Oestrogen-mediated suppression of tumour necrosis factor alpha-induced apoptosis in MCF-7 cells: subversion of Bcl-2 by anti-oestrogens

ERβ1 Sensitizes and ERβ2 Desensitizes ERα-Positive Breast Cancer Cells to the Inhibitory Effects of Tamoxifen, Fulvestrant and Their Combination with All-Trans Retinoic Acid

Adjuvant endocrine therapy (AET) is the treatment of choice for early-stage estrogen receptor alpha (ERα)-positive breast cancer (BC). However, almost 40% of tamoxifen-treated cases display no response or a partial response to AET, thus increasing the need for new treatment options and strong predictors of the therapeutic response of patients at high risk of relapse. In addition to ERα, BC research has focused on ERβ1 and ERβ2 (isoforms of ERβ), the second ER isotype. At present, the impact of ERβ isoforms on ERα-positive BC prognosis and treatment remains elusive. In the present study, we established clones of MCF7 cells constitutively expressing human ERβ1 or ERβ2 and investigated their role in the response of MCF7 cells to antiestrogens [4-hydroxytamoxifen (OHΤ) and fulvestrant (ICI182,780)] and retinoids [all-trans retinoic acid (ATRA)]. We show that, compared to MCF7 cells, MCF7-ERβ1 and MCF7-ERβ2 cells were sensitized and desensitized, respectively, to the antiproliferative effect of the antiestrogens, ATRA and their combination and to the cytocidal effect of the combination of OHT and ATRA. Analysis of the global transcriptional changes upon OHT-ATRA combinatorial treatment revealed uniquely regulated genes associated with anticancer effects in MCF7-ERβ1 cells and cancer-promoting effects in MCF7-ERβ2 cells. Our data are favorable to ERβ1 being a marker of responsiveness and ERβ2 being a marker of resistance of MCF7 cells to antiestrogens alone and in combination with ATRA.

Regulatory Crosstalk of Doxorubicin, Estradiol and TNFα Combined Treatment in Breast Cancer-derived Cell Lines

We present a new model of ESR1 network regulation based on analysis of Doxorubicin, Estradiol, and TNFα combination treatment in MCF-7. We used Doxorubicin as a therapeutic agent, TNFα as marker and mediator of an inflammatory microenvironment and 17β-Estradiol (E2) as an agonist of Estrogen Receptors, known predisposing factor for hormone-driven breast cancer, whose pharmacological inhibition reduces the risk of breast cancer recurrence. Based on the results of transcriptomics analysis, we found 71 differentially expressed genes that are specific for the combination treatment with Doxorubicin + Estradiol + TNFα in comparison with single or double treatments. The responsiveness to the triple treatment was examined for seven genes by qPCR, of which six were validated, and then extended to four additional cell lines differing for p53 and/or ER status. The results of differential regulation enrichment analysis highlight the role of the ESR1 network that included 36 of 71 specific differentially expressed genes. We propose that the combined activation of p53 and NF-kB transcription factors significantly influences ligand-dependent, ER-driven transcriptional responses, also of the ESR1 gene itself. These results provide a model of coordinated interaction of TFs to explain the Doxorubicin, E2 and TNFα induced repression mechanisms.

A preliminary study of 18F-FES PET/CT in predicting metastatic breast cancer in patients receiving docetaxel or fulvestrant with docetaxel

The present explorative study was initiated to evaluate the clinical value of ¹⁸F-FES PET/CT in monitoring the change of estrogen receptor (ER) expression and potential predictive value in metastatic breast cancer patients. Twenty-two pathology-confirmed breast cancer patients were prospectively enrolled and randomly divided into two groups (T: docetaxel, n = 14 and TF: docetaxel + fulvestrant, n = 8). The percentage of patients without disease progression after 12 months (PFS > 12 months) was 62.5% in group TF compared with 21.4% in group T (P = 0.08). According to ¹⁸F-FES PET/CT scans, the SUVmax (maximum standard uptake value) of all the metastatic lesions decreased in group TF after 2 cycles of treatment (6 weeks ± 3 days). However, 6 of 9 patients in group T had at least one lesion with higher post-treatment SUVmax. There was a significant difference in the reduction of ER expression between these two groups (P = 0.028). In group TF, the patients with PFS > 12 months had significantly greater SUVmax changes of ¹⁸F-FES than those with PFS < 12 months (PFS > 12 months: 91.0 ± 12.0% versus PFS < 12 months: 20.7 ± 16.2%; t = −4.64, P = 0.01). Our preliminary study showed that ¹⁸F-FES PET/CT, as a noninvasive method to monitor ER expression, could be utilized to predict prognosis based on changes in SUVmax.

Alterations in estrogen signalling pathways upon acquisition of anthracycline resistance in breast tumor cells

Intrinsic or acquired drug resistance is a major impediment to the successful treatment of women with breast cancer using chemotherapy. We have observed that MCF-7 breast tumor cells selected for resistance to doxorubicin or epirubicin (MCF-7_DOX2 and MCF-7_EPI cells, respectively) exhibited increased expression of several members of the aldo-keto reductase (AKR) gene family (in particular AKR1C3 and AKR1B10) relative to control MCF-7_CC cells selected by propagation in the absence of drug. Normal cellular roles for the AKRs include the promotion of estrogen (E2) synthesis from estrone (E1) and the hydroxylation and detoxification of exogenous xenobiotics such as anthracycline chemotherapy drugs. While hydroxylation of anthracyclines strongly attenuates their cytotoxicity, it is unclear whether the enhanced AKR expression in the above anthracycline-resistant cells promotes E2 synthesis and/or alterations in E2 signalling pathways and whether such changes contribute to enhanced survival and anthracycline resistance. To determine the role of AKRs and E2 pathways in doxorubicin resistance, we examined changes in the expression of E2-related genes and proteins upon acquisition of doxorubicin resistance. We also assessed the effects of AKR overexpression or downregulation or the effects of activators or inhibitors of E2-dependent pathways on previously acquired resistance to doxorubicin. In this study we observed that the enhanced AKR expression upon acquisition of anthracycline resistance was, in fact, associated with enhanced E2 production. However, the expression of estrogen receptor α (ERα) was reduced by 2- to 5-fold at the gene transcript level and 2- to 20-fold at the protein level upon acquisition of anthracycline resistance. This was accompanied by an even stronger reduction in ERα phosphorylation and activity, including highly suppressed expression of two proteins under E2-dependent control (Bcl-2 and cyclin D1). The diminished Bcl-2 and cyclin D1 expression would be expected to reduce the growth rate of the cells, a hypothesis which was confirmed in subsequent cell proliferation experiments. AKR1C3 or AKR1B10 overexpression alone had no effect on doxorubicin sensitivity in MCF-7_CC cells, while siRNA-mediated knockdown of AKR1C3 and/or AKR1B10 expression had no significant effect on sensitivity to doxorubicin in MCF-7_DOX2 or MCF-7_EPI cells. This suggested that enhanced or reduced AKR expression/activity is insufficient to confer anthracycline resistance or sensitivity to breast tumor cells, respectively. Rather, it would appear that AKR overexpression acts in concert with other proteins to confer anthracycline resistance, including reduced E2-dependent expression of both an important apoptosis inhibitor (Bcl-2) and a key protein associated with activation of cell cycle-dependent kinases (cyclin D1).

Estrogen regulation of anti-apoptotic Bcl-2 family member Mcl-1 expression in breast cancer cells

Estrogen is implicated as an important factor in stimulating breast cancer cell proliferation, and presence of estrogen receptor (ER) is an indication of a good prognosis in breast cancer patients. Mcl-1 is an anti-apoptotic Bcl-2 family member that is often over expressed in breast tumors, correlating with poor survival. In breast cancer, it was been previously shown that epidermal growth factor receptors up-regulate Mcl-1 but the role of estrogen in increasing Mcl-1 expression was unknown. In ERα positive cell lines MCF-7 and ZR-75, estrogen treatment increased Mcl-1 expression at both the protein and mRNA level. In two ERα negative cell lines, SK-BR-3 and MDA-MB-231, estrogen failed to increase in Mcl-1 protein expression. We found that ERα antagonists decreased estrogen mediated Mcl-1 expression at both the protein and mRNA level. Upon knockdown of ERα, Mcl-1 mRNA expression after estrogen treatment was also decreased. We also found that ERα binds to the Mcl-1 promoter at a region upstream of the translation start site containing a half ERE site. Streptavidin-pull down assay showed that both ERα and transcription factor Sp1 bind to this region. These results suggest that estrogen is involved in regulating Mcl-1 expression specifically through a mechanism involving ERα.

Antiestrogenic activity of flavonoid phytochemicals mediated via the c-Jun N-terminal protein kinase pathway. Cell-type specific regulation of estrogen receptor alpha

Flavonoid phytochemicals act as both agonists and antagonists of the human estrogen receptors (ERs). While a number of these compounds act by directly binding to the ER, certain phytochemicals, such as the flavonoid compounds chalcone and flavone, elicit antagonistic effects on estrogen signaling independent of direct receptor binding. Here we demonstrate both chalcone and flavone function as cell type-specific selective ER modulators. In MCF-7 breast carcinoma cells chalcone and flavone suppress ERα activity through stimulation of the stress-activated members of the mitogen-activated protein kinase (MAPK) family: c-Jun N-terminal kinase (JNK)1 and JNK2. The use of dominant-negative mutants of JNK1 or JNK2 in stable transfected cells established that the antiestrogenic effects of chalcone and flavone required intact JNK signaling. We further show that constitutive activation of the JNK pathway partially suppresses estrogen (E2)-mediated gene expression in breast, but not endometrial carcinoma cells. Our results demonstrate a role for stress-activated MAPKs in the cell type-specific regulation of ERα function.

BIK/NBK gene as potential marker of prognostic and therapeutic target in breast cancer patients

PURPOSE

The purpose of this study is to determine the association between the BIK/NBK gene expression and estrogen receptor alpha expression.

MATERIALS AND METHODS

We determined the association of BIK/NBK gene expression by real time quantitative reverse transcription polymerase chain reaction and estrogen receptor alpha expression by immunohistochemistry in samples of breast cancer tissue.

RESULTS

We found a statistically significant correlation of BIK/NBK gene expression with the estrogen receptor alpha expression (ρ = 0.751, p = 0.004). For verify differences of BIK/NBK gene expression among ERα+ and ERα- breast cancer tissues, Mann-Whitney U test was performed, obtaining significant differences.

CONCLUSIONS

BIK/NBK gene expression may have important clinical implications and provide predictive, prognostic or therapeutic marker in breast cancer patients according to the estrogen receptor alpha expression.

Combination treatment with fulvestrant and various cytotoxic agents (doxorubicin, paclitaxel, docetaxel, vinorelbine, and 5-fluorouracil) has a synergistic effect in estrogen receptor-positive breast cancer

Patients with estrogen receptor (ER)-positive breast cancers have a better prognosis than those with ER-negative breast cancers, but often have low sensitivity to chemotherapy and a limited survival benefit. We have previously shown a combination effect of taxanes and fulvestrant and suggested that this treatment may be useful for ER-positive breast cancer. In this study, we evaluated the effects of combinations of hormone drugs and chemotherapeutic agents. In vitro, the effects of combinations of five chemotherapeutic agents (doxorubicin, paclitaxel, docetaxel, vinorelbine, and 5-fluorouracil) and three hormone drugs (fulvestrant, tamoxifen, and 4-hydroxytamoxifen) were examined in ER-positive breast cancer cell lines using CalcuSyn software. Changes in chemoresistant factors such as Bcl2, multidrug resistance-associated protein 1, and microtubule-associated protein tau were also examined after exposure of the cells to hormone drugs. In vivo, tumor sizes in mice were evaluated after treatment with docetaxel or doxorubicin alone, fulvestrant alone, and combinations of these agents. Combination treatment with fulvestrant and all five chemotherapeutic agents in vitro showed synergistic effects. In contrast, tamoxifen showed an antagonistic effect with all the chemotherapeutic agents. 4-Hydroxytamoxifen showed an antagonistic effect with doxorubicin and 5-fluorouracil, but a synergistic effect with taxanes and vinorelbine. Regarding chemoresistant factors, Bcl2 and microtubule-associated protein tau were downregulated by fulvestrant. In vivo, a combination of fulvestrant and docetaxel had a synergistic effect on tumor growth, but fulvestrant and doxorubicin did not show this effect. In conclusion, fulvestrant showed good compatibility with all the evaluated chemotherapeutic agents, and especially with docetaxel, in vitro and in vivo.

The estrogen receptor influences microtubule-associated protein tau (MAPT) expression and the selective estrogen receptor inhibitor fulvestrant downregulates MAPT and increases the sensitivity to taxane in breast cancer cells

Introduction

Microtubule-associated protein tau (MAPT) inhibits the function of taxanes and high expression of MAPT decreases the sensitivity to taxanes. The relationship between estrogen receptor (ER) and MAPT in breast cancer is unclear. In this study, we examined the correlation of MAPT expression with the sensitivity of human breast cancer cells to taxanes, and the relationship between ER and MAPT.

Methods

The correlation between MAPT expression and sensitivity to taxanes was investigated in 12 human breast cancer cell lines. Alterations in cellular sensitivity to taxanes were evaluated after knockdown of MAPT expression. ER expression was knocked down or stimulated in MAPT- and ER-positive cell lines to examine the relationship between ER and MAPT. The cells were also treated with hormone drugs (tamoxifen and fulvestrant) and taxanes.

Results

mRNA expression of MAPT did not correlate with sensitivity to taxanes. However, expression of MAPT protein isoforms of less than 70 kDa was correlated with a low sensitivity to taxanes. Downregulation of MAPT increased cellular sensitivity to taxanes. MAPT protein expression was increased by stimulation with 17-β-estradiol or tamoxifen, but decreased by ER downregulation and by fulvestrant, an ER inhibitor. The combination of fulvestrant with taxanes had a synergistic effect, whereas tamoxifen and taxanes had an antagonistic effect.

Conclusions

Expression of MAPT protein isoforms of less than 70 kDa is correlated with a low sensitivity to taxanes in breast cancer cells. ER influences MAPT expression and fulvestrant increases the sensitivity to taxanes in MAPT- and ER-positive breast cancer cells.

The ERalpha coactivator, HER4/4ICD, regulates progesterone receptor expression in normal and malignant breast epithelium

The HER4 intracellular domain (4ICD) is a potent estrogen receptor (ERalpha) coactivator with activities in breast cancer and the developing mammary gland that appear to overlap with progesterone receptor (PgR). In fact, 4ICD has recently emerged as an important regulator and predictor of tamoxifen response, a role previously thought to be fulfilled by PgR. Here we investigated the possibility that the 4ICD coactivator regulates PgR expression thereby providing a mechanistic explanation for their partially overlapping activities in breast cancer. We show that 4ICD is both sufficient and necessary to potentiate estrogen stimulation of gene expression. Suppression of HER4/4ICD expression in the MCF-7 breast tumor cell line completely eliminated estrogen stimulated expression of PgR. In addition, the HER4/4ICD negative MCF-7 variant, TamR, failed to express PgR in response to estrogen. Reintroduction of wild-type HER4 but not the gamma-secretase processing mutant HER4V673I into the TamR cell line restored PgR expression indicating that 4ICD is an essential PgR coactivator in breast tumor cells. These results were substantiated in vivo using two different physiologically relevant experimental systems. In the mouse mammary gland estrogen regulates expression of PgR-A whereas expression of PgR-B is estrogen independent. Consistent with a role for 4ICD in estrogen regulated PgR expression in vivo, PgR-A, but not PgR-B, expression was abolished in HER4-null mouse mammary glands during pregnancy. Coexpression of PgR and 4ICD is also commonly observed in ERalpha positive breast carcinomas. Using quantitative AQUA IHC technology we found that 4ICD potentiated PgR expression in primary breast tumors and the highest levels of PgR expression required coexpression of ERalpha and the 4ICD coactivator. In summary, our results provide compelling evidence that 4ICD is a physiologically important ERalpha coactivator and 4ICD cooperates with ERalpha to potentiate PgR expression in the normal and malignant breast. We propose that direct coupling of these signaling pathways may have important implications for mammary development, breast carcinogenesis, and patient response to endocrine therapy.

Opposing actions of the progesterone metabolites, 5alpha-dihydroprogesterone (5alphaP) and 3alpha-dihydroprogesterone (3alphaHP) on mitosis, apoptosis, and expression of Bcl-2, Bax and p21 in human breast cell lines

Previous studies have shown that breast tissues and breast cell lines convert progesterone (P) to 5alpha-dihydroprogesterone (5alphaP) and 3alpha-dihydroprogesterone (3alphaHP) and that 3alphaHP suppresses, whereas 5alphaP promotes, cell proliferation and detachment. The objectives of the current studies were to determine if the 5alphaP- and 3alphaHP-induced changes in cell numbers are due to altered rates of mitosis and/or apoptosis, and if 3alphaHP and 5alphaP act on tumorigenic and non-tumorigenic cells, regardless of estrogen (E) and P receptor status. The studies were conducted on tumorigenic (MCF-7, MDA-MB-231, T47D) and non-tumorigenic (MCF-10A) human breast cell lines, employing several methods to assess the effects of the hormones on cell proliferation, mitosis, apoptosis and expression of Bcl-2, Bax and p21. In all four cell lines, 5alphaP increased, whereas 3alphaHP decreased cell numbers, [(3)H]thymidine uptake and mitotic index. Apoptosis was stimulated by 3alphaHP and suppressed by 5alphaP. 5alphaP resulted in increases in Bcl-2/Bax ratio, indicating decreased apoptosis; 3alphaHP resulted in decreases in Bcl-2/Bax ratio, indicating increased apoptosis. The effects of either 3alphaHP or 5alphaP on cell numbers, [(3)H]thymidine uptake, mitosis, apoptosis, and Bcl-2/Bax ratio, were abrogated when cells were treated simultaneously with both hormones. The expression of p21 was increased by 3alphaHP, and was unaffected by 5alphaP. The results provide the first evidence that 5alphaP stimulates mitosis and suppresses apoptosis, whereas 3alphaHP inhibits mitosis and stimulates apoptosis. The opposing effects of 5alphaP and 3alphaHP were observed in all four breast cell lines examined and the data suggest that all breast cancers (estrogen-responsive and unresponsive) might be suppressed by blocking 5alphaP formation and/or increasing 3alphaHP. The findings further support the hypothesis that progesterone metabolites are key regulatory hormones and that changes in their relative concentrations in the breast microenvironment determine whether breast tissues remain normal or become cancerous.

L1 mobile element expression causes multiple types of toxicity

LINE-1 (L1) retrotransposons represent one of the most successful families of autonomous retroelements, accounting for at least 17% of the human genome. The expression of these elements can be deleterious to a cell. L1 expression has been shown to result in insertional mutagenesis, genomic deletions and rearrangements as well as double-strand DNA breaks. Also, L1 expression has been linked to the induction of apoptosis. These recent discoveries, in addition to correlations of L1 expression with cancer progression, prompted us to further characterize the effect of L1 expression on cellular viability. We show a marked decrease in the overall cellular vitality with expression of the L1 that was primarily dependent on the second open reading frame (ORF2). Both the endonuclease and reverse transcriptase domains of ORF2 can individually contribute to the deleterious effects of L1 expression. L1 decreases cellular viability both by the previously reported apoptotic signaling, but also by inducing a senescence-like state.

BP1 transcriptionally activates bcl-2 and inhibits TNFalpha-induced cell death in MCF7 breast cancer cells

INTRODUCTION

We have previously shown that the Beta Protein 1 (BP1) homeodomain protein is expressed in 81% of invasive ductal breast carcinomas, and that increased BP1 expression correlates with tumor progression. The purpose of our current investigation was to determine whether elevated levels of BP1 in breast cancer cells are associated with increased cell survival.

METHODS

Effects on cell viability and apoptosis of MCF7 cells stably overexpressing BP1 were determined using MTT and Annexin V assays, and through examination of caspase activation. TNFalpha was used to induce apoptosis. The potential regulation of apoptosis-associated genes by BP1 was studied using real-time PCR and western blot analyses. Electrophoretic mobility shift assays, site-directed mutagenesis, and transient assays were performed to specifically characterize the interaction of BP1 with the promoter of the bcl-2 gene.

RESULTS

Stable overexpression of BP1 led to inhibition of apoptosis in MCF7 breast cancer cells challenged with TNFalpha. Increased BP1 resulted in reduced processing and activation of caspase-7, caspase-8, and caspase-9, and inactivation of the caspase substrate Poly(ADP-Ribose) Polymerase (PARP). Increased levels of full-length PARP and a decrease in procaspase-8 were also associated with BP1 overexpression. The bcl-2 gene is a direct target of BP1 since: (i) BP1 protein bound to a consensus binding sequence upstream of the bcl-2 P1 promoter in vitro. (ii) MCF7 cells overexpressing BP1 showed increased levels of bcl-2 mRNA and protein. (iii) Transient assays indicated that increased bcl-2 promoter activity is due to direct binding and modulation by BP1 protein. BP1 expression also prevented TNFalpha-mediated downregulation of bcl-2 mRNA and protein.

CONCLUSION

These findings suggest mechanisms by which increased BP1 may impart a survival advantage to breast cancer cells, which could lead to increased resistance to therapeutic agents in patients.

Coregulation of estrogen receptor by ERBB4/HER4 establishes a growth-promoting autocrine signal in breast tumor cells

Although crosstalk between cell-surface and nuclear receptor signaling pathways has been implicated in the development and progression of endocrine-regulated cancers, evidence of direct coupling of these signaling pathways has remained elusive. Here we show that estrogen promotes an association between extranuclear estrogen receptor alpha (ER) and the epidermal growth factor receptor (EGFR) family member ERBB4. Ectopically expressed as well as endogenous ERBB4 interacts with and potentiates ER transactivation, indicating that the ERBB4/ER interaction is functional. Estrogen induces nuclear translocation of the proteolytic processed ERBB4 intracellular domain (4ICD) and nuclear translocation of 4ICD requires functional ligand-bound ER. The nuclear ER/4ICD complex is selectively recruited to estrogen-inducible gene promoters such as progesterone receptor (PgR) and stromal cell-derived factor 1 (SDF-1) but not to trefoil factor 1 precursor (pS2). Consistent with 4ICD-selective promoter binding, suppression of ERBB4 expression by interfering RNA shows that 4ICD coactivates ER transcription at the PgR and SDF-1 but not the pS2 promoter. Significantly, ERBB4 itself is an estrogen-inducible gene and the ERBB4 promoter harbors a consensus estrogen response element (ERE) half-site with overlapping activator protein-1 elements that bind ER and 4ICD in response to estrogen. Using a cell proliferation assay and a small interfering RNA approach, we show that ERBB4 expression is required for the growth-promoting action of estrogen in the T47D breast cancer cell line. Our results indicate that ERBB4 is a unique coregulator of ER, directly coupling extranuclear and nuclear estrogen actions in breast cancer. We propose that the contribution of an autocrine ERBB4/ER signaling pathway to tumor growth and therapeutic response should be considered when managing patients with ER-positive breast cancer.

Phosphorylation of MNAR promotes estrogen activation of phosphatidylinositol 3-kinase

Estrogen actions are mediated by a complex interface of direct control of gene expression (the so-called "genomic action") and by regulation of cell signaling/phosphorylation cascades, referred to as the "nongenomic," or extranuclear, action. We have previously described the identification of MNAR (modulator of nongenomic action of estrogen receptor) as a novel scaffold protein that regulates estrogen receptor alpha (ERalpha) activation of cSrc. In this study, we have investigated the role of MNAR in 17beta-estradiol (E2)-induced activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Consistent with our previous results, a direct correlation was established between MNAR expression levels and E2-induced activation of PI3 and Akt kinases. Endogenous MNAR, ERalpha, cSrc, and p85, the regulatory subunit of PI3 kinase, interacted in MCF7 cells treated with E2. The interaction between p85 and MNAR required activation of cSrc and MNAR phosphorylation on Tyr 920. Consequently, the mutation of this tyrosine to alanine (Y920A) abrogated the interaction between MNAR and p85 and the E2-induced activation of the PI3K/Akt pathway, which was required for the E2-induced protection of MCF7 cells from apoptosis. Nonetheless, the Y920A mutant potentiated the E2-induced activation of the Src/MAPK pathway and MCF7 cell proliferation, as observed with the wild-type MNAR. These results provide new and important insights into the molecular mechanisms of E2-induced regulation of cell proliferation and apoptosis.

The ERBB4/HER4 intracellular domain 4ICD is a BH3-only protein promoting apoptosis of breast cancer cells

ERBB4/HER4 (referred to here as ERBB4) is a unique member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. In contrast to the other three members of the EGFR family (i.e., EGFR, ERBB2/HER2/NEU, and ERBB3), which are associated with aggressive forms of human cancers, ERBB4 expression seems to be selectively lost in tumors with aggressive phenotypes. Consistent with this observation, we show that ERBB4 induces apoptosis when reintroduced into breast cancer cell lines or when endogenous ERBB4 is activated by a ligand. We further show that ligand activation and subsequent proteolytic processing of endogenous ERBB4 results in mitochondrial accumulation of the ERBB4 intracellular domain (4ICD) and cytochrome c efflux, the essential and committed step of mitochondrial regulated apoptosis. Our results indicate that 4ICD is functionally similar to BH3-only proteins, proapoptotic members of the BCL-2 family required for initiation of mitochondrial dysfunction through activation of the proapoptotic multi-BH domain proteins BAX/BAK. Similar to other BH3-only proteins, 4ICD cell-killing activity requires an intact BH3 domain and 4ICD interaction with the antiapoptotic protein BCL-2, suppressed 4ICD-induced apoptosis. Unique among BH3-only proteins, however, is the essential requirement of BAK but not BAX to transmit the 4ICD apoptotic signal. Clinically, cytosolic but not membrane ERBB4/4ICD expression in primary human breast tumors was associated with tumor apoptosis, providing a mechanistic explanation for the loss of ERBB4 expression during tumor progression. Thus, we propose that ligand-induced mitochondrial accumulation of 4ICD represents a unique mechanism of action for transmembrane receptors, directly coupling a cell surface signal to the tumor cell mitochondrial apoptotic pathway.

Osteoprotegerin (OPG) expression by breast cancer cells in vitro and breast tumours in vivo--a role in tumour cell survival?

In addition to its role in bone turnover, osteoprotegerin (OPG) has been reported to bind to and inhibit Tumour necrosis factor-related apoptosis inducing ligand (TRAIL). TRAIL is produced in tumours by invading monocytes, inducing apoptosis in neoplastic cells sensitive to this cytokine. OPG production by tumour cells would therefore be a novel mechanism whereby cancer cells evade host defences and gain a growth advantage. In this study we show that OPG produced by breast cancer cells enhances tumour cell survival by inhibiting TRAIL-induced apoptosis. OPG expression by breast cancer cells (MDA-MB 436/231) grown in vitro was examined using PCR and ELISA, and the sensitivity of these cells to TRAIL was determined. The effects of OPG on TRAIL induced apoptosis was investigated by exposing MDA-MB 436 cells to TRAIL, in the presence or absence of OPG, followed by assessment of nuclear morphology. We found that the levels of OPG produced were sufficient to inhibit TRAIL-induced apoptosis, suggesting that OPG may play a role in tumour cell survival. We also examined the expression pattern of OPG in a selection of breast tumours (n=400) by immunohistochemistry, and related OPG expression to the clinico-pathological data for each tumour. OPG expression was found to be negatively correlated with increasing tumour grade. To our knowledge these results are the first to demonstrate that OPG can act as an endocrine survival factor for breast cancer cells, as well as reporting the expression patterns of OPG in a large cohort of human breast tumours.

Opposite effects of estrogen receptors alpha and beta on MCF-7 sensitivity to the cytotoxic action of TNF and p53 activity

We have investigated the effect of estrogen on p53 cellular location and its influence on tumor cell susceptibility to tumor necrosis factor (TNF)-mediated cytotoxic action. For this purpose, we have used the TNF-sensitive human breast adenocarcinoma MCF-7 and its derivative, the TNF-resistant 1001 clone. Our data indicate that although estrogen receptor (ER)alpha is present in both cell lines, estrogen treatment (1x10(-8) M) has an influence only on the MCF-7 cells and protects these cells from the TNF cytotoxicity. This protective effect is associated with translocation of p53 from the nucleus to the cytoplasm in p53 wild-type MCF-7 and not in p53-mutated 1001 cells. The translocation of p53 in MCF-7 cells results in a decrease in its transcriptional activity, as revealed by diminished p21(WAF1/CIP1) induction and an altered ratio of Bax and Bcl-2 proteins. The estrogen-induced effects are reversed by the selective estrogen inhibitor 182, 780 (1x10(-6) M). Interestingly, transient transfection of MCF-7 cells with ERbeta but not ERalpha cDNA encoding plasmid results in retention of p53 in the nucleus, a subsequent potentiation of its transcriptional activity, and in an increased MCF-7 sensitivity to TNF. The estrogen effects on p53 location and transcriptional activity may involve the mdm2 protein since both events were reversed following MCF-7 transfection with plasmid encoding the ARF cDNA. These studies suggest that estrogen-induced MCF-7 cell survival in the presence of TNF requires a transcriptionally active p53 and, more importantly, indicate that introduction of ERbeta can attenuate the estrogen effects on the p53 protein location, its transcriptional activity and also results in a potentiation of cell sensitivity to TNF-mediated cell death.

ERBB4/HER4 potentiates STAT5A transcriptional activity by regulating novel STAT5A serine phosphorylation events

The epidermal growth factor receptor family member ERBB4 is required for mammary gland development and lactation. ERBB4 activities in the breast are mediated through the signal transducer and activator of transcription (STAT) family member STAT5A, and ERBB4 directly activates STAT5A, in part, through phosphorylation of STAT5A at the regulatory Tyr-694. Here we show that STAT5A regulation by ERBB4 is also mediated through STAT5A serine phosphorylation. Using a reverse-phase high performance liquid chromatography tandem mass spectrometry analysis of proteolytically digested STAT5A coexpressed with ERBB4, we identified STAT5A serine phosphorylations at the previously described Ser-779 and at the novel Ser-127/Ser-128. Immunohistochemistry of wild-type and ERBB4-null mammary glands at late pregnancy showed that ERBB4 expression was required for STAT5A phosphorylation at Ser-779. Independent serine-to-alanine residue substitutions in full-length STAT5A revealed that although STAT5A Ser-779 phosphorylation was dispensable for phosphorylation of STAT5A at Tyr-694 and subsequent DNA binding, Ser-779 was required to stabilize an interaction with ERBB4 and mediate ERBB4-induced STAT5A stimulation of gene expression. STAT5A Ser-127/Ser-128, on the other hand, was required for ERBB4-induced phosphorylation of Tyr-694, whereas Ser-779 and as yet unidentified tyrosine residues were phosphorylated in the absence of Ser-127/Ser-128. In addition, STAT5A S127A/S128A remained associated with ERBB4 but failed to bind DNA or activate transcription in response to ERBB4 coexpression. Our studies demonstrate that phosphorylation of STAT5A at Ser-127/Ser-128 and Ser-779 are obligatory events regulating ERBB4-mediated activation of STAT5A.

Presenilin-dependent gamma-secretase processing regulates multiple ERBB4/HER4 activities

Transmembrane receptors typically transmit cellular signals following growth factor stimulation by coupling to and activating downstream signaling cascades. Reports of proteolytic processing of cell surface receptors to release an intracellular domain (ICD) has raised the possibility of novel signaling mechanisms directly mediated by the receptor ICD. The receptor tyrosine kinase ERBB4/HER4 (referred to here as ERBB4) undergoes sequential processing by tumor necrosis factor-alpha converting enzyme and presenilin-dependent gamma-secretase to release the ERBB4 ICD (4ICD). Our recent data suggests that regulation of gene expression by the ERBB4 nuclear protein and the proapoptotic activity of ERBB4 involves the gamma-secretase release of 4ICD. To determine the role gamma-secretase processing plays in ERBB4 signaling, we generated an ERBB4 allele with the transmembrane residue substitution V673I (ERBB4-V673I). We demonstrate that ERBB4-V673I fails to undergo processing by gamma-secretase but retains normal cell surface signaling activity. In contrast to wild-type ERBB4, however, ERBB4-V673I was excluded from the nuclei of transfected cells and failed to activate STAT5A stimulation of the beta-casein promoter. These results support the contention that gamma-secretase processing of ERBB4 is necessary to release a functional 4ICD nuclear protein which directly regulates gene expression. We also demonstrate that 4ICD failed to accumulate within mitochondria of ERBB4-V673I transfected cells and the potent proapoptotic activity of ERBB4 was completely abolished in cells expressing ERBB4-V673I. Our results provide the first formal demonstration that proteolytic processing of ERBB4 is a critical event regulating multiple receptor signaling activities.

Antiestrogens, aromatase inhibitors, and apoptosis in breast cancer

Antiestrogens have been the therapeutic agents of choice for breast cancer patients whose tumors express estrogen receptors, regardless of menopausal status. Unfortunately, many patients will eventually develop resistance to these drugs. Antiestrogens primarily act by preventing endogenous estrogen from activating estrogen receptors and promoting cell growth, which can ultimately lead to tumor cell death. Understanding the mechanisms by which antiestrogens cause cell death or apoptosis is critical to our efforts to develop ways to circumvent resistance. This article focuses on antiestrogen-induced apoptosis both in vitro and in vivo. We review the clinical utility of both antiestrogens and aromatase inhibitors and their apoptogenic mechanisms in cell culture models. Among the key signaling components discussed are the roles of Bcl-2 family members, several cytokines, and their receptors, p53, nuclear factor kappa B (NFkappaB), IRF-1, phosphatidylinositol 3-kinase (PI3K)/Akt, and specific caspases. Finally, we discuss the evidence supporting a role for apoptotic defects in acquired and de novo antiestrogen resistance.

The ERBB4/HER4 receptor tyrosine kinase regulates gene expression by functioning as a STAT5A nuclear chaperone

In the lactating breast, ERBB4 localizes to the nuclei of secretory epithelium while regulating activities of the signal transducer and activator of transcription (STAT) 5A transcription factor essential for milk-gene expression. We have identified an intrinsic ERBB4 NLS (residues 676–684) within the ERBB4 intracellular domain (4ICD) that is essential for nuclear accumulation of 4ICD. To determine the functional significance of 4ICD nuclear translocation in a physiologically relevant system, we have demonstrated that cotransfection of ERBB4 and STAT5A in a human breast cancer cell line stimulates β-casein promoter activity. Significantly, nuclear localization of STAT5A and subsequent stimulation of the β-casein promoter requires nuclear translocation of 4ICD. Moreover, 4ICD and STAT5A colocalize within nuclei of heregulin β1 (HRG)-stimulated cells and both proteins bind to the endogenous β-casein promoter in T47D breast cancer cells. Together, our results establish a novel molecular mechanism of transmembrane receptor signal transduction involving nuclear cotranslocation of the receptor intracellular domain and associated transcription factor. Subsequent binding of the two proteins at transcription factor target promoters results in activation of gene expression.

Regulation of estrogen-mediated cell survival and proliferation by p160 coactivators

BACKGROUND

Estrogen receptor (ER) activity is dependent on coactivator (CoA) proteins. The role of CoA-ER interactions in breast cancer apoptosis remains unexplored.

METHODS

Expression vectors for the p160 CoA genes NCOA-1, NCOA-2, or NCOA-3 were transiently transfected into MCF-7 cells. Cell survival was determined by viability and clonogenic survival assays. Effects of CoA expression on estrogen (E2) signaling were determined by estrogen response element (ERE)-luciferase reporter-gene assay. Clonogenic and reporter-gene survival assays were used to examine the molecular inhibition of CoA function (dominant inhibitory [DI]-decoy-CoA) on cell survival. Statistical significance was established at the P < .05 level.

RESULTS

Overexpression of NCOA-1, NCOA-2, and NCOA-3 enhanced E2-mediated gene expression by 3.17 +/- 0.51-, 2.33 +/- 0.8-, and 3.65 +/- 0.65-fold, respectively, and enhanced cell survival by suppressing tumor necrosis factor alpha (TNF-alpha)-induced cell death from 80.23% +/- 2.66% viability to 101.5% +/- 8.9%, 86.9% +/- 9.9%, and 95.7% +/- 8.5% viability, respectively. NCOA-1 enhancement of cell survival occurred via suppression of TNF-alpha-induced apoptosis as confirmed by viability and morphologic evaluation. Clonogenic survival and E2-stimulated colony formation in MCF-7 cells were suppressed by expression of DI-decoy-NCOA-1 and DI-decoy-NCOA-3 to 34.4% +/- 7.4% and 54% +/- 5.4% of vector control, but not DI-decoy-NCOA-2.

CONCLUSIONS

Overexpression of NCOA-1 and NCOA-3 exerted potent survival effects in breast carcinoma cells. Use of DI-CoA constructs enhanced TNF-alpha-induced cell death and abrogated E2-induced survival. Inhibition of CoA proteins represents a mechanism for enhancing sensitivity therapies in breast carcinoma.

Oestrogen inhibits resveratrol-induced post-translational modification of p53 and apoptosis in breast cancer cells

Resveratrol, a naturally occurring stilbene, induced apoptosis in human breast cancer MCF-7 cells. The mechanism of this effect was dependent on mitogen-activated protein kinase (MAPK, ERK1/2) activation and was associated with serine phosphorylation and acetylation of p53. Treatment of MCF-7 cells with resveratrol in the presence of 17β-oestradiol (E₂) further enhanced MAPK activation, but E₂ blocked resveratrol-induced apoptosis, as measured by nucleosome ELISA and DNA fragmentation assays. E₂ inhibited resveratrol-stimulated phosphorylation of serines 15, 20 and 392 of p53 and acetylation of p53 in a concentration- and time-dependent manner. These effects of E₂ on resveratrol action were blocked by ICI 182,780 (ICI), an inhibitor of the nuclear oestrogen receptor-α (ER). ICI 182,780 did not block the actions of resveratrol, alone. Electrophoretic mobility studies of p53 binding to DNA and of p21 expression indicated that E₂ inhibited resveratrol-induced, p53-directed transcriptional activity. These results suggest that E₂ inhibits p53-dependent apoptosis in MCF-7 cells by interfering with post-translational modifications of p53 which are essential for p53-dependent DNA binding and consequent stimulation of apoptotic pathways. These studies provide insight into the complex pathways by which apoptosis is induced by resveratrol in E₂-depleted and -repleted environments.

A prognostic index for operable, node-negative breast cancer

Clinical data and samples from patients diagnosed, more than 10 years previously, with operable node-negative breast cancer (participants in the Scottish Adjuvant Tamoxifen trial), were revisited. Cases with two distinct categories of outcome were selected; more than 10 years disease-free survival ('good outcome') or distant relapse within 6 years of diagnosis ('poor outcome'). An initial set of cases was analysed for a range of putative prognostic markers and a prognostic index, distinguishing the two outcome categories, was calculated. This index was then validated by testing its predictive power on a second, independent set of cases. A combination of histological grade plus immunochemical staining for BCL-2, p27 and Cyclin D1, generated a useful prognostic index for tamoxifen-treated patients but not for those treated by surgery alone. The value of the index was confirmed in a second set of tamoxifen-treated, early stage breast cancers. Overall, it correctly predicted good and poor outcome in 79 and 74% of cases, respectively (odds ratio 11.0). Other markers assessed added little to prediction of outcome. In the case of molecular assays, sensitivity and reliability were compromised by the age of the tissue specimens and the variability of fixation protocols. In selecting patients for adjuvant systemic chemotherapy, the proposed index improves considerably on current international guidelines and matches the performance reported for 'gene-expression signature' analysis.

The Bik BH3-only protein is induced in estrogen-starved and antiestrogen-exposed breast cancer cells and provokes apoptosis

Evidence has been accumulating that some estrogen-dependent human breast cancers require estrogen for not only proliferation but also survival. To obtain insights into the molecular mechanisms of apoptosis of breast cancer cells subjected to estrogen starvation or exposed to antiestrogens, we characterized changes in the gene expression profile of MCF-7/BUS human breast cancer cells and revealed a strong induction of Bik, a member of the BH3-only proapoptotic proteins. The Bik mRNA transcript and protein were strongly induced by estrogen starvation or exposure to fulvestrant, a pure antiestrogen that competes with the natural estrogens for binding to the estrogen receptors. This Bik induction preceded apoptotic cell death, which was blocked by zVAD-fmk, a pancaspase inhibitor. Amounts of the Bcl-2-related proteins, such as Bcl-2, Bcl-XL, or Bax, showed only marginal changes in the presence or absence of estrogens or antiestrogens. Suppression of Bik expression by using the small interfering RNA effectively blocked the fulvestrant-induced breast cancer cell apoptosis. These results indicate that Bik is induced in MCF-7/BUS cells in the absence of estrogen signaling and plays a critical role in the antiestrogen-provoked breast cancer cell apoptosis.

Tumor necrosis factor-α: molecular and cellular mechanisms in skeletal pathology

Tumor necrosis factor-alpha (TNF) is one member of a large family of inflammatory cytokines that share common signal pathways, including activation of the transcription factor nuclear factor kappa B (Nf-kappa B) and stimulation of the apoptotic pathway. Data derived from early work supported a role for TNF as a skeletal catabolic agent that stimulates osteoclastogenesis while simultaneously inhibiting osteoblast function. The finding that estrogen deficiency was associated with increased production of cytokines led to a barrage of studies and lively debate on the relative contributions of TNF and other cytokines on bone loss, on the potential cell sources of TNF in the bone microenvironment, and on the mechanism of TNF action. TNF has a central role in bone pathophysiology. TNF is necessary for stimulation of osteoclastogenesis along with the receptor activator of Nf-kappa B ligand (RANKL). TNF also stimulates osteoblasts in a manner that hinders their bone-formative action. TNF suppresses recruitment of osteoblasts from progenitor cells, inhibits the expression of matrix protein genes, and stimulates expression of genes that amplify osteoclastogenesis. TNF may also affect skeletal metabolism by inducing resistance to 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) by a mechanism that extends to other members of the steroid hormone nuclear receptor family. Thus, TNF assails bone at many levels. This review will focus on the cellular and molecular mechanisms of TNF action in the skeleton that result in increased bone resorption and impaired formation. TNF and its signal pathway remains an important target for the development of new therapies for bone loss from osteoporosis and inflammatory arthritis.

Estrogen prevention of lacrimal gland cell death and lymphocytic infiltration

Previous studies have shown that ovariectomy causes necrosis of lacrimal acinar cells, apoptosis of plasma cells and gland lymphocytic infiltration. Both, lacrimal gland cell death and lymphocytic infiltration were prevented by androgen treatment. Since estrogens are removed by ovariectomy, and the synthetic estrogen diethylstilbestrol has been shown to affect some biochemical correlates of lacrimal secretion, the purpose of this study was to determine the effect of 17-beta-estradiol treatment on ovariectomy-induced cell death and lymphocytic infiltration. Sexually mature female New Zealand white rabbits (4-4.5 kg) were ovariectomized and divided into two groups. One group was treated with 0.5 mg kg(-1) per day 17-beta-estradiol, and the other group with vehicle alone. A third group of sham operated rabbits was used as controls and they also were treated with vehicle alone. Six days after surgery, the animals were euthanized, the lacrimal glands removed and processed for analysis of apoptosis as assessed by DNA fragmentation, and for morphological examination. DNA fragmentation was determined using the TUNEL assay and agarose gel electrophoresis. Sections were also stained for rabbit thymic lymphocyte antigen (RTLA), and rabbit CD18. Labelled nuclei and stained areas were quantified by automated densitometry. Ovariectomized rabbits showed a significant increase in the values for degraded DNA as a percent of total nuclear area (2.90+/-0.40%) compared to sham operated rabbits (0.73+/-0.22%). 17-beta-estradiol treatment in ovariectomized rabbits prevented the increase in DNA degradation. Examination of TUNEL assay at higher magnification (40x) confirmed previous studies showing that ovariectomy caused apoptosis of interstitial cells. Significant numbers of bulging cells of very pale appearance under light microscopy, also confirm previously identified necrotic cells in acinar regions. Treatment with 17-beta-estradiol prevented this necrosis. Increased numbers of RTLA(+) and CD18(+) interstitial cells were also evident after ovariectomy. 17-beta-estradiol treatment prevented the increase in the number of lymphoid cells. We confirmed previous observations that suggest that glandular atrophy observed after ovariectomy is likely to proceed by necrosis of acinar cells rather than apoptosis, and that ovariectomy triggers an inflammatory response in the gland. These results suggest that in addition to androgens, estrogens also seem to play a role to maintain lacrimal gland structure and function. A decrease in available estrogen levels could trigger both lacrimal gland apoptosis and necrosis, as well as lymphocytic infiltration. Although, the effect of estrogens in these experiments seems to be direct and not through androgens, the possibility of the role of an autocrine and/or paracrine factors, promoted by estrogen on lacrimal gland cells still needs to be investigated.