferase (PRE/Luc) activity at 5 and 10 μM, but not in the parental Ishikawa cells that lack PR expression. In the presence of 100 nM of progesterone, 10 μM apigenin reduced PRE/Luc activity, indicative of mixed agonist activity. Apigenin also triggered degradation of PR in Ishikawa PR-B cells as measured by western blot. Apigenin reduced proliferation of Ishikawa cells, but through a PR-independent mechanism. In contrast, apigenin and progesterone both stimulated proliferation of T47D cells, an effect blocked by RU486. Apigenin activated other nuclear receptors evidenced by increased luciferase activity in MDA-MB-231 cells, which are PR negative. In vivo, apigenin blocked the genistein-stimulated increase in uterine epithelial cell height; stimulated endometrial expression of Hand2, a transcription factor stimulated by PR, and significantly reduced genistein-induced proliferation. In summary, apigenin is a phytoprogestin, with mixed agonist activity that demonstrates activity in vivo by hindering estrogen receptor-mediated uterine proliferation.

Steroid metabolism in breast cancer: Where are we and what are we missing?

It is well-known that breast cancer is hormone-dependent and that steroid hormones exert their mitogenic effects by binding to estrogen, progesterone and androgen receptors. Vital to our understanding and treatment of this malignancy, is the local metabolism of steroid hormones in breast cancer tissue. This review summarises our current knowledge on steroid producing pathways in the adrenal, ovary and breast, while focussing on the availability of specific circulating hormone precursors and steroidogenic enzymes involved in the local synthesis and metabolism of steroid hormones in the breast. Consequently, we highlight alternate pathways that may be instrumental in the etiology of breast cancer.

Extranuclear signaling by sex steroid receptors and clinical implications in breast cancer

Estrogen and progesterone play essential roles in the development and progression of breast cancer. Over 70% of breast cancers express estrogen receptors (ER) and progesterone receptors (PR), emphasizing the need for better understanding of ER and PR signaling. ER and PR are traditionally viewed as transcription factors that directly bind DNA to regulate gene networks. In addition to nuclear signaling, ER and PR mediate hormone-induced, rapid extranuclear signaling at the cell membrane or in the cytoplasm which triggers downstream signaling to regulate rapid or extended cellular responses. Specialized membrane and cytoplasmic proteins may also initiate hormone-induced extranuclear signaling. Rapid extranuclear signaling converges with its nuclear counterpart to amplify ER/PR transcription and specify gene regulatory networks. This review summarizes current understanding and updates on ER and PR extranuclear signaling. Further investigation of ER/PR extranuclear signaling may lead to development of novel targeted therapeutics for breast cancer management.

BCL11B Drives Human Mammary Stem Cell Self-Renewal In Vitro by Inhibiting Basal Differentiation

The epithelial compartment of the mammary gland contains basal and luminal cell lineages, as well as stem and progenitor cells that reside upstream in the differentiation hierarchy. Stem and progenitor cell differentiation is regulated to maintain adult tissue and mediate expansion during pregnancy and lactation. The genetic factors that regulate the transition of cells between differentiation states remain incompletely understood. Here, we present a genome-scale method to discover genes driving cell-state specification. Applying this method, we identify a transcription factor, BCL11B, which drives stem cell self-renewal in vitro, by inhibiting differentiation into the basal lineage. To validate BCL11B's functional role, we use two-dimensional colony-forming and three-dimensional tissue differentiation assays to assess the lineage differentiation potential and functional abilities of primary human mammary cells. These findings show that BCL11B regulates mammary cell differentiation and demonstrate the utility of our proposed genome-scale strategy for identifying lineage regulators in mammalian tissues.

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Novel strategy to identify lineage-specifying genes

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BCL11B drives primary human mammary stem cell self-renewal in vitro

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BCL11B inhibits basal differentiation of mammary stem cells in vitro

Progestin-only and combined oral contraceptives and receptor-defined premenopausal breast cancer risk: The Norwegian Women and Cancer Study

Receptor-defined subtypes of breast cancer represent distinct cancer types and have differences in risk factors. Whether the two main hormonal forms of oral contraceptives (OCs); i.e. progestin-only (POC) and combined oral contraceptives (COC), are differentially associated with these subtypes are not well known. The aim of our study was to assess the effect of POC and COC use on hormone receptor-defined breast cancer risk in premenopausal women in a prospective population-based cohort - The Norwegian Women and Cancer Study (NOWAC). Information on OC use was collected from 74,862 premenopausal women at baseline. Updated information was applied when follow-up information became available. Multiple imputation was performed to handle missing data, and multivariable Cox regression models were used to calculate hazard ratios (HR) for breast cancer. 1,245 incident invasive breast cancer cases occurred. POC use ≥5 years was associated with ER+ (HR = 1.59, 95% CI 1.09- 2.32, p_trend  = 0.03) and ER+/PR+ cancer (HR = 1.63, 95% CI 1.07-2.48, p_trend  = 0.05), and was not associated with ER- (p_{heterogeneity}  = 0.36) or ER-/PR- (p_{heterogeneity}  = 0.49) cancer. COC use was associated with ER- and ER-/PR- cancer, but did not increase risk of ER+ and ER+/PR+ cancer. Current COC use gave different estimates for ER/PR-defined subtypes (p_{heterogeneity}  = 0.04). This is the first study to show significant associations between POC use and hormone receptor-positive breast cancer. The lack of power to distinguish effects of POC use on subtype development calls for the need of larger studies to confirm our finding.

Progesterone receptor isoforms, agonists and antagonists differentially reprogram estrogen signaling

Major roadblocks to developing effective progesterone receptor (PR)-targeted therapies in breast cancer include the lack of highly-specific PR modulators, a poor understanding of the pro- or anti-tumorigenic networks for PR isoforms and ligands, and an incomplete understanding of the cross talk between PR and estrogen receptor (ER) signaling. Through genomic analyses of xenografts treated with various clinically-relevant ER and PR-targeting drugs, we describe how the activation or inhibition of PR differentially reprograms estrogen signaling, resulting in the segregation of transcriptomes into separate PR agonist and antagonist-mediated groups. These findings address an ongoing controversy regarding the clinical utility of PR agonists and antagonists, alone or in combination with tamoxifen, for breast cancer management. Additionally, the two PR isoforms PRA and PRB, bind distinct but overlapping genomic sites and interact with different sets of co-regulators to differentially modulate estrogen signaling to be either pro- or anti-tumorigenic. Of the two isoforms, PRA inhibited gene expression and ER chromatin binding significantly more than PRB. Differential gene expression was observed in PRA and PRB-rich patient tumors and PRA-rich gene signatures had poorer survival outcomes. In support of antiprogestin responsiveness of PRA-rich tumors, gene signatures associated with PR antagonists, but not PR agonists, predicted better survival outcomes. The better patient survival associated with PR antagonists versus PR agonists treatments was further reflected in the higher in vivo anti-tumor activity of therapies that combine tamoxifen with PR antagonists and modulators. This study suggests that distinguishing common effects observed due to concomitant interaction of another receptor with its ligand (agonist or antagonist), from unique isoform and ligand-specific effects will inform the development of biomarkers for patient selection and translation of PR-targeted therapies to the clinic.

Gene Expression Assays for Early-Stage Hormone Receptor-Positive Breast Cancer: Understanding the Differences

Biomarkers are frequently used to guide decisions for treatment of early-stage estrogen (ER) and progesterone (PR) receptor–positive (ER/PR+) invasive breast cancers and have been incorporated into guidelines. The American Society of Clinical Oncology (ASCO) 2016 guideline and a 2017 update were recently published to help clinicians use the tests available. ASCO currently recommends five tests that show evidence of clinical utility based on the parameters defined in the guideline. These include the 21-gene assay (Oncotype DX), Prediction of Analysis of Microarray-50 (PAM50), 12-gene risk score (Endopredict), Breast Cancer Index (BCI), and, most recently, the 70-gene assay (Mammaprint). However, discordance is often seen when the results of these gene assays are compared in a particular patient, for a number of reasons: the assays were initially developed to answer different questions, and the molecular makeup of each signature reflects this; the patient populations that were studied also differed and may not reflect the patient being tested; furthermore, the study design and statistical analysis varied between each test, leading to different scoring scales that may not be comparable. In this review, the background on the development and validation of these assays is discussed, and studies comparing them are reviewed. To provide guidance on which test to choose, the studies that support the level of evidence for clinical utility are presented. However, the choice of a particular test will also be influenced by socioeconomic factors, clinical factors, and patient preferences. We hope that a better understanding of the scientific and clinical rationale for each test will allow patients and providers to make optimal decisions for treatment of early-stage ER/PR+ breast cancer.

O-GlcNAcylation in women's cancers: breast, endometrial and ovarian

O-GlcNAcylation is emerging as a critical regulatory post-translational modification, impacting proteins that regulate cell division, apoptosis, metabolism, cell signaling, and transcription. O-GlcNAc also affects biological homeostasis by integrating information coming from the environment, such as nutrient conditions and extracellular stimuli, with cellular response. Aberrant O-GlcNAc modulation has been linked to metabolic and neurodegenerative diseases, as well as cancers. While many studies have highlighted the significance of O-GlcNAc in cancer, a specific function for O-GlcNAc during tumorigenesis remains unclear and seems to differ according to cancer type. Herein, we review the impact of altered O-GlcNAcylation in breast, ovarian and uterine cancers.

Proof of region-specific multipotent progenitors in human breast epithelia

We have devised a culture system with conditions that allow primary breast myoepithelial cells (MEPs) to be passaged in a manner that sustains either nonmyodifferentiated or myodifferentiated cell populations without permitting contaminating luminal cells to grow. We show that progenitor activity and potency of MEPs to generate luminal cells in culture and in vivo rely on maintenance of myodifferentiation. Specific isolation and propagation of topographically distinct MEPs reveal the existence of multipotent progenitors in terminal duct lobular units. These findings have important implications for our understanding of the emergence of candidate luminal precursor cells to human breast cancer.

The human breast parenchyma consists of collecting ducts and terminal duct lobular units (TDLUs). The TDLU is the site of origin of most breast cancers. The reason for such focal susceptibility to cancer remains poorly understood. Here, we take advantage of a region-specific heterogeneity in luminal progenitors to interrogate the differentiation repertoire of candidate stem cells in TDLUs. We show that stem-like activity in serial passage culture and in vivo breast morphogenesis relies on the preservation of a myoepithelial phenotype. By enrichment for region-specific progenitors, we identify bipotent and multipotent progenitors in ducts and TDLUs, respectively. We propose that focal breast cancer susceptibility, at least in part, originates from region-specific myoepithelial progenitors.

Discovery of 1-(3-aryl-4-chlorophenyl)-3-(p-aryl)urea derivatives against breast cancer by inhibiting PI3K/Akt/mTOR and Hedgehog signalings

PI3K/Akt/mTOR and hedgehog (Hh) signalings are two important pathways in breast cancer, which are usually connected with the drug resistance and cancer migration. Many studies indicated that PI3K/Akt/mTOR inhibitors and Hh inhibitors displayed synergistic effects, and the combination of the two signaling drugs could delay drug resistance and inhibit cancer migration in breast cancer. Therefore, the development of molecules simultaneously inhibiting these two pathways is urgent needed. Based on the structures of PI3K inhibitor buparlisib and Hh inhibitor vismodegib, a series of hybrid structures were designed and synthesized utilizing rational drug design and computer-based drug design. Several compounds displayed excellent antiproliferative activities against several breast cancer cell lines, including triple-negative breast cancer (TNBC) MDA-MB-231 cell. Further mechanistic studies demonstrated that the representative compound 9i could inhibit both PI3K/Akt/mTOR and hedgehog (Hh) signalings by inhibiting the phosphorylation of S6K and Akt as well as decreasing the SAG elevated expression of Gli1. Compound 9i could also induce apoptosis remarkably in T47D and MDA-MB-231 cells. In the transwell assay, 9i showed significant inhibition on the migration of MDA-MB-231.

O-GlcNAc-Dependent Regulation of Progesterone Receptor Function in Breast Cancer

Emerging clinical trial data implicate progestins in the development of breast cancer. While the role for the progesterone receptor (PR) in this process remains controversial, it is clear that PR, a steroid-activated nuclear receptor, alters the transcriptional landscape of breast cancer. PR interacts with many different types of proteins, including transcriptional co-activators and co-repressors, transcription factors, nuclear receptors, and proteins that post-translationally modify PR (i.e., kinases and phosphatases). Herein, we identify a novel interaction between PR and O-GlcNAc transferase (OGT), the enzyme that catalyzes the addition of a single N-acetylglucosamine sugar, referred to as O-GlcNAc, to acceptor serines and threonines in target proteins. This interaction between PR and OGT leads to the post-translational modification of PR by O-GlcNAc. Moreover, we show that O-GlcNAcylated PR is more transcriptionally active on PR-target genes, despite the observation that PR messenger RNA and protein levels are decreased when O-GlcNAc levels are high. O-GlcNAcylation in breast cancer is clinically relevant, as we show that O-GlcNAc levels are higher in breast cancer as compared to matched normal tissues, and PR-positive breast cancers have higher levels of OGT. These data predict that under conditions where O-GlcNAc levels are high (breast cancer), PR, through an interaction with the modifying enzyme OGT, will exhibit increased O-GlcNAcylation and potentiated transcriptional activity. Therapeutic strategies aimed at altering cellular O-GlcNAc levels may have profound effects on PR transcriptional activity in breast cancer.

CHST9 rs1436904 genetic variant contributes to prognosis of triple-negative breast cancer

Triple-negative breast cancer (TNBC) refers to one aggressive histological subtype of breast cancer with high heterogeneity and poor prognosis after standard therapy. Lack of clearly established molecular mechanism driving TNBC progression makes personalized therapy more difficult. Thus, identification of genetic variants associated with TNBC prognosis will show clinic significance for individualized treatments. Our study is aimed to evaluate the prognostic value of the genome wide association study (GWAS)-identified CHST9 rs1436904 and AQP4 rs527616 genetic variants in our established early-stage TNBC sample database. Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). CHST9 rs1436904G allele was significantly associated with decreased disease-free survival time (DFS) (8.5 months shorter in GG genotype carriers compared to TT genotype carriers, HR = 1.70, 95% CI = 1.03–2.81, P = 0.038). Stratified analyses showed an increased risk of cancer progression in CHST9 rs1436904G allele carriers harboring larger tumor (tumor size > 2 cm), without lymph-node metastasis, being premenopausal at diagnosis or with vascular invasion (P = 0.032, 0.017, 0.008 or 0.003). Our findings demonstrate that the GWAS-identified 18q11.2 CHST9 rs1436904 polymorphism significantly contributes to prognosis of early-stage TNBC, suggesting its clinical potential in the screening of high-risk TNBC patients for recurrence and the possibility of patient-tailored therapeutic decisions.

Breast Cancer Suppression by Progesterone Receptors Is Mediated by Their Modulation of Estrogen Receptors and RNA Polymerase III

Greater than 50% of estrogen receptor (ER)-positive breast cancers coexpress the progesterone receptor (PR), which can directly and globally modify ER action to attenuate tumor growth. However, whether this attenuation is mediated only through PR-ER interaction remains unknown. To address this question, we assessed tumor growth in ER/PR-positive patient-derived xenograft models of breast cancer, where both natural and synthetic progestins were found to antagonize the mitogenic effects of estrogens. Probing the genome-wide mechanisms by which this occurs, we documented that chronic progestin treatment blunted ER-mediated gene expression up to 2-fold at the level of mRNA transcripts. Unexpectedly, <25% of all ER DNA binding events were affected by the same treatment. The PR cistrome displayed a bimodal distribution. In one group, >50% of PR binding sites were co-occupied by ER, with a propensity for both receptors to coordinately gain or lose binding in the presence of progesterone. In the second group, PR but not ER was associated with a large fraction of RNA polymerase III-transcribed tRNA genes, independent of hormone treatment. Notably, we discovered that PR physically associated with the Pol III holoenzyme. Select pre-tRNAs and mature tRNAs with PR and POLR3A colocalized at their promoters were relatively decreased in estrogen + progestin-treated tumors. Our results illuminate how PR may indirectly impede ER action by reducing the bioavailability of translational molecules needed for tumor growth. Cancer Res; 77(18); 4934-46. ©2017 AACR.

Interferon-Stimulated Genes Are Transcriptionally Repressed by PR in Breast Cancer

The progesterone receptor (PR) regulates transcriptional programs that drive proliferation, survival, and stem cell phenotypes. Although the role of native progesterone in the development of breast cancer remains controversial, PR clearly alters the transcriptome in breast tumors. This study identifies a class of genes, Interferon (IFN)-stimulated genes (ISGs), potently downregulated by ligand-activated PR which have not been previously shown to be regulated by PR. Progestin-dependent transcriptional repression of ISGs was observed in breast cancer cell line models and human breast tumors. Ligand-independent regulation of ISGs was also observed, as basal transcript levels were markedly higher in cells with PR knockdown. PR repressed ISG transcription in response to IFN treatment, the canonical mechanism through which these genes are activated. Liganded PR is robustly recruited to enhancer regions of ISGs, and ISG transcriptional repression is dependent upon PR's ability to bind DNA. In response to PR activation, key regulatory transcription factors that are required for IFN-activated ISG transcription, STAT2 and IRF9, exhibit impaired recruitment to ISG promoter regions, correlating with PR/ligand-dependent ISG transcriptional repression. IFN activation is a critical early step in nascent tumor recognition and destruction through immunosurveillance. As the large majority of breast tumors are PR positive at the time of diagnosis, PR-dependent downregulation of IFN signaling may be a mechanism through which early PR-positive breast tumors evade the immune system and develop into clinically relevant tumors.Implications: This study highlights a novel transcriptional mechanism through which PR drives breast cancer development and potentially evades the immune system. Mol Cancer Res; 15(10); 1331-40. ©2017 AACR.

Targeting progesterone metabolism in breast cancer with l-proline derived new 14-azasteroids

Breast cancer cell proliferation is promoted by a variety of mitogenic signals. Classically estrogen is considered as most predominant mitogenic signal in hormone-dependent breast cancer and progesterone is primarily considered to have protective effect. However, it is suggested that some progesterone metabolite may promote breast cancer and progesterone metabolites like 5α-pregnane and 4-pregnene could serve as regulators of estrogen-responsiveness of breast cancer cells. Here, we estimated the potential of alternate targeting of breast cancer via progesterone signalling. l-Proline derived novel 14-azasteroid compounds were screened against MCF-7 and MDA-MB-231 cell lines using MTT assay. In silico studies, cell cycle, Annexin-V-FITC/PI, JC-1 mitochondrial assay, ROS analysis were performed to analyse the impact of hit compound 3b on breast cancer cells. Further, we analysed the impact of hit 3b on the progesterone, its metabolites and enzymes responsible for the conversion of progesterone and its metabolites using ELISA. Data suggests that compound 3b binds and down regulates of 5α-reductase by specifically inhibiting production of progesterone metabolites that are capable of promoting breast cancer proliferation, epithelial mesenchymal transition and migration. This study establishes the proof of concept and generation of new leads for additional targeting of breast cancer.

The innate and adaptive infiltrating immune systems as targets for breast cancer immunotherapy

A cancer cell-centric view has long dominated the field of cancer biology. Research efforts have focussed on aberrant cancer cell signalling pathways and on changes to cancer cell DNA. Mounting evidence demonstrates that many cancer-associated cell types within the tumour stroma co-evolve and support tumour growth and development, greatly modifying cancer cell behaviour, facilitating invasion and metastasis and controlling dormancy and sensitivity to drug therapy. Thus, these stromal cells represent potential targets for cancer therapy. Among these cell types, immune cells have emerged as a promising target for therapy. The adaptive and the innate immune system play an important role in normal mammary development and breast cancer. The number of infiltrating adaptive immune system cells with tumour-rejecting capacity, primarily, T lymphocytes, is lower in breast cancer compared with other cancer types, but infiltration occurs in a large proportion of cases. There is strong evidence demonstrating the importance of the immunosuppressive role of the innate immune system during breast cancer progression. A consideration of components of both the innate and the adaptive immune system is essential for the design and development of immunotherapies in breast cancer. In this review, we focus on the importance of immunosuppressive myeloid-derived suppressor cells (MDSCs) as potential targets for breast cancer therapy.