Tamoxifen enhances myoepithelial cell suppression of human breast carcinoma progression in vitro by two different effector mechanisms

Immunolocalization of estrogen alpha and progesterone beta receptors in goat mammary gland

Steroid receptors particularly estrogen receptor alpha and progesterone receptor beta are essential for mammary gland development. Objective of this study was to explore transcript and protein expression profile of steroid receptors in goat mammary glands. A varied expression of ER-alpha and PR-B was observed during lactation, nonlactating/ dry, mastitic and mammary pre-cancer/cancer in goats. During lactation, immunopositivity of ER-alpha was observed only in the nuclei of mammary epithelial cells (MEC) and stromal cells. However, in non-lactating stage, ER-alpha immunopositivity was observed both in nucleus and cytoplasm of MEC. In mammary pre-cancer (based on aberrant expression of CD10, FNDC3B and MUC1) immunoreactivity of ER-alpha (38±12.5%) varied from non-lactating (14.8±3.1%) and lactating (7.9±2.6%) glands. During naturally infected mastitis, a reduction in the expression of ER-alpha and PR-B was observed.We observed similar expression patterns of ER-alpha and PR-B as that of their protein expression. Transcripts of these receptors were highest in mammary precancer. In comparison to lactating glands, expressions of ER-alpha and PR-B was upregulated in mammary precancers by 17- folds and 9.2-folds, respectively. These results showed a reduction in expression of steroid receptors in mastitic glands and upregulation in mammary precancer indicating role of these receptors in cell proliferation.

The Opportunity of Precision Medicine for Breast Cancer With Context-Sensitive Tumor Suppressor Maspin

To improve the precision of molecular diagnosis and to develop and guide targeted therapies of breast cancer, it is essential to determine the mechanisms that underlie the specific tumor phenotypes. To this end, the application of a snapshot of gene expression profile for breast cancer diagnosis and prognosis is fundamentally challenged since the tissue-based data are derived from heterogonous cell types and are not likely to reflect the dynamics of context-dependent tumor progression and drug sensitivity. The intricate network of epithelial differentiation program can be concertedly controlled by tumor suppressor maspin, a homologue of clade B serine protease inhibitors (serpin), through its multifaceted molecular interactions in multiple subcellular localizations. Unlike most other serpins that are expressed in multiple cell types, maspin is epithelial specific and has distinct roles in luminal and myoepithelial cells. Endogenously expressed maspin has been found in the nucleus and cytoplasm, and detected on the surface of cell membrane. It is also secreted free and as an exosomal cargo protein. Research in the field has led to the identification of the maspin targets and maspin-associated molecules, as well as the structural determinants of its suppressive functions. The current review discusses the possibility for maspin to serve as a cell type-specific and context-sensitive marker to improve the precision of breast cancer diagnosis and prognosis. These advancements further suggest a new window of opportunity for designing novel maspin-based chemotherapeutic agents with improved anti-cancer potency. J. Cell. Biochem. 118: 1639-1647, 2017. © 2017 Wiley Periodicals, Inc.

Maspin: molecular mechanisms and therapeutic implications

Maspin, a non-inhibitory member of the serine protease inhibitor superfamily, has been characterized as a tumor suppressor gene in multiple cancer types. Among the established anti-tumor effects of Maspin are the inhibition of cancer cell invasion, attachment to extracellular matrices, increased sensitivity to apoptosis, and inhibition of angiogenesis. However, while significant experimental data support the role of Maspin as a tumor suppressor, clinical data regarding the prognostic implications of Maspin expression have led to conflicting results. This highlights the need for a better understanding of the context dependencies of Maspin in normal biology and how these are perturbed in the context of cancer. In this review, we outline the regulation and roles of Maspin in normal and developmental biology while discussing novel evidence and emerging theories related to its functions in cancer. We provide insight into the immense therapeutic potential of Maspin and the challenges related to its successful clinical translation.

Tamoxifen ameliorates peritoneal membrane damage by blocking mesothelial to mesenchymal transition in peritoneal dialysis

Mesothelial-to-mesenchymal transition (MMT) is an auto-regulated physiological process of tissue repair that in uncontrolled conditions such as peritoneal dialysis (PD) can lead to peritoneal fibrosis. The maximum expression of peritoneal fibrosis induced by PD fluids and other peritoneal processes is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. Tamoxifen, a synthetic estrogen, has successfully been used to treat retroperitoneal fibrosis and EPS associated with PD. Hence, we used in vitro and animal model approaches to evaluate the efficacy of Tamoxifen to inhibit the MMT as a trigger of peritoneal fibrosis. In vitro studies were carried out using omentum-derived mesothelial cells (MCs) and effluent-derived MCs. Tamoxifen blocked the MMT induced by transforming growth factor (TGF)-β1, as it preserved the expression of E-cadherin and reduced the expression of mesenchymal-associated molecules such as snail, fibronectin, collagen-I, α-smooth muscle actin, and matrix metalloproteinse-2. Tamoxifen-treatment preserved the fibrinolytic capacity of MCs treated with TGF-β1 and decreased their migration capacity. Tamoxifen did not reverse the MMT of non-epitheliod MCs from effluents, but it reduced the expression of some mesenchymal molecules. In mice PD model, we demonstrated that MMT progressed in parallel with peritoneal membrane thickness. In addition, we observed that Tamoxifen significantly reduced peritoneal thickness, angiogenesis, invasion of the compact zone by mesenchymal MCs and improved peritoneal function. Tamoxifen also reduced the effluent levels of vascular endothelial growth factor and leptin. These results demonstrate that Tamoxifen is a therapeutic option to treat peritoneal fibrosis, and that its protective effect is mediated via modulation of the MMT process.

A novel parthenin analog exhibits anti-cancer activity: activation of apoptotic signaling events through robust NO formation in human leukemia HL-60 cells

This study describes the anti-cancer activity of P19, an analog of parthenin. P19 induced apoptosis in HL-60 cells and inhibited cell proliferation with 48h IC50 of 3.5μM. At 10mg/kg dose, it doubled the median survival time of L1210 leukemic mice and at 25mg/kg it inhibited Ehrlich ascites tumor growth by 60%. Investigation of the mechanism of P19 induced apoptosis in HL-60 cells revealed that N-acetyl-l-cysteine (NAC) and s-methylisothiourea (sMIT) could reverse several molecular events that lead to cell death by inhibiting nitric oxide (NO) formation. It selectively produced massive NO in cells while quenching the basal ROS levels with concurrent elevation of GSH. P19 disrupted mitochondrial integrity leading to cytochrome c release and caspase-9 activation. P19 also caused caspase-8 activation by selectively elevating the expression of DR4 and DR5. All these events lead to the activation of caspase-3 leading to PARP-1 cleavage and DNA fragmentation. However, knocking down of AIF by siRNA also suppressed the apoptosis substantially thus indicating caspase independent apoptosis, too. Further, contrary to enhanced iNOS expression, its transcription factor, NF-κB (p65) was cleaved with a simultaneous increase in cytosolic IκB-alpha. In addition, P19 potently inhibited pro-survival proteins pSTAT3 and survivin. The multi-modal pro-apoptotic activity of P19 raises its potential usefulness as a promising anti-cancer therapeutic.

Highly increased maspin expression corresponds with up-regulation of miR-21 in endometrial cancer: a preliminary report

BACKGROUND

Maspin and programmed cell death 4 (Pdcd4) are tumor suppressor genes, and miR-21 is overexpressed in many solid tumors and was proven to negatively regulate a number of tumor suppressor genes including maspin and Pdcd4.The purpose of this study was to investigate the expression of maspin, Pdcd4, and miR-21 and their interrelations with clinicopathologic features in endometrial cancer using a quantitative approach.

METHODS

Maspin, Pdcd4, and miR-21 expressions were evaluated by a real-time polymerase chain reaction in 20 endometrial cancer and 10 normal endometrium samples.

RESULTS

Maspin showed a significantly increased expression in endometrial cancer samples compared with the control group and was up-regulated by a mean factor of 46.54 (SE range, 2.367-1160.26; 95% confidence interval, 0.515-15001, P < 0.0001). Expression of miR-21 was found significantly up-regulated in the sample group in comparison to control group by a mean factor of 2.312 (SE range, 0.741-7.778; 95% confidence interval 0.191-15.0, P = 0.028). No significant differences were present in the expression level of Pdcd4 between endometrial cancer and control groups. Comparison between IA and more advanced International Federation of Gynecology and Obstetrics stages of endometrial cancer in regard to expression levels of maspin, Pdcd4, and miR-21 did not reveal any significant differences. Similarly, no differences were encountered when histopathologic grading, myometrial invasion, age, body mass index, and parity were taken into consideration.

CONCLUSIONS

Association between increased maspin expression and up-regulation of miR-21 in endometrial cancer suggests distinct and tissue-specific relationships of the 2 molecules in this type of malignancy and requires further studies that would reveal its clinical relevance.

NO to breast: when, why and why not?

Nitric oxide is a pleiotropic ancestral molecule, which elicits beneficial effect in many physiological settings but is also tenaciously expressed in numerous pathological conditions, particularly breast tumors. Nitric oxide is particularly harmful in adipogenic milieu of the breast, where it initiates and promotes tumorigenesis. Epidemiological studies have associated populations at a greater risk for developing breast cancer, predominantly estrogen receptor positive tumors, to express specific polymorphic forms of endothelial nitric oxide synthase, that produce sustained low levels of nitric oxide. Low sustained nitric oxide generates oxidative stress and inflammatory conditions at susceptible sites in the heterogeneous microenvironment of the breast, where it promotes cancer related events in specific cell types. Inflammatory conditions also stimulate inducible nitric oxide synthase expression, which dependent on the microenvironment, could promote or inhibit mammary tumors. In this review we re-examine the mechanisms by which nitric oxide promotes initiation and progression of breast cancer and address some of the controversies in the field.

Role of prolactin and vasoinhibins in the regulation of vascular function in mammary gland

The formation of new blood vessels has become a major focus of mammary gland research stimulated by the therapeutic opportunities of controlling angiogenesis in breast cancer. Normal growth and involution of the mammary gland are profoundly affected by the expansion and regression of blood vessels, whereas dysregulation of angiogenesis is characteristic of breast cancer growth and metastasis. Prolactin stimulates the growth and differentiation of the mammary gland under normal conditions, but its role in breast cancer is controversial. Its action is complicated by the fact that prolactin itself is angiogenic, but proteases cleave prolactin to generate vasoinhibins, a family of peptides that act on endothelial cells to suppress angiogenesis and vasodilation and to promote apoptosis-mediated vascular regression. This review summarizes our current knowledge about the vascular effects of prolactin and the generation and action of vasoinhibins, and discusses their possible contribution to the regulation of blood vessels in the normal and malignant mammary gland.

Requirement of a myocardin-related transcription factor for development of mammary myoepithelial cells

The mammary gland consists of a branched ductal system comprised of milk-producing epithelial cells that form ductile tubules surrounded by a myoepithelial cell layer that provides contractility required for milk ejection. Myoepithelial cells bear a striking resemblance to smooth muscle cells, but they are derived from a different embryonic cell lineage, and little is known of the mechanisms that control their differentiation. Members of the myocardin family of transcriptional coactivators cooperate with serum response factor to activate smooth muscle gene expression. We show that female mice homozygous for a loss-of-function mutation of the myocardin-related transcription factor A (MRTF-A) gene are unable to effectively nurse their offspring due to a failure in maintenance of the differentiated state of mammary myoepithelial cells during lactation, resulting in apoptosis of this cell population, a consequent inability to release milk, and premature involution. The phenotype of MRTF-A mutant mice reveals a specific and essential role for MRTF-A in mammary myoepithelial cell differentiation and points to commonalities in the transcriptional mechanisms that control differentiation of smooth muscle and myoepithelial cells.

Inactivation of neuregulin-1 by nitration

Nitration is a posttranslational modification that can compromise protein function. We hypothesized that nitration of growth factors secreted in the lung may alter their interaction with their respective receptors and modulate the normal growth and differentiation program induced by ligand-receptor interaction. We tested this hypothesis in vitro by nitration of neuregulin-1's (NRG-1) EGF-like domain and studying the effect on NRG-1's activity. Nitration of NRG-1's (nNRG-1) EGF-like domain resulted in an inability to activate its receptor, the human epidermal growth factor receptors 2 and 3 (HER2/HER3) heterodimer, as defined by loss of HER2 tyrosine phosphorylation induced by nNRG-1 in MCF-7 cells. Receptor activation was not restored with increasing nNRG-1 concentration or exposure times. nNRG-1 did not compete with NRG-1 for HER2/HER3 binding in competition assays. In addition, nNRG-1 no longer induced proliferation of the MCF-7 cell line, as MCF-7 cells exposed to nNRG-1 and NRG-1 concurrently had the same proliferation rate as that induced by NRG-1 alone. Thus nitration of NRG-1's EGF-like domain caused it to lose its ability to bind and activate its receptor with loss of ligand-induced proliferation. Posttranslational nitration of growth factors in states where reactive nitrogen species are increased may be an important means of regulating growth factor receptor effects in the lung.

Mechanisms of disease: breast tumor pathogenesis and the role of the myoepithelial cell

Breast cancer and precancer cells are influenced by important paracrine regulation from the breast microenvironment, which might be as great a determinant of breast cancer behavior as the specific oncogenic or tumor-suppressive alterations occurring within malignant breast cells. Myoepithelial cells exert profound effects on breast tumor cell behavior, and lie in juxtaposition to abnormally proliferating breast epithelial cells in precancerous disease states such as ductal carcinoma in situ (DCIS). Myoepithelial cells also form a natural border separating breast epithelial cells from stromal angiogenesis. These anatomical relationships suggest that myoepithelial cells might inhibit both the progression of DCIS to invasive breast cancer, and carcinoma-induced angiogenesis. Our ability to study myoepithelial cells has been fostered by recent technical advances in cell selection and sorting procedures, improved selective media, and high throughput technologies, which are able to assess the gene and protein expression profiles within cells. In addition, the establishment of a number of immortalized cell lines and xenografts of myoepithelial cells derived from benign human myoepithelial tumors of diverse sources has provided a self-renewing cell source through which to study the phenotype of myoepithelial cells. Studies of primary and immortalized myoepithelial cell lines indicate that these cells exhibit a natural tumor suppressor function. Functional studies show that these cells have anti-invasive and antiangiogenic phenotypes.

Nitric oxide and hormones in breast cancer: allies or enemies?

Unlike other types of cancer, tumors of the breast are greatly influenced by steroid hormones. The effect of estrogen and progesterone depends on the presence of their specific receptors and these constitute important parameters in determining the aggressiveness of the tumor, the feasibility of certain therapies and the prediction of relapse. The molecular mechanisms of steroid hormone action have not been fully elucidated but recent findings implicate the nitric oxide (NO) pathway in some of these effects. Both hormones can regulate the nitric oxide synthases (NOS) and, in turn, the NO produced has profound consequences on tumor cell homeostasis. On one hand, estrogen increases the activity of endothelial NOS (eNOS or NOSIII), while progesterone activates inducible NOS (iNOS or NOSII) expression. The data presented suggest that the low levels of NO produced by NOSIII mediate the proliferative effect of estrogen. On the other hand, the increase in apoptosis in response to progesterone could implicate the high levels of NO produced by induction of NOSII expression. Understanding of the mechanisms and interactions of steroid hormones with the NO pathway could lead to the development of new approaches and strategies for the effective treatment of breast cancer.

Sex steroid regulation of angiogenesis in breast tissue

Angiogenesis is essential for normal function in the female reproductive tract and a prerequisite for growth and metastasis of solid tumors. Several factors, both inducers and inhibitors, play essential roles in the regulation of the angiogenic process. Exposure to sex steroids increases the risk of breast cancer but the mechanisms are poorly understood and the importance of angiogenesis in breast carcinogenesis is undefined. In the female reproductive tract ovarian hormones tightly regulate angiogenesis. The breast is also a target organ for sex steroids but very little is known about sex steroid effects on angiogenesis in normal breast tissue and breast cancer. In this review several regulators of angiogenesis, and their relation to sex steroids, in breast tissue are discussed. Increased knowledge in this area is of utmost importance for future therapeutic treatment options and for breast cancer prevention.

Do myoepithelial cells hold the key for breast tumor progression?

Mammary myoepithelial cells have been a neglected facet of breast cancer biology, largely ignored since they have been considered to be less important for tumorigenesis than luminal epithelial cells from which most of breast carcinomas are thought to arise. In recent years as our knowledge of stem cell biology and the cellular microenvironment has been increasing, myoepithelial cells are slowly starting to gain more attention. Emerging data raise the hypothesis whether myoepithelial cells play a key role in breast tumor progression by regulating the in situ to invasive carcinoma transition and that myoepithelial cells are part of the mammary stem cell niche. Paracrine interactions between myoepithelial and luminal epithelial cells are known to be important for regulation of cell cycle progression, establishing epithelial cell polarity, and inhibiting cell migration and invasion. Based on these functions, normal mammary myoepithelial cells have been called "natural tumor suppressors." However, during tumor progression myoepithelial cells seem to loose these properties, and eventually this cell population diminishes as tumors become invasive. Better understanding of myoepithelial cell function and their role in tumor progression may lead to their exploitation for cancer therapeutic and preventative measures.

Myoepithelial cells: autocrine and paracrine suppressors of breast cancer progression

Host cellular paracrine regulation of tumor progression is an important determinant of tumor biology but one cell that has been ignored in this regulation is the myoepithelial cell. Myoepithelial cells surround normal ducts and precancerous lesions, especially of the breast and form a natural border separating proliferating epithelial cells from proliferating endothelial cells (angiogenesis). Myoepithelial cells may thus negatively regulate tumor invasion and metastasis. Whereas epithelial cells are susceptible targets for transforming events, myoepithelial cells are resistant. Therefore, it can be said that myoepithelial cells function as both autocrine as well as paracrine tumor suppressors. Our laboratory has found that myoepithelial cells secrete a number of suppressor molecules including high amounts of diverse proteinase inhibitors and angiogenic inhibitors but low amounts of proteinases and angiogenic factors compared to common malignant cell lines. This observation has been made in vitro, in mice, and in humans and suggests that myoepithelial cells exert pleiotropic suppressive effects on tumor progression. The gene expression profile of myoepithelial cells may explain the pronounced anti-invasive and anti-angiogenic effects of myoepithelial cells on carcinoma cells and may also account for the reduced malignancy of myoepithelial tumors, which are devoid of appreciable angiogenesis and invasive behavior.

Effect of tamoxifen on serum IL-18, vascular endothelial growth factor and nitric oxide activities in breast carcinoma patients

Vascular endothelial growth factor (VEGF) is a multi-functional cytokine that has been suggested to be a major angiogenic factor in breast cancer. Nitric oxide (NO) is a potent biological molecule that participates in the multi-step process of carcinogenesis. Interleukin (IL)-18 has been shown to have potent anti-tumour effects. In this study, we investigated the effect of tamoxifen therapy on serum VEGF, NO and IL-18 activity in breast cancer patients. Serum levels of VEGF, nitrate + nitrite and IL-18 were measured in 34 postmenopausal breast cancer patients before and 3 months after the tamoxifen therapy. Both serum VEGF and IL-18 levels decreased after tamoxifen therapy (P = 0.051, P < 0.05, respectively). Serum VEGF levels increased in patients with endometrial thickness, while patients without endometrial thickness had a significant reduction in serum VEGF levels after therapy (P < 0.05). Serum nitrate + nitrite levels increased after the therapy, but this was not statistically significant (P > 0.05). A decrease in serum VEGF levels with tamoxifen therapy may be a reflection of reduced angiogenic activity in patients without endometrial thickness. The negative effect of tamoxifen therapy on IL-18, which is known to have a potent antitumour activity, may be related to the decreased tumour growth by induction of NO and reduction of VEGF activity as a feedback mechanism.

Tamoxifen induces the expression of maspin through estrogen receptor-α

Maspin (mammary serine protease inhibitor) is a tumor suppressor gene that plays an important role in inhibiting tumor growth, invasion and metastasis. Maspin expression is down regulated at transcription level in primary and metastatic breast tumor cells. Previous studies on hormonal regulation of maspin prompt us to test whether an estrogen antagonist tamoxifen (TAM) can exert its anti-tumor function by up regulating maspin gene expression. For this purpose, we first tested whether maspin promoter could be activated in normal and several breast tumor cells. We then carried out a series of promoter analysis in which estrogen receptors and TAM were reconstituted in an in vitro cell culture system. Here we report our new finding that tumor suppresser gene maspin is one of the TAM target genes. TAM induces a maspin/luciferase reporter in cell culture and this induction requires the presence of (estrogen receptor alpha) ERalpha but not estrogen receptor-beta (ERbeta). Maspin promoter deletion and mutation analysis showed that the cis element(s) within a region between -90and+87 bp but not the HRE site (-272 bp) was involved in TAM induction of maspin expression. TAM bound ERalpha may directly control maspin gene expression through the interaction with cofactor (s). Analysis using several ERalpha mutants showed that the N-terminal A/B motif (AF-1) was critical for maspin basal level transcription activation. An ERalpha mutant with point mutations at DNA binding domain abolished estrogen induction of an ERE-luciferase reporter but was still active in activating maspin promoter by TAM. LBD-AF2 domain was required for ERalpha-dependent TAM induction. Deletion of LBD-AF2 or a point mutation in the ERalpha LBD-AF2 region (LBDmtL539A) completely abolished the activation of maspin promoter, suggesting that TAM induction of maspin involves the recruitment of cofactor(s) by ERalpha to the maspin promoter region. This finding indicates that one of the pathways for cancer prevention and tumor inhibition by TAM is mediated through the activation of tumor suppressor gene maspin in breast cancer.

Impaired binding of insulin to erythrocyte membrane receptor and the activation of nitric oxide synthase by the hormone in human breast cancer

PURPOSE

Nitric oxide, a messenger molecule has been reported as having various antineoplastic properties. The activation of insulin-activated nitric oxide synthase (IANOS) was found to be related to the production of NO as a result of the binding of insulin to its receptor through the activation of tyrosine kinase in erythrocyte membrane. As nitric oxide is reported to be a systemic anticancer agent, studies were carried out to determine the role of insulin receptor binding that lead to the activation of tyrosine kinase and IANOS in erythrocytes in breast cancer.

METHODS

Blood samples were collected from female breast cancer patients who, at the time of participation in the study, had not undergone any therapeutic intervention but had opted for surgery. The binding of insulin to its receptor in erythrocyte membrane and the activation of both receptor tyrosine kinase and IANOS due to the hormone binding were determined and compared with the appropriate control.

RESULTS

It was found that the impaired NO synthesis in erythrocyte membrane in breast cancer was related to the marked decrease of insulin binding sites of the high-affinity hormone receptor population. This impaired insulin binding to high-affinity receptors resulted in the impairment of both reaction velocity (Vmax) of the IANOS and receptor tyrosine kinase activation.

CONCLUSION

These results indicated that the impairment of interaction between insulin and its high-affinity receptors in erythrocyte membrane might be a critical pathophysiological event in the development of breast cancer.

Regulating the Tumor Suppressor Gene Maspin in Breast Cancer Cells

PURPOSE

Mammary epithelial cells and the majority of breast cancer tumors require estrogen for continued growth. Antiestrogen therapy alone, or in combination with other drugs, has long been a common procedure for breast cancer treatment and prophylaxis. Thus, there is a critical need to elucidate the mechanism(s) of action of antiestrogen treatment, especially for patients who are at risk of breast cancer development or who are currently receiving hormone therapy. In this study, we examined the ability of hormones to regulate the expression of a tumor suppressor gene, maspin, which is a serine protease inhibitor (serpin) that plays an important role in mammary gland development and is silenced during breast cancer progression. Specifically, our hypothesis tested the clinical efficacy of tamoxifen to regulate maspin expression.

EXPERIMENTAL DESIGN

We used maspin promoter luciferase reporter plasmids that were transfected into normal human mammary epithelial (HMEC1331) and MCF-7 breast cancer cells, followed by determination of the effect of hormones and their antagonists on maspin promoter activity. At the protein level, cytosolic fractions from both cell types before and after hormone treatment were subjected to Western blot analysis to determine maspin level.

RESULTS AND CONCLUSIONS

Our studies revealed that the antiestrogen tamoxifen induces maspin promoter activity. Interestingly, antiandrogen flutamide could also induce maspin in both cell lines tested. These observations were further confirmed in patient tissues. These novel findings provide a new mechanism of action for tamoxifen under normal and pathological conditions. More significantly, these findings could have a potential impact on future therapeutic intervention strategies for breast cancer.

Impairment of stimulation by estrogen of insulin-activated nitric oxide synthase in human breast cancer

Nitric oxide (NO) is reported to have several important effects in the control of neoplasm. We have reported before the presence of an insulin-activated constitutive form of membrane-bound nitric oxide synthase (IANOS) in various cells. Since the insulin-induced NO synthesis by IANOS could have important consequences on the pathophysiology of neoplastic cells, the role of estrogen on the activity of IANOS in malignant and nonmalignant breast tissue as well as in erythrocytes in breast cancer patients was determined. It was found that the IANOS activity of nonmalignant breast tissue was maximally stimulated by 4-fold over the basal activity in the presence of physiologic amounts of estrogen (8-32 nM). The enzymic activity was, however, inhibited by estrogen both below and above this range when compared to appropriate controls. In contrast, both the basal IANOS activity and the stimulatory effect of estrogen was markedly impaired in malignant breast tissue and in erythrocytes in these patients. It was also noted that tamoxifen, a widely used nonsteroidal compound in breast cancer, mimicked estrogen both in the stimulation and in the inhibition of IANOS activity in both of the tissues. These results indicated the probable existence of a novel pathway for estrogen effect independent of nuclear receptor for the stimulation of IANOS activity that might have important consequences in breast cancer and suggested that some of the beneficial effects of tamoxifen could be related to its estrogen-mimicking effect on IANOS independent of hormone-responsive elements sequence in the DNA.

The importance of being a myoepithelial cell

The mammary myoepithelial cell was named the 'Cinderella of mammary cell biology' in light of the earlier focus on the luminal cell. Mammary myoepithelial cells have recently been described as 'natural tumour suppressors'. We now need to understand more about their origin and to reconsider their place in the complex process of mammary morphogenesis. In the present review, we discuss the lineage segregation of mammary myoepithelial cells and their functions in mammary gland development. These functions include their effects on luminal cell growth and differentiation, their key role in the establishment of the polarised mammary epithelial bilayer and the control of stromal invasion in breast cancer.

Predicting the clinical status of human breast cancer by using gene expression profiles

Prognostic and predictive factors are indispensable tools in the treatment of patients with neoplastic disease. For the most part, such factors rely on a few specific cell surface, histological, or gross pathologic features. Gene expression assays have the potential to supplement what were previously a few distinct features with many thousands of features. We have developed Bayesian regression models that provide predictive capability based on gene expression data derived from DNA microarray analysis of a series of primary breast cancer samples. These patterns have the capacity to discriminate breast tumors on the basis of estrogen receptor status and also on the categorized lymph node status. Importantly, we assess the utility and validity of such models in predicting the status of tumors in crossvalidation determinations. The practical value of such approaches relies on the ability not only to assess relative probabilities of clinical outcomes for future samples but also to provide an honest assessment of the uncertainties associated with such predictive classifications on the basis of the selection of gene subsets for each validation analysis. This latter point is of critical importance in the ability to apply these methodologies to clinical assessment of tumor phenotype.

Cloning and characterization of a novel gene that is regulated by estrogen and is associated with mammary gland carcinogenesis

Estrogens play a role in mammary gland function and are implicated in mammary carcinogenesis. We report the cloning of a novel gene [steroid-sensitive gene 1 (SSG1)] that is regulated by E(2) in the rat uterus and mammary gland. The full-length SSG1 complementary DNA has an open reading frame of 1158 nucleotides encoding a putative protein of 385 amino acids. A SSG1-specific antibody recognizes a 40-kDa protein localized to myoepithelial cells of normal mammary tissue and to endothelial cells of 7,12-dimethylbenz(a)antracene-induced mammary tumors. Treatment of rats with E(2) at 1.2 or 2.4 microg/kg.day for 21 days increases SSG1 protein levels in mammary tissue by 16-fold compared with controls. Removal of E(2) after a 14-day treatment decreases SSG1 protein levels 6-fold and 3-fold at 120 and 144 h, respectively. Treatment of rats with the estrogen antagonists tamoxifen or ICI 182,780 did not affect SSG1 protein levels compared with controls. SSG1 protein levels in 7,12-dimethylbenz(a)antracene-induced rat mammary tumors were 23-fold greater than SSG1 levels in resting mammary tissue, and 8-fold higher than protein levels expressed in lactating mammary glands. We propose that SSG1 plays a role in estrogen functions, and its overexpression is correlated with mammary carcinogenesis.