Hormonal aspects of breast cancer. Growth factors, drugs and stromal interactions

Hydroxychloroquine inhibits autophagy to potentiate antiestrogen responsiveness in ER+ breast cancer

PURPOSE

Estrogen receptor-α (ERα)-targeted therapies including tamoxifen (TAM) or Faslodex (ICI) are used to treat ER(+) breast cancers. Up to 50% of tumors will acquire resistance to these interventions. Autophagy has been implicated as a major driver of antiestrogen resistance. We have explored the ability of hydroxychloroquine (HCQ), which inhibits autophagy, to affect antiestrogen responsiveness.

EXPERIMENTAL DESIGN

TAM-resistant MCF7-RR and ICI-resistant/TAM cross-resistant LCC9 ER(+) breast cancer cells were injected into mammary fat pads of female athymic mice and treated with TAM and/or ICI in combination with oral low-dose HCQ.

RESULTS

We show that HCQ can increase antiestrogen responsiveness in MCF7-RR and LCC9 cells and tumors, likely through the inhibition of autophagy. However, the combination of ICI+HCQ was less effective than HCQ alone in vivo, unlike the TAM+HCQ combination. Antiestrogen treatment stimulated angiogenesis in tumors but did not prevent HCQ effectiveness. The lower efficacy of ICI+HCQ was associated with ICI effects on cell-mediated immunity within the tumor microenvironment. The mouse chemokine KC (CXCL1) and IFNγ were differentially regulated by both TAM and ICI treatments, suggesting a possible effect on macrophage development/activity. Consistent with these observations, TAM+HCQ treatment increased tumor CD68(+) cells infiltration, whereas ICI and ICI+HCQ reduced peripheral tumor macrophage content. Moreover, macrophage elimination of breast cancer target cells in vitro was reduced following exposure to ICI.

CONCLUSION

HCQ restores antiestrogen sensitivity to resistant tumors. Moreover, the beneficial combination of TAM+HCQ suggests a positive outcome for ongoing neoadjuvant clinical trials using this combination for the treatment of ER(+) ductal carcinoma in situ lesions.

Exposures to synthetic estrogens at different times during the life, and their effect on breast cancer risk

Women are using estrogens for many purposes, such as to prevent pregnancy or miscarriage, or to treat menopausal symptoms. Estrogens also have been used to treat breast cancer which seems puzzling, since there is convincing evidence to support a link between high lifetime estrogen exposure and increased breast cancer risk. In this review, we discuss the findings that maternal exposure to the synthetic estrogen diethylstilbestrol during pregnancy increases breast cancer risk in both exposed mothers and their daughters. In addition, we review data regarding the use of estrogens in oral contraceptives and as postmenopausal hormone therapy and discuss the opposing effects on breast cancer risk based upon timing of exposure. We place particular emphasis on studies investigating how maternal estrogenic exposures during pregnancy increase breast cancer risk among daughters. New data suggest that these exposures induce epigenetic modifications in the mammary gland and germ cells, thereby causing an inheritable increase in breast cancer risk for multiple generations.

Breaking the cycle: An insight into the role of ERα in eukaryotic cell cycles

There have been numerous reviews written to date on estrogen receptor (ER), focusing on topics such as its role in the etiology of breast cancer, its mode of regulation, its role as a transcriptional activator and how to target it therapeutically, just to name a few. One reason for so much attention on this nuclear receptor is that it acts not only as a prognostic marker, but also as a target for therapy. However, a relatively undiscovered area in the literature regarding ER is how its activity in the presence and absence of ligand affects its role in proliferation and cell cycle transition. In this review, we provide a brief overview of ER signaling, ligand dependent and independent, genomic and non-genomic, and how these signaling events affect the role of ER in the mammalian cell cycle.

Selective activation of trophoblast-specific PLAC1 in breast cancer by CCAAT/enhancer-binding protein beta (C/EBPbeta) isoform 2

The trophoblast-specific gene PLAC1 (placenta-specific 1) is ectopically expressed in a wide range of human malignancies, most frequently in breast cancer, and is essentially involved in cancer cell proliferation, migration, and invasion. Here we show that basal activity of the PLAC1 promoter is selectively controlled by ubiquitous transcription factor SP1 and isoform 2 of CCAAT/enhancer-binding protein beta that we found to be selectively expressed in placental tissue and cancer cells. Binding of both factors to their respective elements within the PLAC1 promoter was essential to attain full promoter activity. Estrogen receptor alpha (ERalpha) signaling further augmented transcription and translation of PLAC1 and most likely accounts for the positive correlation between PLAC1 expression levels and the ERalpha status we observed in primary breast cancer specimens. DNA affinity precipitation and chromatin immunoprecipitation assays revealed that transactivation of the PLAC1 promoter by ligand-activated ERalpha is based on a nonclassical pathway independent of estrogen-response elements, by tethering of ERalpha to DNA-bound CCAAT/enhancer-binding protein beta-2, and SP1. Our findings provide first insight into a novel and hitherto unknown regulatory mechanism governing selective activation of trophoblast-specific gene expression in breast cancer.

Combined effect of CCND1 and COMT polymorphisms and increased breast cancer risk

BACKGROUND

Estrogens are crucial tumorigenic hormones, which impact the cell growth and proliferation during breast cancer development. Estrogens are metabolized by a series of enzymes including COMT, which converts catechol estrogens into biologically non-hazardous methoxyestrogens. Several studies have also shown the relationship between estrogen and cell cycle progression through activation of CCND1 transcription.

METHODS

In this study, we have investigated the independent and the combined effects of commonly occurring CCND1 (Pro241Pro, A870G) and COMT (Met108/158Val) polymorphisms to breast cancer risk in two independent Caucasian populations from Ontario (1228 breast cancer cases and 719 population controls) and Finland (728 breast cancer cases and 687 population controls). Both COMT and CCND1 polymorphisms have been previously shown to impact on the enzymatic activity of the coded proteins.

RESULTS

Here, we have shown that the high enzymatic activity genotype of CCND1High (AA) was associated with increased breast cancer risk in both the Ontario [OR: 1.3, 95%CI (1.0-1.69)] and the Finland sample [OR: 1.4, 95%CI (1.01-1.84)]. The heterozygous COMTMedium (MetVal) and the high enzymatic activity of COMTHigh (ValVal) genotype was also associated with breast cancer risk in Ontario cases, [OR: 1.3, 95%CI (1.07-1.68)] and [OR: 1.4, 95%CI (1.07-1.81)], respectively. However, there was neither a statistically significant association nor increased trend of breast cancer risk with COMTHigh (ValVal) genotypes in the Finland cases [OR: 1.0, 95%CI (0.73-1.39)]. In the combined analysis, the higher activity alleles of the COMT and CCND1 is associated with increased breast cancer risk in both Ontario [OR: 2.22, 95%CI (1.49-3.28)] and Finland [OR: 1.73, 95%CI (1.08-2.78)] populations studied. The trend test was statistically significant in both the Ontario and Finland populations across the genotypes associated with increasing enzymatic activity.

CONCLUSION

Using two independent Caucasian populations, we have shown a stronger combined effect of the two commonly occurring CCND1 and COMT genotypes in the context of breast cancer predisposition.

The properties of high-dimensional data spaces: implications for exploring gene and protein expression data

High-throughput genomic and proteomic technologies are widely used in cancer research to build better predictive models of diagnosis, prognosis and therapy, to identify and characterize key signalling networks and to find new targets for drug development. These technologies present investigators with the task of extracting meaningful statistical and biological information from high-dimensional data spaces, wherein each sample is defined by hundreds or thousands of measurements, usually concurrently obtained. The properties of high dimensionality are often poorly understood or overlooked in data modelling and analysis. From the perspective of translational science, this Review discusses the properties of high-dimensional data spaces that arise in genomic and proteomic studies and the challenges they can pose for data analysis and interpretation.

Timing of Dietary Estrogenic Exposures and Breast Cancer Risk

The same dietary component, such as fat or phytochemicals in plant foods, can have an opposite effect on breast cancer risk if exposed in utero through a pregnant mother or at puberty. Dietary exposures during pregnancy often have similar effects on breast cancer risk among mothers and their female offspring. High fat intake and obesity are illustrative examples: excessive pregnancy weight gain that increases high birth weight is associated with increased breast cancer risk among mothers and daughters. High body weight during childhood is inversely linked to later breast cancer risk. The main reason why the age when dietary exposures occur determines their effect on breast cancer risk likely reflects the extensive programming of the mammary gland during fetal life and subsequent reprogramming at puberty and pregnancy. Programming is a series of epigenetic/transcriptional modifications in gene expression that can be influenced by changes in the hormonal environment induced, for example, by diet. Because epigenetic modifications are inherited by daughter cells, they can persist throughout life if they occur in mammary stem cells or uncommitted mammary myoepithelial or luminal progenitor cells. Our results indicate that the estrogen receptor (ER), mitogen-activated protein kinase (MAPK), and the tumor suppressors BRCA1, p53, and caveolin-1 are among the genes affected by diet-induced alterations in programming/reprogramming. Consequently, mammary gland morphology may be altered in a manner that increases or reduces susceptibility to malignant transformation, including an increase/reduction in cell proliferation, differentiation, and survival, or in the number of terminal end buds (TEBs) or pregnancy-induced mammary epithelial cells (PI-MECs) that are the sites where breast cancer is initiated. Thus, dietary exposures during pregnancy and puberty may play an important role in determining later risk by inducing epigenetic changes that modify vulnerability to breast cancer.

Genistein enhances N-nitrosomethylurea-induced rat mammary tumorigenesis

Genistein is of great interest for its implications as an anticancer compound. We compared the effects of daily subcutaneous injections of 1mg/kg BW of genistein and vehicle (2% DMSO in peanut oil) for 20 weeks on N-nitroso-N-methylurea (NMU)-induced tumorigenesis in adult female rats. Genistein significantly increased tumor cross-sectional area and tumor multiplicity but not the tumor incidence and latency period when compared with the vehicle treated group. The serum E(2) levels of genistein treated group were significantly higher than those of the vehicle treated group at 1 and 2 months after treatment which is the time when most of the rats developed tumors. There were no significant differences in the length of the estrous cycle, food consumption and weights of body, livers, uteri and ovaries between the two groups. Our data shows that supplementation of genistein at a dosage comparable to the isoflavone consumption in humans did not affect the reproductive system but resulted in enhancement of NMU-induced tumorigenesis in adult female rats. Thus, the supplementation of soy isoflavone in premenopausal women may potentially potentiate the risk of breast cancer.

Pentagalloylglucose inhibits estrogen receptor alpha by lysosome-dependent depletion and modulates ErbB/PI3K/Akt pathway in human breast cancer MCF-7 cells

Estrogens and estrogen receptors (ER) play important roles in estrogen-dependent and ER-positive breast cancer development. Inhibitors against estrogen biosynthesis or anti-estrogens have been used in breast cancer treatment for many years. The aim of this study was to determine whether pentagalloylglucose (5GG) has inhibitory effects on ER function. In the present study, we found that 5GG significantly reduced the growth of estrogen-responsive human breast cancer MCF-7 cells, and suppressed the phosphorylation and protein level of estrogen receptor alpha (ERalpha). Interestingly, 5GG decreased ERalpha protein levels by promoting the degradation of ERalpha protein in the lysosome. The ERalpha can be activated through a ligand-dependent and/or a ligand-independent pathway. The activated Akt kinase was shown to directly phosphorylate ERalpha at its serine residues and cause ligand independent activation. Our results showed that 5GG might inhibit the phosphatidylinositol 3-kinase (PI3K)/Akt pathway either through directly inhibiting Akt kinase activity or through inhibiting phosphorylation of the upstream receptor tyrosine kinases. The depletion of ErbB family receptors, including epidermal growth factor receptor (EGFR), ErbB2, and ErbB3, was also observed. 5GG treatment also led to a dose-dependent decrease in the expression of the estrogen-activated cyclin D1 expression. These findings suggested that 5GG might be a useful chemopreventive or therapeutic agent for hormone-dependent breast cancer through suppressing the functions of ERalpha by lysosome-dependent depletion and modulating the ErbB/PI3K/Akt pathway.

Pulmonary fibroblasts stimulate the proliferation of cell lines from human lung adenocarcinomas

Human lung cancer cell lines are widely used to test anticancer drugs. These in-vitro tests, however, preclude the detection of responses to paracrine factors from surrounding stroma. We have cocultured pulmonary fibroblasts CCD-19Lu, from a healthy donor, or HLF-A, from a patient with epidermoid carcinoma of the lung, with two human pulmonary adenocarcinoma cell lines to test the hypothesis that the fibroblasts stimulate the growth of the tumor cells. Both fibroblast cell lines significantly increased the proliferation of the pulmonary adenocarcinoma cell lines in 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide assays, with HLF-A fibroblasts yielding the most pronounced responses. The proliferation of the pulmonary adenocarcinoma cell lines in coculture with fibroblasts was blocked by antibodies against the transforming growth factor-alpha and amphiregulin. In addition, reverse transcription-polymerase chain reaction showed expression of mRNA for amphiregulin and transforming growth factor-alpha in all cell lines, whereas mRNA for the epidermal growth factor was detected only in pulmonary adenocarcinoma cell lines. Western blot analysis revealed that medium containing growth factors released by each fibroblast cell line activated extracellular signal-regulated kinase 1/2 in the both tested pulmonary adenocarcinoma cell lines, but activated Akt kinase only in A549 cells. Assessment of protein levels for cyclin D1 and cyclin E by Western blots demonstrated pronounced increases of both proteins in each pulmonary adenocarcinoma cell line, whereas protein levels for cyclin-dependent kinase inhibitor p21 remained unchanged. Immunocytochemical analysis showed positive immunoreactivity for P-extracellular signal-regulated kinase 1/2, cyclin D1 and cyclin E in pulmonary adenocarcinoma cells cocultured with fibroblasts or exposed to fibroblast-conditioned media. Our data suggest that the growth of pulmonary adenocarcinoma is stimulated by amphiregulin and transforming growth factor-alpha released from pulmonary fibroblasts. This may contribute to the disappointing clinical responses to anticancer drugs, which have shown promise in tests with lung cancer cell lines.

Alcohol and postmenopausal breast cancer risk defined by estrogen and progesterone receptor status: a prospective cohort study

BACKGROUND

Alcohol intake has been reported to be positively associated with an increased risk of postmenopausal breast cancer; however, the association with the estrogen receptor (ER) and progesterone receptor (PR) status of the breast tumors remains unclear.

METHODS

Self-reported data on alcohol consumption were collected in 1987 and 1997 from 51,847 postmenopausal women in the population-based Swedish Mammography Cohort. Through June 30, 2004, 1188 invasive breast cancer case patients with known ER and PR status were identified during an average 8.3-year follow-up. We used Cox proportional hazards models to estimate multivariable relative risks (RRs) of breast cancer, adjusting for age; family history of breast cancer; body mass index; height; parity; age at menarche, first birth, and menopause; education level; use of postmenopausal hormones; and diet. Heterogeneity among groups was evaluated using the Wald test. All statistical tests were two-sided.

RESULTS

Alcohol consumption was associated with an increased risk for the development of ER-positive (+) tumors, irrespective of PR status (highest intake [> or = 10 g of alcohol per day] versus nondrinkers, multivariable RR = 1.35, 95% confidence interval [CI] = 1.02 to 1.80; Ptrend < .049 for ER+PR+ tumors; and RR = 2.36, 95% CI = 1.56 to 3.56; Ptrend < .001 for ER+PR-tumors). The absolute rate of ER+ breast cancer (standardized to the age distribution of person-years experienced by all study participants using 5-year age categories) was 232 per 100,000 person-years among women in the highest category of alcohol intake, and 158 per 100,000 person-years among nondrinkers. No association was observed between alcohol intake and the risk of developing ER-tumors. Furthermore, we observed a statistically significant interaction between alcohol intake and the use of postmenopausal hormones on the risk for ER+PR+ tumors (Pinteraction = .039).

CONCLUSION

The observed association between risk of developing postmenopausal ER+ breast cancer and alcohol drinking, especially among those women who use postmenopausal hormones, may be important, because the majority of breast tumors among postmenopausal women overexpress ER.

Antiproliferative activity of melatonin by transcriptional inhibition of cyclin D1 expression: a molecular basis for melatonin-induced oncostatic effects

Melatonin is endowed with a growth inhibitory effect in MCF-7 breast cancer cells whose mechanism has been related to an antiestrogenic activity exerted by inhibition of binding of the estradiol-estrogen receptor complex to its DNA responsive element. Looking for downstream gene determinants of this effect, we performed a transcriptome profiling by high-density microarrays of estrogen-treated MCF-7 cells exposed or not to melatonin. We found that cyclin D1 was one of the main downregulated genes by melatonin. Validation experiments clearly confirm that in MCF-7 cells the estrogen-induced growth inhibitory activity of melatonin is consistently associated with inhibition of estrogen-elicited cyclin D1 induction. This effect is almost purely transcriptional. Reporter gene assays indicate that the same portion of the cyclin D1 promoter which confers estrogen sensitivity, encompassing a potential cAMP responsive element binding site, is repressed by melatonin. Transcriptional downregulation of cyclin D1 is the key molecular event for melatonin's antiproliferative activity, as this activity can be completely and selectively rescued by transient cyclin D1 overexpression. Finally, we provide indirect evidence that the effect of melatonin on the cyclin D1 promoter is mediated by the c-jun and ATF-2 proteins, known to bind the minimal estrogen-sensitive cyclin D1 promoter element. These findings establish for the first time a molecular link between melatonin and its effects on the cell cycle, providing at the same time a rationale for its use in adjuvant chemotherapy.

Aromatase inhibitors and other novel agents in breast cancer treatment

Thirty years after the introduction of tamoxifen, which was expanded from palliation of metastatic cancer to recent application for chemoprevention, the primacy of this drug as the mainline pharmacological intervention is currently being challenged by the third generation aromatase inhibitors and inactivators. In contrast to the oestrogen receptor blockade provided by tamoxifen, aromatase inhibitors result in deprivation of oestrogens in postmenopausal women both through paracrine/intracrine and endocrine modulation. Experimental evidence has shown a significant (97-99%) reduction of in vivo aromatase activity and an equal or sometimes better antitumour activity compared with megestrol acetate when these drugs are used as second-line treatment for metastatic breast cancer. Recent pivotal studies in first-line settings comparing tamoxifen for metastatic breast cancer and preliminary results from the neoadjuvant trials demonstrate that third generation aromatase inhibitors are superior to tamoxifen. With a better understanding of local tissue production of oestrogen through oestrone sulfatase, which hydrolyses oestrone sulfate to oestrone, and 17-beta-hydroxysteroid dehydrogenase Type 1, which in turn catalyses the reduction of oestrone to oestradiol, more powerful tactics for oestrogen starvation of cancer may be realised in future.

Estrogen receptor inhibits c-Jun-dependent stress-induced cell death by binding and modifying c-Jun activity in human breast cancer cells

c-Jun, a major component of the AP-1 transcription factor, is either pro- or anti-apoptotic with cellular determinants unknown. Nuclear estrogen receptor (ER), on the other hand, regulates gene expression through both estrogen response elements and AP-1. Here we show that stress stimulates c-Jun phosphorylation and AP-1 activity in both ER+ and ER- human breast cancer cells and only induces cell death in ER- cells, indicating a determinant role of ER in c-Jun/AP-1 activity. The inhibitory effect of ER in stress-induced cell death is confirmed by ER transfection into ER- cells. Furthermore, inhibition of c-Jun activation by a dominant negative c-Jun blocks AP-1 activity in ER+ cells and attenuates stress-induced cell death but not AP-1 activity in ER- cells, suggesting that the c-Jun/AP-1 activity has distinct properties depending on ER status. ER was shown to inhibit stress-induced cell death through its physical interaction with c-Jun. This is because ER binds c-Jun in breast cancer cells, stress treatment further increases the ER-bound phosphorylated c-Jun, and the c-Jun binding-deficient ER mutant fails to protect stress-induced cell death. Together, our studies reveal a novel function of ER in stress response by modification of c-Jun activity.

Thymine-rich single-stranded DNA activates Mcm4/6/7 helicase on Y-fork and bubble-like substrates

The presence of multiple clusters of runs of asymmetric adenine or thymine is a feature commonly found in eukaryotic replication origins. Here we report that the helicase and ATPase activities of the mammalian Mcm4/6/7 complex are activated specifically by thymine stretches. The Mcm helicase is specifically activated by a synthetic bubble structure which mimics an activated replication origin, as well as by a Y-fork structure, provided that a single-stranded DNA region of sufficient length is present in the unwound segment or 3' tail, respectively, and that it carries clusters of thymines. Sequences derived from the human lamin B2 origin can serve as a potent activator for the Mcm helicase, and substitution of its thymine clusters with guanine leads to loss of this activation. At the fork, Mcm displays marked processivity, expected for a replicative helicase. These findings lead us to propose that selective activation by stretches of thymine sequences of a fraction of Mcm helicases loaded onto chromatin may be the determinant for selection of initiation sites on mammalian genomes.

The circadian clock: pacemaker and tumour suppressor

The circadian rhythms are daily oscillations in various biological processes that are regulated by an endogenous clock. Disruption of these rhythms has been associated with cancer in humans. One of the cellular processes that is regulated by circadian rhythm is cell proliferation, which often shows asynchrony between normal and malignant tissues. This asynchrony highlights the importance of the circadian clock in tumour suppression in vivo and is one of the theoretical foundations for cancer chronotherapy. Investigation of the mechanisms by which the circadian clock controls cell proliferation and other cellular functions might lead to new therapeutic targets.

The biology of breast carcinoma

The biology of breast carcinoma is complex, with multiple factors contributing to its development and progression. The current review focuses on the role of several critical genes including estrogen receptor, progesterone receptor, retinoic acid receptor-beta, epidermal growth factor receptor family members, p53, BRCA1, and BRCA2 as risk factors for the development of disease, predictors of prognosis and response to therapy, and as therapeutic targets. Studies of the biology of these and other genes that contribute to the development and progression of breast carcinoma have had and will continue to have great impact on all aspects of disease management.

Tamoxifen resistance in breast cancer: elucidating mechanisms

Tamoxifen has been used for the systemic treatment of patients with breast cancer for nearly three decades. Treatment success is primarily dependent on the presence of the estrogen receptor (ER) in the breast carcinoma. While about half of patients with advanced ER-positive disease immediately fail to respond to tamoxifen, in the responding patients the disease ultimately progresses to a resistant phenotype. The possible causes for intrinsic and acquired resistance have been attributed to the pharmacology of tamoxifen, alterations in the structure and function of the ER, the interactions with the tumour environment and genetic alterations in the tumour cells. So far no prominent mechanism leading to resistance has been identified. The recent results of a functional screen for breast cancer antiestrogen resis- tance (BCAR) genes responsible for development of tamoxifen resistance in human breast cancer cells are reviewed. Individual BCAR genes can transform estrogen-dependent breast cancer cells into estrogen-independent and tamoxifen-resistant cells in vitro. Furthermore, high levels of BCAR1/pl30Cas protein in ER-positive primary breast tumours are associated with intrinsic resistance to tamoxifen treatment. These results indicate a prominent role for alternative growth control pathways independent of ER signalling in intrinsic tamoxifen resistance of ER-positive breast carcinomas. Deciphering the differentiation characteristics of normal and malignant breast epithelial cells with respect to proliferation control and regulation of cell death (apoptosis) is essential for understanding therapy response and development of resistance of breast carcinoma.

Involvement of breast epithelial-stromal interactions in the regulation of protein tyrosine phosphatase-gamma (PTPgamma) mRNA expression by estrogenically active agents

BACKGROUND

Protein tyrosine phosphatase gamma (PTPgamma) has been implicated as a tumor suppressor gene in kidney and lung cancers. Our previous results indicate that estradiol-17beta (E2)-induced suppression of PTPgamma may play a role in mammary tumorigenesis. Zeranol (Z), a nonsteroidal growth promoter with estrogenic activity that is used by the US meat industry, induces estrogenic responses in primary cultured breast cells and breast cancer cell lines.

METHODS

PTPgamma mRNA expression in human breast tissues and cells isolated from surgical specimens of mammoplasty and breast cancer patients were detected and quantified by RT-PCR. Immunohistochemical staining was used to localize PTPgamma in human breast tissues. Breast epithelial and stromal cells were isolated and co-cultured to determine the involvement of cell-cell interaction in the regulation of PTPgamma mRNA expression by E2 and Z.

RESULTS

PTPgamma mRNA expression was lower in cancerous than in normal breast tissues. Both E2 and Z suppressed PTPgamma mRNA levels in cultured normal breast tissues by approximately 80%, but had a lesser effect in cultured epithelial cells isolated from normal breast tissues. In the co-culture system, both E2 and Z suppressed PTPgamma mRNA to a greater degree in epithelial cells than in stromal cells. In whole breast tissues, PTPgamma was immunolocalized to the epithelium. Treatment with E2 or Z diminished PTPgamma staining indicating reductions in PTPgamma at the protein level.

CONCLUSIONS

The results indicate that both E2 and Z regulate PTPgamma expression in human breast and that epithelial-stromal cells interaction is important in the regulation of PTPgamma expression by estrogenically active agents.

Ovarian steroids and control of proliferation in the normal human breast

Until recently, there has been considerable uncertainty as to how, or even which of the ovarian steroids influence human breast luminal epithelial cell proliferation. It is important that this is known because increased proliferative activity of this particular cell population is associated with increased risk of breast cancer. Review of the available literature suggests that while oestradiol is the major steroid mitogen in pre-menopausal women, the role of progesterone becomes more significant after the menopause when oestradiol levels are reduced. Moreover, recent studies have given new insights into the mechanisms by which oestradiol and progesterone exert their effects. This knowledge may allow development of new strategies for predicting breast cancer risk or preventing the disease.

Increase in the stability and helical content of estrogen receptor alpha in the presence of the estrogen response element: analysis by circular dichroism spectroscopy

Ligand-dependent stabilization of the estrogen receptor (ER) is often postulated, with limited support from experimental data. We studied the thermal unfolding of recombinant ERalpha by circular dichroism (CD) spectroscopy. The T(M) of unfolding of ERalpha was 38 +/- 2.4 degrees C, and the van't Hoff enthalpy of unfolding was 31.7 +/- 3.4 kcal/mol in the absence of ligands. Addition of estradiol (E(2)) increased the T(M) to 43.6 +/- 2.3 degrees C, while addition of E(2) and an oligonucleotide harboring the estrogen response element (ERE) increased the T(M) to 47.9 +/- 1.6 degrees C. Addition of the antiestrogen 4-hydroxytamoxifen (HT) alone did not increase the T(M); however, a combination of HT and the ERE increased the T(M) to 48.9 +/- 1.0 degrees C. The ERE alone increased the T(M) to 46.1 +/- 0.9 degrees C. Addition of E(2) alone had no effect on the apparent enthalpy of unfolding; however, the ERE alone increased the apparent enthalpy from 31.7 to 36.1 kcal/mol. ERalpha samples containing the ERE also exhibited an increase in the negative ellipticity at 208 and 222 nm, relative to that of ligand-free ERalpha, suggesting a stabilization of the alpha-helix. CD data analysis further showed that the presence of the ERE caused a large increase in alpha-helical content of ERalpha in both the presence and absence of the ligands. This increase in alpha-helical content of ERalpha was not observed in the presence of a nonspecific oligonucleotide. These results show that the ERE can increase the thermal stability of ERalpha, enhance its alpha-helical content, and facilitate the cooperativity of the folding transition.

Acceleration of mammary neoplasia in aromatase transgenic mice by 7,12-dimethylbenz[a]anthracene

Our studies using the aromatase transgenic mice model have shown that early exposure of mammary epithelium to in situ estrogen as a result of overexpression of aromatase predispose mammary tissue to preneoplastic changes. Here, we hypothesize that the preneoplastic changes induced by mammary estrogen in aromatase transgenic females may be susceptible to environmental carcinogens like 7,12-dimethylbenz[a]anthracene (DMBA), and may result in the acceleration and/or increase in the incidence of breast cancer. Results presented in this study show that tumors appeared in 25% of the mice that were treated with DMBA and all treated transgenic animals had microscopic evidence of neoplastic progression. Control non-transgenic females did not have significant changes even after treatment with DMBA. Consistent with increased neoplastic changes in DMBA-treated aromatase mice, we have seen an increase in the expression of genes involved in cell proliferation and cell cycle. We have also seen changes in the expression of oxidative stress markers and changes in estrogen-mediated growth factors. These studies indicate that more than one event is required for tumor formation, and that early estrogen exposure leading to preneoplastic changes in the mammary epithelial cells increases susceptibility to environmental carcinogens that may result in acceleration and/or an increase in the incidence of breast cancer.

The orphan nuclear estrogen receptor-related receptor alpha (ERRalpha) is expressed throughout osteoblast differentiation and regulates bone formation in vitro

The orphan nuclear estrogen receptor-related receptor alpha (ERRalpha), is expressed by many cell types, but is very highly expressed by osteoblastic cells in which it transactivates at least one osteoblast-associated gene, osteopontin. To study the putative involvement of ERRalpha in bone, we first assessed its expression in rat calvaria (RC) in vivo and in RC cells in vitro. ERRalpha mRNA and protein were expressed at all developmental stages from early osteoprogenitors to bone-forming osteoblasts, but protein was most abundant in mature cuboidal osteoblasts. To assess a functional role for ERRalpha in osteoblast differentiation and bone formation, we blocked its expression by antisense oligonucleotides in either proliferating or differentiating RC cell cultures and found inhibition of cell growth and a proliferation-independent inhibition of differentiation. On the other hand, ERRalpha overexpression in RC cells increased differentiation and maturation of progenitors to mature bone-forming cells. Our findings show that ERRalpha is highly expressed throughout the osteoblast developmental sequence and plays a physiological role in differentiation and bone formation at both proliferation and differentiation stages. In addition, we found that manipulation of receptor levels in the absence of known ligand is a fruitful approach for functional analysis of this orphan receptor and identification of potential target genes.

Phytochemicals for the prevention of breast and endometrial cancer

Although there is evidence that phytochemicals decrease the incidence of breast and endometrial cancer, many observations are only phenomenologic, and much work needs to be done to explore basic mechanisms and the strategic exploitation of their interactions. The multiplicity of phytochemical actions at different sites in the process of tumorigenesis may eventually lead to the development of a multiagent strategy designed to maximize the complementary effects of different agents. A number of effects with possible relevance to cancer chemoprevention have been excluded from this review, including effects of phytochemicals on the immune response; the question of dietary restriction, which has a profound effect on tumorigenesis; the relatively low methionine levels in some phytochemicals such as soy, which may limit the synthesis of polyamines necessary for tumor growth [151]; and the fact that diets higher in plant products are usually lower in fat and result in leaner individuals with less potential for the synthesis of estradiol in adipose tissue. Also, many studies dealing solely with in vitro mutagenesis were excluded.

Developmental, cellular, and molecular basis of human breast cancer

Breast cancer, which is the most common neoplastic disease in females and accounts for up to one third of all new cases of women's cancer in North America, continues to rise in incidence. In addition, the mortality caused by this disease has remained almost unchanged for the past 5 decades, becoming only second to lung cancer as a cause of cancer-related death. The failure in eradicating this disease is largely due to the lack of identification of a specific etiologic agent, the precise time of initiation, and the molecular mechanisms responsible for cancer initiation and progression. Despite the numerous uncertainties surrounding the origin of cancer, there is substantial evidence that breast cancer risk relates to endocrinologic and reproductive factors. The development of breast cancer strongly depends on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. However, the specific hormone or hormone combinations responsible for cancer initiation have not been identified, and their role as protective or risk factors is still incompletely understood. A highly significant female hormone is estrogen, which is involved in the development of a variety of cancers, but it is still unclear whether estrogens are carcinogenic to the human breast. An understanding of whether estrogens cause mutations, and, if so, whether they act through hormonal effects activated by receptor binding, cytochrome P450-mediated metabolic activation, or compromise the DNA repair system, is essential for determining whether this steroid hormone is involved in the initiation or progression of breast cancer. This knowledge has to be based on a multidisciplinary approach encompassing studies of the development of the breast, influence of hormones on the differentiation of individual structures, and their interrelations in the pathogenesis of breast cancer. The analysis of the mechanisms involved would require confirmation in the adequate in vitro models and determination of the role played by genomic alterations in both cancer initiation and progression.

Molecular and pharmacological aspects of antiestrogen resistance

Endocrine therapy is effective in approximately one-third of all breast cancers and up to 80% of tumors that express both estrogen and progesterone receptors. Despite the low toxicity, good overall response rates, and additional benefits associated with its partial agonist activity, most Tamoxifen-responsive breast cancers acquire resistance. The development of new antiestrogens, both steroidal and non-steroidal, provides the opportunity for the development of non-cross-resistant therapies and the identification of additional mechanisms of action and resistance. Drug-specific pharmacologic mechanisms may confer a resistance phenotype, reflecting the complexities of both tumor biology/pharmacology and the molecular endocrinology of steroid hormone action. However, since all antiestrogens will be effective only in cells that express estrogen receptors (ER), many mechanisms will likely be directly related to ER expression and signaling. For example, loss of ER expression/function is likely to confer a cross-resistance phenotype across all structural classes of antiestrogens. Altered expression of ERalpha and ERbeta, and/or signaling from transcription complexes driven by these receptors, may produce drug-specific resistance phenotypes. We have begun to study the possible changes in gene expression that may occur as cells acquire resistance to steroidal and non-steroidal antiestrogens. Our preliminary studies implicate the altered expression of several estrogen-regulated genes. However, resistance to antiestrogens is likely to be a multigene phenomenon, involving a network of interrelated signaling pathways. The way in which this network is adapted by cells may vary among tumors, consistent with the existence of a highly plastic and adaptable genotype within breast cancer cells.

Bone morphogenetic protein-2 induces cyclin kinase inhibitor p21 and hypophosphorylation of retinoblastoma protein in estradiol-treated MCF-7 human breast cancer cells

The biologic effects and mechanisms by which bone morphogenetic proteins (BMPs) function in breast cancer cells are not well defined. A member of this family of growth and differentiation factors, BMP-2, inhibited both basal and estradiol-induced growth of MCF-7 breast tumor cells in culture. Flow cytometric analysis showed that in the presence of BMP-2, 62% and 45% of estradiol-stimulated MCF-7 cells progressed to S-phase at 24 h and 48 h, respectively. Estradiol mediates growth of human breast cancer cells by stimulating cyclins and cyclin-dependent kinases (CDKs). BMP-2 significantly increased the level of the cyclin kinase inhibitor, p21, which in turn associated with and inactivated cyclin D1. BMP-2 inhibited estradiol-induced cyclin D1-associated kinase activity. Also estradiol-induced CDK2 activity was inhibited by BMP-2. This inhibition of CDK activity resulted in hypophosphorylation of retinoblastoma protein thus keeping it in its active form. These data provide the first evidence by which BMP-2 inhibits estradiol-induced proliferation of human breast cancer cells.

SDZ PSC 833 the drug resistance modulator activates cellular ceramide formation by a pathway independent of P-glycoprotein

SDZ PSC 833 (PSC 833) is a new multidrug resistance modulator. Recent studies have shown that the principal mechanism of action of PSC 833 is to bind P-glycoprotein (P-gp) and prevent cellular efflux of chemotherapeutic drugs. We previously reported that PSC 833 increases cellular ceramide levels. The present study was conducted to determine whether the impact of PSC 833 on ceramide generation is dependent on P-gp. Work was carried out using the drug-sensitive P-gp-deficient human breast adenocarcinoma cell line, MCF-7, and drug resistant MCF-7/MDR1 clone 10.3 cells (MCF-7/MDR1), which show a stable MDR1 P-gp phenotype. Overexpression of P-gp in MCF-7/MDR1 cells did not increase the levels of glucosylceramide, a characteristic which has been associated with multidrug resistant cells. Treatment of MCF-7 and MCF-7/MDR1 cells with PSC 833 caused similar ceramide elevation, in a dose-responsive manner. At 5.0 microM, PSC 833 increased ceramide levels 4- to 5-fold. The increase in ceramide levels correlated with a decrease in survival in both cell lines. The EC50 (concentration of drug that kills 50% of cells) for PSC 833 in MCF-7 and MCF-7/MDR1 cells was 7.2 +/- 0.6 and 11.0 +/- 1.0 microM, respectively. C6-Ceramide exposure diminished survival of MCF-7 cells; whereas, MCF-7/MDR1 cells were resistant to this short chain ceramide analog. Preincubation of cells with cyclosporine A, which has high affinity for P-gp, did not diminish the levels of ceramide generated upon exposure to PSC 833. These results demonstrate that PSC 833-induced cellular ceramide formation occurs independently of P-gp. As such, these data indicate that reversal of drug resistance by classical P-gp blockers may be modulated by factors unrelated to drug efflux parameters.

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.

Estrogen induction of the cyclin D1 promoter: involvement of a cAMP response-like element

Estrogens induce cell proliferation in target tissues by stimulating progression through the G(1) phase of the cell cycle. Induction of cyclin D1 expression is a critical feature of the mitogenic action of estrogen. We have determined a region between -96 and -29 in the cyclin D1 promoter that confers regulation by estrogens in the human mammary carcinoma cells MCF-7. This region encompasses a unique known transcription factor binding site with a sequence of a potential cAMP response element (CRE-D1). The induction is strictly hormone dependent and requires the DNA binding domain as well as both AF-1 and AF-2 domains of the estrogen receptor (ER) alpha. Destruction of the CRE-D1 motif caused complete loss of estrogen responsiveness. Both c-Jun and ATF-2 transactivated the cyclin D1 promoter in transient transfection experiments, and a clear additional increase was detected when ER was cotransfected with either c-Jun or with c-Jun and ATF-2 but not with ATF-2 alone. Furthermore, the expression of a dominant negative variant of c-Jun, TAM67, completely abolished the induction of the cyclin D1 promoter both in the absence and presence of ER. We show that ATF-2 homodimers and ATF-2/c-Jun heterodimers, but not c-Jun homodimers, were able to bind the CRE of the cyclin D1 promoter. To interpret these results, we propose a mechanism in which ATF-2/c-Jun heterodimers bind to the CRE-D1 element and mediate the activation of cyclin D1 promoter by the ER. This mechanism represents a pathway by which estrogens control the proliferation of target cells.

Prepubertal exposure to zearalenone or genistein reduces mammary tumorigenesis

Prepubertal exposure to a pharmacological dose (500 mg kg(-1)) of the phyto-oestrogen genistein can reduce the incidence and multiplicity of carcinogen-induced mammary tumours in rats. However, such an exposure also disrupts the function of the hypothalamic-pituitary-gonadal axis, making it unsuitable for breast cancer prevention. We studied whether prepubertal exposure to genistein at a total body dose broadly comparable to the level typical of Oriental countries, approximately 1 mg kg(-1) body weight, affects mammary tumorigenesis. We also studied whether prepubertal exposure to zearalenone, a major source for phyto-oestrogens in the USA, influences breast cancer risk. Prepubertal rats were treated between postnatal days 7 and 20, with 20 microg (approximately 1 mg kg(-1) body weight) of either genistein or zearalenone. Zearalenone exposure significantly reduced both the incidence and multiplicity of mammary tumours induced by 7,12-dimethylbenz(a)anthracene (DMBA). Genistein exposure significantly reduced tumour multiplicity, but not tumour incidence, when compared with vehicle-treated animals. Furthermore, 60% of the tumours in the genistein group were not malignant, while all the tumours analysed for histopathology in the vehicle and zearalenone groups were adenocarcinomas. A higher number of differentiated alveolar buds, and lower number of terminal ducts, were present in the DMBA-treated mammary glands of the phyto-oestrogen exposed rats. The concentration of oestrogen receptor (ER) binding sites after the DMBA treatment was low in the mammary glands of all groups but a significantly higher proportion of the glands in the zearalenone exposed rats were ER-positive (i.e. ER levels > or = 5 fmol mg(-1) protein) than the glands of the vehicle controls. Our data suggest that a prepubertal exposure to a low dose of either zearalenone or genistein may protect the mammary gland from carcinogen-induced malignant transformation, possibly by increasing differentiation of the mammary epithelial tree.

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Cytokine-regulated urokinase-type-plasminogen-activator (uPA) production by human breast fibroblasts in vitro

It has been shown that, in breast stroma, urokinase-type plasminogen activator (uPA) mRNA is predominantly expressed by myofibroblasts located at the invasive areas of the tumor. To examine which factors present in a tumor environment are candidates responsible for the induction of these uPA-producing myofibroblasts, we studied in vitro the capacity of a paired panel of normal and tumor-derived human breast fibroblasts to produce uPA protein and the myofibroblast marker alpha-smooth-muscle-actin (alpha-SMA) in response to various cytokines implicated in the process of tissue-remodeling during malignant transformation. We found that fibroblasts produced increased amounts of uPA protein after exposure to a-FGF, b-FGF, EGF, PDGF-BB, and IFN-gamma, were unaffected in this respect by IL-6, M-CSF, GM-CSF and Oncostatin M, and produced decreased amounts of uPA protein after exposure to IL-1alpha, TNF-alpha, IGF-I, and IGF-II. None of these cytokines were able to induce a striking increase in the fraction of alpha-SMA-positive fibroblasts. On the other hand, 25 pM TGFbeta1 increased the fraction of alpha-SMA-positive fibroblasts 5-fold in both normal and tumor-tissue-derived fibroblasts. Nonetheless, the normal-derived fibroblasts were unaffected in their uPA-producing capacity by TGFbeta1, and the tumor-derived fibroblasts produced decreased amounts of uPA protein after exposure to this cytokine, implying that at least in vitro the myofibroblast phenotype is not a prerequisite for the production of uPA by human breast fibroblasts. In addition, we established that the basal-uPA-production of both normal and tumor-derived fibroblasts was increased by autocrinely produced b-FGF-like activity, and that the basal-uPA-production of at least the normal-derived fibroblasts was decreased by autocrinely produced IGF-like activity. Altogether, our data suggest an active role for fibroblasts in the process of uPA-directed breast tumor proteolysis.

Differential regulation of normal and tumoral breast epithelial cell growth by fibroblasts and 1,25-dihydroxyvitamin D3

Mesenchymal-epithelial interactions are of paramount importance during normal and tumoral breast developments. We have investigated the paracrine growth regulation of normal and tumoral breast epithelial cells by fibroblasts derived from normal or pathological breast tissues. In some cases, breast cancer MCF-7 cells or normal epithelial cells in primary culture were cocultured with fibroblasts in a Transwell system allowing diffusible factor exchanges. Alternatively, conditioned medium produced by fibroblast cultures was added to epithelial cell cultures. Fibroblasts were shown to stimulate the proliferation of normal and carcinoma cells through paracrine mechanisms. However, the paracrine exchanges appeared to be different in normal versus tumoral breast epithelial cell growth regulation. Moreover, vitamin D-related compounds that have been proposed as anti-tumoral drugs were studied for their ability to affect normal and tumoral mammary epithelial cell proliferation and to interfere with the growth-regulatory activity of fibroblasts. Whereas vitamin D compounds inhibited MCF-7 cell growth, they led to a marked stimulation of the proliferation of normal mammary epithelial cells. Moreover, it was shown that the vitamin D analog EB 1089 can block the mitogenic effect of fibroblast-conditioned medium on tumoral but not normal breast epithelial cells. The differential effects of vitamin D compounds on cell proliferation provide further data in favor of the different behaviours of normal and tumoral mammary epithelial cells. The potential therapeutic use of vitamin D derivatives in the treatment of breast cancer is supported by these results but their growth-stimulatory properties on normal epithelial cells cannot be overlooked.

Pattern of distribution of cells positive for estrogen receptor alpha and progesterone receptor in relation to proliferating cells in the mammary gland

Since cell proliferation is indispensable for the growth and development of the breast, and estrogens are considered to play a major role in promoting cell proliferation, while progesterone influences its differentiation, the present work was designed with the purpose of verifying the relationship between cells containing steroid hormone receptors and proliferating cells in the normal human breast. Twelve breast samples were analyzed for their content of lobules type 1 (Lob1), Lob2, Lob3, and Lob4, and the number of cells containing estrogen receptor alpha (ER-alpha), progesterone receptor (PgR), or expressing Ki67 antibody was determined by double immunocytochemical technique with specific antibodies. The highest percentage of ER-alpha, PgR, and Ki67 positive cells was found in Lob1, with a progressive reduction in the more differentiated Lob2 and Lob3. ER-alpha and PgR positive cells were found exclusively in the breast epithelium and were negative for Ki67, while cells positive for Ki67 did not express receptors. These findings were compared with the distribution of ER-alpha and PgR in the autoradiographs of mammary gland of young virgin rats inoculated with 3H-thymidine for determination of the DNA labeling index (DNA-LI). Both the DNA-LI and the percentage of ER-alpha and PgR positive cells were maximal in the epithelium of terminal end buds, and these values were reduced in alveolar buds and lobules. ER-alpha and PgR positive cells did not proliferate, and those cells that had incorporated 3H-thymidine were negative for both receptors. Our results led us to conclude that the content of ER-alpha and PgR in the normal mammary tissue varies with the degree of lobular development, in parallel with cell proliferation. However, the expression of receptors occurs in cells other than the proliferating cells, indicating that they represent at least two separate cell populations. These findings open new avenues towards the understanding of the mechanisms through which estrogens and progesterone affect the proliferative activity of breast epithelial cells, and their role in the initiation of the cascade of events that leads a normal cell to cancer.

Hypomethylation of an exon I estrogen receptor CpG island in spontaneous and carcinogen-induced mammary tumorigenesis in the rat

Loss of methylation at a CpG island in exon I of the rat ER gene was observed in 48% of the spontaneous mammary tumors in old female Wistar rats and 22% of the contralateral normal mammary tissues. The majority of the methylation losses were total. Similarly, 50% of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors in young Sprague-Dawley rats exhibited a partial or total loss of methylation at this site, while all normal mammary tissues in young rats were fully methylated. Loss of ER methylation also increased with age in normal mammary tissues of tumor-free rats approaching 12.5% in middle-aged and 43% in old rats. In addition, 66% of mammary glands obtained from young rats that are subsequently at an increased risk to develop breast cancer due to manipulation of in utero dietary fat intake, exhibited methylation loss while no methylation changes were observed in rats at no increased risk for breast cancer. Therefore, the loss of ER methylation is more extensive in mammary glands of rats at high than low breast cancer risk, in old than young, and in mammary tumors than in normal tissues. The data suggest that hypomethylation of a growth-associated ER gene may be a common event in mammary tumorigenesis in the rat and may be of predictive value as a marker of increased breast cancer risk in aged individuals.

H19 overexpression in breast adenocarcinoma stromal cells is associated with tumor values and steroid receptor status but independent of p53 and Ki-67 expression

In a previous study we described the expression of the H19 gene by in situ hybridization (ISH) in normal breast and in benign or malignant breast tumors (Dugimont T, Curgy JJ, Wernert N, Delobelle A, Raes MB, Joubel A, Stehelin D, Coll J: Biol Cell 1995, 85:117-124). In the present work, 1) we extend the previous one to a statistically useful number of adenocarcinomas, including 10 subclasses, 2) we provide information on the precise ISH localization of the H19 RNA by using, on serial tissue sections, antibodies delineating specifically the stromal or the epithelial component of the breast, and 3) we consider relationships between the H19 gene expression and various clinicopathological information as tumor values (T0 to T4), grades, steroid receptors, lymph node status, and molecular features as the p53 gene product and the Ki-67/MIB1 protein, which is specific to proliferating cells. Data indicate that 1) in 72.5% of studied breast adenocarcinomas an overall H19 gene expression is increased when compared with healthy tissues, 2) the H19 gene is generally overexpressed in stromal cells (92.2%) and rarely in epithelial cells (2.9% only), 3) an up-regulation of the H19 gene is significantly correlated with the tumor values and the presence of both estrogen and progesterone receptors, and 4) at the cellular level, the H19 gene demonstrates an independent expression versus accumulation of both the p53 protein and the Ki-67/MIB-1 cell-cycle marker.

Aryl hydrocarbon receptor-mediated antiestrogenicity in MCF-7 cells: modulation of hormone-induced cell cycle enzymes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits 17beta-estradiol (E2) mammary tumor growth in rodents and in MCF-7 human breast cancer cells; however, the cell cycle genes/proteins which are inhibited have not been determined. Initial studies showed that treatment of MCF-7 cells with 10 nM E2 significantly increased cyclin D1 (protein and mRNA), cdk2- and cdk4-dependent kinase activities, and hyperphosphorylation of retinoblastoma (RB) protein. In contrast to results of recent studies (M. D. Planas-Silva and R. A. Weinberg, 1997, Mol. Cell. Biol. 17, 4059-4069), E2 induced dissociation of both cdk2 and cdk4 proteins from the p21 protein complex and significantly increased cdk7-dependent kinase activity. Treatment of MCF-7 cells with E2 also induced cdc25A phosphatase protein, which was accompanied by increased cdk2 and cdk4 proteins containing unphosphorylated tyrosine residues. Although TCDD alone has minimal effects on cell cycle proteins/enzymes, several E2-induced responses were significantly inhibited in MCF-7 cells cotreated with E2 plus TCDD. For example, TCDD significantly inhibited E2-induced hyperphosphorylation of RB, cyclin D1 protein, and cdk2-, cdk4-, and cdk7-dependent kinase activities. Inhibition of E2-induced cdk4-dependent kinase activity by TCDD may be related to the parallel decrease of E2-induced cyclin D1 protein, and inhibition of induced cdk2- and cdk4-dependent kinase activities may be due to significantly increased p21 levels in cells cotreated with TCDD plus E2. These results demonstrate that the antiestrogenic activity of TCDD is due to downregulation of several E2-induced cell cycle proteins/activities and this illustrates the complex cross talk between the aryl hydrocarbon and the E2 receptor signaling pathways.

Urokinase-type-plasminogen-activator (uPA) production by human breast (myo) fibroblasts in vitro: influence of transforming growth factor-beta(1) (TGF beta(1)) compared with factor(s) released by human epithelial-carcinoma cells

The urokinase-type plasminogen activator (uPA) may be considered as a key enzyme in the processes of cancer cell invasion and metastasis. Evidence has been presented that, in breast stroma, uPA is expressed predominantly by myofibroblasts located at the invasive areas of the tumor. To examine whether transforming growth factor type-1 (TGF beta(1)) produced by breast-carcinoma cells is a candidate responsible for the induction of uPA-producing myofibroblasts, we studied in vitro the capacity of normal and tumor-derived human breast fibroblasts to express uPA and the myofibroblast marker alpha-smooth-muscle actin in response to TGF beta(1). Next, we compared these influences with those elicited by factor(s) released by epithelial-cancer cells. In all 8 fibroblast strains tested, TGF beta(1) induced a similar concentration-dependent increase in the fraction of alpha-smooth-muscle-actin-positive fibroblasts. While uPA expression was decreased by TGF beta(1) in most of the fibroblast strains, 2 strains were relatively insensitive to TGF beta(1) in this respect. Although factors present in media conditioned by non-uPA-producing epithelial-tumor cells could trigger fibroblasts to become potent producers of uPA, the TGF beta(1) content of the conditioned media were linked to the differential effects of externally added TGF beta(1) with respect to uPA expression. The data demonstrate that, although fibroblasts may utilize TGF beta(1) secreted by tumor cells to differentiate into myofibroblasts, tumor cells secrete factor(s) other than TGF beta(1) ultimately responsible for the generation of powerful uPA-producing fibroblasts.

Identification of BCAR3 by a random search for genes involved in antiestrogen resistance of human breast cancer cells

The antiestrogen tamoxifen is important in the treatment of hormone-dependent breast cancer, although development of resistance is inevitable. To unravel the molecular mechanisms of antiestrogen resistance, a search for involved genes was initiated. Retrovirus-mediated insertional mutagenesis was applied to human ZR-75-1 breast cancer cells. Infected cells were subjected to tamoxifen selection and a panel of resistant cell clones was established. Screening for a common integration site resulted in the identification of a novel gene designated BCAR3. Transfer of this locus by cell fusion or transfection of the BCAR3 cDNA to ZR75-1 and MCF-7 cells induces antiestrogen resistance. BCAR3 represents a putative SH2 domain-containing protein and is partly homologous to the cell division cycle protein CDC48.

Positive regulation of normal and tumoral mammary epithelial cell proliferation by fibroblasts in coculture

In the mammary gland, mesenchymal-epithelial interactions are of paramount importance during normal and tumoral developments. We have studied the paracrine growth regulation of a variety of breast epithelial cells in coculture with normal or pathological breast fibroblasts. Two models of coculture were used in which the two cell types were seeded and grown, either together in microchamber slides or separated by a microporous membrane. Under these two conditions, all fibroblasts were shown to stimulate the proliferation of the hormono-responsive breast carcinoma MCF-7 cell line, suggesting that cell contacts were not indispensable for the paracrine stimulation of MCF-7 cell growth by fibroblasts. Moreover, in the Transwell coculture system, the proliferation of a variety of other breast carcinoma cells (MDA-MB231, T47D, and BT-20) was also stimulated by fibroblasts. However, the amplitude of the proliferative response seemed to be dependent on the carcinoma cell line considered. Moreover, the proliferative response of normal mammary epithelial cells to the presence of fibroblasts was shown to be significantly higher than the tumor cell response. The nature of the tissue of fibroblast origin, normal or pathological, did not influence the growth response of the epithelial cells. In this study, we thus demonstrate that fibroblasts are able to stimulate the proliferation of normal and carcinoma cells through paracrine exchange mechanisms. We also conclude that the target epithelial cell phenotype will essentially determine the extent of the proliferative response.

Feasibility, endocrine and anti-tumour effects of a triple endocrine therapy with tamoxifen, a somatostatin analogue and an antiprolactin in post-menopausal metastatic breast cancer: a randomized study with long-term follow-up

Suppression of the secretion of prolactin, growth hormone and insulin-like growth factor 1 (IGF-1) might be important in the growth regulation and treatment of breast cancer. Because oestrogens may counteract the anti-tumour effects of such treatment, the combination of an anti-oestrogen (tamoxifen), a somatostatin analogue (octreotide) and a potent anti-prolactin (CV 205-502) might be attractive. In this respect, we performed a first exploratory long-term study on the feasibility of combined treatment and possible clear differences in endocrine and anti-tumour effects during such combined treatment vs standard treatment with tamoxifen alone. Twenty-two post-menopausal patients with metastatic breast cancer (ER and/or PR positive or unknown) were randomized to receive either 40 mg of tamoxifen per day or the combination of 40 mg of tamoxifen plus 75 microg of CV 205-502 orally plus 3 x 0.2 mg of octreotide s.c. as first-line endocrine therapy. An objective response was found in 36% of the patients treated with tamoxifen alone and in 55% of the patients treated with combination therapy. Median time to progression was 33 weeks for patients treated with tamoxifen and 84 weeks for patients treated with combination therapy, but the numbers are too small for hard conclusions. There was no difference in overall post-relapse survival between the two treatment arms. With respect to the endocrine parameters, there was a significant decrease of plasma IGF-1 levels in both treatment arms, whereas during combined treatment plasma growth hormone tended to decrease and plasma prolactin levels were strongly suppressed; in some patients insulin and transforming growth factor alpha (TGF-alpha) decreased during the triple therapy. Although there was no significant difference in mean decrease of plasma IGF-1 levels between the two treatment arms, combined treatment resulted in a more uniform suppression of IGF-1. Therefore, the addition of a somatostatin analogue and an anti-prolactin may potentially enhance the efficacy of anti-oestrogens in the treatment of breast cancer owing to favourable endocrine and possible direct anti-tumour effects. Large phase III trials using depot formulations (to increase the feasibility) of somatostatin analogues are warranted to demonstrate the potential extra beneficial anti-tumour effects of such combination therapy.

Estrogen responsiveness and control of normal human breast proliferation

Our understanding of the hormonal control of the proliferation of normal human breast epithelium is still surprisingly meager. However, the results of a number of recent studies have confirmed that estrogen is the major steroid mitogen for the luminal epithelial cell population (the usual targets for neoplastic transformation). Estrogen seemingly exerts its effects on cell division indirectly as there is complete dissociation between the population of luminal epithelial cells expressing the estrogen receptor (ER)4 and those that proliferate. We suggest that the ER-negative proliferating cells represent a precursor or stem cell population that differentiates to ER-containing, nonproliferative cells. In turn, these ER-positive cells act as 'estrogen sensors' and transmit positive or negative paracrine growth signals to the precursor cells depending on the prevailing hormonal environment. As yet there is no direct evidence supporting this hypothesis but we suggest ways in which it may be obtained. The implication of these studies is that inhibition of luminal epithelial proliferation with tamoxifen or pure antiestrogens or by preventing ovarian steroid secretion should be an effective strategy for the prevention of breast cancer. In addition, we may be able to predict the risk of breast cancer in an individual by measuring the intrinsic estrogen sensitivity of her breast epithelium. Finally, study of the paracrine mechanisms of growth control in the normal human breast may provide new, more specific, therapeutic targets for breast cancer prevention.

Alterations in DNA methylation: a fundamental aspect of neoplasia

Neoplastic cells simultaneously harbor widespread genomic hypomethylation, more regional areas of hypermethylation, and increased DNA-methyltransferase (DNA-MTase) activity. Each component of this "methylation imbalance" may fundamentally contribute to tumor progression. The precise role of the hypomethylation is unclear, but this change may well be involved in the widespread chromosomal alterations in tumor cells. A main target of the regional hypermethylation are normally unmethylated CpG islands located in gene promoter regions. This hypermethylation correlates with transcriptional repression that can serve as an alternative to coding region mutations for inactivation of tumor suppressor genes, including p16, p15, VHL, and E-cad. Each gene can be partially reactivated by demethylation, and the selective advantage for loss of gene function is identical to that seen for loss by classic mutations. How abnormal methylation, in general, and hypermethylation, in particular, evolve during tumorigenesis are just beginning to be defined. Normally, unmethylated CpG islands appear protected from dense methylation affecting immediate flanking regions. In neoplastic cells, this protection is lost, possibly by chronic exposure to increased DNA-MTase activity and/or disruption of local protective mechanisms. Hypermethylation of some genes appears to occur only after onset of neoplastic evolution, whereas others, including the estrogen receptor, become hypermethylated in normal cells during aging. This latter change may predispose to neoplasia because tumors frequently are hypermethylated for these same genes. A model is proposed wherein tumor progression results from episodic clonal expansion of heterogeneous cell populations driven by continuous interaction between these methylation abnormalities and classic genetic changes.

Induction of p21 (CIP1/WAF1/SID1) by estradiol in a breast epithelial cell line transfected with the recombinant estrogen receptor gene: a possible mechanism for a negative regulatory role of estradiol

Estrogens stimulate the growth of a majority of estrogen receptor (ER)-positive breast cancer cells. In contrast, estradiol exerted a 75% inhibition of DNA synthesis in the MCF-10AE(wt5) cell line, obtained by the transfection of the ER gene into a normal breast epithelial cell line, MCF-10A. The estradiol-mediated growth inhibitory effect was reversed by ICI 164384, a pure anti-estrogen. Analysis of cell cycle by flow cytometry showed a significant increase of G1 cells by estradiol treatment compared to controls. To understand the mechanism of action of estradiol on MCF-10AE(wt5) cells, we examined the level of a cyclin dependent kinase inhibitor (CKI), p21, by Western blot analysis. Our results showed a 5- to 10-fold increase in the level of p21 in estradiol-treated MCF-10AE(wt5) cells compared to controls. ICI 164384 reversed estradiol-mediated induction of p21. Northern blot analysis of p21 mRNA indicated that estradiol stimulated its message in MCF-10AE(wt5) cells. Analysis of a panel of 6 breast cancer cell lines showed the absence of p21 protein, whereas it was present at a very low level in MCF-10A cells. Comparison of p21 in MCF-10A and MCF-10AE(wt5) cells showed an abundance of p21 in the ER-transfected cells. However, this p21 appears to be inactive in the absence of estradiol. These results suggest a p21-mediated pathway as a possible mechanism for the growth inhibitory effects of estradiol on at least a subset of ER-transfected cell lines.

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.