William L. McGuire Memorial Symposium. Estrogen and progestin effects in human breast carcinogenesis

The Divergent Effects of Ovarian Steroid Hormones in the MCF-7 Model for Luminal A Breast Cancer: Mechanistic Leads for Therapy

The growth modulating effects of the ovarian steroid hormones 17β-estradiol (E₂) and progesterone (PRG) on endocrine-responsive target tissues are well established. In hormone-receptor-positive breast cancer, E₂ functions as a potent growth promoter, while the function of PRG is less defined. In the hormone-receptor-positive Luminal A and Luminal B molecular subtypes of clinical breast cancer, conventional endocrine therapy predominantly targets estrogen receptor function and estrogen biosynthesis and/or growth factor receptors. These therapeutic options are associated with systemic toxicity, acquired tumor resistance, and the emergence of drug-resistant cancer stem cells, facilitating the progression of therapy-resistant disease. The limitations of targeted endocrine therapy emphasize the identification of nontoxic testable alternatives. In the human breast, carcinoma-derived hormone-receptor-positive MCF-7 model treatment with E₂ within the physiological concentration range of 1 nM to 20 nM induces progressive growth, upregulated cell cycle progression, and downregulated cellular apoptosis. In contrast, treatment with PRG at the equimolar concentration range exhibits dose-dependent growth inhibition, downregulated cell-cycle progression, and upregulated cellular apoptosis. Nontoxic nutritional herbs at their respective maximum cytostatic concentrations (IC₉₀) effectively increase the E₂ metabolite ratio in favor of the anti-proliferative metabolite. The long-term exposure to the selective estrogen-receptor modulator tamoxifen selects a drug-resistant phenotype, exhibiting increased expressions of stem cell markers. The present review discusses the published evidence relevant to hormone metabolism, growth modulation by hormone metabolites, drug-resistant stem cells, and growth-inhibitory efficacy of nutritional herbs. Collectively, this evidence provides proof of the concept for future research directions that are focused on novel therapeutic options for endocrine therapy-resistant breast cancer that may operate via E₂- and/or PRG-mediated growth regulation.

Circulating sex steroids and breast cancer risk in premenopausal women

Evidence from both laboratory and epidemiologic studies indicate a key role of hormones in the etiology of breast cancer. In epidemiologic studies, indirect data, including the consistent associations observed between reproductive factors and breast cancer risk, support an important contribution of hormones to risk. Recently, the associations between circulating hormones in premenopausal women and subsequent risk of breast cancer have been evaluated. To date, both positive and null associations have been observed for estrogens and inverse and null associations for progesterone with breast cancer risk. For estrogens, the relationships may vary by menstrual cycle phase (e.g., follicular versus luteal phase), although this requires confirmation. Few studies have evaluated estrogen metabolites in relation to breast cancer risk; hence, no conclusions can yet be drawn. Findings for the largely adrenal-derived dehydroepiandrosterone (DHEA) and DHEA sulfate also are inconsistent and may vary by age. However, relatively consistent positive associations have been observed between testosterone (or free testosterone) levels and breast cancer risk; these associations are of similar magnitude to those confirmed among postmenopausal women. In this review, we summarize current evidence and identify gaps and inconsistencies that need to be addressed in future studies of sex steroids and premenopausal breast cancer risk.

Progesterone receptor B recruits a repressor complex to a half-PRE site of the estrogen receptor alpha gene promoter

In the present study, we demonstrate that elevated levels of the progesterone receptor (PR)-B isoform in breast cancer cells induces down-regulation of estrogen receptor (ER) alpha mRNA and protein content, causing concomitant repression of the estrogen-regulated genes insulin receptor substrate 1, cyclin D1, and pS2, addressing a specific effect of PR/PR-B on ERalpha gene transcription. ERalpha gene promoter activity was drastically inhibited by PR-B overexpression. Promoter analysis revealed a transcriptionally responsive region containing a half-progesterone response element (PRE) site located at -1757 bp to -1752 bp. Mutation of the half-PRE down-regulated the effect induced by PR/PR-B overexpression. Moreover chromatin immunoprecipitation analyses revealed an increase of PR bound to the ERalpha-regulatory region encompassing the half-PRE site, and the recruitment of a corepressor complex containing nuclear receptor corepressor (NCoR) but not silencing mediator of retinoid and thyroid hormone receptor and DAX1, concomitantly with hypoacetylation of histone H4 and displacement of RNA polymerase II. Furthermore, NCoR ablation studies demonstrated the crucial involvement of NCoR in the down-regulatory effects due to PR-B overexpression on ERalpha protein and mRNA. We also demonstrated that the ERalpha regulation observed in MCF-7 cells depended on PR-B expression because PR-B knockdown partially abrogates the feedback inhibition of ERalpha levels after estrogenic stimulus. Our study provides evidence for a mechanism by which overexpressed PR-B is able to actively repress ERalpha gene expression.

Regulation of estrogen receptor (ER) levels in MCF-7 cells by progesterone metabolites

Estradiol-17beta (E2) may participate in carcinoma of mammary cells containing estradiol receptors (ER) at sufficient levels. Hence, the regulation of ER levels may be important for the progression of estrogen-dependent mammary carcinomas. Our previous findings that the progesterone metabolite, 5alpha-pregnane-3,20-dione (5alphaP), exhibits marked mitogenic and metastatic properties, whereas the progesterone metabolites, 4-pregnen-3alpha-ol-20-one (3alphaHP) and 4-pregnen-20alpha-ol-3-one (20alphaHP), oppose these actions, prompted examination of the possible effects of these progesterone metabolites on ER concentration in MCF-7 breast cancer cells. Cells were exposed for 24h to 0 (control) or 10(-10) to 10(-6)M E2, 5alphaP, 3alphaHP, 20alphaHP or combinations of these steroids, and ER concentrations were determined for intracellular estrogen receptors by specific binding of [(3)H]E2. The total ER number (nuclear plus cytosolic) in control samples was 2551+/-164 per cell. E2 and 5alphaP resulted in significant dose-dependent increases in total ER numbers ( approximately 1.6-fold and approximately 2.2-fold at 10(-6)M, respectively). In combination, E2+5alphaP resulted in additive increases in ER numbers. Individually, 3alphaHP and 20alphaHP each resulted in dose-dependent decreases (43% and 54% at 10(-6)M, respectively) in total ER numbers and inhibited the E2- or 5alphaP-induced increases in ER levels. In combination, 3alphaHP+20alphaHP resulted in dose-dependent additive suppression of ER levels. Treatment with cycloheximide or actinomycin D indicated that both transcription and translation are involved in 5alphaP and 3alphaHP action on ER numbers. Real time RT-PCR showed increases in expression of ERalpha transcripts due to 5alphaP and increases in expression of ERbeta due to 3alphaHP; expression levels of either ERalpha or ERbeta were not significantly altered when cells were treated with 5alphaP+3alphaHP. The results are the first to show that the pro- and anti-cancer progesterone metabolites also have marked selective (up or down) regulatory effects on ER levels in MCF-7 breast cancer cells.

Estrogen receptor alpha expression in normal human breast epithelium is consistent over time

If increased expression of estrogen receptor alpha (ER) in benign breast epithelium increases susceptibility to breast cancer, such overexpression should be stable over time. There are no published data regarding this important aspect of ER expression in breast epithelium. We examined the temporal consistency of ER expression in the normal breast tissue of 28 women who had 2 separate breast surgical procedures, at least 6 months apart (mean interval, 2.8 years). Paraffin embedded breast tissue blocks containing an adequate sample of normal breast epithelium and no cancer, were sectioned and processed using the 6F11 antibody and standard immunohistochemical techniques. The ER labelling index (ER LI) was calculated by counting a mean of 2,000 epithelial cells. The median ER LI at first sampling was 13.6 and at second sample 15.5, with R(2) = 0.34 and p = 0.001. The ER LI was categorized into high and low values, using a threshold of 10. Twenty-four women (85.7%) showed concordance of high and low expression between the 2 samples (p = 0.002). There were 11 women who were premenopausal at both time points. Among them, much of the variation in ER LI was explained by differences in the menstrual cycle day at the time of sampling and adding the day of cycle to the regression model substantially improved the correlation between first and second labeling indices. These data suggest that ER expression of normal breast tissue is fairly consistent over time and support the notion that overexpression of ER in normal epithelium is a constant feature of the high risk breast.

High level of EGF-R expression in carcinomatous skin invasion: Does it reflect the tissue characteristics of the breast carcinoma aggressiveness?

Background: The normal function and distribution of EGF-R and its role in breast cancer aggressiveness, prognosis and prediction, have become extremely important in the light of the recently developed methods of EGF-R targeting. In the aim to investigate the relationship between EGF-R and the aggressive tumor behavior, the EGF-R content was analyzed as related to the presence of inflammatory breast skin involvement. Methods: EGF-R, ER and PR content was determined at diagnosis, using the biochemical methods, in the group of 103 unselected breast cancer patients, either in primary tumors (TU), lymph nodes (LN) or skin tissue samples (65, 27 and 11 cases respectively). In 10 patients with inflammatory breast cancers, TU/LN tissue was sampled from 3, and skin from 7 patients. Results: ER and PR content was significantly higher in tumor and LN tissue, compared to the invaded skin the EGF-R content was, on the contrary, significantly higher in skin than in TU or LN tissue. However, no difference was found between TU and LN in all three receptors' content. When the receptor content was analyzed in 10 patients with inflammatory breast cancer, higher levels of both ER and PR were found in tumor biopsies than in skin biopsies, while for the EGF-R the result was opposite. Significantly lower ER content and a trend towards higher EGF-R content was found in the inflammatory breast cancers in comparison to the non-inflammatory ones. Conclusion: Although we examined a small number of patients, our results suggest that the EGF-R could be a marker of breast cancer aggressiveness. However, the influence of the normal skin cells contaminating the biopsied tumor tissue cannot be ruled out. The predictive role of EGF-R deserves to be further investigated especially in locally advanced inflammatory breast cancer patients.

The evaluation of human breast lesions with magnetic resonance imaging and proton magnetic resonance spectroscopy

PURPOSE

MR spectroscopy (MRS) assists in lesion characterization and diagnosis when combined with magnetic resonance imaging (MRI). Cancerous lesions demonstrate elevated composite choline levels arising from increased cellular proliferation. Our study investigated if MR spectroscopy of the breast would be useful for characterizing benign and malignant lesions.

MATERIALS AND METHODS

Single voxel proton MR spectroscopy (MRS) was acquired as part of an MR imaging protocol in 38 patients referred upon surgical consultation. The MR spectra were read independently in a blinded fashion without the MR images by three spectroscopists. The MRI exam was interpreted in two settings: (a) as a clinical exam with detailed histories and results from previous imaging studies such as mammography or ultrasound included and (b) as a blinded study without prior histories or imaging results.

RESULTS

Elevated choline levels were demonstrated by MRS in 19 of the 23 confirmed cancer patients. The sensitivity and specificity for determining malignancy from benign breast disease with MRS alone were 83 and 87%, respectively, while a blinded MRI review reported 95 and 86%, respectively.

CONCLUSIONS

Proton MR spectroscopy provides a noninvasive, biochemical measure of metabolism. The technique can be performed in less than 10 min as part of an MRI examination. MRI in combination with MRS may improve the specificity of breast MR and thereby, influence patient treatment options. This may be particularly true with less experienced breast MRI readers. In exams where MRI and MRS agree, the additional confidence measure provided by MRS may influence the course of treatment.

Growth inhibition and growth stimulation by estradiol of estrogen receptor transfected human breast epithelial cell lines involve different pathways

Epidermal growth factor (EGF) and estradiol (E2) are important mitogens in breast epithelial cells, and expression of epidermal growth factor receptor (EGFR) and estrogen receptor (ER) is often inversely correlated in human breast cancer cells. Stable transfection of ER-negative cells with ER cDNA is not sufficient to restore E2-mediated growth stimulation, on the contrary, E2 often inhibits growth of ER-transfected cell lines. In this study we used the ER-transfected human breast epithelial cell lines HMT-3522F9, growth inhibited by E2 in the presence of EGF, and HMT-3522F9/S3B, growth stimulated by E2 in the absence of EGF. In S3B cells, no active MAP kinase could be detected in response to E2, suggesting that signalling through the MAP kinase is not the major pathway in the E2-mediated growth stimulation. Interestingly, a decreased level of active MAP kinase was observed in HMT-3522F9 cells in response to E2, indicating that in these cells cross-talk between the ER and the MAP kinase signalling pathway could be due to the E2-mediated growth inhibition. Moreover, we found that EGF-induced signalling also could be reduced by E2 in S3B cells, suggesting a general mechanism of action by E2 in cells concomitantly expressing ER and EGFR.

An in vitro model of human breast carcinogenesis: epigenetic aspects

A review is given of 12 years of research on a human breast epithelial cell line, HMT-3522, which has undergone malignant transformation in vitro without being exposed to known carcinogenic agents. Epigenetic aspects of the malignant transformation have been considered and the results have been viewed in a clinical context. It has been concluded that the history and characteristics of the cell line resembles the comedocarcinoma of the human breast. It is hypothesized that progression from benign lesion to comedo in situ carcinoma and invasive carcinoma occurs if low levels of epidermal growth factor are prevailing in the microenvironment. Our data also suggest that breast cancer developed under high epidermal growth factor receptor activity is estrogen receptor negative, while suppression of epidermal growth factor receptor activity promotes estrogen responsive breast cancer.

Association between estradiol, estrogen receptors, total lipids, triglycerides, and cholesterol in patients with benign and malignant breast tumors

This study addresses the correlation between the levels of estradiol (E2), total lipids, triglycerides, and cholesterol in serum and tissue samples of age-matched patients with benign (40 cases; 16 were premenopausal and 24 were postmenopausal) and malignant (50 cases; 17 were premenopausal and 33 were postmenopausal) breast tumors. Estradiol levels were determined in serum and cytosol, estrogen receptors (ER) were assayed in cytosol, and total lipids, triglycerides and cholesterol were determined in serum and membrane fractions of all benign and malignant breast disease patients. Serum E2 was significantly higher in malignant cases than benign ones (P<0.05) with a significant reduction (40%) in postmenopausal than premenopausal women. ER-positive tumors were significantly higher in postmenopausal women with malignant breast tumors than benign cases (P<0.05). Tissue levels of total lipids, triglycerides, and cholesterol were highly significantly increased in breast cancer women than women with benign breast diseases (P<0.05, P<0.005 and P<0.05 respectively) and they were also significantly correlated with estradiol levels. It could be concluded that the uptake of lipids from plasma by the tumor tissue is greatly correlated to estradiol and it may confirm the possible role of lipids as risk factor in breast cancer.

Progestin effects on long-term growth, death, and Bcl-xL in breast cancer cells

The effect of progestins on proliferation of breast cancer has been a controversial area. We have consistently reported progestin stimulation of proliferation in the progesterone receptor-rich human breast cancer cell line T47D. Other authors, under other conditions, have agreed that progestins stimulate, but for just one turn of the cell cycle. To our knowledge, this is the first in vitro report to show progestin stimulation of human breast cancer cell growth for multiple, probably unlimited, cell cycles, while control cells are dying. This is accompanied by progestin up-regulation of the antiapoptotic protein bcl-xL, no effect on the proapoptotic protein bax, and, surprisingly, diminution of the antiapoptotic protein bcl-2. Thus, progestins both serve as survival factors and stimulate proliferation, implying a possible similar role in breast cancer patients. The data support the notion that many patients may benefit more from combined antiprogestin-antiestrogen therapy than from antiestrogen alone, and suggest bcl-x(L) as a possible target for breast cancer therapy.

BCAR1, a human homologue of the adapter protein p130Cas, and antiestrogen resistance in breast cancer cells

BACKGROUND

Treatment of breast cancer with the antiestrogen tamoxifen is effective in approximately one half of the patients with estrogen receptor-positive disease, but tumors recur frequently because of the development of metastases that are resistant to tamoxifen. We have previously shown that mutagenesis of human estrogen-dependent ZR-75-1 breast cancer cells by insertion of a defective retrovirus genome caused the cells to become antiestrogen resistant. In this study, we isolated and characterized the crucial gene at the breast cancer antiestrogen resistance 1 (BCAR1) locus.

METHODS/RESULTS

Transfer of the BCAR1 locus from retrovirus-mutated, antiestrogen-resistant cells to estrogen-dependent ZR-75-1 cells by cell fusion conferred an antiestrogen-resistant phenotype on the recipient cells. The complete coding sequence of BCAR1 was isolated by use of exon-trapping and complementary DNA (cDNA) library screening. Sequence analysis of human BCAR1 cDNA predicted a protein of 870 amino acids that was strongly homologous to rat p130Cas-adapter protein. Genomic analysis revealed that BCAR1 consists of seven exons and is located at chromosome 16q23.1. BCAR1 transcripts were detected in multiple human tissues and were similar in size to transcripts produced by retrovirus-mutated ZR-75-1 cells. Transfection of BCAR1 cDNA into ZR-75-1 cells again resulted in sustained cell proliferation in the presence of antiestrogens, confirming that BCAR1 was the responsible gene in the locus.

CONCLUSIONS

Overexpression of the BCAR1 gene confers antiestrogen resistance on human ZR-75-1 breast cancer cells. Overexpression of BCAR1 in retrovirus-mutated cells appears to result from activation of the gene's promoter. The isolation and characterization of this gene open new avenues to elucidating mechanisms by which the growth of human breast cancer becomes independent of estrogen.

Should prolactin be reconsidered as a therapeutic target in human breast cancer?

Although prolactin (PRL) has been long suspected to be involved in the progression of human breast cancer, the failure of clinical improvement by treatment with dopamine agonists, which lower circulating levels of PRL, rapidly reduced the interest of oncologists concerning a potential role of this pituitary hormone in the development of breast cancer. Within the last few years, however, several studies reported first, that PRL is also synthesized in the mammary gland, and second that it exerts its proliferative action in an autocrine/paracrine manner. These observations have led to a reconsideration of the role of PRL as an active participant in breast cancer and are an impetus to search for alternative strategies aimed at inhibiting the proliferative effects of PRL on tumor mammary cells. In this report, we discuss the three possible levels that can be targeted for this purpose: the mammary synthesis of PRL, the interaction of the hormone with its receptor at the surface of mammary cells, and the intracellular signaling cascades triggered by the activated receptor. For each of these steps, we discuss the molecular event(s) that can be targeted, our understanding of the mechanisms involving these putative targets as well as the tools currently available for their inhibition. Besides its proliferative effect, PRL is also involved in the control of angiogenesis through one of its cleaved fragments, named PRL 16K, which has been shown to inhibit the angiogenic process. In view of this biological activity, we discuss first the cleavage of PRL with respect to the human mammary gland and, second, the hypothesis speculating that a balance between the proliferative effect of intact PRL and the anti-angiogenic activity of its 16K-like fragments might be physiologically relevant in the evolution of mammary tumors. If true, our hypothesis would suggest that the enzymatic cleavage of PRL could represent a new molecular target in the search for alternative strategies in the treatment of breast cancer.

Prognosis and prediction of response in breast cancer: the current role of the main biological markers

In the medical literature there are frequently conflicting reports on the utility of biological tumour markers available in the clinical management of breast cancer. In this review we analyse current information on the relationships between the most widely investigated breast cancer biological markers including oestrogen and progesterone receptors, p53, Bcl-2, c-erbB-2, cyclin expression, proliferative activity, DNA ploidy and the urokinase plasminogen activation system, as well as their relevance to prognosis and response to clinical treatment. By biological prognostic indicator, we mean a marker that correlates with survival and disease-free survival; the term predictor marker indicates a marker that is capable of predicting tumour sensitivity or resistance to various therapies. Similarly to other authors' experiences, our analysis suggests that oestrogen receptors are weak prognostic indicators and good predictors of response to endocrine therapy. Furthermore, there are consistent data suggesting that proliferation indices are good indicators of prognosis, and that they are directly related to response to chemotherapy and closely related to response to hormonotherapy. On the contrary, there is no evidence or conflicting data for all of the other biological markers. These should be considered in the context of randomized trials in order to precisely define their prognostic and predictive roles. p53 and c-erbB-2 seem to be the most promising factors, but their use in routine practice still needs validation.

Estrogen receptor expression in benign breast epithelium and breast cancer risk

BACKGROUND

Estrogen exposure is a major risk factor for breast cancer. Increased estrogen responsiveness of breast epithelium may enhance this effect. We examined the relationship between breast cancer diagnosis and 1) the presence and absence of estrogen receptor expression in benign breast epithelium, 2) the level of expression and 3) its variation during the menstrual cycle, and 4) other established risk factors. e.g., age, age at menarche, parity, and family history.

METHODS

We measured estrogen receptor expression (as % of positive cells) by immunohistochemistry in normal breast epithelium from 376 women undergoing diagnostic or therapeutic breast surgery. Data on established risk factors were collected prior to surgery and those on menstrual cycle dates at the time of surgery. Logistic regression was used to assess risks (odds ratios [ORs]).

RESULTS

The crude OR for breast cancer in women with estrogen receptor-positive breast epithelium versus those without was 3.16 (95% confidence interval [CI] = 1.89-5.28), with an OR of 2.49 (95% CI = 1.25-4.96) for premenopausal and an OR of 3.32 (95% CI = 1.43-7.68) for postmenopausal women. The ORs remained high and statistically significant after controlling for age and other breast cancer risk factors. The level of estrogen receptor expression was higher in patients with breast cancer than in control subjects and it was related to breast cancer risk in postmenopausal women (P trend <.005). Expression declined as expected in premenopausal control subjects as the menstrual cycle progressed but rose in breast cancer patients (P trend <.015).

CONCLUSIONS

The overexpression of estrogen receptors in normal breast epithelium may augment estrogen sensitivity and hence the risk of breast cancer.

Mechanisms by which high maternal fat intake during pregnancy increases breast cancer risk in female rodent offspring

Emerging evidence indicates that a high in utero estrogenic environment increases breast cancer risk in women. We have proposed that a maternal intake of a high-fat diet is a source for high pregnancy estrogen levels and increases breast cancer risk among female offspring. In this review, the role of dietary fat in breast cancer, particularly during fetal life, is discussed. In addition, we provide possible mechanisms of action of the effects of a high-fat diet on the breast. These mechanisms include protein kinase C, estrogens and estrogen receptor, and alterations in mammary parenchymal structures.

Human estrogen receptor (ER) gene promoter-P1: estradiol-independent activity and estradiol inducibility in ER+ and ER- cells

Estrogen receptor (ER) is expressed at a low level in normal tissues such as breast and uterus but at a high level in breast and endometrial carcinomas. A proximal element (ERF-1) located between positions +133 and +204 relative to the promoter P1 major initiation site has been recently identified in ER+ cells and contributes to the differential promoter activity between ER+ and ER- cells. In this study, MCF7 and HeLa cells were transfected with chloramphenicol acetyltransferase constructs containing ER gene promoter P1 sequences. We show here that the sequences lying between nucleotides +13 to +212 are also essential for transcription at the ER gene promoter P1 in ER- cells, which do not express ERF-1. Interestingly, on gel shift experiments, a complex specific to ER- cells forms in the region spanning nucleotides +123 to +210. We also show that promoter P1 is responsive to estradiol in cells expressing endogenous (MCF7) or exogenous ER. We further demonstrate, using mutational analysis and gel retardation assays, that the three half-estrogen response elements located between nucleotides -420 and -892 are responsible for the estradiol inducibility of promoter P1. Because estradiol has a mitogenic effect on both breast and endometrial epithelial cells, our data would give an insight into the role of estrogens in the occurrence of breast and endometrial carcinomas.

Novel progesterone target genes identified by an improved differential display technique suggest that progestin-induced growth inhibition of breast cancer cells coincides with enhancement of differentiation

Progesterone is an important regulator of normal and malignant breast epithelial cells. In addition to stimulating development of normal mammary epithelium, it can be used to treat hormone-dependent breast tumors. However, the mechanism of growth inhibition by progestins is poorly understood, and only a limited number of progesterone target genes are known so far. We therefore decided to clone such target genes by means of differential display polymerase chain reaction. In this paper, we describe an improved differential display strategy that eliminates false positives, along with the identification of nine positive (TSC-22, CD-9, Na+/K+-ATPase alpha1, desmoplakin, CD-59, FKBP51, and three unknown genes) and one negative progesterone target genes (annexin-VI) from the mammary carcinoma cell line T47D, which is growth-inhibited by progestins. None of these genes have been reported before to be progesterone targets. Regulation of desmoplakin, CD-9, CD-59, Na+/K+-ATPase alpha1, and annexin-VI by the progestin suggests that progesterone induces T47D cells to differentiate. Three of these genes were repressed by estradiol and up-regulated by the progestin. Estradiol treatment of T47D cells also leads to formation of lamellipodia and delocalization of two cell adhesion proteins, E-cadherin and alpha-catenin. All these effects were reversed by the progestin. These data suggest that estradiol dedifferentiates T47D cells, while progestins have the opposite effect. This may be linked to the capacity of progestins to inhibit tumor growth.

Genetic mechanisms of estrogen-independence in breast cancer

Endocrine therapy is effective in the treatment of breast cancer. Adjuvant treatment with tamoxifen reduces tumor recurrence and achieves increased survival. In metastatic disease, tamoxifen treatment accomplishes objective responses in +/- 50% of the patients with estrogen receptor-positive primary tumors. However, the response duration is limited due to the inevitable development of metastases resistant to tamoxifen. The mechanisms leading to tamoxifen resistance are largely unknown. We have set out to identify genetic pathways in the tumor cells causing failure of tamoxifen therapy. We selected an estrogen-dependent human breast cancer cell line (ZR-75-1) and demonstrated that genetic and epigenetic alterations can change the hormone-response phenotype of these cells. Subsequently, we applied insertional mutagenesis with defective retroviruses to these ZR-75-1 breast cancer cells. Integration of a retrovirus in the cellular DNA alters the genome structure and may modify the expression of genes in its surroundings. As a result of the altered gene expression, the biological phenotype of the infected cell may be changed. The infected ZR-75-1 cells were subjected to tamoxifen selection and a panel of tamoxifen-resistant cell lines has been established. Screening for a common integration site for the retrovirus has provided, so far, compelling evidence for the involvement of at least one genetic locus (BCAR 1) in breast cancer antiestrogen resistance in vitro.

Characterization of a nontumorigenic human breast epithelial cell line stably transfected with the human estrogen receptor (ER) cDNA

Estrogens play an important role in breast cancer and the effect of estrogen on growth of breast cancer cells has been extensively studied. However, only little information is available about the response of normal breast epithelial cells to estrogen, mainly due to the difficulties in establishing estrogen receptor (ER)-positive human breast epithelial cells in culture. We have stably transfected the human estrogen receptor (hER) wt cDNA into the ER-negative, spontaneously immortalized human breast epithelial cell line, HMT-3522S1, in order to develop a model for studying the effect of estrogen on nonmalignant human breast epithelial cells. Characterization of the transfected clone F9 confirmed incorporation of the estrogen receptor gene in the genome, expression of hER mRNA and hER protein. However, proliferation of F9 cells was inhibited by both estradiol (E2) and tamoxifen, whereas the pure antiestrogen ICI 182,780 had no effect on cell proliferation. This seems paradoxical since E2 stimulated the expression of the endogenous genes, TGF-alpha, cathepsin D, and alpha1-antitrypsin. In breast cancer cell lines, high expression of these genes is correlated to estrogen-stimulated cell proliferation. The spontaneously immortalized HMT-3522S1 cells transfected with wt ER cDNA behave similarly to cell lines from nonmalignant breast tissue immortalized by carcinogens and transfected with mutated ER cDNA as described by others. The discrepancy between growth inhibition and induction of positive growth factors by E2 indicates that either ER-positive nonmalignant breast epithelial cells are growth-inhibited by E2 in contrast to malignant cells or that introduction of the ER into ER-negative cells is not sufficient for restoring "normal' estrogen responsiveness.

Differential responsiveness of proliferation and cytokeratin release to stripped serum and oestrogen in the human breast cancer cell line, MCF-7

In vitro research into hormone sensitivity and the relation to proliferation of cytokeratin release from cancer cells is scarce. Therefore, we examined the stimulation of proliferation and the release of cytokeratins in a breast cancer cell culture model. Cell growth was stimulated by 17 beta-oestradiol (10(-11) M), stripped serum (10%) and by the two together. Cytokeratin release was stimulated only by stripped serum, oestradiol having no effect. After long incubation periods (> 12 h), cytokeratin release also commenced in the control and oestradiol treatments. Release rate versus time analysis suggested that there are two different release processes. Cytokeratin release was first stimulated at a stripped serum concentration approximately 100 times lower than that which initiated proliferation. Pharmacological alteration of proliferation with cordyceptin resulted in growth changes without alterations in cytokeratin release. We conclude that cytokeratin release in these cells is unrelated to proliferation, independent of oestrogen action and probably in some way related to growth factor receptor function.

Genetic alterations in breast cancer

The etiology of breast cancer involves a complex interplay of various factors, including genetic alterations. Many studies have been devoted to the identification and characterization of mutations that occur frequently during breast tumorigenesis. The major types of genetic abnormalities that are frequently observed in breast tumors are amplification of protooncogenes (MYC, ERBB2) and DNA from chromosome band 11q13; mutation of TP53; and loss of heterozygosity from chromosomes and chromosome arms 1, 3p, 6q, 7q, 8p, 11, 13q, 16q, 17, 18q, and 22q. The latter may correspond to losses or inactivations of tumor suppressor genes. Recently, linkage analyses of large families with a predisposition to breast cancer have been performed in order to map breast cancer susceptibility genes (TP53, BRCA1, BRCA2). The findings have thrown light on the molecular mechanisms of breast cancer and have enabled various genetic markers to be used in clinical oncology.

[Hormone replacement therapy in menopause and cancers]

The long term outcome analysis of estrogen replacement therapy shows that the carcinologic risk is far more inferior than the osseous and cardiovascular risks of which the prevention is ensured by estrogen. In the same way, the quality of life improvement during the years following menopause is important. For a female population without personal risk of breast cancer, the substitutive hormone therapy offers numerous advantages which have been for a long time refused to women with previously treated breast cancer. Any dogmatic behaviour is presently justified. On the contrary, the hormonal replacement therapy requires beforehand an analysis as exact as possible of the risks of its prescription as of its non-prescription and a responsibility taking shared between the physician and his patient. The progresses of the molecular biology and the expansion of randomized trials will permit with no doubt to recognize more easily for each patient, even the one who would have been previously treated for a breast cancer, the respective impact of carcinologic, cardiovascular and osseous risks.

The role of TGF-beta production in growth inhibition of breast-tumor cells by progestins

We have studied the influence of synthetic progestins on the estrogen-induced proliferation and type-beta transforming-growth-factor (TGF-beta) production of 3 breast-tumor cell lines. In long-term growth experiments, progestins inhibited proliferation of T47D cells, while a specific T47D variant and MCF7 cells were not affected, despite the presence of functional progesterone receptors. The effect of progestins was biphasic, since an initial stimulation of proliferation was followed by a prolonged inhibition. This response suggests the involvement of a progestin-induced negative growth regulator. We show here that TGF-beta s do not fulfill this role since (i) the progestin-induced T47D cells are not sensitive to TGF-beta 1, -beta 2 or -beta 3, (ii) secretion of TGF-beta s is decreased by progestins in all 3 cell lines, and (iii) TGF-beta neutralizing antibodies do not reverse progestin-induced growth inhibition. Furthermore, evidence was obtained that medium conditioned by T47D cells does not contain any other growth inhibitor to which this cell line responds in a negative autocrine manner. In contrast, MCF7 cells are growth-inhibited by all 3 TGF-beta isoforms, but are not growth-inhibited by progestins, suggesting that there is no correlation between growth inhibition by progestins and responsiveness to and production of TGF-beta in vitro. Although TGF-beta is a strong growth inhibitor of normal mammary tissue, recent evidence suggests that, in malignant tissue, enhanced TGF-beta secretion correlates with increased malignancy. Therefore, a progestin-induced decrease in TGF-beta production, as observed here, may lead to enhanced proliferation of normal but not malignant mammary epithelium.

Potential impact on breast cancer risk of circulating insulin-like growth factor I modifications induced by oral HRT in menopause

Unlike parenteral estrogens, oral estrogen administration in menopause causes, through its hepatocellular action, a significant decrease of circulating insulin-like growth factor I (IGF-I) levels; this effect is opposed by the addition of an androgenic progestogen. In vitro studies show that IGF-I is a potent mitogen for 'estrogen responsive' breast cancer cells. Moreover, some findings in breast cancer patients and in women treated with tamoxifen suggest that reduction of circulating IGF-I could be protective to the breast. However, by also considering (1) the potential action on breast cancer cells of IGF-II, (2) the possible consequences of the growth hormone (GH) increase caused by the IGF-I reduction and (3) the fact that in vitro results are not simply transferable to the in vivo condition, other 'scenarios' can be envisaged, besides the favorable one. In support of the latter, there are epidemiologic data which suggest that oral estrogen use could have some favorable peculiarities with regards to breast cancer risk. The associated decrease in circulating IGF-I level could well be one of these peculiarities.

Cadherins, steroids and cancer

The cadherins are a family of calcium-dependent cell adhesion molecules which are thought to be key regulators of morphogenesis. This review contains a discussion of the structure, function and regulation of these cell adhesion molecules. In particular, we discuss recent studies that demonstrate the ability of steroids to modulate cadherin levelsin vivo. We speculate that steroids and estrogenic organochlorines exert their diverse morphoregulatory actions on tissues by altering cadherin levels.

Estradiol regulates E-cadherin mRNA levels in the surface epithelium of the mouse ovary

E-cadherin is a calcium-dependent cell adhesion molecule which is present in the surface epithelium of the mouse ovary. This cell adhesion molecule has been implicated as a suppressor of tumorigenesis. The regulators of E-cadherin mRNA levels in the ovary have not been identified. We have examined the ability of steroids to influence ovarian E-cadherin mRNA levels in vivo. Immature mice were injected with either progesterone, testosterone, dihydrotestosterone, 17-beta estradiol or 17-alpha estradiol. Only 17-beta estradiol caused a rapid and significant increase in the ovarian E-cadherin mRNA levels. We speculate that this steroid is a key regulator of E-cadherin-mediated epithelial cell interactions in vivo. We also discuss the possibility that the carcinogenic effects of estrogens on the ovary may be related to their ability to regulate E-cadherin levels in this tissue.

A 27 kDa heat shock protein that has anomalous prognostic powers in early and advanced breast cancer

This paper describes a prospective immunohistochemical analysis of 27 kDa heat shock protein (HSP27) in 361 patients with primary breast cancer in relation to disease-free survival (DFS) and survival from first relapse (SR). Oestradiol (ER) and progesterone (PR) receptors were also quantitated and related to the HSP27 data. While ER positively predicted a good outcome for both DFS and SR, HSP27 positivity predicted a prolonged SR but short DFS. The association between HSP27 and DFS only attained statistical significance in node-negative patients. Subgroup analysis reinforced the complementary relationship of HSP27 and ER for SR and opposing influences for DFS. In both node-negative and node-positive women, ER+ HSP27- patients had a longer DFS than ER- HSP27+ counterparts. There was no relationship between HSP27 and overall survival. HSP27 staining was highly correlated with ER but not PR, patient age, tumour size or menstrual status. There was a marginal correlation (P = 0.04) with histological grade with well-differentiated tumours having the highest HSP27. Cox multivariate regression analysis of the contribution of HSP27 in the presence of data on ER, PR, stage, nodal status and histological grade indicated that HSP27 was not of independent prognostic importance for DFS or overall survival and was only of borderline significance for OS (P < 0.07). However, in the absence of ER and PR data, HSP27 staining is an effective way of getting the same prognostic information. HSP27 staining appears to correlate with different biological features in early and advanced breast, high HSP27 being linked with short DFS in node-negative patients but with prolonged survival from first recurrence.

Breast cancer and depot-medroxyprogesterone acetate: a review

Depot-medroxyprogesterone acetate (DMPA) has been used world-wide since 1964 as a contraceptive in spite of the fact that it was only in 1992 licensed for contraceptive use in the USA due to concern about a possible breast cancer risk. Two recent studies have considered DMPA use and risk of breast cancer and these and earlier studies are reviewed here. Overall, the results are reassuring but there is some evidence that breast cancer risk may be increased in women using DMPA when very young and particularly in recent users. Current knowledge of the biology of human breast cancer is such that it is difficult to judge the biological plausibility of this evidence. There is no doubt that DMPA is a highly effective form of contraception and any overall assessment must take into account all the relevant risks and benefits. Thus, the risk-benefit equations in developed and developing countries must allow for different levels of maternal mortality and morbidity, as well as differing underlying cancer rates.