Cell adhesion molecules in the normal and cancerous mammary gland

scNAME: neighborhood contrastive clustering with ancillary mask estimation for scRNA-seq data

MOTIVATION

The rapid development of single-cell RNA sequencing (scRNA-seq) makes it possible to study the heterogeneity of individual cell characteristics. Cell clustering is a vital procedure in scRNA-seq analysis, providing insight into complex biological phenomena. However, the noisy, high-dimensional and large-scale nature of scRNA-seq data introduces challenges in clustering analysis. Up to now, many deep learning-based methods have emerged to learn underlying feature representations while clustering. However, these methods are inefficient when it comes to rare cell type identification and barely able to fully utilize gene dependencies or cell similarity integrally. As a result, they cannot detect a clear cell type structure which is required for clustering accuracy as well as downstream analysis.

RESULTS

Here, we propose a novel scRNA-seq clustering algorithm called scNAME which incorporates a mask estimation task for gene pertinence mining and a neighborhood contrastive learning framework for cell intrinsic structure exploitation. The learned pattern through mask estimation helps reveal uncorrupted data structure and denoise the original single-cell data. In addition, the randomly created augmented data introduced in contrastive learning not only helps improve robustness of clustering, but also increases sample size in each cluster for better data capacity. Beyond this, we also introduce a neighborhood contrastive paradigm with an offline memory bank, global in scope, which can inspire discriminative feature representation and achieve intra-cluster compactness, yet inter-cluster separation. The combination of mask estimation task, neighborhood contrastive learning and global memory bank designed in scNAME is conductive to rare cell type detection. The experimental results of both simulations and real data confirm that our method is accurate, robust and scalable. We also implement biological analysis, including marker gene identification, gene ontology and pathway enrichment analysis, to validate the biological significance of our method. To the best of our knowledge, we are among the first to introduce a gene relationship exploration strategy, as well as a global cellular similarity repository, in the single-cell field.

AVAILABILITY AND IMPLEMENTATION

An implementation of scNAME is available from https://github.com/aster-ww/scNAME.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

3D Modeling of Epithelial Tumors-The Synergy between Materials Engineering, 3D Bioprinting, High-Content Imaging, and Nanotechnology

The current statistics on cancer show that 90% of all human cancers originate from epithelial cells. Breast and prostate cancer are examples of common tumors of epithelial origin that would benefit from improved drug treatment strategies. About 90% of preclinically approved drugs fail in clinical trials, partially due to the use of too simplified in vitro models and a lack of mimicking the tumor microenvironment in drug efficacy testing. This review focuses on the origin and mechanism of epithelial cancers, followed by experimental models designed to recapitulate the epithelial cancer structure and microenvironment, such as 2D and 3D cell culture models and animal models. A specific focus is put on novel technologies for cell culture of spheroids, organoids, and 3D-printed tissue-like models utilizing biomaterials of natural or synthetic origins. Further emphasis is laid on high-content imaging technologies that are used in the field to visualize in vitro models and their morphology. The associated technological advancements and challenges are also discussed. Finally, the review gives an insight into the potential of exploiting nanotechnological approaches in epithelial cancer research both as tools in tumor modeling and how they can be utilized for the development of nanotherapeutics.

Single-Cell RNA Sequencing of a Postmenopausal Normal Breast Tissue Identifies Multiple Cell Types That Contribute to Breast Cancer

Simple Summary

The human body is composed of multiple cell types that form structures and carry out the functions of specific tissues. The human breast is mainly known for the milk ducts organized by epithelial cells, but also contains many other cell types of little-known identity. In this study, we employed the single-cell sequencing technology to ascertain the various cell types present in the normal breast. The results showed 10 distinct cell types that included three epithelial and other novel cell types. The gene signatures of five cell types (three epithelial, one fibroblast subset, and immune cells) matched to the gene expression profiles of >85% breast tumors cataloged in The Cancer Gene Atlas dataset, suggesting their significant contribution to breast cancer. These findings provide a framework for the better mapping of the cellular composition in the breast and its relationship to breast disease.

Abstract

The human breast is composed of diverse cell types. Studies have delineated mammary epithelial cells, but the other cell types in the breast have scarcely been characterized. In order to gain insight into the cellular composition of the tissue, we performed droplet-mediated RNA sequencing of 3193 single cells isolated from a postmenopausal breast tissue without enriching for epithelial cells. Unbiased clustering analysis identified 10 distinct cell clusters, seven of which were nonepithelial devoid of cytokeratin expression. The remaining three cell clusters expressed cytokeratins (CKs), representing breast epithelial cells; Cluster 2 and Cluster 7 cells expressed luminal and basal CKs, respectively, whereas Cluster 9 cells expressed both luminal and basal CKs, as well as other CKs of unknown specificity. To assess which cell type(s) potentially contributes to breast cancer, we used the differential gene expression signature of each cell cluster to derive gene set variation analysis (GSVA) scores and classified breast tumors in The Cancer Gene Atlas (TGGA) dataset (n = 1100) by assigning the highest GSVA scoring cell cluster number for each tumor. The results showed that five clusters (Clusters 2, 3, 7, 8, and 9) could categorize >85% of breast tumors collectively. Notably, Cluster 2 (luminal epithelial) and Cluster 3 (fibroblast) tumors were equally prevalent in the luminal breast cancer subtypes, whereas Cluster 7 (basal epithelial) and Cluster 9 (other epithelial) tumors were present primarily in the triple-negative breast cancer (TNBC) subtype. Cluster 8 (immune) tumors were present in all subtypes, indicating that immune cells may contribute to breast cancer regardless of the subtypes. Cluster 9 tumors were significantly associated with poor patient survival in TNBC, suggesting that this epithelial cell type may give rise to an aggressive TNBC subset.

Curvature-dependent constraints drive remodeling of epithelia

Epithelial tissues function as barriers that separate the organism from the environment. They usually have highly curved shapes, such as tubules or cysts. However, the processes by which the geometry of the environment and the cell's mechanical properties set the epithelium shape are not yet known. In this study, we encapsulated two epithelial cell lines, MDCK and J3B1A, into hollow alginate tubes and grew them under cylindrical confinement forming a complete monolayer. MDCK monolayers detached from the alginate shell at a constant rate, whereas J3B1A monolayers detached at a low rate unless the tube radius was reduced. We showed that this detachment is driven by contractile stresses in the epithelium and can be enhanced by local curvature. This allows us to conclude that J3B1A cells exhibit smaller contractility than MDCK cells. Monolayers inside curved tubes detach at a higher rate on the outside of a curve, confirming that detachment is driven by contraction.

Sinus-like dilatations of the mammary milk ducts, Ki67 expression, and CD3-positive T lymphocyte infiltration, in the mammary gland of wild European rabbits during pregnancy and lactation

Sinus-like dilatations of the mammary duct are recognisable in the mammary gland of pregnant and lactating wild European rabbits. These dilatations exhibit a bilaminar epithelial lining, with luminal epithelial cells expressing basal and lateral E-cadherin. Occasional binucleated mammary epithelial cells are present in the luminal layer. Underlying the luminal epithelial cells is a basal layer of cytokeratin 14-positive cells, supported by a thin layer of fibrous tissue. Multi-segmental epithelial proliferation, as indicated by Ki67 expression, is apparent in the luminal epithelial cells, suggesting a capacity for division during pregnancy and lactation. CD3-positive T lymphocytes are present both intraepithelially, suggesting exocytosis, and in foci subjacent to the ductular epithelium. We consider that sinus-like dilatations of the mammary duct may have the potential to give rise to a subset of the mammary gland neoplasms classified as ductal in origin. Milk accumulation in these sinus-like dilatations is likely to provide a niche for bacterial replication in cases of mastitis in rabbits. These structures are an important component of the innate immune system of the mammary gland, both as a physical barrier and as an interface between the milk and mammary immune cells.

The Role of CSF-1 in Normal Physiology of Mammary Gland and Breast Cancer: An Update

Colony stimulating factor (CSF-1) and its receptor (CSF-1R, product of c-fms proto-oncogene) were initially implicated as essential for normal monocyte development as well as for trophoblastic implantation. However, studies have demonstrated that CSF-1 and CSF-1R have additional roles in mammary gland development during pregnancy and lactation. This apparent role for CSF-1/CSF-1R in normal mammary gland development is very intriguing because this receptor/ligand pair has also been found to be important in the biology of breast cancer in which abnormal expression of CSF-1 and its receptor correlates with tumor cell invasiveness and adverse clinical prognosis. Recent findings also implicate tumor-produced CSF-1 in promotion of bone metastasis in breast cancer, and a certain membrane-associated form of CSF-1 appears to induce immunity against tumors. This review aims to summarize recent findings on the role of CSF-1 and its receptor in normal and neoplastic mammary development that may elucidate potential relationships of growth factor–induced biological changes in the breast during pregnancy and tumor progression.

Circulating tumor cell clusters are oligoclonal precursors of breast cancer metastasis

Circulating tumor cell clusters (CTC clusters) are present in the blood of patients with cancer but their contribution to metastasis is not well defined. Using mouse models with tagged mammary tumors, we demonstrate that CTC clusters arise from oligoclonal tumor cell groupings and not from intravascular aggregation events. Although rare in the circulation compared with single CTCs, CTC clusters have 23- to 50-fold increased metastatic potential. In patients with breast cancer, single-cell resolution RNA sequencing of CTC clusters and single CTCs, matched within individual blood samples, identifies the cell junction component plakoglobin as highly differentially expressed. In mouse models, knockdown of plakoglobin abrogates CTC cluster formation and suppresses lung metastases. In breast cancer patients, both abundance of CTC clusters and high tumor plakoglobin levels denote adverse outcomes. Thus, CTC clusters are derived from multicellular groupings of primary tumor cells held together through plakoglobin-dependent intercellular adhesion, and though rare, they greatly contribute to the metastatic spread of cancer.

Old and new stories: revelations from functional analysis of the bovine mammary transcriptome during the lactation cycle

The cow mammary transcriptome was explored at −30, −15, 1, 15, 30, 60, 120, 240, and 300 d relative to parturition. A total of 6,382 differentially expressed genes (DEG) at a false discovery rate ≤0.001 were found throughout lactation. The greatest number of DEG (>3,500 DEG) was observed at 60 and 120 d vs. −30 d with the largest change between consecutive time points observed at −15 vs. 1 d and 120 vs. 240 d. Functional analysis of microarray data was performed using the Dynamic Impact Approach (DIA). The DIA analysis of KEGG pathways uncovered as the most impacted and induced ‘Galactose metabolism’, ‘Glycosylphosphatidylinositol (GPI)-anchor biosynthesis’, and ‘PPAR signaling’; whereas, ‘Antigen processing and presentation’ was among the most inhibited. The integrated interpretation of the results suggested an overall increase in metabolism during lactation, particularly synthesis of carbohydrates and lipid. A marked degree of utilization of amino acids as energy source, an increase of protein export, and a decrease of the protein synthesis machinery as well cell cycle also were suggested by the DIA analysis. The DIA analysis of Gene Ontology and other databases uncovered an induction of Golgi apparatus and angiogenesis, and the inhibition of both immune cell activity/migration and chromosome modifications during lactation. All of the highly-impacted and activated functions during lactation were evidently activated at the onset of lactation and inhibited when milk production declined. The overall analysis indicated that the bovine mammary gland relies heavily on a coordinated transcriptional regulation to begin and end lactation. The functional analysis using DIA underscored the importance of genes associated with lactose synthesis, lipid metabolism, protein synthesis, Golgi, transport, cell cycle/death, epigenetic regulation, angiogenesis, and immune function during lactation.

Role of DDR1 in the gelatinases secretion induced by native type IV collagen in MDA-MB-231 breast cancer cells

Discoidin domain receptors (DDRs) are receptor tyrosine kinases that get activated by collagens in its native triple-helical form. In mammalian cells, DDR family consists of two members, namely DDR1 and DDR2, which mediates migration and proliferation of several cell types. DDR1 is activated by native type IV collagen and overexpressed in human breast cancer. Type IV collagen is the main component of basement membrane (BM), and the ability to degrade and penetrate BM is related with an increased potential for invasion and metastasis. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that collectively are capable of degrading all components of the extracellular matrix, including the BM. In breast cancer cells, denatured type IV collagen induces MMP-9 secretion and invasion. However, the role of DDR1 in the regulation of gelatinases (MMP-2 and -9) secretion and invasion in breast cancer cells remains to be studied. We demonstrate here that native type IV collagen induces MMP-2 and -9 secretions and invasion through a DDR1 and Src-dependent pathway, together with an increase of MMP-2 and -9-cell surface levels. MMP-2 and -9 secretions require PKC kinase activity, epidermal growth factor receptor (EGFR) activation, arachidonic acid (AA) production and AA metabolites in MDA-MB-231 breast cancer cells. In summary, our data demonstrate, for the first time, that DDR1 mediates MMP-2 and -9 secretions and invasion induced by native type IV collagen in MDA-MB-231 breast cancer cells.

Modulation of mammary gland development in pre-pubertal mice as affected by soya and milk protein supplements

The objective of the present study was to determine the effects of soya and whey milk protein, α-lactalbumin (α-LA), on mammary gland morphology and the structural support of the gland, in pre-pubertal mice after 7 d of treatment. In Expt 1, weaned (day 21) CD1 mice were given one of the four treatments, three included dietary supplements: (1) control diet, casein, (2) soya, (3) α-LA and (4) subcutaneous injection of 2·5 μg oestradiol benzoate in 20 μl maize oil and fed the control diet. All diets were isoenergetic with equal protein concentrations. All groups that were not treated with oestradiol received the vehicle. Whole-mount analyses were performed to determine longitudinal ductal growth and terminal end bud development. DNA was extracted from the gland and assessed by spectrophotometry (260/280 nm). Tissue extracts for extracellular matrix (ECM) proteins, matrix metalloproteinase-2 (MMP(2)), tissue inhibitor of MMP(2) (TIMP(2)), and serum oestradiol and mammary tissue epidermal growth factors (EGF) were measured by immunoassays. Expt 2 utilised the Her2/neu transgenic strain, with the same protocols. Statistical significance was determined by one-way ANOVA. From Expt 1 and 2, soya and α-LA significantly increased ductal elongation when compared with the oestrogen and control groups. These results were corroborated by data on total DNA and the ratio of MMP(2):TIMP(2). The ratio of MMP(2):TIMP(2) was affected by α-LA. Serum oestradiol was decreased only in the oestradiol-treated groups in both experiments. Soya is known to be oestrogenic and can act on epithelia directly. The mechanism by which α-LA affects glandular development is by modulating the ECM or by promoting the synthesis/activity of EGF.

Loss of CSMD1 expression is associated with high tumour grade and poor survival in invasive ductal breast carcinoma

CUB and SUSHI multiple domain protein 1 (CSMD1) is a candidate tumour suppressor gene that maps to chromosome 8p23, a region deleted in many tumour types including 50% of breast cancers. CSMD1 has homologies to proteins implicated in carcinogenesis. We aimed to study the expression pattern of the CSMD1 protein and evaluate its prognostic importance in invasive ductal carcinoma (IDC). An anti-CSMD1 antibody was developed and validated. The expression pattern of CSMD1 in normal breast and IDC samples was investigated by immunohistochemistry in 275 patients. Univariate and multivariate Cox regression analyses were performed. In normal breast duct epithelial cells, luminal, membranous and cytoplasmic CSMD1 staining was identified. Reduced expression of CSMD1 was detected in 79/275 (28.7%) of IDC cases. Low CSMD1 expression was significantly associated with high tumour grade (P = 0.003). CSMD1 expression was associated with overall survival (OS; HR = 0.607, 95%CI: 0.4-0.91, P = 0.018) but not with disease-free survival (DFS; HR = 0.81, 95%CI: 0.46-1.43, P = 0.48). Multivariate analysis showed that CSMD1, together with Nottingham Prognostic Index, was considered an independent predictor of OS (HR = 0.607, 95%CI: 0.4-0.91, P = 0.018) but not DFS (HR = 0.84, 95%CI: 0.46-1.5, P = 0.573). Reduction of CSMD1 expression was significantly associated with high tumour grade and decreased OS. Therefore, our results support the idea that CSMD1 is a tumour suppressor gene and suggest its possible use as a new prognostic biomarker. The membrane expression pattern of CSMD1 suggests that it may be a receptor or co-receptor involved in the process of signal transduction.

Estradiol and tamoxifen differently affects the inhibitory effects of vitamin A and their metabolites on the proliferation and expression of alpha2beta1 integrins in MCF-7 breast cancer cells

PURPOSE

Retinoids are well known inhibitors of estrogen-dependent breast cancer cell growth and differentiation. alpha2beta1 integrins are involved in the normal growth and differentiation of breast cells, they also take part in many pathological processes including malignancies. The aim of the study was to evaluate the effect of estradiol and tamoxifen on the inhibitory action of retinoids on the proliferation of MCF-7 breast cancer cells and alpha2beta1 integrin expression.

MATERIALS AND METHODS

Evaluation was based on [3H]thymidine incorporation and the proliferative activity of PCNA- and Ki 67-positive cells. Expression of alpha2beta1 was assessed through immunocytochemical analysis.

RESULTS

Treatment of cancer cells with the examined compounds and tamoxifen (10 microM) revealed that only 13-cis retinoic acid (13-cis RA) and all-trans retinoic acid (ATRA) (10(-5) M) decreased cells proliferation compared to the tamoxifen group (30.84%+/-3.32, p<0.01 and 31.05%+/-4.67, p<0.01, respectively). The lowest fraction of PCNA positive cells was also observed after the simultaneous addition ATRA (10(-5) M) and tamoxifen (10 microM) (30.75%+/-0.95, p<0.01, compared to the tamoxifen group). Our results showed that the decrease of alpha2beta1 integrin expression by 13-cis RA (10(-5) M, 49.6+/-3.25%) and ATRA (10-9 M, 15.0%+/-5.0) was augmented by tamoxifen and to a lesser extent by estradiol, particularly in the case of ATRA at 10(-7) or 10(-9) M.

CONCLUSIONS

This data suggest that tamoxifen augments the inhibitory effect of retinoids on proliferation and alpha2beta1 integrin expression in MCF-7 cells.

Heterocellular interaction enhances recruitment of alpha and beta-catenins and ZO-2 into functional gap-junction complexes and induces gap junction-dependant differentiation of mammary epithelial cells

Gap junctions (GJ) are required for mammary epithelial differentiation. Using epithelial (SCp2) and myoepithelial-like (SCg6) mouse-derived mammary cells, the role of heterocellular interaction in assembly of GJ complexes and functional differentiation (beta-casein expression) was evaluated. Heterocellular interaction is critical for beta-casein expression, independent of exogenous basement membrane or cell anchoring substrata. Functional differentiation of SCp2, co-cultured with SCg6, is more sensitive to GJ inhibition relative to homocellular SCp2 cultures differentiated by exogenous basement membrane. Connexin (Cx)32 and Cx43 levels were not regulated across culture conditions; however, GJ functionality was enhanced under differentiation-permissive conditions. Immunoprecipitation studies demonstrated association of junctional complex components (alpha-catenin, beta-catenin and ZO-2) with Cx32 and Cx43, in differentiation conditions, and additionally with Cx30 in heterocellular cultures. Although beta-catenin did not shuttle between cadherin and GJ complexes, increased association between connexins and beta-catenin in heterocellular cultures was observed. This was concomitant with reduced nuclear beta-catenin, suggesting that differentiation in heterocellular cultures involves sequestration of beta-catenin in GJ complexes.

The Tammar Wallaby and Fur Seal: Models to Examine Local Control of Lactation

Mammary development and function are regulated by systemic endocrine factors and by autocrine mechanisms intrinsic to the mammary gland, both of which act concurrently. The composition of milk includes nutritional and developmental factors that are crucial to the development of the suckled young, but it is becoming increasingly apparent that milk also has a role in regulating mammary function. This review examines the option of exploiting the comparative biology of species with extreme adaptation to lactation to examine regulatory mechanisms that are present but not readily apparent in other laboratory and livestock species. The tammar wallaby has adopted a reproductive strategy that includes a short gestation (26 d), birth of an immature young, and a relatively long lactation (300 d). The composition of milk changes progressively during the lactation cycle, and this is controlled by the mother and not the sucking pattern of the young. Furthermore, the tammar can practice concurrent asynchronous lactation; the mother provides a concentrated milk high in protein and fat for an older animal that is out of the pouch and a dilute milk low in fat and protein but high in carbohydrates from an adjacent mammary gland for a newborn pouch young. This phenomenon suggests that the mammary gland is controlled locally. The second study species, the Cape fur seal, has a lactation characterized by a repeated cycle of long at-sea foraging trips (up to 28 d) alternating with short suckling periods of 2 to 3 d ashore. Lactation almost ceases while the seal is off shore, but the mammary gland does not progress to apoptosis and involution, most likely because of local control of the mammary gland. Our studies have exploited the comparative biology of these models to investigate how mammary function is regulated by endocrine factors, and particularly by milk. This review reports 3 major findings using these model animals. First, the mammary epithelial cell has an extraordinary intrinsic capacity for survival in our culture model, and the path to either function or death by apoptosis is actively driven. The second outcome is that the route to apoptosis is most likely regulated by specific milk factors. Finally, whey acidic protein, a major milk protein in some species, may play a role in normal mammary development, but that role in vivo may be limited to marsupials. Evolutionary pressure has led to changes in the structure of the protein with an accompanying change in function. Therefore, we propose that a loss of function of this protein in eutherians may relate to a reproductive strategy that is less dependent on lactation.

The fur seal-a model lactation phenotype to explore molecular factors involved in the initiation of apoptosis at involution

Mammary gland involution requires co-ordination of milk production, immune responses, apoptosis and remodeling. Initiation and progression of each of these components involves integral control by the mammary gland. Although cell-based culture models and genetically manipulated animals have shed light on these processes, the factors controlling each step in the involution cascade are still poorly understood. The fur seal displays a unique lactation phenotype. During the lactation cycle the mammary gland downregulates milk production and initiates an immune response but fails to initiate the apoptotic phase of involution, allowing the female fur seal to undertake long foraging trips of up to 28 days between suckling bouts. Upon return to shore the female continues feeding her pup following resumption of lactation and milk production. Expression profiling of genes involved in this lactation cycle provides valuable tools for investigation of the factors responsible for the initiation of apoptosis at involution.

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.

Three-dimensional tissue culture models in cancer biology

Three-dimensional (3D) tissue culture models have an invaluable role in tumour biology today providing some very important insights into cancer biology. As well as increasing our understanding of homeostasis, cellular differentiation and tissue organization they provide a well defined environment for cancer research in contrast to the complex host environment of an in vivo model. Due to their enormous potential 3D tumour cultures are currently being exploited by many branches of biomedical science with therapeutically orientated studies becoming the major focus of research. Recent advances in 3D culture and tissue engineering techniques have enabled the development of more complex heterologous 3D tumour models.

Type IV collagen induces STAT5 activation in MCF7 human breast cancer cells

A rapid increase in the tyrosine phosphorylation of signal transducer and activators of transcription (STAT) proteins has been extensively documented in cells stimulated with cytokines and growth factors, but virtually nothing is known about the regulation of STAT5 activation in breast cancer cells stimulated with basement membrane (BM) components. Stimulation of MCF7 cells with type IV collagen (Col-IV) promoted a striking increase in the phosphorylation of STAT5 at Tyr-694, as revealed by site-specific antibodies that recognized the phosphorylated state of this residue. In addition, Col-IV also stimulated STAT5 nuclear translocation and an increased in STAT5 DNA binding activity. Treatment with the selective Src family inhibitor pyrazolopyrimidine PP-2 prevented STAT5 phosphorylation at Tyr-694, nuclear translocation of STAT5 and the STAT5-DNA complex formation. Our results demonstrate, for the first time, that stimulation with Col-IV induces STAT5 phosphorylation of endogenous STAT5 at Tyr-694, nuclear translocation of STAT5 and increases in STAT5 DNA binding activity via a Src-dependent pathway in MCF7 cells.

Fur Seal Adaptations to Lactation: Insights into Mammary Gland Function

The fur seal (Arctocephalus spp. and Callorhinus spp., members of the pinniped family) is a mammal with the unusual capability to modulate its lactation cycle by turning milk production on and off without the typical mammalian regression and involution of the mammary gland. Lactation has evolved from constraints arising from the spatial and temporal separation of infant nursing and maternal foraging as the mother gives birth and feeds the pup on land while acquisition of nutrients for milk production occurs at sea. The lactation cycle begins with the female fur seal undergoing a perinatal fast of approximately 1 wk, after which time she departs the breeding colony to forage at sea. For the remainder of the long lactation period (116-540 days), the mother alternates between short periods ashore suckling the young with longer periods of up to 4 wk of foraging at sea. Milk production continues while foraging at sea, but at less than 20% the rate of production on land. Fur seals produce one of the richest milk reported, with a very high lipid content contributing up to 85% of total energy. This feature serves as an adaptation to the young's need to produce an insulating blubber layer against heat loss and to serve as an energy store when the mother is away foraging at sea. This atypical pattern of lactation means mothers have long periods with no suckling stimulus and can transfer high-energy milk rapidly while on land to minimize time away from foraging grounds. The absence of suckling stimulus and milk removal during foraging does not result in the onset of involution with associated apoptosis of mammary secretory cells and a subsequent progressive breakdown of the cellular structure of the mammary gland. The mechanisms controlling lactation in the fur seal mammary gland have been investigated using molecular and cellular techniques. These findings have shed light on the processes by which the unique features of lactation in the fur seal are regulated.

Tumour-Stromal Interactions in Breast Cancer: The Role of Stroma in Tumourigenesis

Mammary stromal tissue has a major role in the control and regulation of physiological processes in the breast. Recently, the function of stroma in supporting the tumourigenic process as well as responding to the oncogenic lesion has become clearer. This review differs from the conventional view in that it focuses on and discusses the newly available evidence that points to the fact that mammary stroma has a significant contribution in actively generating transformed lesions and tumours. As such, the oncogenic signals can be dependent or independent of genetic mutations in mammary stromal cells. As a supportive and responsive agent in tumourigenesis, the stroma is induced by tumour cells to express critical signals that drive proliferation, angiogenesis, and motility while suppressing cell death. As an oncogenic agent in tumourigenesis, the stroma can provoke tumourigenicity in adjacent cells in the absence of pre-existing tumour cells leading to the acquisition of genomic changes. Investigating the mechanism by which the tumourigenic cues of the stroma facilitate the generation of malignant epithelial cells will provide invaluable insights into the oncogenic process.

Strategies for engineering the adhesive microenvironment

Cells exist within a complex tissue microenvironment, which includes soluble factors, extracellular matrix molecules, and neighboring cells. In the breast, the adhesive microenvironment plays a crucial role in driving both normal mammary gland development as well tumor initiation and progression. Researchers are designing increasingly more complex ways to mimic the in vivo microenvironment in an in vitro setting, so that cells in culture may serve as model systems for tissue structures. Here, we explore the use of microfabrication technologies to engineer the adhesive microenvironment of cells in culture. These new tools permit the culture of cells on well-defined surface chemistries, patterning of cells into defined geometries either alone or in coculture scenarios, and measurement of forces associated with cell-ECM interactions. When applied to questions in mammary gland development and neoplasia, these new tools will enable a better understanding of how adhesive, structural, and mechanical cues regulate mammary epithelial biology.

Autocrine CSF-1R activation promotes Src-dependent disruption of mammary epithelial architecture

Elevated coexpression of colony-stimulating factor receptor (CSF-1R) and its ligand, CSF-1, correlates with invasiveness and poor prognosis of a variety of epithelial tumors (Kacinski, B.M. 1995. Ann. Med. 27:79–85). Apart from recruitment of macrophages to the tumor site, the mechanisms by which CSF-1 may potentiate invasion are poorly understood. We show that autocrine CSF-1R activation induces hyperproliferation and a profound, progressive disruption of junctional integrity in acinar structures formed by human mammary epithelial cells in three-dimensional culture. Acini coexpressing receptor and ligand exhibit a dramatic relocalization of E-cadherin from the plasma membrane to punctate intracellular vesicles, accompanied by its loss from the Triton-insoluble fraction. Interfering with Src kinase activity, either by pharmacological inhibition or mutation of the Y561 docking site on CSF-1R, prevents E-cadherin translocation, suggesting that CSF-1R disrupts cell adhesion by uncoupling adherens junction complexes from the cytoskeleton and promoting cadherin internalization through a Src-dependent mechanism. These findings provide a mechanistic basis whereby CSF-1R could contribute to invasive progression in epithelial cancers.

Three-dimensional in vitro tissue culture models of breast cancer-- a review

Three-dimensional (3D) in vitro breast tumour models have an invaluable role in tumour biology today providing some very important insights into breast cancer. As well as increasing our understanding of homeostasis, cellular differentiation and tissue organization they provide a well defined environment for cancer research in contrast to the complex host environment of an in vivo model. With the recent availability of relevant stromal elements together with the vast array of extracellular matrix constituents available, in vivo like microenvironments can be recreated. These tissue like structures more realistically model the structural architecture and differentiated function of breast cancer than a cellular monolayer providing in vivo like responses to therapeutic agents. Three dimensional in vitro models allow the study of cell-cell and cell-extracellular matrix interactions, in addition to the influence of the microenvironment on cellular differentiation, proliferation, apoptosis and gene expression. Due to their enormous potential 3D cultures are currently being exploited by many other branches of biomedical science with therapeutically orientated studies becoming the major focus of research. In return great progress in 3D culture techniques have been made, largely due to this greater interaction. At present they are being used in studies ranging from investigating the role of adhesion molecules (e.g., E-cadherin) in invasion/metastasis; VEGF and angiogenesis, to tissue modelling and remodelling. Progress in the development of complex 3D culture systems is more productive than ever, however further research is vital.

Association of rat8 with Fyn protein kinase via lipid rafts is required for rat mammary cell differentiation in vitro

We previously identified rat8 in the pathway involved in epithelial cell differentiation that occurs in the rat mammary gland at pregnancy when tubules and alveoli are formed. rat8, which encodes an IFN-inducible membrane protein, is the rat homologue of the mouse gene fragilis. By differential detergent extraction and isopycnic sucrose density gradients, we show that rat8 protein is associated to lipid membrane domains together with Lyn and Fyn, members of the Src tyrosine kinase family. We also show that recruitment of rat8 to lipid membrane domains is a necessary step in mammary epithelial cell differentiation. Immunoprecipitation analysis, performed with an anti-Fyn protein antibody, shows that rat8 was present in the Fyn immunoprecipitate. Antisense oligonucleotides, used to inhibit Fyn protein expression, block mammary cell differentiation. Taken together, these results suggest that the functional interaction, via lipid membrane domains, of rat8 and Fyn proteins is required for mammary cell differentiation. Therefore, rat8, like fragilis, may be involved in developmental decisions and the demarcation of a subset of cells in the mammary gland that cause epithelial cells to develop into a network of tubuloalveolar structures involved in secretion.

Glucocorticoids control beta-catenin protein expression and localization through distinct pathways that can be uncoupled by disruption of signaling events required for tight junction formation in rat mammary epithelial tumor cells

In Con8 rat mammary epithelial tumor cells, the synthetic glucocorticoid dexamethasone stimulates the remodeling of tight junctions and adherens junctions before formation of highly sealed tight junctions. In this study, the expression and localization of key components of the apical junction were examined as potential targets of glucocorticoid signaling. Western blot and RT-PCR demonstrated that dexamethasone up-regulated beta-catenin protein and transcript expression and nearly ablated beta-catenin phosphorylation under conditions that led to a significant increase in monolayer transepithelial resistance. Indirect immunofluorescence revealed that dexamethasone treatment also caused beta-catenin to localize predominantly at the cell membrane rather than the nucleus. The glucocorticoid regulation of beta-catenin expression and localization was not a consequence of dexamethasone inhibition of cell growth, because both responses were unaltered in the presence of hydroxyurea. The steroid induction of beta-catenin expression and localization can be uncoupled by altering the function of signaling pathways needed for tight junction formation. Expression of dominant-negative RasN17 abolished dexamethasone up-regulation of beta-catenin protein expression without affecting its localization at the membrane. In contrast, exogenous treatment or constitutive production of TGFalpha abolished the dexamethasone-induced alteration of beta-catenin localization without affecting the dexamethasone stimulation of beta-catenin expression. Taken together, our results demonstrate that glucocorticoids control beta-catenin at two distinct levels of cellular regulation that differ in their cell signaling requirements for the glucocorticoid regulation of mammary epithelial junctional dynamics.

Expression of E-cadherin in normal, hyperplastic and neoplastic feline mammary tissue

This paper describes an immunohistochemical study of the expression of E-cadherin in four samples of normal, eight samples of hyperplastic and 19 samples of neoplastic feline mammary tissue. In the normal tissues, the luminal epithelial cells showed a strong pattern of staining for E-cadherin at the cell-cell boundaries, whereas the myoepithelium showed no immunoreactivity. In the hyperplastic tissues and the five benign neoplasms, there were disturbances in the expression of E-cadherin in the luminal epithelium, in the form of the coexistence of membranous and cytoplasmic staining, together with immunoreactivity in a small percentage of myoepithelial cells. In 11 of 14 carcinomas, there was a reduction or absence of E-cadherin expression and abnormalities in the pattern of immunostaining; these changes were more pronounced in cribriform and solid carcinomas.

ECM-induced gap junctional communication enhances mammary epithelial cell differentiation

The relationship between gap junctional intercellular communication (GJIC) and mammary cell (CID-9) differentiation in vitro was explored. CID-9 cells differentiate and express beta-casein in an extracellular matrix (ECM)- and hormone-dependent manner. In response to interaction with the ECM, cells in culture modulated the expression of their gap junction proteins at the transcriptional and post-translational levels. In the presence of EHS-matrix, connexins (Cx)26, 32 and 43 localized predominantly to the plasma membrane, and enhanced GJIC [as measured by Lucifer Yellow (LY) dye transfer assays] was noted. Inhibition of GJIC of cells on EHS-matrix with 18 alpha glycyrrhetinic acid (GA) resulted in reversible downregulation of beta-casein expression. In the presence of cAMP, cells cultured on plastic expressed beta-casein, upregulated Cx43 and Cx26 protein levels and enhanced GJIC. This was reversed in the presence of 18 alpha GA. cAMP-treated cells plated either on a non-adhesive PolyHEMA substratum or on plastic supplemented with function-blocking anti-beta 1 integrin antibodies, maintained beta-casein expression. These studies suggest that cell-ECM interaction alone may induce differentiation through changes in cAMP levels and formation of functional gap junctions. That these events are downstream of ECM signalling was underscored by the fact that enhanced GJIC induced partial differentiation in mammary epithelial cells in the absence of an exogenously provided basement membrane and in a beta 1-integrin- and adhesion-independent manner.

Regulation of mammary gland branching morphogenesis by the extracellular matrix and its remodeling enzymes

A considerable body of research indicates that mammary gland branching morphogenesis is dependent, in part, on the extracellular matrix (ECM), ECM-receptors, such as integrins and other ECM receptors, and ECM-degrading enzymes, including matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). There is some evidence that these ECM cues affect one or more of the following processes: cell survival, polarity, proliferation, differentiation, adhesion, and migration. Both three-dimensional culture models and genetic manipulations of the mouse mammary gland have been used to study the signaling pathways that affect these processes. However, the precise mechanisms of ECM-directed mammary morphogenesis are not well understood. Mammary morphogenesis involves epithelial 'invasion' of adipose tissue, a process akin to invasion by breast cancer cells, although the former is a highly regulated developmental process. How these morphogenic pathways are integrated in the normal gland and how they become dysregulated and subverted in the progression of breast cancer also remain largely unanswered questions.

Aberrant P-cadherin expression: is it associated with estrogen-independent growth in breast cancer?

Breast carcinomas represent a heterogeneous group of tumors, with a diverse biologic behavior, outcome, and response to therapy. Recent studies have demonstrated that alterations in the expression of adhesion molecules in cancer cells are related to aggressiveness and poor prognosis. The aim of our study was to investigate the expression of P-cadherin in breast carcinomas and correlate it with estrogen receptor (ER) status. We selected 73 ductal carcinomas in situ (DCIS) and 149 invasive carcinomas of the breast, and assessed the expression of P-cadherin as well as other biologic markers. P-cadherin expression showed a strong inverse correlation with ER expression in both types of breast carcinoma (in situ and invasive). P-cadherin-positive and ER-negative tumors were related to a higher histologic grade, a high proliferation rate, and expression of c-erbB-2. We demonstrated that P-cadherin identifies a subgroup of breast carcinomas that lacks ER expression, and correlates with higher proliferation rates and other predictors of aggressive behavior. We believe that these tumors represent an advanced step in cancer progression, and our data support the hypothesis that an estrogen-independent pathway regulates P-cadherin expression.

Collagen-IV and laminin-1 regulate estrogen receptor alpha expression and function in mouse mammary epithelial cells

The expression level and functional activity of estrogen receptor alpha is an important determinant of breast physiology and breast cancer treatment. However, it has been difficult to identify the signals that regulate estrogen receptor because cultured mammary epithelial cells generally do not respond to estrogenic signals. Here, we use a combination of two- and three-dimensional culture systems to dissect the extracellular signals that control endogenous estrogen receptor alpha. Its expression was greatly reduced when primary mammary epithelial cells were placed on tissue culture plastic; however, the presence of a reconstituted basement membrane in combination with lactogenic hormones partially prevented this decrease. Estrogen receptor alpha expression in primary mammary fibroblasts was not altered by these culture conditions, indicating that its regulation is cell type specific. Moreover, estrogen receptor-dependent reporter gene expression, as well as estrogen receptor alpha levels, were increased threefold in a functionally normal mammary epithelial cell line when reconstituted basement membrane was added to the medium. This regulatory effect of reconstituted basement membrane was reproduced by two of its components, collagen-IV and laminin-1, and it was blocked by antibodies against alpha2, alpha6 and beta1 integrin subunits. Our results indicate that integrin-mediated response to specific basement membrane components, rather than cell rounding or cell growth arrest induced by reconstituted basement membrane, is critical in the regulation of estrogen receptor alpha expression and function in mammary epithelial cells.

AZU-1: a candidate breast tumor suppressor and biomarker for tumor progression

To identify genes misregulated in the final stages of breast carcinogenesis, we performed differential display to compare the gene expression patterns of the human tumorigenic mammary epithelial cells, HMT-3522-T4-2, with those of their immediate premalignant progenitors, HMT-3522-S2. We identified a novel gene, called anti-zuai-1 (AZU-1), that was abundantly expressed in non- and premalignant cells and tissues but was appreciably reduced in breast tumor cell types and in primary tumors. The AZU-1 gene encodes an acidic 571-amino-acid protein containing at least two structurally distinct domains with potential protein-binding functions: an N-terminal serine and proline-rich domain with a predicted immunoglobulin-like fold and a C-terminal coiled-coil domain. In HMT-3522 cells, the bulk of AZU-1 protein resided in a detergent-extractable cytoplasmic pool and was present at much lower levels in tumorigenic T4-2 cells than in their nonmalignant counterparts. Reversion of the tumorigenic phenotype of T4-2 cells, by means described previously, was accompanied by the up-regulation of AZU-1. In addition, reexpression of AZU-1 in T4-2 cells, using viral vectors, was sufficient to reduce their malignant phenotype substantially, both in culture and in vivo. These results indicate that AZU-1 is a candidate breast tumor suppressor that may exert its effects by promoting correct tissue morphogenesis.

Functional culture models to study mechanisms governing apoptosis in normal and malignant mammary epithelial cells

Mammary tissue homeostasis depends upon dynamic interactions between the epithelial cells, their microenvironment (including the basement membrane and the stroma), and the tissue architecture, which influence each other reciprocally to regulate growth, death and differentiation in the gland. To study how apoptosis is regulated in normal mammary cells, and to understand its role in breast tumor pathogenesis, we need model systems that recapitulate breast tissue architecture and microenvironment in culture. We have established culture models of primary and established nonmalignant mammary cell lines from both rodent and human, and defined procedures to study how cell and tissue architecture affect signaling by the basement membrane. We show that both a basement membrane and an organized tissue structure are required to achieve sustained mammary cell survival. These models could now be used to investigate how the basement membrane represses apoptosis in normal cells, and how breast cancers become death-resistant.

Tissue architecture: the ultimate regulator of epithelial function?

The architecture of a tissue is defined by the nature and the integrity of its cellular and extracellular compartments, and is based on proper adhesive cell-cell and cell-extracellular matrix interactions. Cadherins and integrins are major adhesion-mediators that assemble epithelial cells together laterally and attach them basally to a subepithelial basement membrane, respectively. Because cell adhesion complexes are linked to the cytoskeleton and to the cellular signalling pathways, they represent checkpoints for regulation of cell shape and gene expression and thus are instructive for cell behaviour and function. This organization allows a reciprocal flow of mechanical and biochemical information between the cell and its microenvironment, and necessitates that cells actively maintain a state of homeostasis within a given tissue context. The loss of the ability of tumour cells to establish correct adhesive interactions with their microenvironment results in disruption of tissue architecture with often fatal consequences for the host organism. This review discusses the role of cell adhesion in the maintenance of tissue structure and analyses how tissue structure regulates epithelial function.

Establishment and initial characterization of the ovine mammary epithelial cell line NISH

Analysis of the molecular mechanisms involved in the differentiation and formation of the characteristic three-dimensional structures of the developing mammary gland of the major milk-producing livestock (ducts, end buds, and alveoli) requires in vitro model cell cultures. The few cell lines that have been established from dairy animals do not fully reproduce the entire program of mammary differentiation. Here we present the initial characterization of a unique mammary epithelial cell line derived spontaneously from midpregnant sheep (NISH). These cells form in vitro functional structures resembling ducts, lateral buds, and alveoli that secrete beta-lactoglobulin (BLG) in an ECM (extracellular matrix)-dependent manner. Interestingly, the presence of growth hormone dramatically increased BLG secretion from NISH cells cultured on ECM. It appears that GH is required not only to establish the structural organization but also is continuously needed to maintain BLG expression. Stable transfection of NISH cells with BLG/Human Serum Albumin (HSA) hybrid gene constructs revealed that the relative level of expression was comparable to the in vivo secretion of HSA in transgenic mice carrying these gene sequences. No expression could be detected in cells transfected with hybrid genes carrying either HSA cDNA or the entire HSA gene, and HSA expression was dependent on the presence of intronic sequences. These results demonstrate that NISH cells may prove a useful tool for studying the differentiation and organogenesis of mammary epithelial cells under defined culture conditions. Furthermore, transfected NISH cells may be an alternative for the transgenic mouse model in evaluating the potential of gene constructs to be efficiently expressed in the mammary gland of transgenic farm animals.

Structural cues from the tissue microenvironment are essential determinants of the human mammary epithelial cell phenotype

Historically, the study of normal human breast function and breast disorders has been significantly impaired by limitations inherent to available model systems. Recent improvements in human breast epithelial cell lines and three-dimensional (3-D)3 culture systems have contributed to the development of in vitro model systems that recapitulate differentiated epithelial cell phenotypes with remarkable fidelity. Molecular characterization of these human breast cell models has demonstrated that normal breast epithelial cell behavior is determined in part by the precise interplay that exists between a cell and its surrounding microenvironment. Recent functional studies of integrins in a human model system provide evidence to support the idea that the structural stability afforded by integrin-mediated cell-extracellular matrix interactions is an important determinant of normal cellular behavior, and that alterations in tissue structure can give rise to tumorigenic progression.

Bovine PAS-6/7 binds alpha v beta 5 integrins and anionic phospholipids through two domains

Bovine milk fat globule membranes are a rich source of glycoproteins PAS-6 (52 kDa) and PAS-7 (47 kDa). They are glycosylation variants sharing a common polypeptide core. The PAS-6/7 protein consists of two EGF-like domains and a tandem repeated structure with a high degree of similarity to the C1 and C2 domains found in blood-clotting factors V and VIII. The second EGF-like domain contains an RGD cell adhesion sequence with the possibility of binding integrins, while the C-terminal end of the C2-like domain contains a probable amphipathic alpha-helix. Using a PAS-6/7 column, bovine alpha v beta 5 integrin was purified from mammary gland tissue by affinity chromatography and characterized by Western blotting and N-terminal sequencing. The interaction between PAS-6/7 and the alpha v beta 5 integrin was shown to be RGD dependent. Lipid binding assays showed that PAS-6/7 binds to surfaces of phosphatidylserine, -inositol, and -glycerol, and their precursor, phosphatidic acid, but not phosphatidylcholine. Furthermore, PAS-6/7 displayed the highest affinity toward a total lipid fraction derived from the milk fat globule membrane as compared to pure phospholipids. Using Western blotting technique, PAS-6/7 was shown to be widely expressed in a number of tissues. These results show that PAS-6/7 is a common protein which can bind to membranes by two distinct mechanisms, one through affinity to integrin alpha v beta 5 and another by direct binding to phospholipids.

Reversion of the malignant phenotype of human breast cells in three-dimensional culture and in vivo by integrin blocking antibodies

In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory beta1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory beta1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin-catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21(cip,wat-1), and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either alpha6 or beta4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the alpha6/beta4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.

Sp1 binding plays a critical role in Erb-B2- and v-ras-mediated downregulation of alpha2-integrin expression in human mammary epithelial cells

The human alpha2-integrin gene is transcriptionally downregulated in a nontumorigenic human mammary epithelial cell line, MTSV1-7, and its clonal variant HB2, overexpressing the Erb-B2 oncogene. In this study, we have used deletion mutations within the alpha2-integrin promoter inserted 5' of the chloramphenicol acetyltransferase or luciferase reporter genes to identify the element that is responsible for the Erb-B2-mediated downregulation. The results of the transient-transfection assay showed that the Sp1 binding element located in the core region (positions --64 to +1) of the alpha2-integrin promoter plays an essential role in the alpha2-integrin promoter activity and its downregulation by Erb-B2. By gel shift assay, we have demonstrated that this element binds with a high degree of affinity not only to Sp1, but also to Sp3. The downregulation of the alpha2-integrin promoter activity could also be achieved by overexpression of v-Hras (v-ras), suggesting that the signals generated by Erb-B2, which lead to downregulation of the alpha2-integrin gene expression, may proceed through the ras pathway. Both the Erb-B2- and the v-ras-overexpressing cells exhibited a Sp1 DNA binding activity lower than that of the parental line, while the relative levels of Sp1 protein in these cells were not altered. The Erb-B2- and v-ras-mediated downregulation could be reversed by the overexpression of Sp1 and by a dominant negative variant of ras (rasN17), confirming the importance of Sp1 and the ras pathway. The inhibitory effects of Erb-B2 on transcriptional activity of the alpha2-integrin promoter were observed in transient-cotransfection assays using alpha2-integrin reporter plasmids and plasmids expressing the Erb-B2 or v-ras oncogene. The same effects were seen when an alpha2-integrin reporter gene construct was transfected into MTSV1-7 or HB2 cells permanently overexpressing Erb-B2 or v-ras. The effects of Erb-B2 or v-ras on the transcriptional activity of the alpha2-integrin promoter were observed in nontumorigenic luminal epithelial cell lines (MTSV1-7 and HB2) as well as in the breast cancer cell line T47D. These data suggest that in luminal epithelial cells and the breast cancers which develop from them, the Erb-B2 proto-oncogene signaling leads to inhibition of (alpha)2(beta)1-integrin gene expression and could contribute to the disruption of tissue architecture seen in breast cancers.

The role of cadherin-mediated adhesion in breast cancer

The cell adhesion molecule E-cadherin is expressed on the basolateral surfaces of normal mammary epithelial cells and is lost in a subset of breast cancers. Loss of E-cadherin expression has been postulated to facilitate tumor cell detachment from a primary tumor ultimately leading to metastasis. In this paper, I review the published in vitro data that initially supported this "invasion suppressor" role for E-cadherin as well as more recent in vitro and in vivo data showing that E-cadherin-positive tumor cells can metastasize. I examine other molecules required for E-cadherin function and discuss how defects in the expression or function of these molecules might alter E-cadherin function in E-cadherin-positive tumor cells. For example, loss of expression or function of catenins, intracellular molecules that interact with E-cadherin, can result in the loss of E-cadherin-mediated adhesion and a more invasive phenotype. Altered phosphorylation of E-cadherin or catenins can also influence E-cadherin function. Finally, expression of other cell surface molecules such as mucins may interfere with E-cadherin function. The collective effect of these molecules on the adhesive phenotype of breast cancer cells may be one determinant of metastatic potential.

The importance of the microenvironment in breast cancer progression: recapitulation of mammary tumorigenesis using a unique human mammary epithelial cell model and a three-dimensional culture assay

The extracellular matrix (ECM) is a dominant regulator of tissue development and homeostasis. "Designer microenvironments" in culture and in vivo model systems have shown that the ECM regulates growth, differentiation, and apoptosis in murine and human mammary epithelial cells (MEC) through a hierarchy of transcriptional events involving the intricate interplay between soluble and physical signaling pathways. Furthermore, these studies have shown that these pathways direct and in turn are influenced by the tissue structure. Tissue structure is directed by the cooperative interactions of the cell-cell and cell-ECM pathways and can be modified by stromal factors. Not surprisingly then, loss of tissue structure and alterations in ECM components are associated with the appearance and dissemination of breast tumors, and malignancy is associated with perturbations in cell adhesion, changes in adhesion molecules, and a stromal reaction. Several lines of evidence now support the contention that the pathogenesis of breast cancer is determined (at least in part) by the dynamic interplay between the ductal epithelial cells, the microenvironment, and the tissue structure (acini). Thus, to understand the mechanisms involved in carcinogenesis, the role of the microenvironment (ECM as well as the stromal cells) with respect to tissue structure should be considered and studied. Towards this goal, we have established a unique human MEC model of tumorigenesis, which in concert with a three-dimensional assay, recapitulates many of the genetic and morphological changes observed in breast in cancer in vivo. We are currently using this system to understand the role of the microenvironment and tissue structure in breast cancer progression.