Extracellular matrix and hormones transcriptionally regulate bovine beta-casein 5' sequences in stably transfected mouse mammary cells

Genetically modified animals for use in biopharmacology: from research to production

Introduction: In this review, the analysis of technologies for obtaining biologically active proteins from various sources is carried out, and the comparative analysis of technologies for creating producers of biologically active proteins is presented. Special attention is paid to genetically modified animals as bioreactors for the pharmaceutical industry of a new type. The necessity of improving the technology of development transgenic rabbit producers and creating a platform solution for the production of biological products is substantiated.

The advantages of using TrB for the production of recombinant proteins: The main advantages of using TrB are the low cost of obtaining valuable complex therapeutic human proteins in readily accessible fluids, their greater safety relative to proteins isolated directly from human blood, and the greater safety of the activity of the native protein.

The advantages of the mammary gland as a system for the expression of recombinant proteins: The mammary gland is the organ of choice for the expression of valuable recombinant proteins because milk is easy to collect in large volumes.

Methods for obtaining transgenic animals: The modern understanding of the regulation of gene expression and the discovery of new tools for gene editing can increase the efficiency of creating bioreactors for animals and help to obtain high concentrations of the target protein.

The advantages of using rabbits as bioreactors producing recombinant proteins in milk: The rabbit is a relatively small animal with a short duration of gestation, puberty and optimal size, capable of producing up to 5 liters of milk per year per female, receiving up to 300 grams of the target protein.

A comprehensive review on non-clinical methods to study transfer of medication into breast milk - A contribution from the ConcePTION project

Breastfeeding plays a major role in the health and wellbeing of mother and infant. However, information on the safety of maternal medication during breastfeeding is lacking for most medications. This leads to discontinuation of either breastfeeding or maternal therapy, although many medications are likely to be safe. Since human lactation studies are costly and challenging, validated non-clinical methods would offer an attractive alternative. This review gives an extensive overview of the non-clinical methods (in vitro, in vivo and in silico) to study the transfer of maternal medication into the human breast milk, and subsequent neonatal systemic exposure. Several in vitro models are available, but model characterization, including quantitative medication transport data across the in vitro blood-milk barrier, remains rather limited. Furthermore, animal in vivo models have been used successfully in the past. However, these models don't always mimic human physiology due to species-specific differences. Several efforts have been made to predict medication transfer into the milk based on physicochemical characteristics. However, the role of transporter proteins and several physiological factors (e.g., variable milk lipid content) are not accounted for by these methods. Physiologically-based pharmacokinetic (PBPK) modelling offers a mechanism-oriented strategy with bio-relevance. Recently, lactation PBPK models have been reported for some medications, showing at least the feasibility and value of PBPK modelling to predict transfer of medication into the human milk. However, reliable data as input for PBPK models is often missing. The iterative development of in vitro, animal in vivo and PBPK modelling methods seems to be a promising approach. Human in vitro models will deliver essential data on the transepithelial transport of medication, whereas the combination of animal in vitro and in vivo methods will deliver information to establish accurate in vitro/in vivo extrapolation (IVIVE) algorithms and mechanistic insights. Such a non-clinical platform will be developed and thoroughly evaluated by the Innovative Medicines Initiative ConcePTION.

The not-so-sweet side of sugar: Influence of the microenvironment on the processes that unleash cancer

The role of "aerobic glycolysis" in cancer has been examined often in the past. Results from those studies, most of which were performed on two dimensional conditions (2D, tissue culture plastic), demonstrate that aerobic glycolysis occurs as a consequence of oncogenic events. These oncogenic events often drive malignant cell growth and survival. Although 2D based experiments are useful in elucidating the molecular mechanisms of oncogenesis, they fail to take contributions of the extracellular microenvironment into account. Indeed we, and others, have shown that the cellular microenvironment is essential in regulating processes that induce and/or suppress the malignant phenotype/properties. This regulation between the cell and its microenvironment is both dynamic and reciprocal and involves the integration of cellular signaling networks in the right context. Therefore, given our previous demonstration of the effect of the microenvironment including tissue architecture and media composition on gene expression and the integration of signaling events observed in three-dimension (3D), we hypothesized that glucose uptake and metabolism must also be essential components of the tissue's signal "integration plan" - that is, if uptake and metabolism of glucose were hyperactivated, the canonical oncogenic pathways should also be similarly activated. This hypothesis, if proven true, suggests that direct inhibition of glucose metabolism in cancer cells should either suppress or revert the malignant phenotype in 3D. Here, we review the up-to-date progress that has been made towards understanding the role that glucose metabolism plays in oncogenesis and re-establishing basally polarized acini in malignant human breast cells.

Identification and Characterization of the Lactating Mouse Mammary Gland Citrullinome

Citrullination is a post-translational modification (PTM) in which positively charged peptidyl-arginine is converted into neutral peptidyl-citrulline by peptidylarginine deiminase (PAD or PADI) enzymes. The full protein citrullinome in many tissues is unknown. Herein, we used mass spectrometry and identified 107 citrullinated proteins in the lactation day 9 (L9) mouse mammary gland including histone H2A, α-tubulin, and β-casein. Given the importance of prolactin to lactation, we next tested if it stimulates PAD-catalyzed citrullination using mouse mammary epithelial CID-9 cells. Stimulation of CID-9 cells with 5 µg/mL prolactin for 10 min induced a 2-fold increase in histone H2A citrullination and a 4.5-fold increase in α-tubulin citrullination. We next investigated if prolactin-induced citrullination regulates the expression of lactation genes β-casein (Csn2) and butyrophilin (Btn1a1). Prolactin treatment for 12 h increased β-casein and butyrophilin mRNA expression; however, this increase was significantly inhibited by the pan-PAD inhibitor, BB-Cl-amidine (BB-ClA). We also examined the effect of tubulin citrullination on the overall polymerization rate of microtubules. Our results show that citrullinated tubulin had a higher maximum overall polymerization rate. Our work suggests that protein citrullination is an important PTM that regulates gene expression and microtubule dynamics in mammary epithelial cells.

Membrane-tethered syntaxin-4 locally abrogates E-cadherin function and activates Smad signals, contributing to asymmetric mammary epithelial morphogenesis

Spatial and temporal epithelial-mesenchymal transition (EMT) is a critical event for the generation of asymmetric epithelial architectures. We found that only restricted cell populations in the morphogenic mammary epithelia extrude syntaxin-4, a plasmalemmal t-SNARE protein, and that epithelial cell clusters with artificial heterogenic presentation of extracellular syntaxin-4 undergo asymmetric morphogenesis. A previous study revealed that inducible expression of cell surface syntaxin-4 causes EMT-like cell behaviors in the clonal mammary epithelial cells, where laminin-mediated signals were abolished so that cells readily succumb to initiate EMT. The present study added new mechanistic insight into syntaxin-4-driven EMT-like cell behaviors. Extracellular syntaxin-4 directly perturbs E-cadherin-mediated epithelial cell-cell adhesion and activates Smad signals. We found that the epithelial cells activated Smad2/3 upon induction of expression of extracellular syntaxin-4, leading to the upregulation of certain transcriptional targets of these TGF-β signaling mediators. Intriguingly, however, mRNA expression of canonical EMT initiators, such as Snail and Slug, was unchanged. In addition, E-cadherin protein was steeply decreased, yet its transcriptional expression remained constant for a couple of days. We found that extracellular syntaxin-4 directly bound to E-cadherin and sequestered β-catenin from cell-cell contact sites, perturbing intercellular adhesive property. The functional ablation of E-cadherin by syntaxin-4 was further validated by L cells with stably expressing E-cadherin, in which cells shows intercellular adhesive property solely by E-cadherin. These results underline the role of local exportation of syntaxin-4 for onset of complex epithelial morphogenesis.

The Physical and Biochemical Properties of the Extracellular Matrix Regulate Cell Fate

The extracellular matrix is a complex network of hydrated macromolecular proteins and sugars that, in concert with bound soluble factors, comprise the acellular stromal microenvironment of tissues. Rather than merely providing structural information to cells, the extracellular matrix plays an instructive role in development and is critical for the maintenance of tissue homeostasis. In this chapter, we review the composition of the extracellular matrix and summarize data illustrating its importance in embryogenesis, tissue-specific development, and stem cell differentiation. We discuss how the biophysical and biochemical properties of the extracellular matrix ligate specific transmembrane receptors to activate intracellular signaling that alter cell shape and cytoskeletal dynamics to modulate cell growth and viability, and direct cell migration and cell fate. We present examples describing how the extracellular matrix functions as a highly complex physical and chemical entity that regulates tissue organization and cell behavior through a dynamic and reciprocal dialogue with the cellular constituents of the tissue. We suggest that the extracellular matrix not only transmits cellular and tissue-level force to shape development and tune cellular activities that are key for coordinated tissue behavior, but that it is itself remodeled such that it temporally evolves to maintain the integrated function of the tissue. Accordingly, we argue that perturbations in extracellular matrix composition and structure compromise key developmental events and tissue homeostasis, and promote disease.

Organoids: A historical perspective of thinking in three dimensions

In this perspective, Simian and Bissell discuss the evolution of the 3D culture and organoid research field up to now as well as its future directions.

In the last ten years, there has been a dramatic surge in the number of publications where single or groups of cells are grown in substrata that have elements of basement membrane leading to the formation of tissue-like structures referred to as organoids. However, this field of research began many decades ago, when the pioneers of cell culture began to ask questions we still ask today: How does organogenesis occur? How do signals integrate to make such vastly different tissues and organs given that the sequence of the genome in our trillions of cells is identical? Here, we summarize how work over the past century generated the conceptual framework that has allowed us to make progress in the understanding of tissue-specific morphogenetic programs. The development of cell culture systems that provide accurate and physiologically relevant models are proving to be key in establishing appropriate platforms for the development of new therapeutic strategies.

Extracellularly Extruded Syntaxin-4 Binds to Laminin and Syndecan-1 to Regulate Mammary Epithelial Morphogenesis

Epithelial morphogenesis in the mammary gland proceeds as a consequence of complex cell behaviors including apoptotic cell death and epithelial-mesenchymal transition (EMT); the extracellular matrix (ECM) protein laminin is crucially involved. Syntaxins mediate intracellular vesicular fusion, yet certain plasmalemmal members have been shown to possess latent extracellular functions. In this study, the extracellular subpopulation of syntaxin-4, extruded in response to the induction of differentiation or apoptosis in mammary epithelial cells, was detected. Using a tetracycline-repressive transcriptional system and clonal mammary epithelial cells, SCp2, we found that the expression of cell surface syntaxin-4 elicits EMT-like cell behaviors. Intriguingly, these cells did not up-regulate key transcription factors associated with the canonical EMT such as snail, slug, or twist, and repressed translation of E-cadherin. Concurrently, the cells completely evaded the cellular aggregation/rounding triggered by a potent EMT blocker laminin-111. We found that the recombinant form of syntaxin-4 not only bound to laminin but also latched onto the glycosaminoglycan (GAG) side chains of syndecan-1, a laminin receptor that mediates epithelial morphogenesis. Thus, temporal extracellular extrusion of syntaxin-4 emerged as a novel regulatory element for laminin-induced mammary epithelial cell behaviors. J. Cell. Biochem. 118: 686-698, 2017. © 2016 Wiley Periodicals, Inc.

Transgenic bovine as bioreactors: Challenges and perspectives

The use of recombinant proteins has increased in diverse commercial sectors. Various systems for protein production have been used for the optimization of production and functional protein expression. The mammary gland is considered to be a very interesting system for the production of recombinant proteins due to its high level of expression and its ability to perform post-translational modifications. Cows produce large quantities of milk over a long period of lactation, and therefore this species is an important candidate for recombinant protein expression in milk. However, transgenic cows are more difficult to generate due to the inefficiency of transgenic methodologies, the long periods for transgene detection, recombinant protein expression and the fact that only a single calf is obtained at the end of each pregnancy. An increase in efficiency for transgenic methodologies for cattle is a big challenge to overcome. Promising methodologies have been proposed that can help to overcome this obstacle, enabling the use of transgenic cattle as bioreactors for protein production in milk for industry.

Peptidylarginine Deiminase 3 (PAD3) Is Upregulated by Prolactin Stimulation of CID-9 Cells and Expressed in the Lactating Mouse Mammary Gland

Peptidylarginine deiminases (PADs) post-translationally convert arginine into neutral citrulline residues. Our past work shows that PADs are expressed in the canine and murine mammary glands; however, the mechanisms regulating PAD expression and the function of citrullination in the normal mammary gland are unclear. Therefore, the first objective herein was to investigate regulation of PAD expression in mammary epithelial cells. We first examined PAD levels in CID-9 cells, which were derived from the mammary gland of mid-pregnant mice. PAD3 expression is significantly higher than all other PAD isoforms and mediates protein citrullination in CID-9 cells. We next hypothesized that prolactin regulates PAD3 expression. To test this, CID-9 cells were stimulated with 5 μg/mL of prolactin for 48 hours which significantly increases PAD3 mRNA and protein expression. Use of a JAK2 inhibitor and a dominant negative (DN)-STAT5 adenovirus indicate that prolactin stimulation of PAD3 expression is mediated by the JAK2/STAT5 signaling pathway in CID-9 cells. In addition, the human PAD3 gene promoter is prolactin responsive in CID-9 cells. Our second objective was to investigate the expression and activity of PAD3 in the lactating mouse mammary gland. PAD3 expression in the mammary gland is highest on lactation day 9 and coincident with citrullinated proteins such as histones. Use of the PAD3 specific inhibitor, Cl4-amidine, indicates that PAD3, in part, can citrullinate proteins in L9 mammary glands. Collectively, our results show that upregulation of PAD3 is mediated by prolactin induction of the JAK2/STAT5 signaling pathway, and that PAD3 appears to citrullinate proteins during lactation.

Indirect Immunofluorescence on Frozen Sections of Mouse Mammary Gland

Indirect immunofluorescence is used to detect and locate proteins of interest in a tissue. The protocol presented here describes a complete and simple method for the immune detection of proteins, the mouse lactating mammary gland being taken as an example. A protocol for the preparation of the tissue samples, especially concerning the dissection of mouse mammary gland, tissue fixation and frozen tissue sectioning, are detailed. A standard protocol to perform indirect immunofluorescence, including an optional antigen retrieval step, is also presented. The observation of the labeled tissue sections as well as image acquisition and post-treatments are also stated. This procedure gives a full overview, from the collection of animal tissue to the cellular localization of a protein. Although this general method can be applied to other tissue samples, it should be adapted to each tissue/primary antibody couple studied.

MAC-T cells as a tool to evaluate lentiviral vector construction targeting recombinant protein expression in milk

Prior to generating transgenic animals for bioreactors, it is important to evaluate the vector constructed to avoid poor protein expression. Mammary epithelial cells cultured in vitro have been proposed as a model to reproduce the biology of the mammary gland. In the present work, three lentiviral vectors were constructed for the human growth hormone (GH), interleukin 2 (IL2), and granulocyte colony-stimulating factor 3 (CSF3) genes driven by the bovine β-casein promoter. The lentiviruses were used to transduce mammary epithelial cells (MAC-T), and the transformed cells were cultured on polystyrene in culture medium with and without prolactin. The gene expression of transgenes was evaluated by PCR using cDNA, and recombinant protein expression was evaluated by Western-blotting using concentrated medium and cellular extracts. The gene expression, of the three introduced genes, was detected in both induced and non induced MAC-T cells. The human GH protein was detected in the concentrated medium, whereas CSF3 was detected in the cellular extract. Apparently, the cellular extract is more appropriate than the concentrated medium to detect recombinant protein, principally because concentrated medium has a high concentration of bovine serum albumin. The results suggest that MAC-T cells may be a good system to evaluate vector construction targeting recombinant protein expression in milk.

CCAAT/enhancer binding protein beta (C/EBPβ) isoform balance as a regulator of epithelial-mesenchymal transition in mouse mammary epithelial cells

Activation of the epithelial-mesenchymal transition (EMT) program promotes cell invasion and metastasis, and is reversed through mesenchymal-epithelial transition (MET) after formation of distant metastases. Here, we show that an imbalance of gene products encoded by the transcriptional factor C/EBPβ, LAP (liver-enriched activating protein) and LIP (liver-enriched inhibitory protein), can regulate both EMT- and MET-like phenotypic changes in mouse mammary epithelial cells. By using tetracycline repressive LIP expression constructs, we found that SCp2 cells, a clonal epithelial line of COMMA1-D cells, expressed EMT markers, lost the ability to undergo alveolar-like morphogenesis in 3D Matrigel, and acquired properties of benign adenoma cells. Conversely, we found that inducible expression of LAP in SCg6 cells, a clonal fibroblastic line of COMMA1-D cells, began to express epithelial keratins with suppression of proliferation. The overexpression of the C/EBPβ gene products in these COMMA1-D derivatives was suppressed by long-term cultivation on tissue culture plastic, but gene expression was maintained in cells grown on Matrigel or exposed to proteasome inhibitors. Thus, imbalances of C/EBPβ gene products in mouse mammary epithelial cells, which are affected by contact with basement membrane, are defined as a potential regulator of metastatic potential.

Analysis of Tissue-Specific Expression of Human Type II Collagen cDNA Driven by Different Sizes of the Upstream Region of the β-Casein Promoter

To investigate the ability of 1.8 kb or 3.1 kb bovine beta-casein promoter sequences for the expression regulation of transgene in vivo, transgenic mice were produced with human type II collagen gene fused to 1.8 kb and 3.1 kb of bovine beta-casein promoter by DNA microinjection. Five and three transgenic founder mice were produced using transgene constructs with 1.8 kb and 3.1 kb of bovine beta-casein promoters respectively. Founder mice were outbred with the wild type to produce F1 and F2 progenies. Total RNAs were extracted from four tissues (mammary gland, liver, kidney, and muscle) of female F1 transgenic mice of each transgenic line following parturition. RT-PCR and Northern blot analysis revealed that the expression level of transgene was variable among the transgenic lines, but transgenic mice containing 1.8 kb of promoter sequences exhibited more leaky expression of transgene in other tissues compared to those with 3.1 kb promoter. Moreover, Western blot analysis of transgenic mouse milk showed that human type II collagen proteins secreted into the milk of lactating transgenic mice contained 1.8 kb and 3.1 kb of bovine beta-casein promoter. These results suggest that promoter sequences of 3.1 kb bovine beta-casein gene can be used for induction of mammary gland-specific expression of transgenes in transgenic animals.

CPEB1 promotes differentiation and suppresses EMT in mammary epithelial cells

Downregulation of CPEB1, a sequence-specific RNA-binding protein, in a mouse mammary epithelial cell line (CID-9) causes epithelial-to-mesenchymal transition (EMT), based on several criteria. First, CPEB1 knockdown decreases protein levels of E-cadherin and β-catenin but increases those of vimentin and Twist1. Second, the motility of CPEB1-depleted cells is increased. Third, CID-9 cells normally form growth-arrested, polarized and three-dimensional acini upon culture in extracellular matrix, but CPEB1-deficient CID-9 cells form nonpolarized proliferating colonies lacking a central cavity. CPEB1 downregulates Twist1 expression by binding to its mRNA, shortening its poly(A) tract and repressing its translation. CID-9 cultures contain both myoepithelial and luminal epithelial cells. CPEB1 increases during CID-9 cell differentiation, is predominantly expressed in myoepithelial cells, and its knockdown prevents expression of the myoepithelial marker p63. CPEB1 is present in proliferating subpopulations of pure luminal epithelial cells (SCp2) and myoepithelial cells (SCg6), but its depletion increases Twist1 only in SCg6 cells and fails to downregulate E-cadherin in SCp2 cells. We propose that myoepithelial cells prevent EMT by influencing the polarity and proliferation of luminal epithelial cells in a mechanism that requires translational silencing of myoepithelial Twist1 by CPEB1.

Three-dimensional cultures of mouse mammary epithelial cells

The mammary gland is an ideal "model organism" for studying tissue specificity and gene expression in mammals: it is one of the few organs that develop after birth and it undergoes multiple cycles of growth, differentiation and regression during the animal's lifetime in preparation for the important function of lactation. The basic "functional differentiation" unit in the gland is the mammary acinus made up of a layer of polarized epithelial cells specialized for milk production surrounded by myoepithelial contractile cells, and the two-layered structure is surrounded by basement membrane. Much knowledge about the regulation of mammary gland development has been acquired from studying the physiology of the gland and of lactation in rodents. Culture studies, however, were hampered by the inability to maintain functional differentiation on conventional tissue culture plastic. We now know that the microenvironment, including the extracellular matrix and tissue architecture, plays a crucial role in directing functional differentiation of organs. Thus, in order for culture systems to be effective experimental models, they need to recapitulate the basic unit of differentiated function in the tissue or organ and to maintain its three-dimensional (3D) structure. Mouse mammary culture models evolved from basic monolayers of cells to an array of complex 3D systems that observe the importance of the microenvironment in dictating proper tissue function and structure. In this chapter, we focus on how 3D mouse mammary epithelial cultures have enabled investigators to gain a better understanding of the organization, development and function of the acinus, and to identify key molecular, structural, and mechanical cues important for maintaining mammary function and architecture. The accompanying chapter of Vidi et al. describes 3D models developed for human cells. Here, we describe how mouse primary epithelial cells and cell lines--essentially those we use in our laboratory--are cultured in relevant 3D microenvironments. We focus on the design of functional assays that enable us to understand the intricate signaling events underlying mammary gland biology, and address the advantages and limitations of the different culture settings. Finally we also discuss how advances in bioengineering tools may help towards the ultimate goal of building tissues and organs in culture for basic research and clinical studies.

Transcriptome analysis of epithelial and stromal contributions to mammogenesis in three week prepartum cows

Transcriptome analysis of bovine mammary development has provided insight into regulation of mammogenesis. However, previous studies primarily examined expression of epithelial and stromal tissues combined, and consequently did not account for tissue specific contribution to mammary development. Our objective was to identify differences in gene expression in epithelial and intralobular stromal compartments. Tissue was biopsied from non-lactating dairy cows 3 weeks prepartum, cut into explants and incubated for 2 hr with insulin and hydrocortisone. Epithelial and intralobular stromal tissues were isolated with laser capture microdissection. Global gene expression was measured with Bovine Affymetrix GeneChips, and data were preprocessed using RMA method. Moderated t-tests from gene-specific linear model analysis with cell type as a fixed effect showed more than 3,000 genes were differentially expressed between tissues (P<0.05; FDR<0.17). Analysis of epithelial and stromal transcriptomes using Database for Annotation, Visualization and Integrated Discovery (DAVID) and Ingenuity Pathways Analysis (IPA) showed that epithelial and stromal cells contributed distinct molecular signatures. Epithelial signatures were enriched with gene sets for protein synthesis, metabolism and secretion. Stromal signatures were enriched with genes that encoded molecules important to signaling, extracellular matrix composition and remodeling. Transcriptome differences also showed evidence for paracrine interactions between tissues in stimulation of IGF1 signaling pathway, stromal reaction, angiogenesis, neurogenesis, and immune response. Molecular signatures point to the dynamic role the stroma plays in prepartum mammogenesis and highlight the importance of examining the roles of cell types within the mammary gland when targeting therapies and studying mechanisms that affect milk production.

β-casein gene expression by in vitro cultured bovine mammary epithelial cells derived from developing mammary glands

Epithelial cells from mammary gland tissue that are cultured in vitro are able to maintain specific functions of this gland, such as cellular differentiation and milk protein synthesis. These characteristics make these cells a useful model to study mammary gland physiology, development and differentiation; they can also be used for production of exogenous proteins of pharmaceutical interest. Bovine mammary epithelial cells were cultured in vitro after isolation from mammary gland tissue of animals at different stages of development. The cells were plated on Petri dishes and isolated from fibroblasts using saline/EDTA treatment, followed by trypsinization. Cells isolated on plastic were capable of differentiating into alveolus-like structures; however, only cells derived from non-pregnant and non-lactating animals expressed β-casein. Real-time qPCR and epifluorescence microscopy analyses revealed that alveolus-like structures were competent at expressing Emerald green fluorescent protein (EmGFP) driven by the β-casein promoter, independent of β-casein expression.

Mammary ductal growth is impaired in mice lacking leptin-dependent signal transducer and activator of transcription 3 signaling

Mice lacking leptin (ob/ob) or its full-length receptor (db/db) are obese and reproductively incompetent. Fertility, pregnancy, and lactation are restored, respectively, in ob/ob mice treated with leptin through mating, d 6.5 post coitum, and pregnancy. Therefore, leptin signaling is needed for lactation, but the timing of its action and the affected mammary process remain unknown. To address this issue, we used s/s mice lacking only leptin-dependent signal transducer and activator of transcription (STAT)3 signaling. These mice share many features with db/db mice, including obesity, but differ by retaining sufficient activity of the hypothalamic-pituitary-ovarian axis to support reproduction. The s/s mammary epithelium was normal at 3 wk of age but failed to expand through the mammary fat pad (MFP) during the subsequent pubertal period. Ductal growth failure was not corrected by estrogen therapy and did not relate to inadequate IGF-I production by the MFP or to the need for epithelial or stromal leptin-STAT3 signaling. Ductal growth failure coincided with adipocyte hypertrophy and increased MFP production of leptin, TNFalpha, and IL6. These cytokines, however, were unable to inhibit the proliferation of a collection of mouse mammary epithelial cell lines. In conclusion, the very first step of postnatal mammary development fails in s/s mice despite sufficient estrogen IGF-I and an hypothalamic-pituitary-ovarian axis capable of supporting reproduction. This failure is not caused by mammary loss of leptin-dependent STAT3 signaling or by the development of inflammation. These data imply the existence of an unknown mechanism whereby leptin-dependent STAT3 signaling and obesity alter mammary ductal development.

A complex 3D human tissue culture system based on mammary stromal cells and silk scaffolds for modeling breast morphogenesis and function

Epithelial-stromal interactions play a crucial role in normal embryonic development and carcinogenesis of the human breast while the underlying mechanisms of these events remain poorly understood. To address this issue, we constructed a physiologically relevant, three-dimensional (3D) culture surrogate of complex human breast tissue that included a tri-culture system made up of human mammary epithelial cells (MCF10A), human fibroblasts and adipocytes, i.e., the two dominant breast stromal cell types, in a Matrigel/collagen mixture on porous silk protein scaffolds. The presence of stromal cells inhibited MCF10A cell proliferation and induced both alveolar and ductal morphogenesis and enhanced casein expression. In contrast to the immature polarity exhibited by co-cultures with either fibroblasts or adipocytes, the alveolar structures formed by the tri-cultures exhibited proper polarity similar to that observed in breast tissue in vivo. Only alveolar structures with reverted polarity were observed in MCF10A monocultures. Consistent with their phenotypic appearance, more functional differentiation of epithelial cells was also observed in the tri-cultures, where casein alpha- and -beta mRNA expression was significantly increased. This in vitro tri-culture breast tissue system sustained on silk scaffold effectively represents a more physiologically relevant 3D microenvironment for mammary epithelial cells and stromal cells than either co-cultures or monocultures. This experimental model provides an important first step for bioengineering an informative human breast tissue system, with which to study normal breast morphogenesis and neoplastic transformation.

TCDD exposure disrupts mammary epithelial cell differentiation and function

Mammary gland growth and differentiation during pregnancy is a developmental process that is sensitive to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD is a widespread environmental contaminant and a potent ligand for the aryl hydrocarbon receptor (AhR). We demonstrate reduced beta-casein protein induction in mouse mammary glands and in cultured SCp2 mammary epithelial cells following exposure to TCDD. SCp2 cells exposed to TCDD also show reduced cell clustering and less alveolar-like structure formation. SCp2 cells express transcriptionally active AhR, and exposure to TCDD induces expression of the AhR target gene CYP1B1. Exposure to TCDD during pregnancy reduced expression of the cell adhesion molecule E-cadherin in the mammary gland and decreased phosphorylation of STAT5, a known regulator of beta-casein gene expression. These data provide morphological and molecular evidence that TCDD-mediated AhR activation disrupts structural and functional differentiation of the mammary gland, and present an in vitro model for studying the effects of TCDD on mammary epithelial cell function.

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 role of native bovine α-lactalbumin in bovine mammary epithelial cell apoptosis and casein expression

Folding variants of α-lactalbumin (α-la) are known to induce cell death in a number of cell types, including mammary epithelial cells (MEC). The native conformation of α-la however has not been observed to exhibit this biological activity. Here we report that native bovine α-la reduced the viability of primary bovine mammary epithelial cells (BMEC) and induced caspase activity in mammospheres, which are alveolar-like structures formed by culturing primary BMEC on extracellular matrix in the presence of lactogenic hormones. These observations suggest a possible role for bovine α-la in involution and/or maintaining the luminal space in mammary alveoli during lactation. In addition, co-incubation of bovine α-la in an in-vitro mammosphere model resulted in decreased β-casein mRNA expression and increased αs1- and κ-casein mRNA expression. This differential effect on casein expression levels is unusual and raises the possibility of manipulating expression levels of individual caseins to alter dairy processing properties. Manipulation of α-la levels could be further investigated for its potential to enhance milk protein expression and/or improve lactational persistency by influencing the balance between proliferation and apoptosis of BMEC, which has a major influence on the milk-producing capacity of the mammary gland.

Translational regulation of milk protein synthesis at secretory activation

Studies conducted since the 1970s have revealed that the production of milk proteins in the mammary gland under the influence of lactogenic hormones (insulin, prolactin, and glucocorticoids) is regulated at multiple levels. Whereas earlier studies concentrated on transcriptional regulation and stabilization of milk protein mRNAs, more recent studies have revealed that translation of milk protein mRNAs is also dependent on lactogenic hormones. A general stimulation of translation in mammary epithelial cells is caused by amino acids (as signaling molecules) or by phosphorylation of the translational regulator 4E-BP1 in a synergistic response to signals from insulin and prolactin. However, a selective enhancement of milk protein mRNA translation is caused by cytoplasmic polyadenylation of mRNA, again in a synergistic response to these two hormones. Preliminary evidence indicates that the latter effect depends on the existence of a cytoplasmic polyadenylation element (CPE) in milk protein mRNAs and phosphorylation of its binding protein, CPEB. Experiments in whole animals, organ explants, and cell culture have shown that the poly(A) length of milk protein mRNAs changes as a function of the lactation cycle. Interestingly, cytoplasmic polyadenylation is likely to be responsible for the selective hormone-dependent enhancement of both translation and stability of milk protein mRNAs.

The role of glucocorticoids in secretory activation and milk secretion, a historical perspective

In this review we present our current understanding of the role of glucocorticoids in secretory activation and milk secretion by looking at the literature from a historical perspective. We begin with the early endocrine ablation experiments and continue from there to show that glucocorticoids are not just necessary for secretory activation and milk secretion--but mandatory. Specifically, we discuss the importance of glucocorticoids to: (1) induce the formation of ultrastructural components necessary to support milk synthesis and secretion, including rough endoplasmic reticulum and tight junction sealing; (2) regulate milk protein gene expression; and (3) prevent the second phase of involution, possibly by preventing the breakdown of the extracellular matrix.

Architecture Is the Message: The role of extracellular matrix and 3-D structure in tissue-specific gene expression and breast cancer

I was honored to deliver the 2(nd) Stanley Korsmeyer memorial Lecture on May 9(th), 2007 in Padova, Italy. Stan will always occupy a very special place in my heart: I admired him greatly not only for his magnificent and original science but also for his integrity and his grace. This review, which summarizes my laboratory's contribution to cell and cancer biology in the last 30 years, is dedicated to Stan's memory, and to Elaine Fuchs, one of my most cherished friends without whose support this work would not have gained the degree of recognition it enjoys today. My thanks also to the Pezcoller Foundation for making that week in May, 2007 one of the most memorable in my scientific life.

Extracellular matrix-regulated gene expression requires cooperation of SWI/SNF and transcription factors

Extracellular cues play crucial roles in the transcriptional regulation of tissue-specific genes, but whether and how these signals lead to chromatin remodeling is not understood and subject to debate. Using chromatin immunoprecipitation assays and mammary-specific genes as models, we show here that extracellular matrix molecules and prolactin cooperate to induce histone acetylation and binding of transcription factors and the SWI/SNF complex to the beta- and gamma-casein promoters. Introduction of a dominant negative Brg1, an ATPase subunit of SWI/SNF complex, significantly reduced both beta- and gamma-casein expression, suggesting that SWI/SNF-dependent chromatin remodeling is required for transcription of mammary-specific genes. Chromatin immunoprecipitation analyses demonstrated that the ATPase activity of SWI/SNF is necessary for recruitment of RNA transcriptional machinery, but not for binding of transcription factors or for histone acetylation. Co-immunoprecipitation analyses showed that the SWI/SNF complex is associated with STAT5, CCAAT/enhancer-binding protein beta, and glucocorticoid receptor. Thus, extracellular matrix- and prolactin-regulated transcription of the mammary-specific casein genes requires the concerted action of chromatin remodeling enzymes and transcription factors.

Expression of cytosolic NADP+-dependent isocitrate dehydrogenase in bovine mammary epithelium: Modulation by regulators of differentiation and metabolic effectors

The cytosolic NADP+-dependent isocitrate dehydrogenase (IDH1) catalyzes the conversion of isocitrate to alpha-ketoglutarate in the cytosol, and generates NADPH as a primary source of reducing equivalents for de novo fatty acid synthesis in bovine mammary gland. The enzymatic activity of IDH1 increases dramatically in early lactation in bovine mammary tissue. We hypothesized that the expression of IDH1 in bovine is modulated by regulators of mammary epithelial differentiation. To test this hypothesis, we first examined the changes in IDH1 expression in late pregnancy (-20 days) and at various stages (14, 90, 120, and 240 days) of lactation in bovine mammary tissue. IDH1 mRNA levels increased by 2.3-fold after parturition compared to late pregnancy and remained elevated thereafter. Next, we examined the effects of extracellular matrix and lactogenic hormones on the expression of IDH1 in cultured BME-UV bovine mammary epithelial cells. We found that expression of IDH1 mRNA increased in parallel with beta-casein expression induced by extracellular matrix. Fetal calf serum and insulin repressed, whereas prolactin stimulated the expression of IDH1 mRNA in a dose-dependent fashion. The inhibitory effects of insulin on IDH1 mRNA levels were antagonized by cotreatment with prolactin. In contrast, treatment with prolactin in the presence of extracellular matrix further increased IDH1 mRNA and protein accumulation. Prolactin-induced IDH1 expression was inhibited by the mitogen-activated protein kinase (MAPK) inhibitors PD98059 and U0126, and Janus tyrosine kinase 2 (Jak2) inhibitor AG490, suggesting that both MAPK and Jak2 contribute to regulation of IDH1 expression by prolactin. Finally, we report that treatment of BME-UV cells with alpha-ketoglutarate and palmitic acid reduced IDH1 transcript levels. Taken together, our data suggest that the expression of IDH1 in bovine mammary epithelium is modulated by regulators of differentiation including extracellular matrix and lactogenic hormones as well as metabolic effectors.

Development of a human mammary epithelial cell culture model for evaluation of drug transfer into milk

In the present study, a human mammary epithelial cell (HMEC) culture model was developed to evaluate the potential involvement of carrier-mediated transport systems in drug transfer into milk. Trypsin-resistant HMECs were seeded on Matrigel-coated filters to develop monolayers of functionally differentiated HMEC. Expression of the specific function of HMEC monolayers was dependent of the number of trypsin treatments. Among the monolayers with different numbers of treatment (treated 1 to 3 times), the monolayer treated 3 times (3-t-HMEC monolayer) showed the highest maximal transepithelial resistance and expression of beta-casein mRNA as an index of differentiation. Transport of tetraethylammonium (TEA) across the 3-t-HMEC monolayer in the basolateral-to-apical direction was significantly higher than that in the apical-to-basolateral direction (p < 0.05), whereas such directionality was not observed for p-amino-hippurate, suggesting the existence of organic cation transporters, but not organic anion transporters. In fact, expression of mRNAs of human organic cation transporter (OCT) 1 and 3 were detected in the 3-t-HMEC monolayer. These results indicate that the 3-t-HMEC monolayer is potentially useful for the evaluation of carrier-mediated secretion of drugs including organic cations into human milk.

Of extracellular matrix, scaffolds, and signaling: tissue architecture regulates development, homeostasis, and cancer

The microenvironment influences gene expression so that the behavior of a cell is largely determined by its interactions with the extracellular matrix, neighboring cells, and soluble local and systemic cues. We describe the essential roles of context and organ structure in directing mammary gland development and differentiated function and in determining the response to oncogenic insults, including mutations. We expand on the concept of "dynamic reciprocity" to present an integrated view of development, cancer, and aging and posit that genes are like the keys on a piano: Although they are essential, it is the context that makes the music.

Modeling dynamic reciprocity: engineering three-dimensional culture models of breast architecture, function, and neoplastic transformation

In order to understand why cancer develops as well as predict the outcome of pharmacological treatments, we need to model the structure and function of organs in culture so that our experimental manipulations occur under physiological contexts. This review traces the history of the development of a prototypic example, the three-dimensional (3D) model of the mammary gland acinus. We briefly describe the considerable information available on both normal mammary gland function and breast cancer generated by the current model and present future challenges that will require an increase in its complexity. We propose the need for engineered tissues that faithfully recapitulate their native structures to allow a greater understanding of tissue function, dysfunction, and potential therapeutic intervention.

Chromatin organization measured by AluI restriction enzyme changes with malignancy and is regulated by the extracellular matrix and the cytoskeleton

Given that expression of many genes changes when cells become malignant or are placed in different microenvironments, we asked whether these changes were accompanied by global reorganization of chromatin. We reasoned that sequestration or exposure of chromatin-sensitive sites to restriction enzymes could be used to detect this reorganization. We found that AluI-sensitive sites of nonmalignant cells were relatively more exposed compared to their malignant counterparts in cultured cells and human tumor samples. Changes in exposure and sequestration of AluI-sensitive sites in normal fibroblasts versus fibrosarcoma or those transfected with oncogenes, nonmalignant breast cells versus carcinomas and poorly metastatic versus highly invasive melanoma were shown to be independent of the cell cycle and may be influenced by proteins rich in disulfide bonds. Remarkably, regardless of degree of malignancy, AluI-sensitive sites became profoundly sequestered when cells were incubated with laminin, Matrigel, or a circular RGD peptide (RGD-C), but became exposed when cells were placed on collagen I or in serum-containing medium. Disruption of the actin cytoskeleton led to exposure, whereas disruption of microtubules or intermediate filaments exerted a sequestering effect. Thus, AluI-sensitive sites are more sequestered with increasing malignant behavior, but the sequestration and exposure of these sites is exquisitely sensitive to information conferred to the cell by molecules and biomechanical forces that regulate cellular and tissue architecture.

BLG-e1 - a novel regulatory element in the distal region of the beta-lactoglobulin gene promoter

beta-Lactoglobulin (BLG) is a major ruminant milk protein. A regulatory element, termed BLG-e1, was defined in the distal region of the ovine BLG gene promoter. This 299-bp element lacks the established cis-regulatory sequences that affect milk-protein gene expression. Nevertheless, it alters the binding of downstream BLG sequences to histone H4 and the sensitivity of the histone-DNA complexes to trichostatin A treatment. In mammary cells cultured under favorable lactogenic conditions, BLG-e1 acts as a potent, position-independent silencer of BLG/luciferase expression, and similarly affects the promoter activity of the mouse whey acidic protein gene. Intragenic sequences upstream of BLG exon 2 reverse the silencing effect of BLG-e1 in vitro and in transgenic mice.

Expression of {beta}1 integrin receptors during rat pancreas development--sites and dynamics

The integrin receptors link to extracellular matrix proteins and exert a dynamic role in development by providing the physical basis for cell adhesion and controlling cell growth. In the present study, we examined changes in the expression of beta1 integrins and its associated alpha-subunits to islet cell development in the rat pancreas. A significant increase in protein expression of integrin alpha3, alpha6, and beta1 was observed from fetal to postnatal life. High mRNA levels of these integrin subunits was detected at embryonic d 18 and dropped significantly after birth with relatively low expression throughout postnatal life. Integrins alpha3, alpha5, alpha6, and beta1 were expressed in a cell-specific manner in the pancreas with high integrin immunoreactivity in duct and islet regions during fetal life, and a progressive increase later into postnatal life. The coexpression with islet and putative islet precursor markers during fetal and postnatal development suggest a role for these integrin subunits in differentiation and maturation of islets. Functional studies in vitro showed that anti-beta1 antibody treatment inhibited islet cell adhesion to extracellular matrices and disrupted islet architecture. Blockade of beta1 integrin receptor and knockdown beta1 mRNA resulted in a decrease in the expression of insulin mRNA and increased islet cell death. These results suggest that progression in islet cell development is accompanied by and dependent upon cell adhesion via beta1 integrin and its respective alpha-subunits and suggest that the beta1 family of integrins may play a critical role in islet cell architecture, development, integrity, and function.

Coordination of chondrocyte differentiation and joint formation byα5β1 integrin in the developing appendicular skeleton

The control point by which chondrocytes take the decision between the cartilage differentiation program or the joint formation program is unknown. Here, we have investigated the effect of α5β1 integrin inhibitors and bone morphogenetic protein (BMP) on joint formation. Blocking ofα5β1 integrin by specific antibodies or RGD peptide(arginine-glycine-aspartic acid) induced inhibition of pre-hypertrophic chondrocyte differentiation and ectopic joint formation between proliferating chondrocytes and hypertrophic chondrocytes. Ectopic joint expressed Wnt14,Gdf5, chordin, autotaxin, type I collagen and CD44, while expression of Indian hedgehog and type II collagen was downregulated in cartilage. Expression of these interzone markers confirmed that the new structure is a new joint being formed. In the presence of BMP7, inhibition of α5β1 integrin function still induced the formation of the ectopic joint between proliferating chondrocytes and hypertrophic chondrocytes. By contrast,misexpression of α5β1 integrin resulted in fusion of joints and formation of pre-hypertrophic chondrocytes. These facts indicate that the decision of which cell fate to make pre-joint or pre-hypertrophic is made on the basis of the presence or absence of α5β1 integrin on chondrocytes.

DNA methylation control of tissue polarity and cellular differentiation in the mammary epithelium

Alterations in gene expression accompany cell-type-specific differentiation. In complex systems where functional differentiation depends on the organization of specific cell types into highly specialized structures (tissue morphogenesis), it is not known how epigenetic mechanisms that control gene expression influence this stepwise differentiation process. We have investigated the effect of DNA methylation, a major epigenetic pathway of gene silencing, on the regulation of mammary acinar differentiation. Our in vitro model of differentiation encompasses human mammary epithelial cells that form polarized and hollow tissue structures (acini) when cultured in the presence of basement membrane components. We found that acinar morphogenesis was accompanied with chromatin remodeling, as shown by alterations in histone 4 acetylation, heterochromatin 1 protein, and histone 3 methylated on lysine 9, and with an increase in expression of MeCP2, a mediator of DNA-methylation-induced gene silencing. DNA hypomethylation induced by treatment with 5-aza-2' deoxycytidine during acinar differentiation essentially prevented the formation of apical tissue polarity. This treatment also induced the expression of CK19, a marker of cells that are in a transitional differentiation stage. These results suggest that DNA methylation is a mechanism by which mammary epithelial differentiation is coordinated both at the tissue and cellular levels.

The effect of endotoxin on functional parameters of mammary CID-9 cells

The effect of endotoxin on mammary CID-9 cells, which differentiate in culture and express beta-casein, was investigated. Cells in culture supplemented with lactogenic hormones and dripped with EMS-Matrix (EMS-drip), were treated daily with endotoxin (0.5-500 microg/ml). Endotoxin at concentrations of less or equal to 10 microg/ml did not affect cell growth and viability up to 5 days post endotoxin treatment. Endotoxin (0.01-10 microg/ml) was added to the culture medium, upon confluence, and functional parameters were examined within 48 h post endotoxin treatment. Nuclear factor-kappaB (NF-kappaB) (p52) increased in nuclear extracts from endotoxin-stimulated cells within 1 h of treatment, while beta-casein mRNA and protein expression decreased in a concentration-dependent manner at 24 and 48 h post treatment. Zymography showed that the 72 and 92 kDa gelatinase activity increased in cells at 24 and 48 h post endotoxin treatment at 10 and 50 microg/ml. At the latter concentration, the active form of 72 kDa gelatinase was induced at 48 h. Interleukin-6 and tumor necrosis factor-alpha levels increased at 1-3 h post endotoxin treatment and peaked at 6 h in cells on plastic and EHS-drip. Nerve growth factor (NGF) levels increased in control and endotoxin-treated cells in a time-dependent manner, and endotoxin increased NGF levels in culture at 6 and 9 h post endotoxin treatment. This study shows that endotoxin activated NF-kappaB, suppressed beta-casein expression and upregulated gelatinases, cytokines and NGF. This model could be used to investigate the role of mammary cells in initiating and propagating inflammation and to test candidate molecules for potential anti-inflammatory properties.

A role for the cytoskeleton in prolactin-dependent mammary epithelial cell differentiation

The function of exocrine glands depends on signals within the extracellular environment. In the mammary gland, integrin-mediated adhesion to the extracellular matrix protein laminin co-operates with soluble factors such as prolactin to regulate tissue-specific gene expression. The mechanism of matrix and prolactin crosstalk and the activation of downstream signals are not fully understood. Because integrins organize the cytoskeleton, we analysed the contribution of the cytoskeleton to prolactin receptor activation and the resultant stimulation of milk protein gene expression. We show that the proximal signalling events initiated by prolactin (i.e. tyrosine phosphorylation of receptor and the associated kinase Jak2) do not depend on an intact actin cytoskeleton. However, actin networks and microtubules are both necessary for continued mammary cell differentiation, because cytoskeletal integrity is required to transduce the signals between prolactin receptor and Stat5, a transcription factor necessary for milk protein gene transcription. The two different cytoskeletal scaffolds regulate prolactin signalling through separate mechanisms that are specific to cellular differentiation but do not affect the general profile of protein synthesis.

Id-1 as a molecular target in therapy for breast cancer cell invasion and metastasis

Mammary epithelial cells constitutively expressing Id-1 protein are unable to differentiate, acquire the ability to proliferate, and invade the extracellular matrix. In addition, Id-1 is aberrantly over-expressed in aggressive and metastatic breast cancer cells, as well as in human breast tumor biopsies from infiltrating carcinomas, suggesting Id-1 might be an important regulator of breast cancer progression. We show that human metastatic breast cancer cells become significantly less invasive in vitro and less metastatic in vivo when Id-1 is down-regulated by stable transduction with antisense Id-1. Expression of the matrix metalloproteinase MT1-MMP is decreased in proportion to the decrease in Id-1 protein levels, representing a potential mechanism for the reduction of invasiveness. Further, to more accurately recapitulate the biology of and potential therapeutic approaches to tumor metastasis, we targeted Id-1 expression systemically in tumor-bearing mice by using a nonviral approach. We demonstrate significant reduction of both Id-1 and MT1-MMP expressions as well as the metastatic spread of 4T1 breast cancer cells in syngeneic BALB/c mice. In conclusion, our studies have identified Id-1 as a critical regulator of breast cancer progression and suggest the feasibility of developing novel therapeutic approaches to target Id-1 expression to reduce breast cancer metastasis in humans.

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.

Functional consequence of exposure to dieldrin on mammary development and function

The effect of dieldrin (Dln) on the development of the mammary gland and on functional parameters of CID-9 mammary cells in culture was investigated. One-month-old Sprague-Dawley female rats were bred and received intraperitoneal injection with 2.5 or 15 microM Dln during the last trimester of their gestation. Mammary glands of 15-microM Dln-treated rats showed immature alveolar structures by day 18 of gestation and abundant adipose tissue. Dln-treated rats had a lower number of pups, and the weight of pups between days 14 and 31 of age compared with non-treated rats was significantly lower. Long-term exposure of CID-9 mammary cells, cultured under non-differentiation conditions, on plastic, or under differentiation permissive conditions, dripped with EHS-matrix, to 5 or 25 microM Dln was detrimental to cell growth. The short-term effect of Dln exposure (up to 9 h) on CID-9 cells, under the same culture conditions, did not affect their beta-casein mRNA levels, but induced apoptosis, down regulated gap junction intracellular communication and induced IL-6 and TNF-alpha expression.

Id proteins in epithelial cells

Id helix-loop-helix (Id HLH) proteins are negative regulators of basic HLH transcription factors. They are expressed during embryonic development and are important for the regulation of cell phenotypes in adults. They participate in the molecular networks controlling cell growth, differentiation, and carcinogenesis, through specific basic HLH and non-basic HLH protein interactions. Recent in vitro and in vivo data implicate Id HLH as important orchestrating proteins of homeostasis in glandular and protective epithelia. In particular, Id proteins have been reported to be involved in cell behavior in epidermis, respiratory system, digestive tract, pancreas, liver, thyroid, urinary system, prostate, testis, endometrium, cervix, ovary, and mammary gland. The purpose of this review is to summarize the evidence implicating Id proteins in the regulation of mammalian epithelial cell phenotypes.

Helix-loop-helix proteins in mammary gland development and breast cancer

The basic helix-loop-helix (bHLH) family of transcription factors functions in the coordinated regulation of gene expression, cell lineage commitment, and cell differentiation in most mammalian tissues. Helix-loop-helix Id (Inhibitor of DNA binding) proteins are distinct from bHLH transcription factors in that they lack the basic domain necessary for DNA binding. Id proteins thus function as dominant negative regulators of bHLH transcription factors. The inhibition of bHLH factor activity by forced constitutive expression of Id proteins is closely associated with the inhibition of differentiation in a number of different cell types, including mammary epithelial cells. Moreover, recent literature suggests important roles of HLH proteins in many normal and transformed tissues, including mammary gland. Therefore, future directions for prognosis or therapeutic treatments of breast cancer may be able to exploit bHLH and Id genes as useful molecular targets. The purpose of this review is to summarize the evidence implicating HLH proteins in the regulation of normal and transformed mammary epithelial cell phenotypes.

Engineering cellular microenvironments to improve cell-based drug testing

Recent progress in the biology of cell adhesion is enabling cell culture models to better reproduce in vivo functions. Cues from adhesion to extracellular matrix and neighboring cells are important regulators of cell behaviors. The recent adaptation of semiconductor tools to spatially organize cells and their adhesions has enhanced our ability to engineer cell functions ex vivo. By using these tools to create more in vivo-like cultures, cell-based drug discovery and target validation could be improved. This review explores the biological advances made by these microfabrication tools and discusses how they could enable high-throughput cell-based assays.

Characterization of an epithelial cell line from bovine mammary gland

Elucidation of the bovine mammary gland's unique characteristics depends on obtaining an authentic cell line that will reproduce its function in vitro. Representative clones from bovine mammary cell populations, differing in their attachment capabilities, were cultured. L-1 cells showed strong attachment to the plate, whereas H-7 cells detached easily. Cultures established from these clones were nontumorigenic upon transplantation to an immunodeficient host; they exhibited the epithelial cell characteristics of positive cytokeratin but not smooth muscle actin staining. Both cell lines depended on fetal calf serum for proliferation. They exhibited distinct levels of differentiation on Matrigel in serum-free, insulin-supplemented medium on the basis of their organization and beta-lactoglobulin (BLG) secretion. H-7 cells organized into mammospheres, whereas L-1 cells arrested in a duct-like morphology. In both cell lines, prolactin activated phosphorylation of the signal transducer and activator of transcription, Stat5-a regulator of milk protein gene transcription, and of PHAS-I-an inhibitor of translation initiation in its nonphosphorylated form. De novo synthesis and secretion of BLG were detected in differentiated cultures: in L-1 cells, BLG was dependent on lactogenic hormones for maximal induction but was less stringently controlled than was beta-casein in the mouse CID-9 cell line. L-1 cells also encompassed a near-diploid chromosomal karyotype and may serve as a tool for studying functional characteristics of the bovine mammary gland.

Studying actin-dependent processes in tissue culture

The cytoskeletal organization of cells that are grown in tissue culture is often very different from that of cells in living organisms. This casts some doubt as to whether information that comes from studying actin-dependent cellular processes--such as cell motility or differentiation--in cells that are cultured under these conditions is physiologically relevant. Studies on cells grown in improved two-dimensional- and three-dimensional-culture systems that closely mimic the in vivo extracellular-matrix environment should provide a more accurate picture of actin-cytoskeletal function in the living organism.

Id-1, ITF-2, and Id-2 comprise a network of helix-loop-helix proteins that regulate mammary epithelial cell proliferation, differentiation, and apoptosis

Mammary epithelial cells proliferate, invade the stroma, differentiate, and die in adult mammals by mechanisms that are poorly understood. We found that Id-1, an inhibitor of basic helix-loop-helix transcription factors, regulates mammary epithelial cell growth, differentiation, and invasion in culture. Here, we show that Id-1 is expressed highly during mammary development in virgin mice and during early pregnancy, when proliferation and invasion are high. During mid-pregnancy, Id-1 expression declined to undetectable levels as the epithelium differentiated fully. Surprisingly, Id-1 increased during involution, when the epithelium undergoes extensive apoptosis. To determine whether Id-1 regulates both proliferation and apoptosis, we constitutively expressed Id-1 in mammary epithelial cell cultures. Id-1 stimulated proliferation in sparse cultures but induced apoptosis in dense cultures, which reflect epithelial cell density during early pregnancy and involution, respectively. To understand how Id-1 acts, we screened a yeast two-hybrid library from differentiating mammary epithelial cells and identified ITF-2, a basic helix-loop-helix transcription factor, as an Id-1-interacting protein. Overexpression of ITF-2 significantly reduced Id-1-stimulated proliferation and apoptosis. We show further that, in contrast to Id-1, Id-2 was expressed highly in differentiated mammary epithelial cells in vivo and in culture. In culture, Id-2 antisense transcripts blocked differentiation. Our results suggest that Id-1, ITF-2, and Id-2 comprise a network of interacting molecular switches that govern mammary epithelial cell phenotypes.