Expression of transforming growth factor alpha and its messenger ribonucleic acid in human breast cancer: its regulation by estrogen and its possible functional significance

Endocrine therapy plus HER2-targeted therapy, another favorable option for HR+/HER2+ advanced breast cancer patients

Advanced breast cancer (ABC) that is positive for hormone receptors (HRs) and human epidermal growth factor receptor 2 (HER2) is a cancer subtype with distinctive characteristics. The primary treatment guidelines suggest that a combination therapy comprising anti-HER2 therapy and chemotherapy should be administered as the initial treatment for HR-positive/ HER2-positive (HR+/HER2+) ABC. However, crosstalk between the HR and HER2 pathways can partially account for the resistance of HR+/HER2+ disease to HER2-targeted therapy. This, in turn, provides a rationale for the concomitant administration of HER2-targeted therapy and endocrine therapy (ET). Many clinical studies have confirmed that the combination of HER2-targeted therapy and ET as a first-line treatment is not inferior to the combination of HER2-targeted therapy and chemotherapy, and support its use as a first-line treatment choice for HR+/HER2+ ABC. Other drugs, such as antibody-drug conjugates, cyclin-dependent kinase 4/6 inhibitors, phosphatidylinositol 3-kinase-protein kinase B (AKT)-mammalian target of rapamycin inhibitors, and programmed cell death protein 1 or programmed cell death ligand 1 inhibitors, may also improve the prognosis of patients with breast cancer by blocking signaling pathways associated with tumor proliferation and break new ground for the treatment of HR+/HER2+ ABC.

Assessing the Link between Diabetic Metabolic Dysregulation and Breast Cancer Progression

Diabetes mellitus is a burdensome disease that affects various cellular functions through altered glucose metabolism. Several reports have linked diabetes to cancer development; however, the exact molecular mechanism of how diabetes-related traits contribute to cancer progression is not fully understood. The current study aimed to explore the molecular mechanism underlying the potential effect of hyperglycemia combined with hyperinsulinemia on the progression of breast cancer cells. To this end, gene dysregulation induced by the exposure of MCF7 breast cancer cells to hyperglycemia (HG), or a combination of hyperglycemia and hyperinsulinemia (HGI), was analyzed using a microarray gene expression assay. Hyperglycemia combined with hyperinsulinemia induced differential expression of 45 genes (greater than or equal to two-fold), which were not shared by other treatments. On the other hand, in silico analysis performed using a publicly available dataset (GEO: GSE150586) revealed differential upregulation of 15 genes in the breast tumor tissues of diabetic patients with breast cancer when compared with breast cancer patients with no diabetes. SLC26A11, ALDH1A3, MED20, PABPC4 and SCP2 were among the top upregulated genes in both microarray data and the in silico analysis. In conclusion, hyperglycemia combined with hyperinsulinemia caused a likely unique signature that contributes to acquiring more carcinogenic traits. Indeed, these findings might potentially add emphasis on how monitoring diabetes-related metabolic alteration as an adjunct to diabetes therapy is important in improving breast cancer outcomes. However, further detailed studies are required to decipher the role of the highlighted genes, in this study, in the pathogenesis of breast cancer in patients with a different glycemic index.

The Aryl Hydrocarbon Receptor-Dependent TGF-α/VEGF-B Ratio Correlates With Disease Subtype and Prognosis in Multiple Sclerosis

OBJECTIVE

To evaluate the aryl hydrocarbon receptor (AHR)-dependent transforming growth factor alpha (TGF-α)/vascular endothelial growth factor B (VEGF-B) ratio, which regulates the effects of metabolic, dietary, and microbial factors on acute and chronic CNS inflammation, as a potential marker in multiple sclerosis (MS).

METHODS

TGF-α, VEGF-B, and AHR agonistic activity were determined in serum of 252 patients with relapsing-remitting (RR) MS, primary and secondary progressive MS, as well as during active disease (clinically isolated syndrome [CIS] and RRMS relapse).

RESULTS

The TGF-α/VEGF-B ratio and AHR agonistic activity were decreased in all MS subgroups with a stable disease course as compared to controls. During active CNS inflammation in CIS and RRMS relapse, the TGF-α/VEGF-B ratio and AHR agonistic activity were increased. Conversely, in patients with minimal clinical impairment despite long-standing disease, the TGF-α/VEGF-B ratio and AHR agonistic activity were unaltered. Finally, the TGF-α/VEGF-B ratio and AHR agonistic activity correlated with neurologic impairment and time to conversion from CIS to MS.

CONCLUSIONS

The AHR-dependent TGF-α/VEGF-B ratio is altered in a subtype, severity, and disease activity-specific manner and correlates with time to conversion from CIS to MS. It may thus represent a novel marker and serve as additive guideline for immunomodulatory strategies in MS.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that serum levels of AHR, TGF-α, and VEGF-B distinguish subtypes of MS and predict the severity and disease activity of MS.

Identification of Drug Candidates for Breast Cancer Therapy Through Scaffold Repurposing: A Brief Review

Conventional drug discovery is a time consuming and expensive expedition with less clinical preference achievement proportion intended for breast cancer therapy. Even if numerous novel approaches to the conformation of drugs have been introduced for breast cancer therapy, they are yet to be implemented in clinical practice. This tempting strategy facilitates a remarkable chance to take the entire benefit of existing drugs. Despite drug repurposing significantly decrease the investigational period and cost, it has got many objections and issues. Scaffold repurposing is an approach that procures a novel significance on the decrepit motto of "to commencement with a pristine drug" . Hence, we move into a probable and nearer approach, the exploitation of scaffolds, which was originally developed for other purposes, including anti-tumor activity. In this review, we summarize different drugs and scaffolds used in breast cancer therapy.

Genome wide predictions of miRNA regulation by transcription factors

MOTIVATION

Reconstructing regulatory networks from expression and interaction data is a major goal of systems biology. While much work has focused on trying to experimentally and computationally determine the set of transcription-factors (TFs) and microRNAs (miRNAs) that regulate genes in these networks, relatively little work has focused on inferring the regulation of miRNAs by TFs. Such regulation can play an important role in several biological processes including development and disease. The main challenge for predicting such interactions is the very small positive training set currently available. Another challenge is the fact that a large fraction of miRNAs are encoded within genes making it hard to determine the specific way in which they are regulated.

RESULTS

To enable genome wide predictions of TF-miRNA interactions, we extended semi-supervised machine-learning approaches to integrate a large set of different types of data including sequence, expression, ChIP-seq and epigenetic data. As we show, the methods we develop achieve good performance on both a labeled test set, and when analyzing general co-expression networks. We next analyze mRNA and miRNA cancer expression data, demonstrating the advantage of using the predicted set of interactions for identifying more coherent and relevant modules, genes, and miRNAs. The complete set of predictions is available on the supporting website and can be used by any method that combines miRNAs, genes, and TFs.

AVAILABILITY AND IMPLEMENTATION

Code and full set of predictions are available from the supporting website: http://cs.cmu.edu/~mruffalo/tf-mirna/

CONTACT

zivbj@cs.cmu.edu

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Hormonal Modulation of Breast Cancer Gene Expression: Implications for Intrinsic Subtyping in Premenopausal Women

Clinics are increasingly adopting gene-expression profiling to diagnose breast cancer subtype, providing an intrinsic, molecular portrait of the tumor. For example, the PAM50-based Prosigna test quantifies expression of 50 key genes to classify breast cancer subtype, and this method of classification has been demonstrated to be superior over traditional immunohistochemical methods that detect proteins, to predict risk of disease recurrence. However, these tests were largely developed and validated using breast cancer samples from postmenopausal women. Thus, the accuracy of such tests has not been explored in the context of the hormonal fluctuations in estrogen and progesterone that occur during the menstrual cycle in premenopausal women. Concordance between traditional methods of subtyping and the new tests in premenopausal women is likely to depend on the stage of the menstrual cycle at which the tissue sample is taken and the relative effect of hormones on expression of genes versus proteins. The lack of knowledge around the effect of fluctuating estrogen and progesterone on gene expression in breast cancer patients raises serious concerns for intrinsic subtyping in premenopausal women, which comprise about 25% of breast cancer diagnoses. Further research on the impact of the menstrual cycle on intrinsic breast cancer profiling is required if premenopausal women are to benefit from the new technology of intrinsic subtyping.

Effects of the lifestyle habits in breast cancer transcriptional regulation

Through research carried out in the last 25 years about the breast cancer etiology, it has been possible to estimate that less than 10 % of patients who are diagnosed with the condition are carriers of some germline or somatic mutation. The clinical reports of breast cancer patients with healthy twins and the development of disease in women without high penetrance mutations detected, warn the participation more factors in the transformation process. The high incidence of mammary adenocarcinoma in the modern woman and the urgent need for new methods of prevention and early detection have demanded more information about the role that environment and lifestyle have on the transformation of mammary gland epithelial cells. Obesity, alcoholism and smoking are factors that have shown a close correlation with the risk of developing breast cancer. And although these conditions affect different cell regulation levels, the study of its effects in the mechanisms of transcriptional and epigenetic regulation is considered critical for a better understanding of the loss of identity of epithelial cells during carcinogenesis of this tissue. The main objective of this review was to establish the importance of changes occurring to transcriptional level in the mammary gland as a consequence of acute or chronic exposure to harmful products such as obesity-causing foods, ethanol and cigarette smoke components. At analyze the main studies related to topic, it has concluded that the understanding of effects caused by the lifestyle factors in performance of the transcriptional mechanisms that determine gene expression of the mammary gland epithelial cells, may help explain the development of this disease in women without genetic propensity and different phenotypic manifestations of this cancer type.

From bench to bedside: What do we know about hormone receptor-positive and human epidermal growth factor receptor 2-positive breast cancer?

Breast cancer is a heterogeneous disease. Thanks to extensive efforts from research scientists and clinicians, treatment for breast cancer has advanced into the era of targeted medicine. With the use of several well-established biomarkers, such as hormone receptors (HRs) (i.e., estrogen receptor [ER] and progesterone receptor [PgR]) and human epidermal growth factor receptor-2 (HER2), breast cancer patients can be categorized into multiple subgroups with specific targeted treatment strategies. Although therapeutic strategies for HR-positive (HR+) HER2-negative (HER2-) breast cancer and HR-negative (HR-) HER2-positive (HER2+) breast cancer are well-defined, HR+ HER2+ breast cancer is still an overlooked subgroup without tailored therapeutic options. In this review, we have summarized the molecular characteristics, etiology, preclinical tools and therapeutic options for HR+ HER2+ breast cancer. We hope to raise the attention of both the research and the medical community on HR+ HER2+ breast cancer, and to advance patient care for this subtype of disease.

Modulation of Estrogen Response Element-Driven Gene Expressions and Cellular Proliferation with Polar Directions by Designer Transcription Regulators

Estrogen receptor α (ERα), as a ligand-dependent transcription factor, mediates 17β-estradiol (E2) effects. ERα is a modular protein containing a DNA binding domain (DBD) and transcription activation domains (AD) located at the amino- and carboxyl-termini. The interaction of the E2-activated ERα dimer with estrogen response elements (EREs) of genes constitutes the initial step in the ERE-dependent signaling pathway necessary for alterations of cellular features. We previously constructed monomeric transcription activators, or monotransactivators, assembled from an engineered ERE-binding module (EBM) using the ERα-DBD and constitutively active ADs from other transcription factors. Monotransactivators modulated cell proliferation by activating and repressing ERE-driven gene expressions that simulate responses observed with E2-ERα. We reasoned here that integration of potent heterologous repression domains (RDs) into EBM could generate monotransrepressors that alter ERE-bearing gene expressions and cellular proliferation in directions opposite to those observed with E2-ERα or monotransactivators. Consistent with this, monotransrepressors suppressed reporter gene expressions that emulate the ERE-dependent signaling pathway. Moreover, a model monotransrepressor regulated DNA synthesis, cell cycle progression and proliferation of recombinant adenovirus infected ER-negative cells through decreasing as well as increasing gene expressions with polar directions compared with E2-ERα or monotransactivator. Our results indicate that an ‘activator’ or a ‘repressor’ possesses both transcription activating/enhancing and repressing/decreasing abilities within a chromatin context. Offering a protein engineering platform to alter signal pathway-specific gene expressions and cell growth, our approach could also be used for the development of tools for epigenetic modifications and for clinical interventions wherein multigenic de-regulations are an issue.

Distinct effects of EGFR ligands on human mammary epithelial cell differentiation

Based on gene expression patterns, breast cancers can be divided into subtypes that closely resemble various developmental stages of normal mammary epithelial cells (MECs). Thus, understanding molecular mechanisms of MEC development is expected to provide critical insights into initiation and progression of breast cancer. Epidermal growth factor receptor (EGFR) and its ligands play essential roles in normal and pathological mammary gland. Signals through EGFR is required for normal mammary gland development. Ligands for EGFR are over-expressed in a significant proportion of breast cancers, and elevated expression of EGFR is associated with poorer clinical outcome. In the present study, we examined the effect of signals through EGFR on MEC differentiation using the human telomerase reverse transcriptase (hTERT)-immortalized human stem/progenitor MECs which express cytokeratin 5 but lack cytokeratin 19 (K5⁺K19^- hMECs). As reported previously, these cells can be induced to differentiate into luminal and myoepithelial cells under appropriate culture conditions. K5⁺K19^- hMECs acquired distinct cell fates in response to EGFR ligands epidermal growth factor (EGF), amphiregulin (AREG) and transforming growth factor alpha (TGFα) in differentiation-promoting MEGM medium. Specifically, presence of EGF during in vitro differentiation supported development into both luminal and myoepithelial lineages, whereas cells differentiated only towards luminal lineage when EGF was replaced with AREG. In contrast, substitution with TGFα led to differentiation only into myoepithelial lineage. Chemical inhibition of the MEK-Erk pathway, but not the phosphatidylinositol 3-kinase (PI3K)-AKT pathway, interfered with K5⁺K19^- hMEC differentiation. The present data validate the utility of the K5⁺K19^- hMEC cells for modeling key features of human MEC differentiation. This system should be useful in studying molecular/biochemical mechanisms of human MEC differentiation.

Tamoxifen-poly(ethylene glycol)-thiol gold nanoparticle conjugates: enhanced potency and selective delivery for breast cancer treatment

The breast cancer treatment drug tamoxifen has been widely administered for more than three decades. This small molecule competes with 17beta-estradiol for binding to estrogen receptor, a hormone receptor upregulated in a majority of breast cancers, subsequently initiating programmed cell death. We have synthesized a thiol-PEGylated tamoxifen derivative that can be used to selectively target and deliver plasmonic gold nanoparticles to estrogen receptor positive breast cancer cells with up to 2.7-fold enhanced drug potency in vitro. Optical microscopy/spectroscopy, time-dependent dose-response data, and estrogen competition studies indicate that augmented activity is due to increased rates of intracellular tamoxifen transport by nanoparticle endocytosis, rather than by passive diffusion of the free drug. Both ligand- and receptor-dependent intracellular delivery of gold nanoparticles suggest that plasma membrane localized estrogen receptor alpha may facilitate selective uptake and retention of this and other therapeutic nanoparticle conjugates. Combined targeting selectivity and enhanced potency provides opportunities for both multimodal endocrine treatment strategies and adjunctive laser photothermal therapy.

Effect of Obesity on Breast Cancer Development

In recent years, obesity has been identified as a risk factor for the development of breast cancer in postmenopausal women, and it has been associated with a poor outcome. Many factors appear to be important in the mechanism of this increased risk, including estrogen, estrogen receptors, and the adipokines leptin and adiponectin. Estrogen, a potent mitogen for mammary cells, has long been implicated in the development of mammary tumors. Because adipose-associated aromatase activity increases the conversion of androgen to estrogen, mammary adipose tissue is thought to be an important source of local estrogen production. Leptin, which increases in the circulation in proportion to body fat stores, has been demonstrated in vitro to promote breast cancer cell growth. Animal models have also identified leptin as an important factor for the development of mammary tumors. In contrast to leptin, serum adiponectin concentrations are inversely related to body fat stores, and the addition of adiponectin to human breast cancer cells reduces cell proliferation and enhances apoptosis. This review explores the relationship between these factors and the development of mammary cancer in humans and mouse models.

EGFR may couple moderate alcohol consumption to increased breast cancer risk

Alcohol consumption is an established risk factor for breast cancer. Nonetheless, the mechanism by which alcohol contributes to breast tumor initiation or progression has yet to be definitively established. Studies using cultured human tumor cell lines have identified signaling molecules that may contribute to the effects of alcohol, including reactive oxygen species and other ethanol metabolites, matrix metalloproteases, the ErbB2/Her2/Neu receptor tyrosine kinase, cytoplasmic protein kinases, adenylate cyclase, E-cadherins, estrogen receptor, and a variety of transcription factors. Emerging data suggest that the epidermal growth factor receptor (EGFR) tyrosine kinase may contribute to breast cancer genesis and progression. Here we integrate these findings and propose three mechanisms by which alcohol contributes to breast cancer. A common feature of these mechanisms is increased EGFR signaling. Finally, we discuss how these mechanisms suggest strategies for addressing the risks associated with alcohol consumption.

Expression of Oestrogen Receptor and Transforming Growth Factor-α in MCF-7 Cells after Exposure to Fractionated Irradiation

The expression of critical growth controlling genes was studied in MCF-7 cells after exposure to cumulative radiation doses of 20 and 60 Gy yielding cell lines called MCF-IR-1 and MCF-IR-3, respectively. The irradiated cell lines exhibited increased plating efficiencies but no differences in growth rates. MCF-IR-1/-IR-3 cells showed a reduced oestrogen responsiveness as indicated by their diminished response to tamoxifen-induced growth arrest and 17 beta-oestradiol (E2)-induced growth stimulation. The reduced expression of oestrogen receptor (ER) was determined by quantitative immune peroxidase staining of single cells and by total cellular E2 binding. There was also a radiation dose-dependent increase in the radiosensitivity of MCF-IR-3 cells as determined by the radiobiological parameters alpha, beta, and D (mean inactivation dose). Using RNA protection assays the irradiated cell lines produced steady-state ER mRNA at reduced levels while the levels of TGF-alpha were unchanged in MCF-IR-1 cells but increased 2.8-fold in MCF-IR-3 cells. A similar pattern was seen for TGF-alpha protein. While the current analyses cannot differentiate between radiation-induced altered gene expression or cell selection the results demonstrate that reduced ER expression and increased TGF-alpha expression are associated with the survival of MCF-7 cells after fractionated irradiation in vitro. In contrast, the MCF-IR cells were found to be more radiosensitive in acute survival experiments.

Genomic responses from the estrogen-responsive element-dependent signaling pathway mediated by estrogen receptor alpha are required to elicit cellular alterations

Estrogen (E2) signaling is conveyed by the transcription factors estrogen receptor (ER) alpha and beta. ERs modulate the expression of genes involved in cellular proliferation, motility, and death. The regulation of transcription by E2-ERalpha through binding to estrogen-responsive elements (EREs) in DNA constitutes the ERE-dependent signaling pathway. E2-ERalpha also modulates gene expression by interacting with transregulators bound to cognate DNA-regulatory elements, and this regulation is referred to as the ERE-independent signaling pathway. The relative importance of the ERE-independent pathway in E2-ERalpha signaling is unclear. To address this issue, we engineered an ERE-binding defective ERalpha mutant (ERalpha(EBD)) by changing residues in an alpha-helix of the protein involved in DNA binding to render the receptor functional only through the ERE-independent signaling pathway. Using recombinant adenovirus-infected ER-negative MDA-MB-231 cells derived from a breast adenocarcinoma, we found that E2-ERalpha(EBD) modulated the expression of a subset of ERalpha-responsive genes identified by microarrays and verified by quantitative PCR. However, E2-ERalpha(EBD) did not affect cell cycle progression, cellular growth, death, or motility in contrast to E2-ERalpha.ERalpha(EBD) in the presence of E2 was also ineffective in inducing phenotypic alterations in ER-negative U-2OS cells derived from an osteosarcoma. E2-ERalpha, on the other hand, effectively repressed growth in this cell line. Our findings suggest that genomic responses from the ERE-dependent signaling pathway are required for E2-ERalpha to induce alterations in cellular responses.

Tamoxifen inhibits transforming growth factor-alpha gene expression in human breast carcinoma samples treated with triiodothyronine

OBJECTIVES

To examine the effects of triiodothyronine (T3), 17beta-estradiol (E2), and tamoxifen (TAM) on transforming growth factor (TGF)-alpha gene expression in primary breast cancer cell cultures and interactions between the different treatments.

METHODS AND RESULTS

Patients included in the study (no.=12) had been newly diagnosed with breast cancer. Fresh human breast carcinoma tissue was cut into 0.3- mm slices. These slices were placed in six 35-mm dishes on 2-ml organ culture medium. Dishes received the following treatments: dish 1: ethanol; dish 2: T3; dish 3: T3+TAM; dish 4: TAM; dish 5: E2; dish 6: E2+TAM. TGF-alpha mRNA content was normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA levels. All tissues included in this study were positive for estrogen receptor (ER) and thyroid hormone receptor expression. Treatment with T3 for 48 h significantly increased TGF-alpha mRNA levels compared to controls (15-fold), and concomitant treatment with TAM reduced expression to 3.4-fold compared to controls. When only TAM was added to the culture medium, TGF-alpha mRNA expression increased 5.3-fold, significantly higher than with all other treatment modalities.

CONCLUSION

We demonstrate that TGF-alpha mRNA expression is more efficiently upregulated by T3 than E2. Concomitant treatment with TAM had a mitigating effect on the T3 effect, while E2 induced TGF-alpha upregulation. Our findings show some similarities between primary culture and breast cancer cell lines, but also some important differences: a) induction of TGF-alpha, a mitogenic protein, by TAM; b) a differential effect of TAM that may depend on relative expression of ER alpha and beta; and c) supraphysiological doses of T3 may induce mitogenic signals in breast cancer tissue under conditions of low circulating E2.

Molecular mechanisms of aromatase inhibition by new A, D-ring modified steroids

A recent approach for treatment and prevention of estrogen-dependent breast cancer focuses on the inhibition of aromatase, the enzyme that catalyzes the final step of estrogen biosynthesis. Some synthetic steroids, such as formestane and exemestane, resembling the natural enzyme substrate androstenedione, revealed to be potent and useful aromatase inhibitors (AIs) and were approved for the treatment of estrogen-dependent breast cancer in postmenopausal women. Recently, we found that five newly synthesized steroids with chemical features in the A- and D-rings considered important for drug-receptor interaction efficiently inhibit aromatase derived from human placental microsomes. In this work, these steroids showed a similar pattern of anti-aromatase activity in several aromatase-expressing cell lines. 5alpha-androst-3-en-17-one and 3alpha,4alpha-epoxy-5alpha-androstan-17-one were revealed to be the most potent inhibitors. These compounds induced a time-dependent inhibition of aromatase, showing to be irreversible AIs. The specific interactions of these compounds with aromatase active sites were further demonstrated by site-directed mutagenesis studies and evaluated by computer-aided molecular modeling. Both compounds were able to suppress hormone-dependent proliferation of MCF-7aro cells in a dose-dependent manner. These findings are important for the elucidation of a structure-activity relationship on aromatase, which may help in the development of new AIs.

New steroidal aromatase inhibitors: suppression of estrogen-dependent breast cancer cell proliferation and induction of cell death

BACKGROUND

Aromatase, the cytochrome P-450 enzyme (CYP19) responsible for estrogen biosynthesis, is an important target for the treatment of estrogen-dependent breast cancer. In fact, the use of synthetic aromatase inhibitors (AI), which induce suppression of estrogen synthesis, has shown to be an effective alternative to the classical tamoxifen for the treatment of postmenopausal patients with ER-positive breast cancer. New AIs obtained, in our laboratory, by modification of the A and D-rings of the natural substrate of aromatase, compounds 3a and 4a, showed previously to efficiently suppress aromatase activity in placental microsomes. In the present study we have investigated the effects of these compounds on cell proliferation, cell cycle progression and induction of cell death using the estrogen-dependent human breast cancer cell line stably transfected with the aromatase gene, MCF-7 aro cells.

RESULTS

The new steroids inhibit hormone-dependent proliferation of MCF-7aro cells in a time and dose-dependent manner, causing cell cycle arrest in G0/G1 phase and inducing cell death with features of apoptosis and autophagic cell death.

CONCLUSION

Our in vitro studies showed that the two steroidal AIs, 3a and 4a, are potent inhibitors of breast cancer cell proliferation. Moreover, it was also shown that the antiproliferative effects of these two steroids on MCF-7aro cells are mediated by disrupting cell cycle progression, through cell cycle arrest in G0/G1 phase and induction of cell death, being the dominant mechanism autophagic cell death. Our results are important for the elucidation of the cellular effects of steroidal AIs on breast cancer.

Transgenic models to study actions of prolactin in mammary neoplasia

Transgenic models to explore the role of prolactin and its interactions with other factors in mammary oncogenesis have begun to reveal the dynamic contributions of prolactin to the development and progression of this disease. Targeting prolactin to mammary epithelial cells mimics the local production of this hormone that is prominent in women, and permits studies in the absence of effects on the ovarian steroid milieu. These models have demonstrated that local production of prolactin is sufficient to induce mammary tumors after a long latency. Prolactin also can potentiate actions of other oncogenic stimuli, decreasing tumor latency and increasing incidence in several models. Augmented proliferation, without alteration of apoptosis, is a consistent feature. Pathways in addition to the well-characterized Jak2-Stat5 pathway, including ERK1/2 and Akt1/2, are implicated in these actions. These studies have also revealed a complex relationship with estrogen; while prolactin increases ERalpha expression, it does not require estrogenic ligand for lesion development, and indeed, in combination with the EGFR ligand, TGFalpha, prolactin can contribute to estrogen insensitivity. These studies highlight the utility of these models to decipher the interplay between prolactin and other oncogenic factors in breast cancer, with implications for preventative and therapeutic strategies.

A peptide derived from alpha-fetoprotein inhibits the proliferation induced by estradiol in mammary tumor cells in culture

This study was aimed to obtain additional information on the activity of a cyclized 9-amino acid peptide (cP) containing the active site of alpha fetoprotein, which inhibits the estrogen-stimulated proliferation of tumor cells in culture and of xenografts in immunodeficient mice. Breast cancer cells cultured in the presence of 2 nM estradiol were exposed to cP for different periods and their proliferation, estradiol binding parameters, clustering tendency and expression of E-cadherin and p21Cip1 were analyzed by biochemical and cell biology methods. The proliferation of MCF7 cells was significantly decreased by the addition of 2 microg/ml cP to the medium. cP did not increase cell death rate nor alter the number of binding sites for estradiol nor the endogenous aromatase activity of MCF7 cells. cP also decreased the proliferation of estrogen-dependent ZR75-1 cells but had no effect on estrogen-independent MDA-MB-231 cells. An increased nuclear p21Cip1 expression detected after cP treatment suggests that cP slows MCF7 cell proliferation via this regulator. We propose that cP could represent a novel breast cancer therapeutic agent whose mechanism of action is different from that of tamoxifen or of inhibitors of aromatase.

Cyclooxygenase-2 mRNA expression correlates with aromatase expression in human breast cancer

INTRODUCTION

The cyclooxygenase-2 (COX-2), responsible for the conversion of arachidonic acid into prostaglandin (PG) E2, is known to increase intracellular cAMP and estrogen production in malignant breast tissue. The aromatase enzyme complex is responsible for local production of estrogens in breast cancer. Increasing evidence supports a role for COX-2 in upregulation of aromatase activity. The aim of this study was to examine the relationship between COX-2 and aromatase mRNA expression in human breast cancer.

METHODS

A total of 160 breast samples (127 tumor tissues and 33 normal tissues) were analyzed. Levels of transcription were determined using real-time quantitative PCR. COX-2 and aromatase mRNA expression were normalized against CK19. Levels of expression of COX-2 were correlated with those of aromatase using Pearson's correlation method.

RESULTS

Levels of expression of COX-2/CK19 of both benign and malignant tissues were positively correlated with aromatase/CK19 transcript levels (correlation coefficient = +0.536, P < 0.0001). When we compared levels of expression of both genes in malignant samples only, there was a highly significant positive correlation (r = +0.611, P < 0.00001).

CONCLUSION

This study demonstrates a strong positive relationship between COX-2 and aromatase mRNA expression, and lends further support to the hypothesis that COX-2 is an upregulator of aromatase in breast tissue.

Transforming growth factor alpha dependent cancer progression is modulated by Muc1

Transforming growth factor alpha (TGFalpha) is a potent inducer of cellular transformation, through its binding and activation of the epidermal growth factor receptor (EGFR). Previous studies in our laboratory showed that EGFR could also be affected by the glycoprotein MUC1, which inhibits ligand-stimulated degradation of EGFR in breast epithelial cell lines. To determine the effect of Muc1 expression on TGFalpha/EGFR-dependent breast transformation, we crossed the WAP-TGFalpha transgenic mouse model of breast cancer onto a Muc1-null background. We found that the loss of Muc1 expression dramatically affects mammary gland transformation and progression. Although 100% of WAP-TGFalpha/Muc1(+/+) mice form mammary gland tumors by 1 year, only 37% of WAP-TGFalpha/Muc1(-/-) form tumors by this time. This difference is also associated with a delay in onset, with a doubling of onset time observed in the WAP-TGFalpha/Muc1(-/-) compared with the WAP-TGFalpha/Muc1(+/+) mice. Analysis of signal transduction pathways revealed that activation of cyclin D1 expression is significantly suppressed in tumors derived from WAP-TGFalpha/Muc1(-/-) animals compared with those expressing Muc1. The loss of Muc1 expression also results in a significant inhibition in the formation of hyperplastic lesions during tumor progression. On the C57Bl/6 inbred background, pulmonary lesions were observed in 28 of 29 WAP-TGFalpha/Muc1(+/+) animals (including one metastatic pulmonary adenocarcinoma and multiple perivascular lymphomas), although none were detected in the WAP-TGFalpha/Muc1(-/-) animals. Together, these data indicate that Muc1 is an important modulator of TGFalpha-dependent tumor progression.

Amphiregulin is an essential mediator of estrogen receptor alpha function in mammary gland development

Most mammary gland development occurs after birth under the control of systemic hormones. Estrogens induce mammary epithelial cell proliferation during puberty via epithelial estrogen receptor alpha (ERalpha) by a paracrine mechanism. Epidermal growth factor receptor (EGFR) signaling has long been implicated downstream of ERalpha signaling, and several EGFR ligands have been described as estrogen-target genes in tumor cell lines. Here, we show that amphiregulin is the unique EGF family member to be transcriptionally induced by estrogen in the mammary glands of puberal mice at a time of exponential expansion of the ductal system. In fact, we find that estrogens induce amphiregulin through the ERalpha and require amphiregulin to induce proliferation of the mammary epithelium. Like ERalpha, amphiregulin is required in the epithelium of puberal mice for epithelial proliferation, terminal end buds formation, and ductal elongation. Subsequent stages, such as side-branching and alveologenesis, are not affected. When amphiregulin(-/-) mammary epithelial cells are in close vicinity to wild-type cells, they proliferate and contribute to all cell compartments of the ductal outgrowth. Thus, amphiregulin is an important paracrine mediator of estrogen function specifically required for puberty-induced ductal elongation, but not for any earlier or later developmental stages.

Farnesylthiosalicylic acid blocks mammalian target of rapamycin signaling in breast cancer cells

Estradiol (E2) stimulates proliferation of hormone-dependent breast cancer and exerts downstream effects on growth factors and their receptors. Key among the pathways' mediating growth factor action is the MAP kinase signaling cascade and the PI-3 kinase pathway with its downstream effector mTOR. We postulated that farnesylthiosalicylic acid (FTS), a novel anti-Ras drug, could effectively inhibit hormone-dependent breast cancer because Ras activates both the MAP kinase and the PI3 kinase pathways. Wild-type MCF-7 cells and a long-term estrogen-deprived subline (LTED) were used to examine the effect of FTS on cell growth and on several biochemical parameters. FTS inhibited growth of both cell lines by reducing proliferation and inducing apoptosis. These effects correlated best with blockade of phosphorylation of PHAS-I and p70 S6 kinase, 2 downstream effectors of mTOR. We observed only minimal inhibition of Akt, an effector upstream of mTOR. Taken together, these findings demonstrate a novel effect of FTS to inhibit mTOR signaling and also suggest that mTOR has a key role in breast cancer cell proliferation. Unexpectedly, only minimal inhibition of MAP kinase occurred in response to FTS at concentrations that markedly reduced cell growth. These later data provide support for the concept that FTS exerts its effects predominantly by blocking mTOR and to a lesser effect by inhibition of MAP kinase in breast cancer cells.

Bidirectional cross talk between ERalpha and EGFR signalling pathways regulates tamoxifen-resistant growth

We have previously demonstrated that oestrogen receptor alpha (ERalpha) modulates epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase (MAPK) signalling efficiency in a tamoxifen-resistant MCF-7 breast cancer cell line (Tam-R). In the present study we have investigated whether this cross-talk between EGFR/MAPK and ERalpha signalling pathways is bidirectional by examining the effects of EGFR/MAPK activity on ER functionality in the same cell line. Elevated expression levels of phosphorylated serine 118 (S118) ERalpha were observed in the Tam-R compared to the parental wild type MCF-7 cell line (WT-MCF-7) under basal growth conditions. Phosphorylation of ERalpha at S118 was regulated by the EGFR/MAPK pathway in Tam-R cells being increased in response to amphiregulin (AR) and inhibited by the selective EGFR tyrosine kinase inhibitor, gefitinib and the MEK1/2 inhibitor, PD184352. Recruitment of the co-activators p68 RNA helicase and SRC1 to ERalpha, oestrogen response element (ERE) activity and Tam-R cell growth were similarly EGFR/MAPK-regulated. Chromatin immunoprecipitation (ChIP) studies revealed that in Tam-R cells the ERalpha assembled on the AR gene promoter and this was associated with elevated basal expression of AR mRNA. Furthermore, AR mRNA expression was under the regulation of the EGFR/MAPK and ERalpha signalling pathways. Neutralising antibodies to AR inhibited EGFR/ERK1/2 activity, reduced S118 ERalpha phosphorylation and reduced AR mRNA expression in TAM-R cells. These findings suggest that ERalpha function in Tam-R cells is maintained as a consequence of EGFR/MAPK-mediated phosphorylation at serine residue 118 resulting in the generation of a self-propogating autocrine growth-regulatory loop through the ERalpha-mediated production of AR.

Letrozole-, anastrozole-, and tamoxifen-responsive genes in MCF-7aro cells: a microarray approach

Antiestrogens and aromatase inhibitors are important drugs in the treatment of estrogen-dependent breast cancer. To investigate the effects of these drugs on gene expression in breast cancer cells, we treated estrogen receptor-positive MCF-7 cells stably transfected with the aromatase gene (known as MCF-7aro cells) with testosterone, 17 beta-estradiol, two aromatase inhibitors (letrozole and anastrozole), and an antiestrogen (tamoxifen). We found that testosterone or 17 beta-estradiol induced the proliferation of MCF-7aro cells at a rate six times faster than the untreated cells. In addition, the testosterone-induced proliferation of MCF-7aro cells was effectively suppressed by letrozole, anastrozole, or tamoxifen. Microarray analyses on Affymetrix Human Genome U133A GeneChips (Affymetrix, Santa Clara, CA) were carried out using total RNA isolated from the control and treated cells. At the false discovery rate of 0.05 and a minimum fold-change criteria of 1.5, 104 genes were identified that were up-regulated and 109 genes were identified that were down-regulated by both androgen and estrogen. More than 50% of these hormone-regulated genes were counter-regulated by all three inhibitors and >90% were counter-regulated by at least one of the inhibitors. Comparing the effect of each inhibitor on gene expression, we observed that letrozole and anastrozole are more similar in terms of the genes they affect compared with treatment with tamoxifen. To validate the gene expression profiles identified from microarray analyses, the expression patterns of 13 representative genes were examined by Northern analysis. Finally, the genes identified as statistically significant were classified based on their expression patterns and biological function/pathways. The results of this study provide us with a better understanding of the actions of both aromatase inhibitors and antiestrogens at the molecular level. We believe that the results of this study serve as the first step in identifying unique expression patterns following drug treatment, and that this will ultimately be useful in customizing patient treatment strategies for hormone-dependent breast cancer.

Expression of ZER6 in ERalpha-positive breast cancer

BACKGROUND

ZER6 is a C2H2 zinc finger transcription factor with two isoforms (p52-ZER6 and p71-ZER6), which are differentially repressed by a ligand-dependent interaction with estrogen receptor-alpha (ERalpha). We sought to determine if ZER6 proteins are expressed in ERalpha-positive breast cancer cells and if ZER6 is expressed in association with ERalpha in breast cancers.

METHODS

The expression of ZER6 protein was examined by Western blot and the pattern of ZER6 expression was examined in a panel of ERalpha-positive and ERalpha-negative breast cancers using RT-PCR.

RESULTS

COS-1 cells transfected with expression vectors for p52-ZER6 express a major protein of 52 kDa and a minor protein of 75 kDa, whereas cells transfected with the p71-ZER6 expression vector express a major protein of 77 kDa and a minor protein of 100 kDa. Breast carcinoma cells express ZER6-specific proteins of similar size, and expression of the p52-ZER6 isoform was only detected in the ERalpha-positive cell lines. In primary breast cancer tissue, 8/16 (50%) of the ERalpha-positive tumors had high ZER6 expression, whereas only 1/12 (8%) of the ERalpha-negative tumors had a high ZER6 level of expression. The relative abundance of ZER6 mRNA in the ERalpha-positive group was statistically greater than the ERalpha-negative group (188 versus 106, P < 0.05).

CONCLUSIONS

We have confirmed that breast carcinoma cells express ZER6 proteins and identified an association between the level of ZER6 expression and ERalpha expression in primary breast cancers. These data support a role for the ZER6 transcription factors in regulating the expression of genes in hormone-responsive breast cancer.

A role of melatonin in neuroectodermal-mesodermal interactions: the hair follicle synthesizes melatonin and expresses functional melatonin receptors

Since mammalian skin expresses the enzymatic apparatus for melatonin synthesis, it may be an extrapineal site of melatonin synthesis. However, evidence is still lacking that this is really the case in situ. Here, we demonstrate melatonin-like immunoreactivity (IR) in the outer root sheath (ORS) of mouse and human hair follicles (HFs), which corresponds to melatonin, as shown by radioimmunoassay and liquid chromatography/tandem mass spectrometry (LC/MS/MS). The melatonin concentration in organ-cultured mouse skin, mouse vibrissae follicles, and human scalp HFs far exceeds the respective melatonin serum level and is significantly increased ex vivo by stimulation with norepinephrine (NE), the key stimulus for pineal melatonin synthesis. By real-time PCR, transcripts for the melatonin membrane receptor MT2 and for the nuclear mediator of melatonin signaling, retinoid orphan receptor alpha (ROR)alpha, are detectable in murine back skin. Transcript levels for these receptors fluctuate in a hair cycle-dependent manner, and are maximal during apoptosis-driven HF regression (catagen). Melatonin may play a role in hair cycle regulation, since its receptors (MT2 and RORalpha) are expressed in murine skin in a hair cycle-dependent manner, and because it inhibits keratinocyte apoptosis and down-regulates ERalpha expression. Therefore, the HF is both, a prominent extrapineal melatonin source, and an important peripheral melatonin target tissue. Regulated intrafollicular melatonin synthesis and signaling may play a previously unrecognized role in the endogenous controls of hair growth, for example, by modulating keratinocyte apoptosis during catagen and by desensitizing the HF to estrogen signaling. As a prototypic neuroectodermal-mesodermal interaction model, the HF can be exploited for dissecting the obscure role of melatonin in such interactions in peripheral tissues.

Prolactin and estrogen enhance the activity of activating protein 1 in breast cancer cells: role of extracellularly regulated kinase 1/2-mediated signals to c-fos

Despite the important roles of both prolactin (PRL) and 17beta-estradiol (E2) in normal mammary development as well as in breast cancer, and coexpression of the estrogen receptor (ER) and PRL receptor in many mammary tumors, the interactions between PRL and E2 in breast cancer have not been well studied. The activating protein 1 (AP-1) transcription factor, a known regulator of processes essential for normal growth and development as well as carcinogenesis, is a potential site for cross-talk between these hormones in breast cancer cells. Here we demonstrate that PRL and E2 cooperatively enhance the activity of AP-1 in MCF-7-derived cells. In addition to the acute PRL-induced ERK1/2 activation, PRL and E2 also individually elicited delayed, sustained rises in levels of phosphorylated p38 and especially ERK1/2. Together, these hormones increased the dynamic phosphorylation of ERK1/2 and c-Fos, and induced c-fos promoter activity. Synergistic activation of the transcription factor, Elk-1, reflected the PRL-E2 interaction at ERK1/2 and is a likely mechanism for activation of the c-fos promoter via the serum response element. The enhanced AP-1 activity resulting from the interaction of these hormones may increase expression of many target genes that are critical for oncogenesis and may contribute to neoplastic progression.

Estrogen receptor-associated expression of keratinocyte growth factor and its possible role in the inhibition of apoptosis in human breast cancer

Although estrogen is known to play a crucial role in the pathogenesis of breast cancer, the molecular mechanisms underlying the action of estrogen remain elusive. In the present study, we focused on keratinocyte growth factor (KGF) and its receptor (KGFR) in the pathogenesis of breast cancer, as a growth factor mediating estrogen action, since significant roles of KGF were demonstrated in various steroid hormone-dependent tissues. First, using paraffin-embedded specimens from 42 breast cancer patients, we examined expression patterns of KGF and KGFR by both immunohistochemistry using newly generated antibodies and nonradioactive in situ hybridization with T-T dimerized synthetic oligonucleotide probes. We next compared the results with the expression of estrogen receptor (ER) alpha and beta, proliferative activity and apoptotic frequency (TUNEL staining). Also, the similar approaches were taken to analyze the expression and role of KGF in ER-positive (MCF7, ZR-75-1) and ER-negative (SK-BR-3, MDA-MB-231) human breast cancer cell lines in vitro. In the surgical specimens, KGF was expressed in cancer cells as well as stromal cells in 19/42 cases (45%), while KGFR was found in cancer cells in 24/42 cases (57%). The distribution of protein and mRNA in the analysis of both KGF and KGFR expression generally coincided. Moreover, KGF expression was closely associated with the expression of ER alpha, and the coexpression of KGF and KGFR significantly correlated with lower TUNEL index, but not with proliferative activity. In accordance with the in vivo findings, KGF expression was detected only in ER alpha-positive MCF7 and ZR-75-1 cells in vitro. And more importantly, we found the inhibitory effect of KGF upon the induction of apoptosis by anticancer drugs in MCF7 cells. Collectively, our results indicate that ER alpha may be involved in KGF expression, and that KGF may play antiapoptotic roles, rather than mitogenic, in human breast cancer.

Estrogen/EGF receptor interactions in breast cancer: rationale for new therapeutic combination strategies

In the therapy of estrogen receptor (ER) positive human mammary carcinomas, the treatment with the antiestrogen tamoxifen has been well established. However, the development of hormone resistance is an important factor in breast cancer progression against endocrine therapy. The presence of the receptor for EGF (EGFR) correlates with lack of response towards antiestrogen therapy. The EGFR is not only involved in tumor cell growth, survival signaling, cell migration, metastasis formation and angiogenesis, but also seems to confer reduced responses of tumor cells towards anti-hormones. Concomitant inhibition of both, the receptors for estrogen and EGF may be necessary to improve breast cancer therapy.

Adaptive hypersensitivity following long-term estrogen deprivation: involvement of multiple signal pathways

Long-term estrogen deprivation causes hypersensitivity of MCF-7 cells to the mitogenic effect of estradiol (E2) which is associated with activation of mitogen-activated protein kinase (MAPK). However, several lines of evidence indicate that MAPK activation is not the exclusive mechanism for E2 hypersensitivity and multiple signal pathways might be involved. The current study explores the possible role of the PI3 kinase (PI3K) pathway in development of E2 hypersensitivity. Basal PI3K activity in long-term estrogen deprived MCF-7 cells (LTED) was elevated as evidenced by increased phosphorylation of three downstream effectors, Akt, p70 S6 kinase, and eukaryotic initiation factor-4E binding protein (4E-BP1), which was blocked by the specific inhibitor of PI3K, LY294002. Dual blockade of both MAPK and PI3K completely reversed E2 hypersensitivity of LTED cells. Enhancement in aromatase activity is another phenomenon accompanied with E2 hypersensitivity. In aromatase over-expressing MCF-7 cells, aromatase activity was reduced by inhibitors of MAPK and PI3K suggesting the involvement of protein phosphorylation in the regulation of aromatase activity. Our data suggest that in addition to the MAP kinase pathway, activation of the PI3 kinase pathway is involved in E2 hypersensitivity, which develops during adaptation of MCF-7 cells to the low estrogen environment.

Oestrogen Receptor-Mediated Modulation of the EGFR/MAPK Pathway in Tamoxifen-Resistant MCF-7 Cells

Oestrogen receptor (ER) levels are usually maintained on acquisition of tamoxifen resistance in the clinic, however, tumour re-growth is associated with increased expression of epidermal growth factor receptor (EGFR) and activation of the mitogen activated protein kinase (MAPK) pathway. In the present study we have used the ER down-regulator fulvestrant ('Faslodex') to investigate the influence of the ER on growth of a tamoxifen-resistant (TAM-R) human breast cancer cell line. Expression levels of ER mRNA and protein were equivalent in parental wild-type MCF-7 (WT) and TAM-R cells. Fulvestrant eliminated ER protein expression and inhibited proliferation in both cell lines. The growth inhibitory effects of fulvestrant were associated with a decrease in basal EGFR, c-erbB2 and ERK1/2 activity in TAM-R but not WT cells. ER functionality as determined by oestrogen response element (ERE)-luciferase reporter activity and expression of PgR, pS2 and transforming growth factor alpha (TGFalpha) was significantly reduced in TAM-R compared to WT cells and was further decreased by fulvestrant treatment in both cell lines. Epidermal growth factor (EGF) and TGFalpha significantly increased EGFR/MAPK pathway activity in both cell lines. Ligand-induced EGFR/MAPK activation promoted TAM-R cell growth in both the absence and presence of fulvestrant, whereas no proliferative activity was observed under the same conditions in WT cells. These results suggest that the ER modulates EGFR/MAPK signalling efficiency in TAM-R cells possibly through the regulation of TGFalpha availability. This effect may be overcome by the action of exogenous EGFR ligands, which strengthen EGFR/MAPK signalling activity to generate endocrine-insensitive cell growth.

An in vitro model of epithelial cell growth stimulation in the rodent mammary gland

Mouse mammary epithelial cell cultures previously described bring about extensive proliferation and a cell population with the appropriate markers for luminal ductal epithelial cells, and also the ability to form normal tissue after implantation into mice. This success may result from a culture environment that resembles certain aspects of the environment in the mammary gland. Mouse mammary epithelial cells, whose proliferation is limited when plated alone, can be stimulated to multiply by contact with lethally irradiated cells of the LA7 rat mammary tumour line. Most of the proliferative stimulus is imparted by direct cell contact between LA7 and mouse mammary cells. Junctions, including adherens junctions, form among all cells in the culture, much as junctions form in the mammary gland. LA7 cells secrete TGFalpha and bFGF, factors found in the mammary gland, and factors to which mouse mammary cells respond in culture. Mouse mammary cells express keratins 8 and 18, markers for luminal cells of the mammary duct. LA7 cells express keratin 14 and vimentin, markers for myoepithelial cells. These facts, taken together, fit a model of cell replacement in an epithelial tissue and also imitate the relationship between luminal ductal cells and myoepithelial cells in the mammary gland. This method of culturing cells is useful, not only for in vitro-in vivo carcinogenesis studies, but also for the study of mechanisms by which growth signals are imparted from one cell to another.

Epidermal growth factor receptor (EGFR) as a target in cancer therapy: understanding the role of receptor expression and other molecular determinants that could influence the response to anti-EGFR drugs

The epidermal growth factor receptor (EGFR) is a rational target for cancer therapy because it is commonly expressed at a high level in a variety of solid tumours and it has been implicated in the control of cell survival, proliferation, metastasis and angiogenesis. However, despite evidence to suggest that EGFR expression is associated with a poor prognosis in some tumours (e.g. breast, head and neck carcinomas), the situation is by no means clear-cut. A number of issues are worthy of particular consideration, including how EGFR is measured and whether these assays are sensitive and reproducible, which mechanisms other than increased EGFR expression might cause the EGFR signalling drive to be increased, and the relationship, if any, between EGFR expression and the response to EGFR-targeted agents.

Modulation of estrogen receptor alpha function and stability by tamoxifen and a critical amino acid (Asp-538) in helix 12

Estrogen receptor alpha (ER) is a ligand-activated transcription factor implicated in breast cancer growth. Selective estrogen receptor modulators (SERMs), such as tamoxifen (4-OHT), bind to the ER and affect the position of helix 12, thereby influencing coregulator binding and ER transcriptional activation. Previous studies have shown that a triple mutation in helix 12 (3m; D538A/E542A/D545A) caused a change in ER stability and obliterated 4-OHT action (Liu, H., Lee, E. S., de los Reyes, A., Zapf, J. W., and Jordan, V. C. (2001) Cancer Res. 61, 3632-3639). Two approaches were taken to determine the role of individual mutants (D538A, L540Q, E542A, and D545A) on the activity and stability of the 4-OHT.ER complex. First, mutants were evaluated using transient transfection into ER-negative T47D:C4:2 cells with an ERE3-luciferase reporter, and second, transforming growth factor alpha (TGFalpha) mRNA was used as a gene target in situ for stable transfectants of MDA-MB-231 cells. Transcriptional activity occurred in the presence of estrogen in all of the mutants, although a decreased response was observed in the L540Q, 3m, and D538A cells. The 3m and D538A mutants lacked any estrogenic responsiveness to 4-OHT, whereas the other mutations retained estrogen-like activity with 4-OHT. Unlike the other mutants, the ER was degraded in the D538A mutant with 4-OHT treatment. However, increasing the protein levels of the mutant with the proteasome inhibitor MG132 did not restore the ability of 4-OHT to induce TGFalpha mRNA. We suggest that Asp-538 is a critical amino acid in helix 12 that not only reduces the estrogen-like actions of 4-OHT but also facilitates the degradation of the 4-OHT.D538A complex. These data further illustrate the complex role of specific surface amino acids in the modulation of the concentration and the estrogenicity of the 4-OHT.ER complex.

Estrogen Receptor-dependent and Estrogen Receptor-independent Pathways for Tamoxifen and 4-Hydroxytamoxifen-induced Programmed Cell Death

The therapeutic efficacy of tamoxifen (TAM) in cancer therapy is thought to arise primarily from its ability to compete with estrogens for binding to the estrogen receptor (ER). We show that TAM and its active metabolite, 4-hydroxytamoxifen (OHT), can actively induce programmed cell death through distinct ER-dependent and ER-independent pathways. The ER-independent pathway is activated by 10-20 microm TAM and OHT and by 10-20 microm 17beta-estradiol and raloxifene, and occurs in ER-negative cells. The ER dependence of a second pathway, caused by submicromolar concentrations of TAM and OHT, was demonstrated by the ability of the ER ligands 17beta-estradiol, raloxifene, and ICI 182,780 to effectively block the cell death-inducing effects of TAM and OHT. Because the p38-specific inhibitor SB203580 blocks OHT.ER-induced cell death, stress kinase pathways are likely involved. ER-independent cell death triggers classic caspase-dependent apoptosis. However, although OHT.ER triggers some hallmarks of apoptosis, including Bax translocation and cytochrome c release, the absence of poly(ADP-ribose) polymerase cleavage or DNA laddering indicates that the death pathway involved is caspase-independent. The OHT.ER-dependent cell death pathway appears to diverge from classical apoptosis at the level of caspase 9 activation. The ability to promote ER-dependent programmed cell death represents a novel activity of TAM and OHT.

Role of steroid hormones and growth factors in breast cancer

Breast cancer is the most common cancer in women worldwide and its incidence is increasing. Oestrogens and mitogenic growth factors may play an important role in the development of breast cancer, whereas inhibitory growth factors may prevent the development of breast cancer. Only about 5 to 10% of cases of breast cancer are due to inheritance of mutations in the BRCA1 or BRCA2 tumour suppressor genes. Mutations in the p53 tumour suppressor gene are commonly found in sporadic breast cancers. Retinoic acid and carotenoids may play a protective role in breast cancer since they inhibit the growth of the oestrogen receptor-positive MCF-7 breast cancer cell line. The presence of oestrogen and progesterone receptors predicts the likelihood of benefit from hormonal therapy. Amplification of the c-erbB2 oncogene in breast cancers is associated with a poor prognosis. It is now apparent that there is a complex, productive cross-talk between oestrogen-directed and growth factor-directed pathways which are believed to markedly reinforce their individual cellular effects on growth and gene responses.

The docking protein Gab2 is overexpressed and estrogen regulated in human breast cancer

Grb2-associated binder 2 (Gab2) is a recently identified member of the Gab/Daughter of sevenless family of docking proteins, which localize, amplify and integrate signaling pathways activated by various receptors including receptor tyrosine kinases (RTKs). To date, Gab2 signaling has been primarily investigated in hematopoietic cells. Here we report marked overexpression of Gab2 in a subset of breast cancer cell lines relative to normal breast epithelial strains and a trend for increased Gab2 expression in estrogen receptor (ER)-positive lines. Overexpression relative to normal ductal epithelium was also observed in some primary breast cancers. In MCF-7 breast cancer cells Gab2 was markedly tyrosine phosphorylated in response to heregulin and also following EGF, insulin or bFGF administration, indicating that a variety of RTKs implicated in breast cancer development or progression couple to this docking protein. In hormone-responsive breast cancer cells, GAB2 mRNA and protein expression were induced by estradiol in a manner sensitive to the pure anti-estrogen ICI 182780, indicating that this regulation is mediated via the ER. Gab2 therefore represents a novel link between steroid and growth factor signaling in breast cancer, and when overexpressed, may modulate the sensitivity of breast cancer cells to these important growth regulators.

Adaptive mechanisms induced by long-term estrogen deprivation in breast cancer cells

Clinical observations suggest that human breast tumors can adapt in response to endocrine therapy by developing hypersensitivity to estradiol. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided evidence that long-term deprivation of estradiol causes adaptive hypersensitivity. The enhanced responses to estradiol do not involve mechanisms acting at the level of transcription of estrogen regulated genes. We found no evidence of hypersensitivity when examining the effects of estradiol on regulation of c-myc, pS2, progesterone receptor, several ER reporter genes or c-myb in hypersensitive cells. On the other hand, deprivation of breast cells long term was found to up-regulate a separate pathway whereby the estrogen receptor co-opts a classical growth factor pathway and induces rapid non-genomic effects. Through this pathway, estradiol caused rapid activation of mitogen-activated protein (MAP) kinase. In exploring the mechanisms mediating this event, we found that estradiol binds to cell membrane associated estrogen receptors and causes phosphorylation of Shc, an adaptor protein usually involved in growth factor signaling pathways. ERalpha was found to complex with Shc under these conditions. In turn, Shc bound Grb-2 and Sos which resulted in the activation of MAP kinase. The pure antiestrogen, ICI 182,780, blocked several steps in the rapidly responding ER alpha, Shc, MAP kinase pathway. These non-genomic effects of estradiol produced biologic effects by activating Elk and by inducing morphologic changes in cell membranes. Using confocal microscopy, we demonstrated that estradiol caused a rapid alteration in membrane ruffling, the formation of pseudopodia and translocation of ER alpha to regions contiguous with the cell membrane. These morphologic effects could be blocked with a pure anti-estrogen. We conclude that long-term estradiol deprived cells utilize both genomic (transcriptional) and rapid, non-genomic estradiol induced pathways. We postulate that synergy between these two pathways acting at the level of the cell cycle is responsible for adaptive hypersensitivity.

Modulation of epidermal growth factor receptor in endocrine-resistant, estrogen-receptor-positive breast cancer

An increasing body of evidence demonstrates that growth factor networks are highly interactive with estrogen receptor signaling in the control of breast cancer growth. As such, tumor responses to antihormones are likely to be a composite of the estrogen receptor and growth factor inhibitory activity of these agents. The modulation of growth factor networks during endocrine response is examined, and in vitro and clinical evidence is presented that epidermal growth factor receptor signaling, maintained in either an estrogen receptor-dependent or a receptor-independent manner, is critical to antihormone-resistant breast cancer cell growth. The considerable potential of the epidermal growth factor receptor-selective tyrosine kinase inhibitor Iressa (ZD 1839) to efficiently treat, and perhaps even prevent, endocrine-resistant breast cancer is highlighted.

A novel zinc finger transcription factor with two isoforms that are differentially repressed by estrogen receptor-alpha

Estrogen receptor-alpha (ERalpha) can induce the expression of genes in response to estrogen by binding to estrogen response elements in the promoters of target genes. There is growing evidence that ERalpha can alter patterns of gene expression in response to ligand by regulating the activity of other factors through a direct protein-protein interaction. To identify other factors that are regulated by ERalpha, a yeast two-hybrid screen was performed that identified a novel Cys(2)His(2) zinc finger protein named ZER6. The ZER6 protein contains a Kruppel-associated box domain and six Cys(2)His(2) zinc fingers. Transcripts from the ZER6 gene can have alternate 5' exons and encode either a p71 or p52 isoform. The p52-ZER6 protein interacts strongly with ERalpha in the presence of 17beta-estradiol, whereas the p71-ZER6 isoform has a HUB-1 amino-terminal domain that inhibits the interaction with ERalpha. A consensus ZER6 binding element was defined using PCR-assisted binding site selection. In COS-1 cells, both the p52 and p71 isoforms can activate transcription through the ZER6 binding element; however, in the presence of ERalpha, transactivation by the p52 isoform is specifically repressed. Overexpression of the p52 isoform was able to abrogate activation by p71-ZER6. Expression of ZER6 was largely restricted to the mammary gland with a lower level of expression in the kidney. We conclude that ZER6 is a novel zinc finger transcription factor in which regulation of transcription in hormone-responsive cells can be controlled by the relative level of expression of two distinct isoforms.

Selective coactivation of estrogen-dependent transcription by CITED1 CBP/p300-binding protein

CITED1, a CBP/p300-binding nuclear protein that does not bind directly to DNA, is a transcriptional coregulator. Here, we show evidence that CITED1 functions as a selective coactivator for estrogen-dependent transcription. When transfected, CITED1 enhanced transcriptional activation by the ligand-binding/AF2 domain of both estrogen receptor-alpha (ERalpha) and ERbeta in an estrogen-dependent manner, but it affected transcriptional activities of other nuclear receptors only marginally. CITED1 bound directly to ERalpha in an estrogen-dependent manner through its transactivating domain, and this binding activity was separable from its p300-binding activity. CITED1 was strongly expressed in nulliparous mouse mammary epithelial cells and, when expressed in ER-positive MCF-7 breast cancer cells by transduction, exogenous CITED1 enhanced sensitivity of MCF-7 cells to estrogen, stabilizing the estrogen-dependent interaction between p300 and ERalpha. The estrogen-induced expression of the transforming growth factor-alpha (TGF-alpha) mRNA transcript was enhanced in the CITED1-expressing MCF-7 cells, whereas estrogen-induced expression of the mRNA transcripts for progesterone receptor or pS2 was not affected. Chromatin immunoprecipitation assay revealed that endogenous CITED1 is recruited to the chromosomal TGF-alpha promoter in MCF-7 cells in an estrogen-dependent manner but not to the pS2 promoter. These results suggest that CITED1 may play roles in regulation of estrogen sensitivity in a gene-specific manner.

Estrogen suppression of EGFR expression in breast cancer cells: a possible mechanism to modulate growth

Epidermal growth factor receptor (EGFR) is a transmembrane receptor whose overexpression in breast cancer predicts for poor prognosis and is inversely correlated with expression of estrogen receptor (ER). This study was designed to investigate whether estrogen plays an active role in suppression of EGFR expression in estrogen-responsive breast cancer cell lines expressing low levels of EGFR. Upon withdrawal of estrogen, EGFR mRNA and protein increased 3-6 fold in MCF-7, T47D, and BT474 ER+ breast cancer cells. This was reversible upon addition of estradiol back to the culture media, but only after prolonged treatment. Nuclear run-on assays and studies with the transcription inhibitor actinomycin D demonstrated that regulation is at the transcriptional level. These results indicate that in the presence of estrogen, ER+ breast cancer cells possess active mechanisms to suppress EGFR expression. Up-regulation of EGFR in response to estrogen depletion and growth inhibition could represent an attempt to rescue cell growth by utilizing an alternative pathway. Indeed, we found that estrogen-depleted breast cancer cells are more sensitive to the mitogenic effects of EGF and TGF-alpha, and simultaneous blockade of both estrogen and EGFR signaling pathways induced cell death. J. Cell. Biochem. Suppl. 36: 232-246, 2001.