The interplay of matrix metalloproteinases, morphogens and growth factors is necessary for branching of mammary epithelial cells

Mammary branch initiation and extension are inhibited by separate pathways downstream of TGFβ in culture

During the branching morphogenesis process that builds epithelial trees, signaling from stimulatory and inhibitory growth factors is integrated to control branch initiation and extension into the surrounding stroma. Here, we examined the relative roles played by these stimulatory and inhibitory signals in the patterning of branch initiation and extension of model mammary epithelial tubules in culture. We found that although several growth factors could stimulate branching, they did not determine the sites at which new branches formed or the lengths to which branches extended. Instead, branch initiation and extension were defined by two separate signals downstream of the inhibitory morphogen, transforming growth factor (TGF)-β. Branch initiation was controlled by signaling through p38 mitogen-activated protein kinase, whereas branch extension was controlled by Smad-mediated induction of a second diffusible inhibitor, Wnt5a. These data suggest that mammary epithelial branching is patterned predominately by repulsive signaling, and that TGFβ activates multiple inhibitory pathways to refine the architecture of the tree.

Cell budding from pre-invasive tumors: Intrinsic precursor of invasive breast lesions?

Our previous studies showed that in patients with ductal carcinoma in situ (DCIS) of the breast, the tumor cells that overlie focal myoepithelial cell layer disruptions (FMCLDs) are generally arranged as finger-like projections that bud into the stroma. These budding cells have significantly more genetic instability and invasion-related gene expression, and less estrogen receptor (ER) expression, than their epithelial cell counterparts. This study aimed to assess these cells for potential molecular markers that are uniquely associated with cell adhesion and motility. Seventeen ER-positive DCIS cases were screened by immunostaining for ER, and 7 cases which harbored FMCLD lesions were used to examine the expression of the potential markers. Two cases with both DCIS and invasive lesions were selected for comparing the differences in molecular expression between these lesion types. The results showed that expression levels of talin, E-cadherin and focal adhesion kinase (FAK) in tumor cells overlying FMCLDs were higher than those within the corresponding duct. Integrin β1 staining was detected only in a small number of the tumor cells overlying the FMCLDs. Vinculin staining was weak (18%) or not detected (82%), and no expression was found in the tumor cells within the corresponding duct or in the pure isolated DCIS. By contrast, the expression levels of talin, vinculin and integrin β1 in the invasive tumors were distinctly higher than those in DCIS, and the expression of FAK and E-cadherin was lower. Using electron microscopy, we found that the tight junctions between tumor cells overlying the FMCLDs were reduced compared to the adjacent tumor cells in the lumen. These results indicate that the tumor cells overlying FMCLDs are likely to represent the specific precursors of invasive breast lesions. Our findings may also facilitate the identification of specific targets for further molecular profiling, which will more completely characterize this important cell population.

Snail1, Snail2, and E47 promote mammary epithelial branching morphogenesis

Several E-box-binding transcription factors regulate individual and collective cell migration and enhance the motility of epithelial cells by promoting epithelial-mesenchymal transition (EMT). Here, we characterized the role of a subset of these transcription factors and the EMT proteome in branching morphogenesis of mammary epithelial tissues using a three-dimensional organotypic culture model of the mammary duct. We found that the transcription factors Snail1, Snail2, and E47 were transiently upregulated at branch sites; decreasing the expression of these transcription factors inhibited branching. Conversely, ectopic expression of Snail1, Snail2, and E47 induced branching in the absence of exogenous stimuli. These changes correlated with the expression of mesenchymal markers and repression of E-cadherin, which was essential for branching. Snail1 and Snail2 also promoted cell survival at branch sites, but this was not sufficient to induce branching. These findings indicate that Snail1, Snail2, and E47 can promote collective migration during branching morphogenesis of mammary epithelial tissues through key regulators of EMT.

Proteomics characterization of cell model with renal fibrosis phenotype: osmotic stress as fibrosis triggering factor

Renal fibroblasts are thought to play a major role in the development of renal fibrosis (RF). The mechanisms leading to this renal alteration remain poorly understood. We performed differential proteomic analyses with two established fibroblast cell lines with RF phenotype to identify new molecular pathways associated with RF. Differential 2-DE combined with mass spectrometry analysis revealed the alteration of more than 30 proteins in fibrotic kidney fibroblasts (TK188) compared to normal kidney fibroblast (TK173). Among these proteins, markers of the endoplasmic reticulum (ER) stress- and the unfolded protein response (UPR) pathway (GRP78, GRP94, ERP57, ERP72, and CALR) and the oxidative stress pathway proteins (PRDX1, PRDX2, PRDX6, HSP70, HYOU1) were highly up-regulated in fibrotic cells. Activation of these stress pathways through long time exposition of TK173, to high NaCl or glucose concentrations resulted in TK188 like phenotype. Parallel to an increase in reactive oxygen species, the stressed cells showed significant alteration of fibrosis markers, ER-stress and oxidative stress proteins. Similar effects of osmotic stress could be also observed on renal proximal tubule cells. Our data suggest an important role of the ER-stress proteins in fibrosis and highlights the pro-fibrotic effect of osmotic stress through activation of oxidative stress and ER-stress pathways.

Cellular mechanisms regulating epithelial morphogenesis and cancer invasion

The cellular mechanisms driving mammalian epithelial morphogenesis are of significant fundamental and practical interest. Historically, these processes have been difficult to study directly, owing to the opacity and relative inaccessibility of mammalian tissues. Recent experimental advances in timelapse imaging and in 3D organotypic culture have enabled direct observation of epithelial morphogenesis. In the mammary gland, branching morphogenesis is observed to proceed through a novel form of collective epithelial migration. The active unit of morphogenesis is a multilayered epithelium with reduced apico-basal polarity, within which cells rearranged vigorously. From within this multilayered state, new ducts initiate and elongate into the matrix without leading cellular extensions or dedicated leaders. We discuss the implications of these findings on our understanding of epithelial morphogenesis in other organs and in cancer progression.

Characterization of mammary stromal remodeling during the dry period

During the dry period between successive lactations, the mammary gland of dairy cows undergoes extensive remodeling that is marked by phases of involution and mammogenesis. Changes in the mammary epithelium during the dry period have been well characterized; however, few studies have examined the changes that occur in stromal tissue. The objective of this study was to characterize changes that occur in mammary stroma during the dry period. Mammary biopsies were taken from 9 multigravid Holstein cows in late lactation, at 1 wk after dry-off, 3 wk before expected calving date, and 1 wk before expected calving date. Tissue was fixed in formalin, embedded in paraffin, and cut into 5-mum sections. Sections were stained with hematoxylin and eosin or with immunohistochemistry for expression of smooth muscle alpha actin (SMA), fibronectin, stromelysin-1 (MMP-3), transforming growth factor-beta1 (TGF-beta1), and TGF-beta receptor 2 (TGF-betaR2). Images of tissues were captured with light microscopy, and imaging software was used to measure intralobular stromal area, number of activated fibroblasts, as identified by expression of SMA, and percentage of intralobular stromal area expressing fibronectin, MMP3, TGF-beta1, and TGF-betaR2. Analyses of variance were conducted and statistical differences were based on the least squares means of biopsy stage. Number of activated fibroblasts was greater at 1 wk dry than at 1 wk before calving (2,720 vs. 1,800 cells/mm(2)), percentage intralobular stromal area was greater at 1 wk dry (32%) and 3 wk before calving (37%) than at 1 wk before calving (25%), and TGF-beta1 expression decreased 15% from late lactation to the dry period. The percentages of stromal area expressing fibronectin, MMP-3, and TGF-betaR2 and the percentage of myofibroblasts were not different across biopsy stages. These results support the concept that stromal expression of transforming growth factor-beta1 and fibroblast proliferation may be important for remodeling during the dry period.

Adipose stroma induces branching morphogenesis of engineered epithelial tubules

The mammary gland and other treelike organs develop their characteristic fractal geometries through branching morphogenesis, a process in which the epithelium bifurcates and invades into the surrounding stroma. Controlling the pattern of branching is critical for engineering these organs. In vivo, the branching process is instructed by stromal-epithelial interactions and adipocytes form the largest component of the fatty stroma that surrounds the mammary epithelium. Here, we used microlithographic approaches to engineer a three-dimensional culture model that enables analysis of the effect of adipocytes on the pattern of branching morphogenesis of mammary epithelial cells. We found that adipocyte-rich stroma induces branching through paracrine signals, including hepatocyte growth factor, but does not affect the branching pattern per se. This tissue engineering approach can be expanded to other organs, and should enable piecemeal analysis of the cellular populations that control patterning during normal development.

Human 21T breast epithelial cell lines mimic breast cancer progression in vivo and in vitro and show stage-specific gene expression patterns

Early breast cancer progression involves advancement through specific morphological stages including atypical ductal hyperplasia (ADH), ductal carcinoma in situ (DCIS) and invasive mammary carcinoma (IMC), although not necessarily always in a linear fashion. Observational studies have examined genetic, epigenetic and gene expression differences in breast tissues representing these stages of progression, but model systems which would allow for experimental testing of specific factors influencing transition through these stages are scarce. The 21T series cell lines, all originally derived from the same patient with metastatic breast cancer, have been proposed to represent a mammary tumor progression series. We report here that three of the 21T cell lines indeed mimic specific stages of human breast cancer progression (21PT-derived cells, ADH; 21NT-derived cells, DCIS; 21MT-1 cells, IMC) when grown in the mammary fat pad of nude mice, albeit after a year. To develop a more rapid, readily manipulatable in vitro assay for examining the biological differences between these cell lines, we have used a 3D Matrigel system. When the three cell lines were grown in 3D Matrigel, they showed characteristic morphologies, in which quantifiable aspects of stage-specific in vivo behaviors (ie, differences in acinar structure formation, cell polarization, colony morphology, cell proliferation, cell invasion) were recapitulated in a reproducible fashion. Gene expression profiling revealed a characteristic pattern for each of the three cell lines. Interestingly, Wnt pathway alterations are particularly predominant in the early transition from 21PTci (ADH) to 21NTci (DCIS), whereas alterations in expression of genes associated with control of cell motility and invasion phenomena are more prominent in the later transition of 21NTci (DCIS) to 21MT-1 (IMC). This system thus reveals potential therapeutic targets and will provide a means of testing the influences of identified genes on transitions between these stages of pre-malignant to malignant growth.

Involvement of epimorphin in the repair of experimental renal fibrosis in mice

Interaction between epithelial cells and mesenchymal cells is essential in normal organ morphogenesis and in tissue repair after injury. Epimorphin, a mesenchymal protein that regulates epithelial morphogenesis through epithelial-mesenchymal interactions, has recently attracted attention as an important modulator of tissue repair. In this study we analyzed the role of epimorphin in renal fibrosis. We first found a progressive increase in epimorphin expression corresponding to the progression of renal fibrosis in mice with unilateral ureteral obstruction (UUO). To determine whether this expression has a role in the repair or progression of renal fibrosis, we analyzed a model of renal fibrosis repair, the UUO-release (UUO-R) model. Epimorphin expression was increased at 3 and 7 days after the UUO-R rather than on the day of release, but was decreased at 21 days after the release. Inhibition of endogenous epimorphin with anti-epimorphin antibody (MC-1) significantly delayed the repair of fibrosis. When compared with normal-IgG-injected mice, MC-1-injected mice showed significantly decreased renal matrix metalloproteinase (MMP)-2 and MMP-9 expressions by western blotting and increased expression of TGF-beta and collagen-I mRNA by real-time RT-PCR. Recombinant epimorphin induced prominent increases in MMP-2 and MMP-9 activities in the culture media of renal interstitial fibroblasts in vitro. These findings indicate that epimorphin has a pivotal role in the repair of renal fibrosis by modulating both extracellular matrix (ECM) degradation and its production.

Familial tumoral calcinosis: from characterization of a rare phenotype to the pathogenesis of ectopic calcification

Familial tumoral calcinosis (FTC) refers to a heterogeneous group of inherited disorders characterized by the occurrence of cutaneous and subcutaneous calcified masses. Two major forms of the disease are now recognized. Hyperphosphatemic FTC has been shown to result from mutations in three genes: fibroblast growth factor-23 (FGF23), coding for a potent phosphaturic protein, KL encoding Klotho, which serves as a co-receptor for FGF23, and GALNT3, which encodes a glycosyltransferase responsible for FGF23 O-glycosylation; defective function of any one of these three proteins results in hyperphosphatemia and ectopic calcification. The second form of the disease is characterized by absence of metabolic abnormalities, and is, therefore, termed normophosphatemic FTC. This variant was found to be associated with absence of functional SAMD9, a putative tumor suppressor and anti-inflammatory protein. The data gathered through the study of these rare disorders have recently led to the discovery of novel aspects of the pathogenesis of common disorders in humans, underscoring the potential concealed within the study of rare diseases.

Analysis of gene expression in PTHrP-/- mammary buds supports a role for BMP signaling and MMP2 in the initiation of ductal morphogenesis

Parathyroid hormone-related protein (PTHrP) acts on the mammary mesenchyme and is required for proper embryonic mammary development. In order to understand PTHrP's effects on mesenchymal cells, we profiled gene expression in WT and PTHrP(-/-) mammary buds, and in WT and K14-PTHrP ventral skin at E15.5. By cross-referencing the differences in gene expression between these groups, we identified 35 genes potentially regulated by PTHrP in the mammary mesenchyme, including 6 genes known to be involved in BMP signaling. One of these genes was MMP2. We demonstrated that PTHrP and BMP4 regulate MMP2 gene expression and MMP2 activity in mesenchymal cells. Using mammary bud cultures, we demonstrated that MMP2 acts downstream of PTHrP to stimulate ductal outgrowth. Future studies on the functional role of other genes on this list should expand our knowledge of how PTHrP signaling triggers the onset of ductal outgrowth from the embryonic mammary buds.

Fibroblast hepatocyte growth factor promotes invasion of human mammary ductal carcinoma in situ

Stromal-derived hepatocyte growth factor (HGF) acting through its specific proto-oncogene receptor c-Met has been suggested to play a paracrine role in the regulation of tumor cell migration and invasion. The transition from preinvasive ductal carcinoma in situ (DCIS) to invasive breast carcinoma is marked by infiltration of stromal fibroblasts and the loss of basement membrane. We hypothesized that HGF produced by the infiltrating fibroblasts may alter proteolytic pathways in DCIS cells, and, to study this hypothesis, established three-dimensional reconstituted basement membrane overlay cocultures with two human DCIS cell lines, MCF10.DCIS and SUM102. Both cell lines formed large dysplastic structures in three-dimensional cultures that resembled DCIS in vivo and occasionally developed invasive outgrowths. In coculture with HGF-secreting mammary fibroblasts, the percentage of DCIS structures with invasive outgrowths was increased. Activation of c-Met with conditioned medium from HGF-secreting fibroblasts or with recombinant HGF increased the percentage of DCIS structures with invasive outgrowths, their degradation of collagen IV, and their secretion of urokinase-type plasminogen activator and its receptor. In agreement with the in vitro findings, coinjection with HGF-secreting fibroblasts increased invasiveness of MCF10.DCIS xenografts in severe combined immunodeficient mice. Our study shows that paracrine HGF/c-Met signaling between fibroblasts and preinvasive DCIS cells enhances the transition to invasive carcinomas and suggests that three-dimensional cocultures are appropriate models for testing therapeutics that target tumor microenvironment-enhanced invasiveness.

Origin and function of tumor stroma fibroblasts

Tumor development is critically dependent on the formation of a supporting stroma consisting of neovasculature, inflammatory cells and activated fibroblasts. Activated fibroblasts present a heterogeneous cell population not only in regard to the expression of marker molecules but also to their origin and molecular signaling properties. The plasticity of this cell type is pointed out by the multiple transdifferentiation events that lead to the generation of activated fibroblasts which can arise from resting fibroblasts, epithelial and endothelial cells as well as from mesenchymal stem cells. Cellular in vitro and in vivo experiments have changed the perspective of fibroblasts from passive "bystanders" in the tumor microenvironment to that of important drivers of tumor progression. Here, we describe the multiple origins of fibroblast recruitment to the tumor tissue as well as the function of activated fibroblasts during tumor initiation, progression, metastasis and anti-VEGF resistance. The identification of markers present in activated fibroblasts as well as a better understanding how these cells influence other tumor compartments has led to the clinical development of anti-tumor therapies.

Innate immune responses of pulmonary epithelial cells to Burkholderia pseudomallei infection

BACKGROUND

Burkholderia pseudomallei, a facultative intracellular pathogen, causes systemic infection in humans with high mortality especially when infection occurs through an infectious aerosol. Previous studies indicated that the epithelial cells in the lung are an active participant in host immunity. In this study, we aimed to investigate the innate immune responses of lung epithelial cells against B. pseudomallei.

METHODOLOGY AND PRINCIPAL FINDINGS

Using a murine lung epithelial cell line, primary lung epithelial cells and an inhalational murine infection model, we characterized the types of innate immunity proteins and peptides produced upon B. pseudomallei infection. Among a wide panel of immune components studied, increased levels of major pro-inflammatory cytokines IL-6 and TNFalpha, chemokine MCP-1, and up-regulation of secretory leukocyte protease inhibitor (SLPI) and chemokine (C-C motif) ligand 20 (CCL20) were observed. Inhibition assays using specific inhibitors suggested that NF-kappaB and p38 MAPK pathways were responsible for these B. pseudomallei-induced antimicrobial peptides.

CONCLUSIONS

Our findings indicate that the respiratory epithelial cells, which form the majority of the cells lining the epithelial tract and the lung, have important roles in the innate immune response against B. pseudomallei infection.

Morphogenesis of epithelial tubes: Insights into tube formation, elongation, and elaboration

Epithelial tubes are a fundamental tissue across the metazoan phyla and provide an essential functional component of many of the major organs. Recent work in flies and mammals has begun to elucidate the cellular mechanisms driving the formation, elongation, and branching morphogenesis of epithelial tubes during development. Both forward and reverse genetic techniques have begun to identify critical molecular regulators for these processes and have revealed the conserved role of key pathways in regulating the growth and elaboration of tubular networks. In this review, we discuss the developmental programs driving the formation of branched epithelial networks, with specific emphasis on the trachea and salivary gland of Drosophila melanogaster and the mammalian lung, mammary gland, kidney, and salivary gland. We both highlight similarities in the development of these organs and attempt to identify tissue and organism specific strategies. Finally, we briefly consider how our understanding of the regulation of proliferation, apicobasal polarity, and epithelial motility during branching morphogenesis can be applied to understand the pathologic dysregulation of these same processes during metastatic cancer progression.

Self-organization of engineered epithelial tubules by differential cellular motility

Patterning of developing tissues arises from a number of mechanisms, including cell shape change, cell proliferation, and cell sorting from differential cohesion or tension. Here, we reveal that differences in cell motility can also lead to cell sorting within tissues. Using mosaic engineered mammary epithelial tubules, we found that cells sorted depending on their expression level of the membrane-anchored collagenase matrix metalloproteinase (MMP)-14. These rearrangements were independent of the catalytic activity of MMP14 but absolutely required the hemopexin domain. We describe a signaling cascade downstream of MMP14 through Rho kinase that allows cells to sort within the model tissues. Cell speed and persistence time were enhanced by MMP14 expression, but only the latter motility parameter was required for sorting. These results indicate that differential directional persistence can give rise to patterns within model developing tissues.

Mesenchymal epimorphin is important for pancreatic duct morphogenesis

Epithelial-mesenchymal interactions are crucial for the proper development of many organs, including the pancreas. Within the pancreas, the ducts are thought to harbor stem/progenitor cells, and possibly to give rise to pancreatic ductal carcinoma. Little is known about the mechanism of formation of pancreatic ducts in the embryo. Pancreatic mesenchyme contains numerous soluble factors which help to sustain the growth and differentiation of exocrine and endocrine structures. Here, we report that one such morphoregulatory mesenchymal protein, epimorphin, plays an important role during pancreatic ductal proliferation and differentiation. We found that epimorphin is expressed in pancreatic mesenchyme during early stages of development, and at mesenchymal-epithelial interfaces surrounding the ducts at later stages. Strong upregulation of epimorphin expression was seen during in vitro pancreatic duct differentiation. Similarly, in vitro pancreatic duct formation was inhibited by a neutralizing antibody against epimorphin, whereas addition of recombinant epimorphin partially rescued duct formation. Together, our study demonstrates the role of epimorphin in pancreatic ductal morphogenesis.

Homology with vesicle fusion mediator syntaxin-1a predicts determinants of epimorphin/syntaxin-2 function in mammary epithelial morphogenesis

We have shown that branching morphogenesis of mammary ductal structures requires the action of the morphogen epimorphin/syntaxin-2. Epimorphin, originally identified as an extracellular molecule, is identical to syntaxin-2, an intracellular molecule that is a member of the extensively investigated syntaxin family of proteins that mediate vesicle trafficking. We show here that, although epimorphin/syntaxin-2 is highly homologous to syntaxin-1a, only epimorphin/syntaxin-2 can stimulate mammary branching morphogenesis. We construct a homology model of epimorphin/syntaxin-2 based on the published structure of syntaxin-1a, and we use this model to identify the structural motif responsible for the morphogenic activity. We identify four residues located within the cleft between helices B and C that differ between syntaxin-1a and epimorphin/syntaxin-2; through site-directed mutagenesis of these four amino acids, we confer the properties of epimorphin for cell adhesion, gene activation, and branching morphogenesis onto the inactive syntaxin-1a template. These results provide a dramatic demonstration of the use of structural information about one molecule to define a functional motif of a second molecule that is related at the sequence level but highly divergent functionally.

GALNT3, a gene associated with hyperphosphatemic familial tumoral calcinosis, is transcriptionally regulated by extracellular phosphate and modulates matrix metalloproteinase activity

GALNT3 encodes UDP-N-acetyl-alpha-d-galactosamine: polypeptide N-acetylgalactosaminyl-transferarase 3 (ppGalNacT3), a glycosyltransferase which has been suggested to prevent proteolysis of FGF23, a potent phosphaturic protein. Accordingly, loss-of-function mutations in GALNT3 cause hyperphosphatemic familial tumoral calcinosis (HFTC), a rare autosomal recessive disorder manifesting with increased kidney reabsorption of phosphate, resulting in severe hyperphosphatemia and widespread ectopic calcifications. Although these findings definitely attribute a role to ppGalNacT3 in the regulation of phosphate homeostasis, little is currently known about the factors regulating GALNT3 expression. In addition, the effect of decreased GALNT3 expression in peripheral tissues has not been explored so far. In the present study, we demonstrate that GALNT3 expression is under the regulation of a number of factors known to be associated with phosphate homeostasis, including inorganic phosphate itself, calcium and 1,25-dihydroxyvitamin D(3). In addition, we show that decreased GALNT3 expression in human skin fibroblasts leads to increased expression of FGF7 and of matrix metalloproteinases, which have been previously implicated in the pathogenesis of ectopic calcification. Thus, the present data suggest that ppGalNacT3 may play a role in peripheral tissues of potential relevance to the pathogenesis of disorders of phosphate metabolism.

Extracellular matrix control of mammary gland morphogenesis and tumorigenesis: insights from imaging

The extracellular matrix (ECM), once thought to solely provide physical support to a tissue, is a key component of a cell's microenvironment responsible for directing cell fate and maintaining tissue specificity. It stands to reason, then, that changes in the ECM itself or in how signals from the ECM are presented to or interpreted by cells can disrupt tissue organization; the latter is a necessary step for malignant progression. In this review, we elaborate on this concept using the mammary gland as an example. We describe how the ECM directs mammary gland formation and function, and discuss how a cell's inability to interpret these signals -- whether as a result of genetic insults or physicochemical alterations in the ECM -- disorganizes the gland and promotes malignancy. By restoring context and forcing cells to properly interpret these native signals, aberrant behavior can be quelled and organization re-established. Traditional imaging approaches have been a key complement to the standard biochemical, molecular, and cell biology approaches used in these studies. Utilizing imaging modalities with enhanced spatial resolution in live tissues may uncover additional means by which the ECM regulates tissue structure, on different length scales, through its pericellular organization (short-scale) and by biasing morphogenic and morphostatic gradients (long-scale).

Biomechanical regulation of cell orientation and fate

Biomechanical regulation of tumor phenotypes have been noted for several decades, yet the function of mechanics in the co-evolution of the tumor epithelium and altered cancer extracellular matrix has not been appreciated until fairly recently. In this review, we examine the dynamic interaction between the developing epithelia and the extracellular matrix, and discuss how similar interactions are exploited by the genetically modified epithelium during tumor progression. We emphasize the process of mechanoreciprocity, which is a phenomenon observed during epithelial transformation, in which tension generated within the extracellular microenvironment induce and cooperate with opposing reactive forces within transformed epithelium to drive tumor progression and metastasis. We highlight the importance of matrix remodeling, and present a new, emerging paradigm that underscores the importance of tissue morphology as a key regulator of epithelial cell invasion and metastasis.

Role of stromal tenascin-C in mouse prostatic development and epithelial cell differentiation

Deregulation of epithelial-stromal interactions is considered to play a critical role in the initiation and promotion of benign prostatic hyperplasia (BPH) and prostate carcinoma (PCa). Expression of tenascin-C (TN-C), an extracellular matrix (ECM) glycoprotein, is reportedly higher in BPH and PCa as compared with normal prostate. Remodeling of the ECM alters the homeostatic balance between epithelium and stroma, resulting in physiological changes in cellular functions. To investigate the role of TN-C in prostatic development and differentiation, we evaluated the morphological phenotype of TN-C knockout (KO) mouse prostate (ventral: VP, dorsolateral: DLP, and anterior: AP) and examined tissue recombinants composed of adult mouse DLP epithelium and fetal TN-C KO urogenital sinus mesenchyme (UGM). Histological analysis showed epithelial cell clusters protruding into the ductal lumens in TN-C KO AP and DLP. Interestingly, binucleated cells appeared in epithelium of TN-C KO DLP at 8 weeks. Simultaneously, androgen receptor (AR)-positive cells were decreased in TN-C KO epithelia. Similar to the TN-C KO phenotype, protruded epithelial clusters, binucleated cells, and AR-negative nuclei were induced in DLP epithelium by recombining with TN-C KO UGM. Our results suggest that stromal TN-C might be involved in maintaining epithelial cytodifferentiation, morphogenesis, and androgen receptor expression of normal prostate glands in adult mice.

Genetic mosaic analysis reveals FGF receptor 2 function in terminal end buds during mammary gland branching morphogenesis

FGF signaling is associated with breast cancer and is required for mammary placode formation in the mouse. In this study, we employed a genetic mosaic analysis based on Cre-mediated recombination to investigate FGF receptor 2 (Fgfr2) function in the postnatal mammary gland. Mosaic inactivation of Fgfr2 by the MMTV-Cre transgene enabled us to compare the behavior of Fgfr2 null and Fgfr2 heterozygous cells in the same gland. Fgfr2 null cells were at a competitive disadvantage to their Fgfr2 heterozygous neighbors in the highly proliferative terminal end buds (TEBs) at the invasion front, owing to a negative effect of loss of Fgfr2 function on cell proliferation. However, Fgfr2 null cells were tolerated in mature ducts. In these genetic mosaic mammary glands, the epithelial network is apparently built by TEBs that over time are composed of a progressively larger proportion of Fgfr2-positive cells. However, subsequently, most cells lose Fgfr2 function, presumably due to additional rounds of Cre-mediated recombination. Using an independent strategy to create mosaic mammary glands, which employed an adenovirus-Cre that acts only once, we confirmed that Fgfr2 null cells were out-competed by neighboring Fgfr2 heterozygous cells. Together, our data demonstrate that Fgfr2 functions in the proliferating and invading TEBs, but it is not required in the mature ducts of the pubertal mammary gland.

Mammary gland development in transforming growth factor beta1 null mutant mice: systemic and epithelial effects

The cytokine-transforming growth factor beta1 (TGFB1) is implicated in development of the mammary gland through regulation of epithelial cell proliferation and differentiation during puberty and pregnancy. We compared mammary gland morphogenesis in virgin Tgfb1(+/+), Tgfb1(+/-), and Tgfb1(-/-) mice and transplanted Tgfb1(+/+) and Tgfb1(-/-) epithelium to determine the impact of TGFB1 deficiency on development. When mammary gland tissue was evaluated relative to the timing of puberty, invasion through the mammary fat pad of the ductal epithelium progressed similarly, irrespective of genotype, albeit fewer terminal end buds were observed in mammary glands from Tgfb1(-/-) mice. The terminal end buds appeared to be normal morphologically, and a comparable amount of epithelial proliferation was evident. When transplanted into wild-type recipients, however, Tgfb1(-/-) epithelium showed accelerated invasion compared with Tgfb1(+/+) epithelium. This suggests that the normal rate of ductal extension in Tgfb1(-/-) null mutant mice is the net result of impaired endocrine or paracrine support acting to limit the consequences of unrestrained epithelial growth. By adulthood, mammary glands in cycling virgin Tgfb1(-/-) mice were morphologically similar to those in Tgfb1(+/+) and Tgfb1(+/-) animals, with a normal branching pattern, and the tissue differentiated into early alveolar structures in the diestrous phase of the ovarian cycle. Transplanted mammary gland epithelium showed a similar extent of ductal branching and evidence of secretory differentiation of luminal cells in pregnancy. These results reveal two opposing actions of TGFB1 during pubertal mammary gland morphogenesis: autocrine inhibition of epithelial ductal growth, and endocrine or paracrine stimulation of epithelial ductal growth.

Gene expression profiling distinguishes between spontaneous and radiation-induced rat mammary carcinomas

The ability to distinguish between spontaneous and radiation-induced cancers in humans is expected to improve the resolution of estimated risk from low dose radiation. Mammary carcinomas were obtained from Sprague-Dawley rats that were either untreated (n = 45) or acutely gamma-irradiated (1 Gy; n = 20) at seven weeks of age. Gene expression profiles of three spontaneous and four radiation-induced carcinomas, as well as those of normal mammary glands, were analyzed by microarrays. Differential expression of identified genes of interest was then verified by quantitative polymerase chain reaction (qPCR). Cluster analysis of global gene expression suggested that spontaneous carcinomas were distinguished from a heterogeneous population of radiation-induced carcinomas, though most gene expressions were common. We identified 50 genes that had different expression levels between spontaneous and radiogenic carcinomas. We then selected 18 genes for confirmation of the microarray data by qPCR analysis and obtained the following results: high expression of Plg, Pgr and Wnt4 was characteristic to all spontaneous carcinomas; Tnfsf11, Fgf10, Agtr1a, S100A9 and Pou3f3 showed high expression in a subset of radiation-induced carcinomas; and increased Gp2, Areg and Igf2 expression, as well as decreased expression of Ca3 and non-coding RNA Mg1, were common to all carcinomas. Thus, gene expression analysis distinguished between spontaneous and radiogenic carcinomas, suggesting possible differences in their carcinogenic mechanism.

Platelet-derived growth factor receptor regulates salivary gland morphogenesis via fibroblast growth factor expression

A coordinated reciprocal interaction between epithelium and mesenchyme is involved in salivary gland morphogenesis. The submandibular glands (SMGs) of Wnt1-Cre/R26R mice have been shown positive for mesenchyme, whereas the epithelium is beta-galactosidase-negative, indicating that most mesenchymal cells are derived from cranial neural crest cells. Platelet-derived growth factor (PDGF) receptor alpha is one of the markers of neural crest-derived cells. In this study, we analyzed the roles of PDGFs and their receptors in the morphogenesis of mouse SMGs. PDGF-A was shown to be expressed in SMG epithelium, whereas PDGF-B, PDGFRalpha, and PDGFRbeta were expressed in mesenchyme. Exogenous PDGF-AA and -BB in SMG organ cultures demonstrated increased levels of branching and epithelial proliferation, although their receptors were found to be expressed in mesenchyme. In contrast, short interfering RNA for Pdgfa and -b as well as neutralizing antibodies for PDGF-AB and -BB showed decreased branching. PDGF-AA induced the expression of the fibroblast growth factor genes Fgf3 and -7, and PDGF-BB induced the expression of Fgf1, -3, -7, and -10, whereas short interfering RNA for Pdgfa and Pdgfb inhibited the expression of Fgf3, -7, and -10, indicating that PDGFs regulate Fgf gene expression in SMG mesenchyme. The PDGF receptor inhibitor AG-17 inhibited PDGF-induced branching, whereas exogenous FGF7 and -10 fully recovered. Together, these results indicate that fibroblast growth factors function downstream of PDGF signaling, which regulates Fgf expression in neural crest-derived mesenchymal cells and SMG branching morphogenesis. Thus, PDGF signaling is a possible mechanism involved in the interaction between epithelial and neural crest-derived mesenchyme.

The ADAM17-amphiregulin-EGFR axis in mammary development and cancer

In order to fulfill its function of producing and delivering sufficient milk to newborn mammalian offspring, the mammary gland first has to form an extensive ductal network. As in all phases of mammary development, hormonal cues elicit local intra- and inter-cellular signaling cascades that regulate ductal growth and differentiation. Among other things, ductal development requires the epidermal growth factor receptor (EGFR), its ligand amphiregulin (AREG), and the transmembrane metalloproteinase ADAM17, which can cleave and release AREG from the cell surface so that it may interact with its receptor. Tissue recombination and transplantation studies demonstrate that EGFR phosphorylation and ductal development proceed only when ADAM17 and AREG are expressed on mammary epithelial cells and EGFR is present on stromal cells, and that local administration of soluble AREG can rescue the development of ADAM17-deficient transplants. Thus proper mammary morphogenesis requires the ADAM17-mediated release of AREG from ductal epithelial cells, the subsequent activation of EGFR on stromal cells, and EGFR-dependent stromal responses that in return elicit a new set of epithelial responses, all culminating in the formation of a fully functional ductal tree. This, however, raises new issues concerning what may act upstream, downstream or in parallel with the ADAM17-AREG-EGFR axis, how it may become hijacked or corrupted during the onset and evolution of cancer, and how such ill effects may be confronted.

Metastatic cancer cell

Metastasis is the result of cancer cell adaptation to a tissue microenvironment at a distance from the primary tumor. Metastatic cancer cells require properties that allow them not only to adapt to a foreign microenvironment but to subvert it in a way that is conducive to their continued proliferation and survival. Recent conceptual and technological advances have contributed to our understanding of the role of the host tissue stroma in promoting tumor cell growth and dissemination and have provided new insight into the genetic makeup of cancers with high metastatic proclivity.

Controlled microaspiration for high-pressure freezing: a new method for ultrastructural preservation of fragile and sparse tissues for TEM and electron tomography

High-pressure freezing is the preferred method to prepare thick biological specimens for ultrastructural studies. However, the advantages obtained by this method often prove unattainable for samples that are difficult to handle during the freezing and substitution protocols. Delicate and sparse samples are difficult to manipulate and maintain intact throughout the sequence of freezing, infiltration, embedding and final orientation for sectioning and subsequent transmission electron microscopy. An established approach to surmount these difficulties is the use of cellulose microdialysis tubing to transport the sample. With an inner diameter of 200 microm, the tubing protects small and fragile samples within the thickness constraints of high-pressure freezing, and the tube ends can be sealed to avoid loss of sample. Importantly, the transparency of the tubing allows optical study of the specimen at different steps in the process. Here, we describe the use of a micromanipulator and microinjection apparatus to handle and position delicate specimens within the tubing. We report two biologically significant examples that benefit from this approach, 3D cultures of mammary epithelial cells and cochlear outer hair cells. We illustrate the potential for correlative light and electron microscopy as well as electron tomography.

Progestin-regulated luminal cell and myoepithelial cell-specific responses in mammary organoid culture

Normal mammary gland development requires the coordinated proliferation and morphogenesis of both mammary luminal epithelial cells (LECs) and myoepithelial cells (MECs). Cell proliferation in cultured mammary organoids containing both LECs and MECs is not increased by progestin (R5020) or 17beta-estradiol (E2) alone or R5020+E2 but is increased by E2-regulated, mammary stroma-derived Hepatocyte growth factor (HGF) and further increased by HGF+R5020. We investigated the effects of HGF and/or R5020 on morphology and LEC- and MEC-specific in vitro proliferation in organoids. HGF-induced tubulogenesis was initiated and carried out by LECs starting with cellular extensions, followed by the formation of chains and cords, and culminating in tubule formation. MECs did not appear to have an active role in this process. Whereas HGF by itself caused maximal proliferation of LECs, HGF+R5020 produced a synergistic and specific increase in MEC proliferation. Because only LECs expressed progesterone receptors (PRs), we investigated the role of receptor activator of nuclear factor-kappaB ligand (RANKL), a progestin-induced paracrine factor, in mediating increased MEC proliferation. Quantitative RT-PCR showed that RANKL mRNA was induced by R5020 or HGF+R5020 and RANKL protein colocalized with PRs in LECs. The increased proliferation of MECs in response to HGF+R5020 could be blocked by neutralizing antibody to RANKL and reproduced by treatment with HGF plus exogenous RANKL in place of R5020. Neither R5020, nor exogenously administered RANKL increased proliferation of LECs. These results led us to conclude that RANKL, induced by progestin in PR-positive cells, is secreted and interacts with HGF to specifically increase proliferation of PR-negative MECs.

Ets-1 triggers and orchestrates the malignant phenotype of mammary cancer cells within their matrix environment

Acquisition of invasive characteristics is a hallmark of breast carcinoma progression. During this phenomenon, Ets-1 transcription factor overexpression is induced and associated with breast cancer invasiveness, and poor prognosis. We hypothesized that Ets-1 transcription factor could be the orchestrator of a genetic program inducing the expression of genes necessary for cell motility, as postulated by the tumor microenvironment invasion model. We aimed at elucidating the role of Ets-1 in the molecular control of mammary cancer cell invasion and aggressiveness within their matrix environment. To that purpose, mouse mammary tumor MMT epithelial cells were engineered to stably overexpress Ets-1, or the dominant negative Ets-1 DNA Binding domain. The biological function of Ets-1 was assessed in three-dimensional extracellular matrix systems recreating a microenvironmental architecture resembling in vivo geometric constraints. Ets-1 overexpression provided MMT cells with a motile and invasive phenotype, leading to cell scattering, and impairing multicellular organization in matrix-mimicking gels. We evidenced that Ets-1 promoted HGF/SF activation, and the expression of its receptor, c-Met. Ets-1 also orchestrated switches in integrin expression pattern, towards a pro-migratory and malignant phenotype. Moreover, Ets-1 concomitantly triggered matrix metalloproteinases (MMP) expression and activation, thus contributing to cell scattering. Functional relevance of these observations was confirmed with blocking antibodies or MMP inhibitors. Our data highlight a critical role for Ets-1 in the orchestration of a network of molecular and phenotypic events, converging to enhance malignant features and invasion by mammary cancer cells of their environment. Ets-1 overexpression hence appears as a probable key step for breast cancer progression.

Collective epithelial migration and cell rearrangements drive mammary branching morphogenesis

Epithelial organs are built through the movement of groups of interconnected cells. We observed cells in elongating mammary ducts reorganize into a multilayered epithelium, migrate collectively, and rearrange dynamically, all without forming leading cellular extensions. Duct initiation required proliferation, Rac, and myosin light-chain kinase, whereas repolarization to a bilayer depended on Rho kinase. We observed that branching morphogenesis results from the active motility of both luminal and myoepithelial cells. Luminal epithelial cells advanced collectively, whereas myoepithelial cells appeared to restrain elongating ducts. Significantly, we observed that normal epithelium and neoplastic hyperplasias are organized similarly, suggesting common mechanisms of epithelial growth.

Stem cells and breast cancer

Proliferation in continuously renewing tissues, including the mammary gland, is hierarchically organized with a small number of slowly dividing stem cells and a greater number of more rapidly proliferating 'transit amplifying' cells. Mammary stem cells have been recently identified and purified based on their surface antigen expression. The recognition of mammary epithelial stem cells had led to the hypothesis that these may be at the root of breast cancer. In support of this, a highly tumorigenic subpopulation of cancer cells - cancer stem cells - has recently been identified in primary and metastatic breast cancer samples and in a number of established breast cancer cell lines. The existence of cancer stem cells would explain why only a small minority of cancer cells is capable of extensive proliferation and transferral of the tumour. In this article we aim to review the evidence in support of the existence of both normal mammary stem cells and breast cancer stem cells, and provide further insight into how taking this subpopulation of cells into account may affect the way we treat epithelial cancers in the future.

The Triad of Idiopathic Normal-Pressure Hydrocephalus: A Clinical Practice Case Report

An 89-year-old white male presented with memory impairment, slowness in responsiveness, and frequent falls over a two-year duration. Six months earlier, the patient was believed to have had a “dementia with parkinsonian features,” but showed no response to incrementing doses of both donepezil and carbidopa-levodopa. Urinary urgency was believed to have been due to prostate hypertrophy. A head CT with contrast revealed moderate ventriculomegaly in the setting of mild diffuse cortical atrophy. A diagnosis of idiopathic normal-pressure hydrocephalus (INPH) was made.

PEGylated DX-1000: pharmacokinetics and antineoplastic activity of a specific plasmin inhibitor

Novel inhibitors of the urokinase-mediated plasminogen (plg) activation system are potentially of great clinical benefit as anticancer treatments. Using phage display, we identified DX-1000 a tissue factor pathway inhibitor-derived Kunitz domain protein which is a specific high-affinity inhibitor of plasmin (pln) (K(i) = 99 pM). When tested in vitro, DX-1000 blocks plasmin-mediated pro-matrix metalloproteinase-9 (proMMP-9) activation on cells and dose-dependently inhibits tube formation, while not significantly affecting hemostasis and coagulation. However, this low-molecular weight protein inhibitor ( approximately 7 kDa) exhibits rapid plasma clearance in mice and rabbits, limiting its potential clinical use in chronic diseases. After site-specific PEGylation, DX-1000 retains its activity and exhibits a decreased plasma clearance. This PEGylated derivative is effective in vitro, as well as potent in inhibiting tumor growth of green fluorescent protein (GFP)-labeled MDA-MB-231 cells. 4PEG-DX-1000 treatment causes a significant reduction of urokinase-type plasminogen activator (uPA) and plasminogen expressions, a reduction of tumor proliferation, and vascularization. 4PEG-DX-1000 treatment significantly decreases the level of active mitogen-activated protein kinase (MAPK) in the primary tumors and reduces metastasis incidence. Together, our results demonstrate the potential value of plasmin inhibitors as therapeutic agents for blocking breast cancer growth and metastasis.

Stem cells and the stem cell niche in the breast: an integrated hormonal and developmental perspective

The mammary gland is a unique organ in that it undergoes most of its development after birth under the control of systemic hormones. Whereas in most other organs stem cells divide in response to local stimuli, to replace lost cells, in the mammary gland large numbers of cells need to be generated at specific times during puberty, estrous cycles and pregnancy to generate new tissue structures. This puts special demands on the mammary stem cells and requires coordination of local events with systemic needs. Our aim is to understand how the female reproductive hormones control mammary gland development and influence tumorigenesis. We have shown that steroid hormones act in a paracrine fashion in the mammary gland delegating different functions to locally produced factors. These in turn, affect cell-cell interactions that result in changes of cell behavior required for morphogenesis and differentiation. Here, we discuss how these hormonally regulated paracrine interactions may impinge on stem cells and the stem cell niche and how this integration of signals adds extra levels of complexity to current mammary stem cell models. We propose a model whereby the stem cell niches change depending on the developmental stages and the hormonal milieu. According to this model, repeated hormone stimulation of stem cells and their niches in the course of menstrual cycles may be an important early event in breast carcinogenesis and may explain the conundrum why breast cancer risk increases with the number of menstrual cycles experienced prior to a first pregnancy.

Epimorphin, a morphogenic protein, induces proteases in rodent hepatocytes through NF-kappaB

BACKGROUND/AIMS

Epimorphin, expressed by hepatic stellate cells in the liver, directs normal morphogenesis in various organs. The aim of this study was to clarify the mechanism by which epimorphin functions as a morphogen in vitro.

METHODS

Male Balb/c mice and Sprague-Dawley rats were used. First, we explored the relationship between epimorphin expression and distribution of protease-positive cells in carbon tetrachloride-induced acute liver injury. We then examined protease levels in cultured hepatocytes and signal transduction of epimorphin. Finally, we determined the requirement for proteases and NF-kappaB in spheroid formation induced by epimorphin.

RESULTS

Epimorphin expression was enhanced in injured areas during late recovery phase, in which protease-positive hepatocytes were localized adjacent to epimorphin-expressing cells. In vitro, epimorphin induced matrix metalloproteinase (MMP) 9, MMP 3 and urokinase type plasminogen activator (uPA) in hepatocytes. NF-kappaB mediated these protease expressions in hepatocytes. These proteases were required for epimorphin-induced and Matrigel induced spheroid. An epimorphin-neutralizing antibody also blocked spheroid formation on Matrigel, which contained epimorphin. In addition, NF-kappaB activation was also required for spheroid formation.

CONCLUSION

Epimorphin elicits hepatocyte spheroids by inducing proteases in rodent hepatocytes through NF-kappaB.

Estrogen receptors: how do they signal and what are their targets

During the past decade there has been a substantial advance in our understanding of estrogen signaling both from a clinical as well as a preclinical perspective. Estrogen signaling is a balance between two opposing forces in the form of two distinct receptors (ER alpha and ER beta) and their splice variants. The prospect that these two pathways can be selectively stimulated or inhibited with subtype-selective drugs constitutes new and promising therapeutic opportunities in clinical areas as diverse as hormone replacement, autoimmune diseases, prostate and breast cancer, and depression. Molecular biological, biochemical, and structural studies have generated information which is invaluable for the development of more selective and effective ER ligands. We have also become aware that ERs do not function by themselves but require a number of coregulatory proteins whose cell-specific expression explains some of the distinct cellular actions of estrogen. Estrogen is an important morphogen, and many of its proliferative effects on the epithelial compartment of glands are mediated by growth factors secreted from the stromal compartment. Thus understanding the cross-talk between growth factor and estrogen signaling is essential for understanding both normal and malignant growth. In this review we focus on several of the interesting recent discoveries concerning estrogen receptors, on estrogen as a morphogen, and on the molecular mechanisms of anti-estrogen signaling.

The properties of a mammary gland cancer stem cell

The cancer stem cell hypothesis posits that tumors are derived from a single cancer-initiating cell with stem cell properties. The task of identifying and characterizing a single cancer-initiating cell with stem cell properties has proven technically difficult because of the scarcity of the cancer stem cells in the tissue of origin and the lack of specific markers for cancer stem cells. Here we show that a single LA7 cell derived from rat mammary adenocarcinoma has the following properties: the differentiation potential to generate all of the cell lineages of the mammary gland; the ability to generate branched duct-like structures that recapitulate morphologically and functionally the ductal-alveolar-like architecture of the mammary tree; and the capacity to initiate heterogeneous tumors in nonobese diabetic-SCID mice. In addition, we show that cultured cells derived from tumors generated by a single LA7 cell-injection have properties similar to LA7 cells, can generate all of the cell lineages of the mammary gland, and recapitulate the ductal-alveolar-like architecture of the mammary tree. The properties of self-renewal, extensive capacity for proliferation, multilineage differentiation potential, and single-cell tumor-initiation potential suggest that LA7 cells are cancer stem cells and can be used as a model system to study the dynamics of tumor formation at the single-cell level.

The MAPK(ERK-1,2) pathway integrates distinct and antagonistic signals from TGFalpha and FGF7 in morphogenesis of mouse mammary epithelium

Transforming growth factor-alpha (TGFalpha) and fibroblast growth factor-7 (FGF7) exhibit distinct expression patterns in the mammary gland. Both factors signal through mitogen-activated kinase/extracellular regulated kinase-1,2 (MAPK(ERK1,2)); however, their unique and/or combined contributions to mammary morphogenesis have not been examined. In ex vivo mammary explants, we show that a sustained activation of MAPK(ERK1,2) for 1 h, induced by TGFalpha, was necessary and sufficient to initiate branching morphogenesis, whereas a transient activation (15 min) of MAPK(ERK1,2), induced by FGF7, led to growth without branching. Unlike TGFalpha, FGF7 promoted sustained proliferation as well as ectopic localization of, and increase in, keratin-6 expressing cells. The response of the explants to FGF10 was similar to that to FGF7. Simultaneous stimulation by FGF7 and TGFalpha indicated that the FGF7-induced MAPK(ERK1,2) signaling and associated phenotypes were dominant: FGF7 may prevent branching by suppression of two necessary TGFalpha-induced morphogenetic effectors, matrix metalloproteinase-3 (MMP-3/stromelysin-1), and fibronectin. Our findings indicate that expression of morphogenetic effectors, proliferation, and cell-type decisions during mammary organoid morphogenesis are intimately dependent on the duration of activation of MAPK(ERK1,2) activation.

Morphogens, morphostats, microarchitecture and malignancy

Morphogenetic fields organize tissue morphology in the embryo. By analogy, morphostatic fields maintain normal cell behaviour and normal tissue microarchitecture in the adult. The most prominent feature of cancer is the disruption of tissue microarchitecture. Cancer occurs much more frequently when morphostatic influences fail (metaplasia) or at the junction of two different morphostatic fields. This Review will describe what we know about morphostats and morphostasis, discuss the evidence for the role of disruption of morphostasis in malignancy, and address some testable hypotheses.

Modeling mammary gland morphogenesis as a reaction-diffusion process

Mammary ducts are formed through a process of branching morphogenesis. We present results of experiments using a simulation model of this process, and discuss their implications for understanding mammary duct extension and bifurcation. The model is a cellular automaton approximation of a reaction-diffusion process in which matrix metalloproteinases represent the activator, inhibitors of matrix metalloproteinases represent the inhibitor, and growth factors serve as a substrate. We compare results from the simulation model with those from in-vivo experiments as part of an assessment of whether duct extension and bifurcation during morphogenesis may be a consequence of a reaction-diffusion mechanism mediated by MMPs and TIMPs.

FGF 10 and Sprouty 2 modulate trophoblast invasion and branching morphogenesis

Branching morphogenesis (BM) of the chorionic villous tree is a crucial component of early placental formation. Fibroblast growth factors (FGFs), their receptor tyrosine kinase (RTK) and negative regulators like Sprouty (Spry) proteins are pivotal factors in the development of diverse branching organ systems. The aim of this study was to examine the effect of FGF10 and Sprouty 2 on BM of the chorionic villi in vitro. Villous explants of first trimester placentas were cultured and their outgrowths were monitored. The effect of FGF10 was tested on matrigel migration/invasion assay, collagenolytic activity of single cell trophoblasts and on villous explants outgrowths. siRNA of Spry2 was used to reduce its expression and to investigate the role of Sprouty 2 in villous explants outgrowths. Quantitative RT-PCR and immunohistochemistry were performed to determine Sprouty 2 and HLA-G (a marker of invasion) expression. FGF 10 stimulated by 8-fold the migration/invasion of single cell trophoblast enhanced their collagenolytic activity. Reduction of Spry2 expression in villous explants showed a marked increase in villous outgrowths. This was accompanied by enhanced staining for HLA-G and by the reduction of Spry2 expression that was confirmed by immunohistochemistry and by quantitative RT-PCR. We conclude that trophoblast outgrowth and invasion (part of placental villi sprouting) at the fetal maternal interface is in part under delicate control of FGF 10 and Sprouty 2. FGF 10 promotes invasion and outgrowth of trophoblasts. In addition, it increases Spry2 expression, which attenuates trophoblast sprouting.

Expression and localization of extracellular matrix-degrading proteinases and their inhibitors in the bovine mammary gland during development, function, and involution

In degrading the extracellular matrix, matrix metalloproteinases (MMP) and the plasminogen activator (PA) system may play a critical role in extensive remodeling that occurs in the bovine mammary gland during development, lactation, and involution. Therefore, the aim of our study was to investigate the mRNA expression of MMP-1, MMP-2, MMP-14, MMP-19, tissue inhibitor of metalloproteinases (TIMP)-1, TIMP-2, urokinase-type PA, tissue-type PA, urokinase-type PA receptor, and PA inhibitor-1 by quantitative PCR and to localize with immunohistochemistry MMP-1, MMP-2, MMP-14, and TIMP-2 proteins in the bovine mammary gland during pubertal mammogenesis, lactogenesis, galactopoiesis, and involution. Expression of mRNA for each of the studied factors was relatively lower during galactopoiesis and early involution but was markedly increased during mammogenesis and late involution, 2 stages in which tissue remodeling is especially pronounced. The localization of proteins for MMP-1, MMP-14, and TIMP-2 showed a similar trend with strong staining intensity in cytoplasm of mammary duct and alveolar epithelial cells during pubertal mammogenesis and late involution. Interestingly, MMP-2 protein was localized only in the cytoplasm of endothelial cells during late involution. Our study demonstrated clearly that expression of extracellular matrix-degrading proteinases coincides with a concomitant expression of their inhibitors. High expression levels of MMP, TIMP, and PA family members seem to be a typical feature of the nonlactating mammary gland.

The EGF repeat and discoidin domain protein, SED1/MFG-E8, is required for mammary gland branching morphogenesis

SED1, also known as MFG-E8, is a secreted protein composed of two EGF repeats (the second of which contains an RGD motif) and two discoidin/Factor V/VIII C domains. SED1 is expressed by a wide range of cell types, where it participates in diverse cellular interactions, such as sperm binding to the egg coat and macrophage recognition of apoptotic lymphocytes. Although SED1 was originally identified as a milk protein, its function in the mammary gland remains unclear; suggested functions include inhibition of viral infection and clearance of apoptotic cells during mammary gland involution. We report here that SED1 has an unexpected obligatory role during mammary gland development. Unlike that seen in WT glands, SED1-null glands show severely reduced branching from epithelial ducts and from terminal end buds, which are thin and poorly developed. SED1 is expressed by both luminal and myoepithelial cells in the developing epithelial duct, and binds to alpha(v) integrin receptors on myoepithelial cells leading to MAPK activation and cell proliferation. The absence of SED1 leads to greatly reduced levels of activated MAPK and a concomitant reduction in cell proliferation and branching throughout the epithelial tree. These results suggest that SED1 contributes, at least partly, to the intercellular signaling between luminal and myoepithelial cells that is required for branching morphogenesis.

A transgenic model reveals important roles for the NF-kappa B alternative pathway (p100/p52) in mammary development and links to tumorigenesis

A regulated pattern of nuclear factor kappaB (NF-kappaB) activation is essential for normal development of the mammary gland. An increase in NF-kappaB activity has been implicated in breast cancer. We have generated a novel transgenic mouse model to investigate the role of the alternative NF-kappaB pathway in ductal development and identify possible mediators of tumorigenesis downstream of p100/p52. By overexpressing the NF-kappaB p100/p52 subunit in mammary epithelium using the beta-lactoglobulin milk protein promoter, we found that transgene expression resulted in increased overall NF-kappaB activity during late pregnancy. During pregnancy, p100/p52 expression resulted in delayed ductal development with impaired secondary branching and increased levels of Cyclin D1, matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9), and cyclo-oxygenase-2 (COX-2) in the mammary gland. After multiple pregnancies the p100 transgenics exhibited a ductal thickening accompanied by small hyperplastic foci. In tumors from mice expressing the polyoma middle T oncoprotein (PyVT) in the mammary gland, increased levels of p100/p52 were present at the time of tumor development. These results show that increased p100/p52 disrupts normal ductal development and provides insight into the mechanism by which this may contribute to human breast cancer.