Expression of estrogen receptors in estrogen receptor-negative human breast carcinoma cells: modulation of epidermal growth factor-receptor (EGF-R) and transforming growth factor alpha (TGF alpha) gene expression

Molecular shifts in breast cancer following neoadjuvant chemotherapy: a prospective study and review of literature

BACKGROUND

Standard clinical guidelines recommend evaluating Estrogen & progesterone Receptor (ER, PR), Human epidermal growth factor receptor-2 (HER-2), and Ki-67 in breast cancer biopsy samples. This study investigates the changes in molecular subtype following neoadjuvant chemotherapy (NACT) in breast cancer patients.

METHODS

Patients aged 18 to 65 years who underwent core needle biopsy before NACT and received at least four chemotherapy cycles were included in the study. Patients with inflammatory breast cancer, de novo metastatic or bilateral breast cancer, pregnancy, lactation, prior endocrine/radiation therapy, or achieved pathological complete response (pCR) were excluded. Molecular profiles (ER, PR, HER-2, Ki-67) were analyzed pre- and post-NACT.

RESULTS

The study involved 100 breast cancer patients with a median age of 51.78 years. 47% of patients underwent breast-conserving surgery (BCS), while 53% underwent modified radical mastectomy (MRM). Seventy-six percent of patients had tumors larger than 5 cm, and 72% presented with axillary lymph node metastasis. Initially, 90% and 89% of patients were ER, and PR positive, respectively, which decreased to 81% and 75% post-surgery. Ki67 expression showed a significant reduction following chemotherapy. Larger tumors and lymph node-positivity had significant changes in molecular subtypes.

CONCLUSION

The study revealed significant alterations in ER, PR, HER-2, and Ki-67 levels post-NACT, prompting reassessment for tailored therapy.

Nuclear Estrogen Receptors in Prostate Cancer: From Genes to Function

Estrogens are almost ubiquitous steroid hormones that are essential for development, metabolism, and reproduction. They exert both genomic and non-genomic action through two nuclear receptors (ERα and ERβ), which are transcription factors with disregulated functions and/or expression in pathological processes. In the 1990s, the discovery of an additional membrane estrogen G-protein-coupled receptor augmented the complexity of this picture. Increasing evidence elucidating the specific molecular mechanisms of action and opposing effects of ERα and Erβ was reported in the context of prostate cancer treatment, where these issues are increasingly investigated. Although new approaches improved the efficacy of clinical therapies thanks to the development of new molecules targeting specifically estrogen receptors and used in combination with immunotherapy, more efforts are needed to overcome the main drawbacks, and resistance events will be a challenge in the coming years. This review summarizes the state-of-the-art on ERα and ERβ mechanisms of action in prostate cancer and promising future therapies.

Hormone Receptor Loss in Breast Cancer: Molecular Mechanisms, Clinical Settings, and Therapeutic Implications

Hormone receptor-positive breast cancer (HR+ BC) accounts for approximately 75% of new BC diagnoses. Despite the undisputable progresses obtained in the treatment of HR+ BC in recent years, primary or acquired resistance to endocrine therapies still represents a clinically relevant issue, and is largely responsible for disease recurrence after curative surgery, as well as for disease progression in the metastatic setting. Among the mechanisms causing primary or acquired resistance to endocrine therapies is the loss of estrogen/progesterone receptor expression, which could make BC cells independent of estrogen stimulation and, consequently, resistant to estrogen deprivation or the pharmacological inhibition of estrogen receptors. This review aims at discussing the molecular mechanisms and the clinical implications of HR loss as a result of the therapies used in the neoadjuvant setting or for the treatment of advanced disease in HR+ BC patients.

In vitro comparative models for canine and human breast cancers

During the past four decades, an increased number of similarities between canine mammary tumors and human breast cancer have been reported: molecular, histological, morphological, clinical and epidemiological, which lead to comparative oncological studies. One of the most important goals in human and veterinary oncology is to discover potential molecular biomarkers that could detect breast cancer in an early stage and to develop new effective therapies. Recently, cancer cell lines have successfully been used as an in vitro model to study the biology of cancer, to investigate molecular pathways and to test the efficiency of anticancer drugs. Moreover, establishment of an experimental animal model for the study of human breast cancer will improve testing potential anti-cancer therapies and the discovery of effective therapeutic schemes suitable for human clinical trials.

In this review, we collected data from previous studies that strengthen the value of canine mammary cancer cell lines as an in vitro model for the study of human breast cancer.

Inhibition of histone deacetylase suppresses EGF signaling pathways by destabilizing EGFR mRNA in ER-negative human breast cancer cells

Estrogen receptor alpha (ER)-negative human breast cancer cells frequently overexpress epidermal growth factor receptor (EGFR) and respond poorly to endocrine therapies. Our previous studies demonstrate that histone deacetylation plays a key role in ER gene silencing, and ER expression can be restored with histone deacetylase (HDAC) inhibitors in ER-negative human breast cancer cells. Whether inhibition of HDAC also alters epidermal growth factor (EGF) signaling pathways is not defined. Here we present evidence that reexpression of ER protein by a clinically available HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA or vorinostat), is coupled with loss of EGFR in ER-negative human breast cancer cells. Consistent with this observation, MDA-MB-231 cells, which are ER-negative and overexpress EGFR, that are engineered to express ER show a decrease in EGFR protein expression. Down-regulation of EGFR by SAHA results from attenuation of its mRNA stability. We also confirm that new protein synthesis is required for maintaining EGFR mRNA stability. Further experiments indicate that a decrease in EGFR abolished EGF-initiated signaling pathways including phosphorylated PAK1, p38MAPK and AKT. Thus, SAHA may not only reactivate silenced ER, but also simultaneously deplete EGFR expression. These data suggest that inhibition of HDAC is a promising epigenetic therapy for ER-negative human breast cancer.

Effects of a novel DNA methyltransferase inhibitor zebularine on human breast cancer cells

Because DNA methyltransferase (DNMT) inhibitors like azacytidine and decitabine are known to be effective in the clinic for diseases like myelodysplastic syndromes that may result in part from transcriptional dysregulation due to epigenetic changes, there is interest in developing novel DNMT inhibitors that would be more effective and less toxic. The effects of one such agent, zebularine, which inhibits DNMT and cytidine deaminase, were assessed in two human breast cancer cell lines, MDA-MB-231 and MCF-7. Zebularine treatment inhibited cell growth in a dose and time dependent manner with an IC-50 of approximately 100 microM and 150 microM in MDA-MB-231 and MCF-7 cells, respectively, on 96 h exposure. This was associated with increased expression of p21, decreased expression of cyclin-D, and induction of S-phase arrest. At high doses zebularine induced changes in apoptotic proteins in a cell line specific manner manifested by alteration in caspase-3, Bax, Bcl2 and PARP cleavage. Like other DNMT inhibitors, zebularine decreased expression of DNMTs post-transcriptionally as well as expression of other epigenetic regulators like methyl CpG binding proteins and global acetyl H3 and H4 protein levels. Its capacity to reexpress epigenetically silenced genes in human breast cancer cells at low doses was confirmed by its ability to induce expression of estrogen and progesterone receptor mRNA in association with changes suggestive of active chromatin at the ER promoter as evidenced by ChIP. Finally, its effect in combination with other DNMT or HDAC inhibitors like decitabine or vorinostat was explored. The combination of 50 muM zebularine with decitabine or vorinostat significantly inhibited cell proliferation and colony formation in MDA-MB-231 cells compared with either drug alone. These findings suggest that zebularine is an effective DNMT inhibitor and demethylating agent in human breast cancer cell lines and potentiates the effects of other epigenetic therapeutics like decitabine and vorinostat.

The silent estrogen receptor--can we make it speak?

One of the most common cancers in women world wide, breast cancer is classically an endocrine-dependent cancer. It has been known for over a century that development, progression and metastasis of breast cancer are strongly influenced by hormonal factors. Indeed about two-thirds of breast cancers express the estrogen receptor α (ERα) protein, a key predictor of prognosis and response to endocrine therapy. These cancers are frequently amenable to therapies that target estrogen signaling pathways, including selective estrogen receptor modulators like tamoxifen, selective estrogen receptor downregulators like fulvestrant; and agents that reduce estrogen ligand like aromatase inhibitors and ovarian suppression through luteinizing hormone-releasing hormone (LHRH) agonists. It is likely that these approaches, especially adjuvant tamoxifen, have contributed to the reduction in breast cancer mortality that has been observed in recent years. However, data from clinical studies have suggested that only about 60% of ERα-positive breast cancers respond to hormonal therapy. Further, those tumors that lack expression of ERα and the estrogen-regulated progesterone receptor (PgR) are unresponsive to hormone therapy. Thus the problem of acquired or de novo endocrine resistance is a substantial one. Recent molecular and biological advances have contributed to our understanding about potential underlying mechanisms. Here we will focus especially on silencing the expression of ERα as one such endocrine-resistance mechanism and how it might be exploited clinically.

Estrogen negatively regulates epidermal growth factor (EGF)-mediated signal transducer and activator of transcription 5 signaling in human EGF family receptor-overexpressing breast cancer cells

Breast cancer cell growth may be stimulated by 17beta-estradiol (E2) or growth factors like epidermal growth factor (EGF). However, tumors typically depend on only one of these pathways and may overexpress either estrogen receptor (ER) or EGF receptor (EGFR) and related family members. Tumors overexpressing EGFR are more aggressive than those expressing ER. Intracellular mediators of these growth-stimulatory pathways are not completely defined, but one potential common mediator of EGF and E2 signaling is the transcription factor signal transducer and activator of transcription 5 (STAT5). To investigate the role of STAT5 in potential crosstalk between E2 and EGF, MDA-MB231 and SKBr3 breast cancer cells, which are ER-negative and overexpress human EGF family receptors, were used. Introduction of ERalpha and treatment with E2 decreased EGF-induced tyrosine phosphorylation of STAT5b, basal and EGF-induced STAT5-mediated transcription, and EGF-stimulated DNA synthesis in these cells. Suppressive effects of E2-EpsilonRalpha were specific for STAT5, as EGF stimulation of MAPK was unaffected. Deletion/mutation analysis of ERalpha demonstrated that the DNA-binding domain was insufficient, and that the ligand-binding domain was required for these responses. ERalpha transcriptional activity was not necessary for suppression of STAT5 activity. Overexpression of c-Src did not prevent suppression of STAT5 activity by E2 and ERalpha. However, ERalpha did prevent basal increases in STAT5 activity with overexpressed c-Src. In the context of human EGF receptor family overexpression, E2-ER opposes EGF signaling by regulating STAT5 activity. STAT5 may be a crucial point of signaling for both E2 and growth factors in breast cancer cells, allowing targeted therapy for many types of breast tumors.

Epidermal Growth Factor Induces WISP-2/CCN5 Expression in Estrogen Receptor-α-Positive Breast Tumor Cells through Multiple Molecular Cross-talks

Epidermal growth factor (EGF) is a mitogen for estrogen receptor (ER)–positive breast tumor cells, and it has been proven that EGF occasionally mimicked estrogen action and cross-talks with ER-α to exert its activity. Therefore, the present study was undertaken to explore whether EGF is able to modulate the expression of Wnt-1-induced signaling protein-2/connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed 5 (WISP-2/CCN5), an estrogen-responsive gene, in normal and transformed cell lines of the human breast and, if so, whether this induction is critical for EGF mitogenesis and what downstream signaling pathways are associated with this event. Here, we show that EGF-induced WISP-2 expression in ER- and EGF receptor–positive noninvasive MCF-7 breast tumor cells was dose and time dependent and that expression was modulated at transcription level. A synergism was seen in combination with estrogen. Moreover, small interfering RNA–mediated inhibition of WISP-2/CCN5 activity in MCF-7 cells resulted in abrogation of proliferation by EGF. The multiple molecular cross-talks, including the interactions between phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase signaling pathways and two diverse receptors (i.e., ER-α and EGFR), were essential in the event of EGF-induced WISP-2/CCN5 up-regulation in MCF-7 cells. Moreover, EGF action on WISP-2/CCN5 is restricted to ER- and EGFR-positive noninvasive breast tumor cells, and this effect of EGF cannot be instigated in ER-α-negative and EGFR-positive normal or invasive breast tumor cells by introducing ER-α. Finally, regulation of phosphorylation of ER-α and EGFR may play critical roles in EGF-induced transcriptional activation of WISP-2 gene in breast tumor cells.

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

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

Identification of a novel AU-Rich element in the 3' untranslated region of epidermal growth factor receptor mRNA that is the target for regulated RNA-binding proteins

The epidermal growth factor receptor (EGF-R) plays an important role in the growth and progression of estrogen receptor-negative human breast cancers. EGF binds with high affinity to the EGF-R and activates a variety of second messenger pathways that affect cellular proliferation. However, the underlying mechanisms involved in the regulation of EGF-R expression in breast cancer cells are yet to be described. Here we show that the EGF-induced upregulation of EGF-R mRNA in two human breast cancer cell lines that overexpress EGF-R (MDA-MB-468 and BT-20) is accompanied by stabilization (>2-fold) of EGF-R mRNA. Transient transfections using a luciferase reporter identified a novel EGF-regulated approximately 260-nucleotide (nt) cis-acting element in the 3' untranslated region (3'-UTR) of EGF-R mRNA. This cis element contains two distinct AU-rich sequences (~75 nt), EGF-R1A with two AUUUA pentamers and EGF-R2A with two AUUUUUA extended pentamers. Each independently regulated the mRNA stability of the heterologous reporter. Analysis of mutants of the EGF-R2A AU-rich sequence demonstrated a role for the 3' extended pentamer in regulating basal turnover. RNA gel shift analysis identified cytoplasmic proteins (~55 to 80 kDa) from breast cancer cells that bound specifically to the EGF-R1A and EGF-R2A cis-acting elements and whose binding activity was rapidly downregulated by EGF and phorbol esters. RNA gel shift analysis of EGF-R2A mutants identified a role for the 3' extended AU pentamer, but not the 5' extended pentamer, in binding proteins. These EGF-R mRNA-binding proteins were present in multiple human breast and prostate cancer cell lines. In summary, these data demonstrate a central role for mRNA stabilization in the control of EGF-R gene expression in breast cancer cells. EGF-R mRNA contains a novel complex AU-rich 260-nt cis-acting destabilizing element in the 3'-UTR that is bound by specific and EGF-regulated trans-acting factors. Furthermore, the 3' extended AU pentamer of EGF-R2A plays a central role in regulating EGF-R mRNA stability and the binding of specific RNA-binding proteins. These findings suggest that regulated RNA-protein interactions involving this novel cis-acting element will be a major determinant of EGF-R mRNA stability.

Effects of histone deacetylase inhibitors on the Ah receptor gene promoter

The aromatic hydrocarbon receptor (AhR) is a ligand-dependent basic helix-loop-helix-PAS-containing transcription factor which is activated by chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin. Constitutive expression of the AhR gene occurs in a tissue- and developmentally specific manner and appears to be altered by chemicals which affect histone deacetylase (HDAC) activity in cells in culture. Here we have directly characterized the effects of two HDAC inhibitors, n-butyrate and trichostatin A, on the promoter activity of the murine AhR gene. HDAC inhibitors increased the constitutive activity of the AhR gene promoter in a luciferase reporter construct by five- to sevenfold in a dose- and time-dependent manner in several cell lines and was correlated with an increase in endogenous AhR activity in an AhR-deficient cell line. Deletion analysis of the upstream region of the AhR gene localized the HDAC inhibitor effect to a 167-bp region encompassing -77 to +90 of the AhR gene promoter. Cotransfection of an AhR promoter-luciferase reporter plasmid with a vector expressing the E1A(12s) oncoprotein, a negative regulator of p300, a protein with histone acetylase activity, decreased AhR promoter activity fivefold. Overall, our results support a role for histone acetylation in the transcriptional activity of the AhR gene promoter.

Differential distribution of protein phosphatase 2A in human breast carcinoma cell lines and its relation to estrogen receptor status

Protein phosphatase 2A (PP2A) acts as a growth suppressor and is negatively influenced by oncogenic signals. We determined its activity in various human breast carcinoma (HBC) cell types to understand its relationship to estrogen receptor (ER) expression as well as to the distribution of protein kinase C (PKC), an opposing enzyme. PP2A activity was measured using a preferred substrate, histone H1 phosphorylated by PKC. PP2A activity was higher in both the soluble and nuclear fractions of ER-positive cell lines (MCF-7, T47D and ZR-75-1) than in the ER-negative cell lines (MDA-MB-231, Hs578T and BT-20). PP2A multiple forms (2A0, 2A1, 2A2), separated by DEAE-cellulose chromatography and immunoblot analysis of PP2A catalytic subunit, also showed similar differences in these two HBC cell types. In all cases, PP2A distribution was inversely correlated with the PKC activity profile. Moreover, PP2A activity in MCF-7 cells maintained in estrogen-depleted medium was low. Nonetheless, it was induced by a prolonged treatment with 17beta-estradiol, this induction being blocked by the antiestrogens, tamoxifen and ICI-182,780. Studies in both MCF-7 transfectants stably overexpressing ras and MDA-MB-231 transfectants stably expressing ER, suggested that a low PP2A distribution in ER-negative HBC cell types may be related to tumor progression rather than the loss of ER. Conceivably, the presence of high PP2A along with low PKC in ER-positive HBC cell types may be related to the restricted cell growth associated with the retention of a certain degree of differentiation or hormonal control. Conversely, the presence of low PP2A along with high PKC in ER-negative cell types may be related to hormone-independent enhanced cell growth.

Immunohistochemical expression of c-erbB-2 oncoprotein and EGF-R in pre- and postmenopausal breast cancer

Tissues from 40 cases each of premenopausal and postmenopausal breast cancer were studied immunohistochemically for epidermal growth factor receptor (EGF-R) and c-erbB-2 oncoprotein. In the premenopausal group, immunopositivity for c-erbB-2 was 15% and for EGF-R 22.5%, whereas in the postmenopausal group, 45% of cases were positive for c-erbB-2 and 42.5% for EGF-R. The difference in immunoexpression of c-erbB-2 between the two groups was significant. A significant correlation was observed between the concomitant expression of c-erbB-2 as well as EGF-R and lymph node involvement. Furthermore, an association was found between c-erbB-2 positivity and histological grading of the tumour. It is interesting that the pattern of the investigated parameters indicates the difference in the pathological events of pre- and postmenopausal breast cancer.

Oncostatin M induces the differentiation of breast cancer cells

We have recently described the action of Oncostatin M (OSM) to inhibit the proliferation of breast cancer cells. In this study we examined the action of OSM on 2 breast cancer cell lines to further characterize the nature of OSM inhibition of cellular proliferation. Treatment with OSM for 6 days resulted in an approximately 2- to 5-fold decrease in cell number, which was independent of estrogen receptor status. Consistent with this, colony formation was reduced to approximately 50% when cells were exposed to OSM in primary agar cultures. Clonogenicity was further inhibited following 7 days treatment with OSM in monolayer cultures: the total number of clonogenic cells was suppressed approximately 10-fold. Analysis of cell cycle status in OSM-treated cells demonstrated a 40% reduction in the proportion of cells in S phase within 12 hr, with an increase in cells in G0/G1. After 6 days, there was a 10-fold reduction in the absolute number of cells in S phase in OSM-treated cultures. These changes were associated with striking changes in cellular morphology, including disruption of intercellular junctions and the production of lipid droplets. There was a 5-fold increase of c-fos and c-myc mRNA within 30 min of commencing treatment with OSM. In addition, in the ER positive cells there was a decrease in ER mRNA (evident within approximately 2 hr) and ER protein expression following treatment with OSM. Conversely, there was a 5-fold increase in epidermal growth factor receptor (EGFR) mRNA within 4 hr, and a 2.5-fold rise in mRNA for transforming growth factor alpha (TGF alpha). Thus, the inhibition of breast cancer cells by OSM was associated with decreased clonogenicity, a decrease in S phase cells and a variety of phenotypic changes, all consistent with the induction of differentiation.

Hormonal regulation of type I receptor tyrosine kinase expression in the mammary gland

Hormones guide mammary gland development and differentiation by regulating the expression of local growth factors and their receptors at the cell surface. In line with this principle the expression of the epidermal growth factor receptor (EGFR)3 and ErbB2 receptors varies in the mammary gland during pregnancy, following the changing hormonal profile. In breast cancer, expression of EGFR and ErbB2 is clearly related to the absence of estrogen and progesterone receptors. In breast cancer cells in vitro, the expression of these receptors is modulated by hormones and other growth-modulatory reagents. Moreover, transcriptional regulation of both EGFR and ERBB2 by estrogens has been demonstrated. The action of hormones may therefore result in the differential availability of individual ErbB family members at the cell surface, in this way determining the specific response of the cell to EGF-like factors and heregulins.

Short-chain carboxylic-acid-stimulated, PMN-mediated gingival inflammation

This communication reviews the effects of short-chain carboxylic acids on human cells of importance to the periodontium. The central hypothesis is that these acids can alter both cell function and gene expression, and thus contribute to the initiation and prolongation of gingival inflammation. Short-chain carboxylic acids [CH3-(CH2)x-COOH, x < 3] are metabolic intermediates with a broad range of apparently paradoxical biological effects. For example, lactic acid (CH3-CHOH-COOH), a 3-carbon alpha-hydroxy-substituted acid, is widely recognized for its cariogenicity. Lactic acid, however, also occurs in tropical fruits, and is the active ingredient in a variety of anti-wrinkle creams developed by dermatologists. In marked contrast, the unsubstituted 3-carbon propionic acid (CH3-CH2-COOH) is used as a food preservative and is the active principle for one class of non-steroidal anti-inflammatory agents. Interestingly, the addition of one carbon to propionic acid dramatically changes the biological effects. The unsubstituted 4-carbon butyric acid (CH3-CH2-CH2-COOH) is used by hematologists as a de-differentiating agent for the treatment of sickle cell anemia, but by oncologists as a differentiating agent for cancer chemotherapy. Finally, acting either individually or in concert, these acids can increase vascular dilation. Clearly, these acids, while metabolically derived, have a number of very divergent activities which are cell-type-specific (Fig. 1). It may be telling that periodontal bacteria produce these acids in millimolar concentrations, and that these bacteria can be characterized by their acid production profiles. It is no less interesting that these acids occur in the gingival crevices of human subjects with severe periodontal disease at millimolar levels which are > 10-fold higher than those found in mildly diseased subjects, and are undetectable in healthy subjects. Further, when applied directly to healthy human gingiva, short-chain carboxylic acids stimulate a gingival inflammatory response and inflammatory cytokine release. At the cellular level, these acids inhibit proliferation of gingival epithelial and endothelial cells, and inhibit leukocyte apoptosis and function, but can stimulate leukocyte cytokine release. At the molecular level, these acids can stimulate neutrophil gene transcription, translation, and protein expression. Thus, the likelihood is high that these acids, in addition to their cariogenic activity, can promote and prolong gingival inflammation. Our challenge will be to identify the cell or cells of the periodontium which respond to short-chain carboxylic acids, to delineate their responses and the molecular mechanism(s) of these effects, and to categorize the aspects of the inflammatory components which damage and those which protect the host. With this information, it may be possible to begin to rationally identify and test pharmaceutical agents which diminish the harmful aspects, while enhancing the beneficial components, of the inflammatory response.

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.