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

Gene transcriptional networks integrate microenvironmental signals in human breast cancer

A significant amount of evidence shows that microenvironmental signals generated from extracellular matrix (ECM) molecules, soluble factors, and cell-cell adhesion complexes cooperate at the extra- and intracellular level. This synergetic action of microenvironmental cues is crucial for normal mammary gland development and breast malignancy. To explore how the microenvironmental genes coordinate in human breast cancer at the genome level, we have performed gene co-expression network analysis in three independent microarray datasets and identified two microenvironment networks in human breast cancer tissues. Network I represents crosstalk and cooperation of ECM microenvironment and soluble factors during breast malignancy. The correlated expression of cytokines, chemokines, and cell adhesion proteins in Network II implicates the coordinated action of these molecules in modulating the immune response in breast cancer tissues. These results suggest that microenvironmental cues are integrated with gene transcriptional networks to promote breast cancer development.

Recruitment of SWI/SNF complex is required for transcriptional activation of the SLC11A1 gene during macrophage differentiation of HL-60 cells

The solute carrier family 11 member 1 (SLC11A1) gene is strictly regulated and exclusively expressed in myeloid lineage cells. However, little is known about the transcriptional regulation of the SLC11A1 gene during myeloid development. In this study, we used HL-60 cells as a model to investigate the regulatory elements/factors involved in the transactivation of the SLC11A1 gene during phorbol 12-myristate 13-acetate (PMA)-induced macrophage differentiation of HL-60 cells. Promoter deletion analysis showed that a 7-base AP-1-like element (TGACTCT) was critical for the responsiveness of the SLC11A1 promoter to PMA. Stimulation by PMA induced the binding of ATF-3 and the recruitment of two components of the SWI/SNF complex, BRG1 and β-actin, to this element in an ATF-3-dependent manner. RNAi-mediated depletion of ATF-3 or BRG1 markedly decreased SLC11A1 gene expression and its promoter activity induced by PMA. Luciferase reporter experiments demonstrated that ATF-3 cooperated with BRG1 and β-actin to activate the SLC11A1 promoter. Furthermore, we showed that PMA can induce the proximal (GT/AC)(n) repeat sequence to convert to the Z-DNA structure in the SLC11A1 gene promoter, and depletion of BRG1 resulted in a significant decrease of Z-DNA formation. Our results demonstrated that recruitment of the SWI/SNF complex initiated Z-DNA formation and subsequently helped to transactivate the SLC11A1 gene.

Chromatin remodeling enzyme Brg1 is required for mouse lens fiber cell terminal differentiation and its denucleation

Background

Brahma-related gene 1 (Brg1, also known as Smarca4 and Snf2β) encodes an adenosine-5'-triphosphate (ATP)-dependent catalytical subunit of the (switch/sucrose nonfermentable) (SWI/SNF) chromatin remodeling complexes. SWI/SNF complexes are recruited to chromatin through multiple mechanisms, including specific DNA-binding factors (for example, heat shock transcription factor 4 (Hsf4) and paired box gene 6 (Pax6)), chromatin structural proteins (for example, high-mobility group A1 (HMGA1)) and/or acetylated core histones. Previous studies have shown that a single amino acid substitution (K798R) in the Brg1 ATPase domain acts via a dominant-negative (dn) mechanism. Genetic studies have demonstrated that Brg1 is an essential gene for early (that is, prior implantation) mouse embryonic development. Brg1 also controls neural stem cell maintenance, terminal differentiation of multiple cell lineages and organs including the T-cells, glial cells and limbs.

Results

To examine the roles of Brg1 in mouse lens development, a dnBrg1 transgenic construct was expressed using the lens-specific αA-crystallin promoter in postmitotic lens fiber cells. Morphological studies revealed abnormal lens fiber cell differentiation in transgenic lenses resulting in cataract. Electron microscopic studies showed abnormal lens suture formation and incomplete karyolysis (that is, denucleation) of lens fiber cells. To identify genes regulated by Brg1, RNA expression profiling was performed in embryonic day 15.5 (E15.5) wild-type and dnBrg1 transgenic lenses. In addition, comparisons between differentially expressed genes in dnBrg1 transgenic, Pax6 heterozygous and Hsf4 homozygous lenses identified multiple genes coregulated by Brg1, Hsf4 and Pax6. DNase IIβ, a key enzyme required for lens fiber cell denucleation, was found to be downregulated in each of the Pax6, Brg1 and Hsf4 model systems. Lens-specific deletion of Brg1 using conditional gene targeting demonstrated that Brg1 was required for lens fiber cell differentiation, for expression of DNase IIβ, for lens fiber cell denucleation and indirectly for retinal development.

Conclusions

These studies demonstrate a cell-autonomous role for Brg1 in lens fiber cell terminal differentiation and identified DNase IIβ as a potential direct target of SWI/SNF complexes. Brg1 is directly or indirectly involved in processes that degrade lens fiber cell chromatin. The presence of nuclei and other organelles generates scattered light incompatible with the optical requirements for the lens.

Laminin regulates PI3K basal localization and activation to sustain STAT5 activation

Extracellular matrix (ECM) is a key regulator of tissue morphogenesis and functional differentiation in the mammary gland. We showed recently that laminin-111 (LN1) together with prolactin induces β-casein expression in mammary epithelial cells (MECs) by sustaining STAT5 activation. Others have shown that Rac1 is required for integrin-mediated STAT5 activation, but molecules upstream of Rac1 remain to be elucidated. Here, we show that exposure to three-dimensional (3D) laminin-rich ECM (LrECM) gels changes the localization of phosphoinositide 3-kinase (PI3K) in MECs from diffuse to basal accompanied with the activation of PI3K-Rac1 signaling pathway. We show by co-immunoprecipitation that Rac1 associates with STAT5, and that LrECM treatment enhances this interaction. Blocking PI3K with LY294002 inhibits LrECM-dependent Rac1 activation, attenuates sustained STAT5 phosphorylation and blocks β-casein gene transcription. These results indicate that PI3K is a key mediator of the LN1-induced signaling cascade which controls the activity of transcription factors essential for tissue-specific gene expression.

The contribution of adhesion signaling to lactogenesis

The mammary gland undergoes hormonally controlled cycles of pubertal maturation, pregnancy, lactation, and involution, and these processes rely on complex signaling mechanisms, many of which are controlled by cell-cell and cell-matrix adhesion. The adhesion of epithelial cells to the extracellular matrix initiates signaling mechanisms that have an impact on cell proliferation, survival, and differentiation throughout lactation. The control of integrin expression on the mammary epithelial cells, the composition of the extracellular matrix and the presence of secreted matricellular proteins all contribute to essential adhesion signaling during lactogenesis. In vitro and in vivo studies, including the results from genetically engineered mice, have shed light on the regulation of these processes at the cell and tissue level and have led to increased understanding of the essential signaling components that are regulated in temporal and cell specific manner during lactogenesis. Recent studies suggest that a secreted matricellular protein, CTGF/CCN2, may play a role in lactogenic differentiation through binding to β1 integrin complexes, enhancing the production of extracellular matrix components and contributions to cell adhesion signaling.

Physico-mechanical aspects of extracellular matrix influences on tumorigenic behaviors

Tumor progression in vitro has traditionally been studied in the context of two-dimensional (2D) environments. However, it is now well accepted that 2D substrates are unnaturally rigid compared to the physiological substrate known as extracellular matrix (ECM) that is in direct contact with both normal and tumorigenic cells in vivo. Hence, the patterns of interactions, as well as the strategies used by cells in order to penetrate the ECM, and migrate through a three-dimensional (3D) environment are notoriously different than those observed in 2D. Several substrates, such as collagen I, laminin, or complex mixtures of ECM components have been used as surrogates of native 3D ECM to more accurately study cancer cell behaviors. In addition, 3D matrices developed from normal or tumor-associated fibroblasts have been produced to recapitulate the mesenchymal 3D environment that assorted cells encounter in vivo. Some of these substrates are being used to evaluate physico-mechanical effects on tumor cell behavior. Physiological 3D ECMs exhibit a wide range of rigidities amongst different tissues while the degree of stromal stiffness is known to change during tumorigenesis. In this review we describe some of the physico-mechanical characteristics of tumor-associated ECMs believed to play important roles in regulating epithelial tumorigenic behaviors.

Connective Tissue Growth Factor (CTGF/CCN2) enhances lactogenic differentiation of mammary epithelial cells via integrin-mediated cell adhesion

Background

Connective Tissue Growth Factor (CTGF/CCN2), a known matrix-associated protein, is required for the lactogenic differentiation of mouse mammary epithelial cells. An HC11 mammary epithelial cell line expressing CTGF/CCN2 was constructed to dissect the cellular responses to CTGF/CCN2 that contribute to this differentiation program.

Results

Tetracycline-regulated expression of CTGF/CCN2 in HC11 cells enhanced multiple markers of lactogenic differentiation including β-casein transcription and mammosphere formation. In a separate measure of mammary differentiation the addition of CTGF/CCN2 to cultures of MCF10A cells increased the development of acini in vitro. In HC11 cells the elevated levels of CTGF/CCN2 diminished the requirement for extracellular matrix proteins in the activation of β-casein transcription, indicating that CTGF/CCN2 contributed to lactogenic differentiation through the regulation of matrix dependent cell adhesion. CTGF/CCN2 expression in HC11 cells increased expression of extracellular matrix proteins and integrins, enhanced the formation of focal adhesion complexes, and increased survival signaling. In addition, HC11 cells adhered to immobilized CTGF/CCN2 and this was inhibited by function-blocking antibodies to the integrins α6 and β1, and to a lesser degree by antibody to β3 integrin.

Conclusions

CTGF/CCN2 expression in HC11 cells led to an increase in multiple markers of lactogenic differentiation. The mechanisms by which CTGF/CCN2 contributed to lactogenic differentiation include direct binding of CTGF/CCN2 to integrin complexes and CTGF/CCN2-induced matrix protein expression resulting in elevated integrin functionality.

Intracardiac injection of matrigel induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Matrigel promotes angiogenesis in the myocardium from ischemic injury and prevents remodelling of the left ventricle. We assessed the therapeutic efficacy of intracardiac matrigel injection and matrigel-mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, matrigel (250 μl) or phosphate-buffered solution (PBS) was delivered by intracardiac injection. Compared to the MI control group (MI-PBS), matrigel significantly improved left ventricular function (n= 11, P < 0.05) assessed by pressure–volume loops after 4 weeks. There is no significant difference in infarct size between MI-matrigel (MI-M; 21.48 ± 1.49%, n= 10) and MI-PBS hearts (20.98 ± 1.25%, n= 10). The infarct wall thickness of left ventricle is significantly higher (P < 0.01) in MI-M (0.72 ± 0.02 mm, n= 10) compared with MI-PBS (0.62 ± 0.02 mm, n= 10). MI-M hearts exhibited higher capillary density (border 130.8 ± 4.7 versus 115.4 ± 6.0, P < 0.05; vessels per high-power field [HPF; 400×], n= 6) than MI-PBS hearts. c-Kit⁺ stem cells (38.3 ± 5.3 versus 25.7 ± 1.5 c-Kit⁺ cells per HPF [630×], n= 5, P < 0.05) and CD34⁺ cells (13.0 ± 1.51 versus 5.6 ± 0.68 CD34⁺ cells per HPF [630×], n= 5, P < 0.01) were significantly more numerous in MI-M than in MI-PBS in the infarcted hearts (n= 5, P < 0.05). Intracardiac matrigel injection restores myocardial functions following MI, which may attribute to the improved recruitment of CD34⁺ and c-Kit⁺ stem cells.

Epigenetic modifications in 3D: nuclear organization of the differentiating mammary epithelial cell

During the development of tissues, complex programs take place to reach terminally differentiated states with specific gene expression profiles. Epigenetic regulations such as histone modifications and chromatin condensation have been implicated in the short and long-term control of transcription. It has recently been shown that the 3D spatial organization of chromosomes in the nucleus also plays a role in genome function. Indeed, the eukaryotic interphase nucleus contains sub-domains that are characterized by their enrichment in specific factors such as RNA Polymerase II, splicing machineries or heterochromatin proteins which render portions of the genome differentially permissive to gene expression. The positioning of individual genes relative to these sub-domains is thought to participate in the control of gene expression as an epigenetic mechanism acting in the nuclear space. Here, we review what is known about the sub-nuclear organization of mammary epithelial cells in connection with gene expression and epigenetics. Throughout differentiation, global changes in nuclear architecture occur, notably with respect to heterochromatin distribution. The positions of mammary-specific genes relative to nuclear sub-compartments varies in response to hormonal stimulation. The contribution of tissue architecture to cell differentiation in the mammary gland is also seen at the level of nuclear organization, which is sensitive to microenvironmental stimuli such as extracellular matrix signaling. In addition, alterations in nuclear organization are concomitant with immortalization and carcinogenesis. Thus, the fate of cells appears to be controlled by complex pathways connecting external signal integration, gene expression, epigenetic modifications and chromatin organization in the nucleus.

The epigenetic landscape of mammary gland development and functional differentiation

Most of the development and functional differentiation in the mammary gland occur after birth. Epigenetics is defined as the stable alterations in gene expression potential that arise during development and proliferation. Epigenetic changes are mediated at the biochemical level by the chromatin conformation initiated by DNA methylation, histone variants, post-translational modifications of histones, non-histone chromatin proteins, and non-coding RNAs. Epigenetics plays a key role in development. However, very little is known about its role in the developing mammary gland or how it might integrate the many signalling pathways involved in mammary gland development and function that have been discovered during the past few decades. An inverse relationship between marks of closed (DNA methylation) or open chromatin (DnaseI hypersensitivity, certain histone modifications) and milk protein gene expression has been documented. Recent studies have shown that during development and functional differentiation, both global and local chromatin changes occur. Locally, chromatin at distal regulatory elements and promoters of milk protein genes gains a more open conformation. Furthermore, changes occur both in looping between regulatory elements and attachment to nuclear matrix. These changes are induced by developmental signals and environmental conditions. Additionally, distinct epigenetic patterns have been identified in mammary gland stem and progenitor cell sub-populations. Together, these findings suggest that epigenetics plays a role in mammary development and function. With the new tools for epigenomics developed in recent years, we now can begin to establish a framework for the role of epigenetics in mammary gland development and disease.

Gene expression in the third dimension: the ECM-nucleus connection

Decades ago, we and others proposed that the dynamic interplay between a cell and its surrounding environment dictates cell phenotype and tissue structure. Whereas much has been discovered about the effects of extracellular matrix molecules on cell growth and tissue-specific gene expression, the nuclear mechanisms through which these molecules promote these physiological events remain unknown. Using mammary epithelial cells as a model, the purpose of this review is to discuss how the extracellular matrix influences nuclear structure and function in a three-dimensional context to promote epithelial morphogenesis and function in the mammary gland.

Nonlinear modelling of cancer: bridging the gap between cells and tumours

Despite major scientific, medical and technological advances over the last few decades, a cure for cancer remains elusive. The disease initiation is complex, and including initiation and avascular growth, onset of hypoxia and acidosis due to accumulation of cells beyond normal physiological conditions, inducement of angiogenesis from the surrounding vasculature, tumour vascularization and further growth, and invasion of surrounding tissue and metastasis. Although the focus historically has been to study these events through experimental and clinical observations, mathematical modelling and simulation that enable analysis at multiple time and spatial scales have also complemented these efforts. Here, we provide an overview of this multiscale modelling focusing on the growth phase of tumours and bypassing the initial stage of tumourigenesis. While we briefly review discrete modelling, our focus is on the continuum approach. We limit the scope further by considering models of tumour progression that do not distinguish tumour cells by their age. We also do not consider immune system interactions nor do we describe models of therapy. We do discuss hybrid-modelling frameworks, where the tumour tissue is modelled using both discrete (cell-scale) and continuum (tumour-scale) elements, thus connecting the micrometre to the centimetre tumour scale. We review recent examples that incorporate experimental data into model parameters. We show that recent mathematical modelling predicts that transport limitations of cell nutrients, oxygen and growth factors may result in cell death that leads to morphological instability, providing a mechanism for invasion via tumour fingering and fragmentation. These conditions induce selection pressure for cell survivability, and may lead to additional genetic mutations. Mathematical modelling further shows that parameters that control the tumour mass shape also control its ability to invade. Thus, tumour morphology may serve as a predictor of invasiveness and treatment prognosis.

Tissue architecture and function: dynamic reciprocity via extra- and intra-cellular matrices

Mammary gland development, functional differentiation, and homeostasis are orchestrated and sustained by a balance of biochemical and biophysical cues from the organ's microenvironment. The three-dimensional microenvironment of the mammary gland, predominantly 'encoded' by a collaboration between the extracellular matrix (ECM), hormones, and growth factors, sends signals from ECM receptors through the cytoskeletal intracellular matrix to nuclear and chromatin structures resulting in gene expression; the ECM in turn is regulated and remodeled by signals from the nucleus. In this chapter, we discuss how coordinated ECM deposition and remodeling is necessary for mammary gland development, how the ECM provides structural and biochemical cues necessary for tissue-specific function, and the role of the cytoskeleton in mediating the extra--to intracellular dialogue occurring between the nucleus and the microenvironment. When operating normally, the cytoskeletal-mediated dynamic and reciprocal integration of tissue architecture and function directs mammary gland development, tissue polarity, and ultimately, tissue-specific gene expression. Cancer occurs when these dynamic interactions go awry for an extended time.

Lactogenic hormonal induction of long distance interactions between beta-casein gene regulatory elements

Lactogenic hormone regulation of beta-casein gene expression in mammary epithelial cells provides an excellent model in which to study the mechanisms by which steroid and peptide hormone signaling control gene expression. Prolactin- and glucocorticoid-mediated induction of beta-casein gene expression involves two principal regulatory regions, a proximal promoter and a distal enhancer located in the mouse approximately -6 kb upstream of the transcription start site. Using a chromosome conformation capture assay and quantitative real time PCR, we demonstrate that a chromatin loop is created in conjunction with the recruitment of specific transcription factors and p300 in HC11 mammary epithelial cells. Stimulation with both prolactin and hydrocortisone is required for the induction of these long range interactions between the promoter and enhancer, and no DNA looping was observed in nontreated cells or cells treated with each of the hormones separately. The lactogenic hormone-induced interaction between the proximal promoter and distal enhancer was confirmed in hormone-treated primary three-dimensional mammary acini cultures. In addition, the developmental regulation of DNA looping between the beta-casein regulatory regions was observed in lactating but not in virgin mouse mammary glands. Furthermore, beta-casein mRNA induction and long range interactions between these regulatory regions were inhibited in a progestin-dependent manner following stimulation with prolactin and hydrocortisone in HC11 cells expressing human PR-B. Collectively, these data suggest that the communication between these regulatory regions with intervening DNA looping is a crucial step required to both create and maintain active chromatin domains and regulate transcription.

The morphologies of breast cancer cell lines in three-dimensional assays correlate with their profiles of gene expression

3D cell cultures are rapidly becoming the method of choice for the physiologically relevant modeling of many aspects of non-malignant and malignant cell behavior ex vivo. Nevertheless, only a limited number of distinct cell types have been evaluated in this assay to date. Here we report the first large scale comparison of the transcriptional profiles and 3D cell culture phenotypes of a substantial panel of human breast cancer cell lines. Each cell line adopts a colony morphology of one of four main classes in 3D culture. These morphologies reflect, at least in part, the underlying gene expression profile and protein expression patterns of the cell lines, and distinct morphologies were also associated with tumor cell invasiveness and with cell lines originating from metastases. We further demonstrate that consistent differences in genes encoding signal transduction proteins emerge when even tumor cells are cultured in 3D microenvironments.

Activation and repression domains within the promoter of the rat cathepsin L gene orchestrate sertoli cell-specific and stage-specific gene transcription in transgenic mice

In murine testes, only Sertoli cells express the cathepsin L (Ctsl) gene, and this expression is restricted to stages V-VIII of the cycle. Our previous transgenic analysis of Tg (-2065/+977) demonstrated that this expression is regulated by a approximately 2-kb promoter. To begin to elucidate this regulation, we analyzed the in vivo expression of two new transgenes, Tg (-935/+977) and Tg (-451/+977). Tg (-935/+977) was expressed by Sertoli cells but, in contrast to Tg (-2065/+977), was expressed at all stages of the cycle, by spermatocytes, by the vascular endothelium, and by seven other organs. Tg (-451/+977) was not expressed by Sertoli cells but by spermatogenic cells and by the brain. Lack of expression of Tg (-451/+977) by Sertoli cells was not due to a lack of essential cis-acting elements. Transient transfection analysis of primary cultures of mature rat Sertoli cells demonstrated that in mature Sertoli cells, most of the activity of the Ctsl promoter is accounted for by one of two redundant upstream GC motifs and an Initiator that are within 100 bp of the transcription start site. We conclude that transcriptional repressors upstream from nucleotide -935 of the rat Ctsl gene restrict testicular expression of this gene to Sertoli cells at stages V-VIII. At these stages, transcriptional activators located between nucleotides -935 and -452 promote access of the transcriptional machinery to the two GC boxes and to the Initiator. Thus, upstream repressors and activators as well as cis-acting elements near the transcription start site control stage-specific Ctsl transcription by Sertoli cells.

Differentiation of monkey embryonic stem cells into hepatocytes and mRNA expression of cytochrome p450 enzymes responsible for drug metabolism: comparison of embryoid body formation conditions and matrices

We investigated the effects of embryoid body (EB) forming conditions on the expression of hepatocyte marker genes such as alpha-fetoprotein, albumin and CYP7A1 in cells cultured on Matrigel-coated plates for 15 d. The expression levels of hepatocyte marker genes in the cells cultured for 2 d for EB formation from cynomolgus monkey embryonic stem (cmES) cells was higher than those in cells cultured for 5 d. However, the fragment-size of cmES colonies did not markedly affect the expression levels. The expression levels of hepatocyte marker genes, and CYP1A1 and CYP2C43 in cells cultured on Matrigel were considerably higher than those on Matrigel reduced and collagen I. CYP1A1 and CYP3A8 mRNAs were significantly induced by 3-methylcholanthrene and rifampicin, respectively. However, CYP2C43 and CYP2D17 were not induced by these compounds. These results suggested that the differentiation into hepatocytes is affected by the incubation period for EB formation, and that Matrigel successfully promoted in vitro differentiation of cmES cells to hepatocytes.

Contributions of extracellular matrix signaling and tissue architecture to nuclear mechanisms and spatial organization of gene expression control

Post-translational modification of histones, ATP-dependent chromatin remodeling, and DNA methylation are interconnected nuclear mechanisms that ultimately lead to the changes in chromatin structure necessary to carry out epigenetic gene expression control. Tissue differentiation is characterized by a specific gene expression profile in association with the acquisition of a defined tissue architecture and function. Elements critical for tissue differentiation, like extracellular stimuli, adhesion and cell shape properties, and transcription factors all contribute to the modulation of gene expression and thus, are likely to impinge on the nuclear mechanisms of epigenetic gene expression control. In this review, we analyze how these elements modify chromatin structure in a hierarchical manner by acting on the nuclear machinery. We discuss how mechanotransduction via the structural continuum of the cell and biochemical signaling to the cell nucleus integrate to provide a comprehensive control of gene expression. The role of nuclear organization in this control is highlighted, with a presentation of differentiation-induced nuclear structure and the concept of nuclear organization as a modulator of the response to incoming signals.

Calcitonin, a regulator of the 25-hydroxyvitamin D3 1alpha-hydroxylase gene

Although parathyroid hormone (PTH) induces 25-hydroxyvitamin D(3) (25(OH)D(3)) 1alpha-hydroxylase (1alpha(OH)ase) under hypocalcemic conditions, previous studies showed that calcitonin, not PTH, has an important role in the maintenance of serum 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) under normocalcemic conditions. In this study we report that 1alpha(OH)ase transcription is strongly induced by calcitonin in kidney cells and indicate mechanisms that underlie this regulation. The transcription factor C/EBPbeta is up-regulated by calcitonin in kidney cells and results in a significant enhancement of calcitonin induction of 1alpha(OH)ase transcription and protein expression. Mutation constructs of the 1alpha(OH)ase promoter demonstrate the importance of the C/EBPbeta binding site at -79/-73 for activation of the 1alpha(OH)ase promoter by calcitonin. The SWI/SNF chromatin remodeling complex was found to cooperate with calcitonin in the regulation of 1alpha(OH)ase. Chromatin immunoprecipitation analysis showed that calcitonin recruits C/EBPbeta to the 1alpha(OH)ase promoter, and Re-chromatin immunoprecipitation analysis (sequential chromatin immunoprecipitations using different antibodies) showed that C/EBPbeta and BRG1, an ATPase that is a component of the SWI/SNF complex, bind simultaneously to the 1alpha(OH)ase promoter. These findings are the first to address the dynamics between calcitonin, C/EBPbeta, and SWI/SNF in the regulation of 1alpha(OH)ase and provide a mechanism, for the first time, for calcitonin induction of 1alpha(OH)ase. Because plasma calcitonin as well as 1,25(OH)(2)D(3) have been reported to be increased during pregnancy and lactation and in early development, these findings suggest a mechanism that may account, at least in part, for the increase in plasma 1,25(OH)(2)D(3) during these times of increased calcium requirement.

Sustained activation of STAT5 is essential for chromatin remodeling and maintenance of mammary-specific function

Epithelial cells, once dissociated and placed in two-dimensional (2D) cultures, rapidly lose tissue-specific functions. We showed previously that in addition to prolactin, signaling by laminin-111 was necessary to restore functional differentiation of mammary epithelia. Here, we elucidate two additional aspects of laminin-111 action. We show that in 2D cultures, the prolactin receptor is basolaterally localized and physically segregated from its apically placed ligand. Detachment of the cells exposes the receptor to ligation by prolactin leading to signal transducers and activators of transcription protein 5 (STAT5) activation, but only transiently and not sufficiently for induction of milk protein expression. We show that laminin-111 reorganizes mammary cells into polarized acini, allowing both the exposure of the prolactin receptor and sustained activation of STAT5. The use of constitutively active STAT5 constructs showed that the latter is necessary and sufficient for chromatin reorganization and β-casein transcription. These results underscore the crucial role of continuous laminin signaling and polarized tissue architecture in maintenance of transcription factor activation, chromatin organization, and tissue-specific gene expression.

The MAPK signaling cascade is a central hub in the regulation of cell cycle, apoptosis and cytoskeleton remodeling by tripeptidyl-peptidase II

Tripeptidyl-peptidase II (TPPII) is a serine peptidase highly expressed in malignant Burkitt's lymphoma cells (BL). We have previously shown that overexpression of TPPII correlates with chromosomal instability, centrosomal and mitotic spindle abnormalities and resistance to apoptosis induced by spindle poisons. Furthermore, TPPII knockdown by RNAi was associated with endoreplication and the accumulation of polynucleated cells that failed to complete cell division, indicating a role of TPPII in the cell cycle. Here we have applied a global approach of gene expression analysis to gain insights on the mechanism by which TPPII regulates this phenotype. mRNA profiling of control and TPPII knockdown BL cells identified one hundred and eighty five differentially expressed genes. Functional categorization of these genes highlighted major physiological functions such as apoptosis, cell cycle progression, cytoskeleton remodeling, proteolysis, and signal transduction. Pathways and protein interactome analysis revealed a significant enrichment in components of MAP kinases signaling. These findings suggest that TPPII influences a wide network of signaling pathways that are regulated by MAPKs and exerts thereby a pleiotropic effect on biological processes associated with cell survival, proliferation and genomic instability.

The nuclear localization of WAP and CSN genes is modified by lactogenic hormones in HC11 cells

Whey acidic protein (WAP) and casein (CSN) genes are among the most highly expressed milk protein genes in the mammary gland of the lactating mouse. Their tissue-specific regulation depends on the activation and recruitment of transcription factors, and chromatin modifications in response to hormonal stimulation. We have investigated if another mechanism, such as specific positioning of the genes in the nucleus, could be involved in their functional regulation. Fluorescent in situ hybridization was used to study the nuclear localization of WAP and CSN genes in mouse mammary epithelial cells (HC11) cultured in the absence and presence of lactogenic hormones. Automatic 3D image processing and analysis tools were developed to score gene positions. In the absence of lactogenic hormones, both genes are distributed non-uniformly within the nucleus: the CSN locus was located close to the nuclear periphery and the WAP gene tended to be central. Stimulation by lactogenic hormones induced a statistically significant change to their distance from the periphery, which has been described as a repressive compartment. The detection of genes in combination with the corresponding chromosome-specific probe revealed that the CSN locus is relocated outside its chromosome territory following hormonal stimulation, whereas the WAP gene, which is already sited more frequently outside its chromosome territory in the absence of hormones, is not affected. We conclude that milk protein genes are subject to nuclear repositioning when activated, in agreement with a role for nuclear architecture in gene regulation, but that they behave differently as a function of their chromosomal context.

Laminin and biomimetic extracellular elasticity enhance functional differentiation in mammary epithelia

In the mammary gland, epithelial cells are embedded in a ‘soft' environment and become functionally differentiated in culture when exposed to a laminin-rich extracellular matrix gel. Here, we define the processes by which mammary epithelial cells integrate biochemical and mechanical extracellular cues to maintain their differentiated phenotype. We used single cells cultured on top of gels in conditions permissive for β-casein expression using atomic force microscopy to measure the elasticity of the cells and their underlying substrata. We found that maintenance of β-casein expression required both laminin signalling and a ‘soft' extracellular matrix, as is the case in normal tissues in vivo, and biomimetic intracellular elasticity, as is the case in primary mammary epithelial organoids. Conversely, two hallmarks of breast cancer development, stiffening of the extracellular matrix and loss of laminin signalling, led to the loss of β-casein expression and non-biomimetic intracellular elasticity. Our data indicate that tissue-specific gene expression is controlled by both the tissues' unique biochemical milieu and mechanical properties, processes involved in maintenance of tissue integrity and protection against tumorigenesis.

Peroxisome proliferator-activated receptor-gamma regulates the expression of alveolar macrophage macrophage colony-stimulating factor

Macrophage CSF (M-CSF) regulates monocyte differentiation, activation, and foam cell formation. We have observed that it is elevated in human pulmonary alveolar proteinosis (PAP) and in the GM-CSF knockout mouse, a murine model for PAP. A potential regulator of M-CSF, peroxisome proliferator-activated receptor-gamma (PPARgamma), is severely deficient in both human PAP and the GM-CSF knockout mouse. To investigate the role of PPARgamma in alveolar macrophage homeostasis, we generated myeloid-specific PPARgamma knockout mice using the Lys-Cre method to knock out the floxed PPARgamma gene. Similar to the GM-CSF-deficient mouse, absence of alveolar macrophage PPARgamma resulted in development of lung pathology resembling PAP in 16-wk-old mice, along with excess M-CSF gene expression and secretion. In ex vivo wild-type alveolar macrophages, we observed that M-CSF itself is capable of inducing foam cell formation similar to that seen in PAP. Overexpression of PPARgamma prevented LPS-stimulated M-CSF production in RAW 264.7 cells, an effect that was abrogated by a specific PPARgamma antagonist, GW9662. Use of proteasome inhibitor, MG-132 or a PPARgamma agonist, pioglitazone, prevented LPS-mediated M-CSF induction. Using chromatin immunoprecipitation, we found that PPARgamma is capable of regulating M-CSF through transrepression of NF-kappaB binding at the promoter. Gel-shift assay experiments confirmed that pioglitazone is capable of blocking NF-kappaB binding. Taken together, these data suggest that M-CSF is an important mediator of alveolar macrophage homeostasis, and that transcriptional control of M-CSF production is regulated by NF-kappaB and PPARgamma.

Janus-kinase-3-dependent signals induce chromatin remodeling at the Ifng locus during T helper 1 cell differentiation

Differentiation of naive CD4+ T cells into T helper type 1 (Th1) effector cells requires both T cell receptor (TCR) signaling and cytokines such as interleukin-12 and interferon gamma (IFN-gamma). Here, we report that a third cytokine signal, mediated by the Janus family tyrosine kinase 3 (Jak3) and signal transducer and activator of transcription 5 (STAT5) pathway, is also required for Th1 cell differentiation. In the absence of Jak3-dependent signals, naive CD4+ T cells proliferate robustly but produce little IFN-gamma after Th1 cell polarization in vitro. This defect is not due to reduced activation of STAT1 or STAT4 or to impaired upregulation of the transcription factor T-bet. Instead, we find that T-bet binding to the Ifng promoter is greatly diminished in the absence of Jak3-dependent signals, correlating with a decrease in Ifng promoter accessibility and histone acetylation. These data indicate that Jak3 regulates epigenetic modification and chromatin remodeling of the Ifng locus during Th1 cell differentiation.

Paradigm-shifters: phosphorylated prolactin and short prolactin receptors

Since the discovery of physiologically-regulated prolactin (PRL) phosphorylation, one focus of the laboratory has been an examination of the different functions of the unmodified and phosphorylated hormone. In the mammary gland, unmodified PRL promotes growth activities, whereas phosphorylated or pseudophosphorylated PRL antagonizes this while also being a superior agonist for changes that favor differentiation. Phosphorylated PRL also increases expression of the short forms of the PRL receptor. These short forms of the receptor have functions beyond the accepted dominant negative and in mammary epithelial cells are capable of generating an intracellular signal leading to increased tight junction formation and beta-casein expression.

Physical and functional interactions between STAT5 and Runx transcription factors

The signal transducers and activators of transcription (STAT) and the Runt-related (Runx) are two of major transcription factor families that play essential roles in lymphocyte development. Although the interaction of Runx2 with STAT1 and STAT3 has been reported before, the interaction between STAT5 and Runx family proteins has not been characterized. In this study, we first showed that STAT5 physically interacts with Runx1, Runx2 and Runx3 by co-immunoprecipitation experiments. The Runt domain of Runx proteins and the DNA-binding domain and alpha-helix loop structure of STAT5 are responsible for the interaction. When expressed in CHO cells, STAT5 inhibits the nuclear localization of Runx proteins and retains them in the cytoplasm. In addition, we showed by reporter assay that the interaction between STAT5 and Runx proteins mutually inhibits their transcriptional activity. Furthermore, Runx proteins inhibit the DNA-binding activity of STAT5. Finally, we found that Runx proteins suppress the transcription of an endogenous STAT5 target gene, cytokine-inducible SH2 protein-1, in an interleukin-3-dependent pro-B cell line, Ba/F3. These results collectively suggested that STAT5 and Runx proteins physically and functionally interact to mutually inhibit their transcriptional activity. Thus, this study implies a potential role of the STAT5-Runx interaction in lymphocyte development.

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.

Cell shape regulates global histone acetylation in human mammary epithelial cells

Extracellular matrix (ECM) regulates cell morphology and gene expression in vivo; these relationships are maintained in three-dimensional (3D) cultures of mammary epithelial cells. In the presence of laminin-rich ECM (lrECM), mammary epithelial cells round up and undergo global histone deacetylation, a process critical for their functional differentiation. However, it remains unclear whether lrECM-dependent cell rounding and global histone deacetylation are indeed part of a common physical-biochemical pathway. Using 3D cultures as well as nonadhesive and micropatterned substrata, here we showed that the cell 'rounding' caused by lrECM was sufficient to induce deacetylation of histones H3 and H4 in the absence of biochemical cues. Microarray and confocal analysis demonstrated that this deacetylation in 3D culture is associated with a global increase in chromatin condensation and a reduction in gene expression. Whereas cells cultured on plastic substrata formed prominent stress fibers, cells grown in 3D lrECM or on micropatterns lacked these structures. Disruption of the actin cytoskeleton with cytochalasin D phenocopied the lrECM-induced cell rounding and histone deacetylation. These results reveal a novel link between ECM-controlled cell shape and chromatin structure and suggest that this link is mediated by changes in the actin cytoskeleton.