The role of c-Myc in estrogen regulation of vascular endothelial growth factor (VEGF) and of the vasculature function has been investigated in breast cancer cells and tumors. The studies were performed on MCF7 wild-type cells and MCF7-35im clone, stably transfected with an inducible c-Myc gene. In vitro and ex vivo methods for investigating molecular events were integrated with in vivo magnetic resonance imaging of the vascular function. The results showed that the c-Myc upregulation by estrogen is necessary for the transient induction of VEGF transcription; however, overexpression of c-Myc alone is not sufficient for this induction. Furthermore, both c-Myc and the activated estrogen receptor α (ERα) were shown to co-bind the VEGF promoter in close proximity, indicating a novel mechanism for estrogen regulation of VEGF. Studies of long-term estrogen treatment and overexpression of c-Myc alone demonstrated regulation of stable VEGF expression levels in vitro and in vivo, maintaining steady vascular permeability in tumors. However, withdrawal of estrogen from the tumors resulted in increased VEGF and elevated vascular permeability, presumably due to hypoxic conditions that were found to dominate VEGF overexpression in cultured cells. This work revealed a cooperative role for ERα and c-Myc in estrogen regulation of VEGF and the ability of c-Myc to partially mimic estrogen regulation of angiogenesis. It also illuminated the differences in estrogen regulation of VEGF during transient and long-term sustained treatments and under different microenvironmental conditions, providing a complementary picture of the in vitro and in vivo results.
Maya Dadiani, Dalia Seger, Tamar Kreizman, Daria Badikhi, Raanan Margalit, Raya Eilam, and Hadassa Degani
S M Hyder
Angiogenesis is a key event, which occurs in both normal and pathological expansion of tissues and provides the nourishment necessary for growth. The role of angiogenic growth factors in breast pathology is rapidly gaining recognition since scientists and clinicians realized that these factors could function as molecular targets event 550 209822 for controlling tumor expansion. Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis. Although significant advances have been made in understanding the sex-steroid-dependent regulation of this key factor, the role of VEGF in controlling breast tumors is not well understood. In this review, I discuss recent studies describing the role of the female sex steroids estrogens and progestins in the regulation of VEGF in breast cancer cells. Furthermore, I present a summary of recent studies from other biological systems (mainly focused on tumor biology) directed towards providing us with a better understanding of the regulation of classical VEGF and VEGF receptors. I propose that by extending such studies we will gain deeper insights into how we might combat the progression of breast cancer by controlling hormone-dependent angiogenesis within tumor tissue. I believe that information gained from such studies will permit us to target angiogenic growth factors and their initiated signal transduction pathways in a more precise and selective manner, and thereby to control the formation of new blood vessels that fuel the rapid growth of breast tumors. Finally, it is my hope that the concepts discussed here will help elucidate molecular targets in the hormone-dependent angiogenesis pathway that will ultimately allow us to overcome anti-hormone resistance and to provide insights into how we might pursue the concept of chemoprevention by considering ‘angioprevention’ as the end point.
Maria Eugenia Sabatino, Juan Pablo Petiti, Liliana del Valle Sosa, Pablo Anibal Pérez, Silvina Gutiérrez, Carolina Leimgruber, Alexandra Latini, Alicia Inés Torres, and Ana Lucía De Paul
Although pituitary adenomas represent 25% of intracranial tumors, they are usually benign, with the mechanisms by which these tumors usually avoid an invasive profile and metastatic growth development still remaining unclear. In this context, cellular senescence might constitute a plausible explanation for the benign nature of pituitary adenomas. In this study, we investigated the emergence of cellular senescence as a growth control mechanism during the progression of estrogen-induced pituitary tumors. The quantification of Ki67-immunopositive cells in the pituitaries of estrogenized male rats after 10, 20, 40, and 60 days revealed that the mitogenic potential rate was not sustained for the whole period analyzed and successively decreased after 10 days of estrogen exposure. In addition, the expression of cellular senescence features, such as the progressive rise in the enzymatic senescence-associated b-galactosidase (SA-b-gal) activity, IL6, IL1b, and TGFb expression, was observed throughout pituitary tumor development. Furthermore, tumoral pituitary cells also displayed nuclear pATM expression, indicating activated DNA damage signaling, with a significant increase in p21 expression also being detected. The associations among DNA damage signaling activation, SA-b-gal expression, and p21 may provide a reliable combination of senescence-associated markers for in vivo pituitary senescence detection. These results suggest a role for this cellular process in the regulation of pituitary cell growth. Thus, cellular senescence should be conceived as a contributing component to the benign nature of pituitary adenomas, thereby influencing the capability of the pituitary gland to avoid unregulated cell proliferation.
W F Symmans, D J Fiterman, S K Anderson, M Ayers, R Rouzier, V Dunmire, J Stec, V Valero, N Sneige, C Albarracin, Y Wu, J S Ross, P Wagner, R L Theriault, B Arun, H Kuerer, K R Hess, W Zhang, G N Hortobagyi, and L Pusztai
The pathogenesis of breast cancers that do not express estrogen receptors or Her-2/neu receptors (ER−/HER2− phenotype) is incompletely understood. We had observed markedly elevated gene expression of gamma-aminobutyric acid type A (GABAA) receptor subunit π (GABAπ, GABRP) in some breast cancers with ER−/HER2− phenotype. In this study, transcriptional profiles (TxPs) were obtained from 82 primary invasive breast cancers by oligonucleotide microarrays. Real-time reverse transcription–polymerase chain reaction (RT–PCR) was used to measure GABAπ gene expression in a separate cohort of 121 invasive breast cancers. GABAπ gene expression values from TxP and RT–PCR were standardized and compared with clinicopathologic characteristics in the 203 patients. GABAπ gene expression was increased in 16% of breast cancers (13/82 TxP, 20/ 121 RT–PCR), particularly in breast cancers with ER−/HER2− phenotype (60%), and breast cancers with basal-like genomic profile (60%). The profile of genes coexpressed with GABAπ in these tumors was consistent with an immature cell type. In multivariate linear regression analysis, the level of GABAπ gene expression was associated with ER−/HER2− phenotype (P<0.0001), younger age at diagnosis (P=0.0003), and shorter lifetime duration of breastfeeding (≤ 6 months) in all women (P=0.017) and specifically in parous women (P=0.013). GABAπ gene expression was also associated with combinations of high grade with ER−/HER2− phenotype (P=0.002), and with Hispanic ethnicity (P=0.036). GABAπ gene expression is increased in breast cancers of immature (undifferentiated) cell type and is significantly associated with shorter lifetime history of breastfeeding and with high-grade breast cancer in Hispanic women.
Teresa Elo, Lan Yu, Eeva Valve, Sari Mäkelä, and Pirkko Härkönen
Estrogens contribute to the development and growth of the prostate and are implicated in prostate tumorigenesis. In their target tissues, estrogens mediate their effects via estrogen receptor α (ERα (ESR1)) and β (ERβ (ESR2)). Hyperplasia and decreased differentiation of epithelial cells in the prostate have been reported in ER β knockout (BERKO) mice. Herein, we studied the effect of ERβ deficiency on prostate tumorigenesis by crossing BERKOFVB mice with prostate-targeted human fibroblast growth factor 8b transgenic (FGF8b-Tg) mice. Consistent with results described in our previous report, the prostates of 1-year-old FGF8b-Tg mice displayed stromal aberrations, prostatic intraepithelial neoplasia (mPIN) lesions, inflammation, and occasionally cancer. The prostates of BERKOFVB mice exhibited mild epithelial hypercellularity and inflammation. The prostate phenotypes of FGF8b-Tg-BERKOFVB mice closely resembled those of FGF8b-Tg mice. However, mucinous metaplasia, indicated by Goblet-like cells in the epithelium, was significantly more frequent in the prostates of FGF8b-Tg-BERKOFVB mice when compared with FGF8b-Tg mice. Furthermore, compared with FGF8b-Tg mice, there was a tendency for increased frequency of inflammation but milder hyperplasias in the prostate stroma of FGF8b-Tg-BERKOFVB mice. The expression levels of mRNAs for FGF8b-regulated genes including osteopontin (Spp1), connective tissue growth factor (Ctgf), fibroblast growth factor receptors (Fgfrs), and steroid hormone receptors and cytokines were similar in the prostates of FGF8b-Tg and FGF8b-Tg-BERKOFVB mice. Our results indicate that ERβ plays a role in the differentiation of the prostatic epithelium and, potentially, in the defensive mechanism required for protection against inflammation but do not support a direct tumor-suppressive function of ERβ in the prostate of FGF8b-Tg mice.
Joanna E Burdette and Teresa K Woodruff
Activin is a member of the transforming growth factor β superfamily that regulates mammary cell function during development, lactation, and in cancer. Activin slows the growth of breast cancer cells by inducing G0/G1 cell cycle arrest. Estrogen is a steroid hormone that stimulates the proliferation of mammary epithelial cells in development and oncogenesis. The crosstalk between estrogen and activin that regulates activin ligand expression, activin and estrogen signal transduction, and cell cycle arrest was investigated in this study. Estrogen antagonized activin-dependent production of plasminogen activator inhibitor 1 (PAI-1) mRNA, while activin repressed estrogen-dependent transcription of trefoil factor 1. The repression of estrogen signaling by activin was recapitulated using a simple estrogen response element-luciferase construct and was enhanced in the presence of overexpressed estrogen receptor α (ERα). In contrast, estrogen-mediated repression of activin signaling could not be recapitulated on a simple CAGA Smad-binding element but did inhibit the short PAI-1 promoter, p3TP-luciferase, especially when ERα was overexpressed. Repression of both estrogen- and activin-regulated transcription was found to be ligand induced and Smad3 dependent. In addition to transcriptional repression, estrogen also reduced the amount of activin B mRNA and protein produced by MCF7 breast cancer cells. These studies demonstrate the importance of activin and estrogen crosstalk during mammary cell growth and cancer initiation.
Adena E Rosenblatt, Maria Ines Garcia, Leah Lyons, Yingqiu Xie, Carol Maiorino, Laurent Désiré, Joyce Slingerland, and Kerry L Burnstein
Rac1, a Rho GTPase, modulates diverse cellular processes and is hyperactive in some cancers. Estrogen receptor-alpha (ERα) in concert with intracellular signaling pathways regulates genes associated with cell proliferation, tumor development, and breast cancer cell survival. Therefore, we examined the possibility of Rac1 and ERα crosstalk in breast cancer cells. We found that Rac1 enhanced ERα transcriptional activity in breast cancer cells. Vav3, a Rho guanine nucleotide exchange factor that activates Rac1, was an upstream mediator, and P21/Cdc42/Rac1 activating kinase-1 (Pak-1) was a downstream effector of Rac1 enhancement of ERα activity. These results suggest that Rac1 may prove to be a therapeutic target. To test this hypothesis, we used a small molecule Rac inhibitor, EHT 1864, and found that EHT 1864 inhibited ERα transcriptional activity. Furthermore, EHT 1864 inhibited estrogen-induced cell proliferation in breast cancer cells and decreased tamoxifen-resistant breast cancer cell growth. EHT 1864 decreased activity of the promoter of the ERα gene resulting in down-regulation of ERα mRNA and protein levels. Therefore, ERα down-regulation by EHT 1864 is the likely mechanism of EHT 1864-mediated inhibition of ERα activity and estrogen-stimulated breast cancer cell proliferation. Since ERα plays a critical role in the pathogenesis of breast cancer and the Rac inhibitor EHT 1864 down-regulates ERα expression and breast cancer cell proliferation, further investigation of the therapeutic potential of Rac1 targeting in the treatment of breast cancer is warranted.
Daniele Generali, Stephen B Fox, Alfredo Berruti, Maria P Brizzi, Leticia Campo, Simone Bonardi, Simon M Wigfield, Paolo Bruzzi, Alessandra Bersiga, Giovanni Allevi, Manuela Milani, Sergio Aguggini, Luigi Dogliotti, Alberto Bottini, and Adrian L Harris
The purpose of this study is to investigate the role of carbonic anhydrase IX (CAIX) expression in predicting the response to epirubicin and disease-free survival (DFS) in breast cancer patients enrolled in a single institution trial of primary anthracycline and tamoxifen therapy. CAIX expression was assessed in 183 patients with T2–4 N0–1 breast cancer enrolled in a randomized trial comparing four cycles of single agent epirubicin versus epirubicin + tamoxifen as primary systemic treatment. All patients received postoperatively four cycles of the four weekly i.v. cyclophosphamide, methotrexate, 5-fluorouracil regimen. Patients with estrogen receptor (ER)-positive primary tumors received 5 years of adjuvant tamoxifen. Pretreatment, p53 (P = 0.007), c-erbB2 (P < 0.01), and Ki67 (P = 0.02) were directly associated with CAIX expression, while bcl2 (P < 0.000) and ER (P = 0.000) and progesterone receptor (PgR; P < 0.01) were inversely correlated. In multivariate analysis, only high p53 and low bcl2 were independently associated with CAIX positivity. CAIX immunostaining was significantly associated with poor outcome for DFS (P < 0.002) and overall survival (P = 0.001). In multivariate analysis, a significant interaction was found between CAIX and markers of hormone sensitivity, bcl2 (P = 0.01), ER (P = 0.02), PgR (P = 0.02), and lymph node involvement (P = 0.04), in predicting DFS. Presently, there are few clinical markers of resistance to tamoxifen treatment in ER-positive tumors. CAIX expression in breast cancer patients shows a negative predictive role of treatment efficacy in ER-positive patients on the adjuvant tamoxifen after primary chemo-endocrine therapy. Studies investigating the effects of pH on tamoxifen uptake and the effects of therapy with CA inhibitors are planned.
R J Santen and H A Harvey
Aromatase, a cytochrome P-450 enzyme that catalyzes the conversion of androgens to estrogens, is the major mechanism of estrogen synthesis in the post-menopausal woman. We review some of the recent scientific advances which shed light on the biologic significance, physiology, expression and regulation of aromatase in breast tissue. Inhibition of aromatase, the terminal step in estrogen biosynthesis, provides a way of treating hormone-dependent breast cancer in older patients. Aminoglutethimide was the first widely used aromatase inhibitor but had several clinical drawbacks. Newer agents are considerably more selective, more potent, less toxic and easier to use in the clinical setting. This article reviews the clinical data supporting the use of the potent, oral competitive aromatase inhibitors anastrozole, letrozole and vorozole and the irreversible inhibitors 4-OH androstenedione and exemestane. The more potent compounds inhibit both peripheral and intra-tumoral aromatase. We discuss the evidence supporting the notion that aromatase inhibitors lack cross-resistance with antiestrogens and suggest that the newer, more potent compounds may have a particular application in breast cancer treatment in a setting of adaptive hypersensitivity to estrogens. Currently available aromatase inhibitors are safe and effective in the management of hormone-dependent breast cancer in post-menopausal women failing antiestrogen therapy and should now be used before progestational agents. There is abundant evidence to support testing these compounds as first-line hormonal therapy for metastatic breast cancer as well as part of adjuvant regimens in older patients and quite possibly in chemoprevention trials of breast cancer.
Annu Makker and Madhu Mati Goel
Endometrioid endometrial carcinoma (EEC), also known as type 1 endometrial cancer (EC), accounts for over 70–80% of all cases that are usually associated with estrogen stimulation and often develops in a background of atypical endometrial hyperplasia. The increased incidence of EC is mainly confined to this type of cancer. Most EEC patients present at an early stage and generally have a favorable prognosis; however, up to 30% of EEC present as high risk tumors, which have invaded deep into the myometrium at diagnosis and progressively lead to local or extra pelvic metastasis. The poor survival of advanced EC is related to the lack of effective therapies, which can be attributed to poor understanding of the molecular mechanisms underlying the progression of disease toward invasion and metastasis. Multiple lines of evidence illustrate that epithelial–mesenchymal transition (EMT)-like events are central to tumor progression and malignant transformation, endowing the incipient cancer cell with invasive and metastatic properties. The aim of this review is to summarize the current knowledge on molecular events associated with EMT in progression, invasion, and metastasis of EEC. Further, the role of epigenetic modifications and microRNA regulation, tumor microenvironment, and microcystic elongated and fragmented glands like invasion pattern have been discussed. We believe this article may perhaps stimulate further research in this field that may aid in identifying high risk patients within this clinically challenging patient group and also lead to the recognition of novel targets for the prevention of metastasis – the most fatal consequence of endometrial carcinogenesis.