A novel regulatory mechanism for whey acidic protein gene expression

Misregulation of stromelysin-1 expression in mouse mammary tumor cells accompanies acquisition of stromelysin-1-dependent invasive properties

Stromelysin-1 is a member of the metalloproteinase family of extracellular matrix-degrading enzymes that regulates tissue remodeling. We previously established a transgenic mouse model in which rat stromelysin-1 targeted to the mammary gland augmented expression of endogenous stromelysin-1, disrupted functional differentiation, and induced mammary tumors. A cell line generated from an adenocarcinoma in one of these animals and a previously described mammary tumor cell line generated in culture readily invaded both a reconstituted basement membrane and type I collagen gels, whereas a nonmalignant, functionally normal epithelial cell line did not. Invasion of Matrigel by tumor cells was largely abolished by metalloproteinase inhibitors, but not by inhibitors of other proteinase families. Inhibition experiments with antisense oligodeoxynucleotides revealed that Matrigel invasion of both cell lines was critically dependent on stromelysin-1 expression. Invasion of collagen, on the other hand, was reduced by only 40-50%. Stromelysin-1 was expressed in both malignant and nonmalignant cells grown on plastic substrata. Its expression was completely inhibited in nonmalignant cells, but up-regulated in tumor cells, in response to Matrigel. Thus misregulation of stromelysin-1 expression appears to be an important aspect of mammary tumor cell progression to an invasive phenotype.

Mammary gland morphogenesis is inhibited in transgenic mice that overexpress cell surface beta1,4-galactosyltransferase

Mammary gland morphogenesis is facilitated by a precise sequence of cell-cell and cell-matrix interactions, which are mediated in part through a variety of cell surface receptors and their ligands (Boudreau, N., Myers, C. and Bissell, M. J. (1995). Trends in Cell Biology 5, 1–4). Cell surface beta1,4-galactosyltransferase (GalTase) is one receptor that participates in a variety of cell-cell and cell-matrix interactions during fertilization and development, including mammary epithelial cell-matrix interactions (Barcellos-Hoff, M. H. (1992). Exp. Cell Res. 201, 225–234). To analyze GalTase function during mammary gland morphogenesis in vivo, we created transgenic animals that overexpress the long isoform of GalTase under the control of a heterologous promoter. As expected, mammary epithelial cells from transgenic animals had 2.3 times more GalTase activity on their cell surface than did wild-type cells. Homozygous transgenic females from multiple independent lines failed to lactate, whereas transgenic mice overexpressing the Golgi-localized short isoform of GalTase lactated normally. Glands from transgenic females overexpressing surface GalTase were characterized by abnormal and reduced ductal development with a concomitant reduction in alveolar expansion during pregnancy. The phenotype was not due to a defect in proliferation, since the mitotic index for transgenic and wild-type glands was similar. Morphological changes were accompanied by a dramatic reduction in the expression of milk-specific proteins. Immunohistochemical markers for epithelia and myoepithelia demonstrated that both cell types were present. To better understand how overexpression of surface GalTase impairs ductal morphogenesis, primary mammary epithelial cultures were established on basement membranes. Cultures derived from transgenic mammary glands were unable to form anastomosing networks of epithelial cells and failed to express milk-specific proteins, unlike wild-type mammary cultures that formed epithelial tubules and expressed milk proteins. Our results suggest that cell surface GalTase is an important mediator of mammary cell interaction with the extracellular matrix. Furthermore, perturbing surface GalTase levels inhibits the expression of mammary-specific gene products, implicating GalTase as a component of a receptor-mediated signal transduction pathway required for normal mammary gland differentiation.

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

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

Three-dimensional mammary primary culture model systems

Model systems have been developed to investigate the complex and coordinated regulation of mammary gland development and transformation. Primary cultures, using newly isolated cells or tissue, are optimal for such studies since, in comparison to immortalized cell lines, the normal signal transduction pathways are presumed to be intact. Three such models are described, including whole organ culture, mammary epithelial cell (MEC) organoids, and MEC-stromal cocultures. Studies using whole-organ culture have the advantage that the normal glandular architecture remains intact, the MEC can undergo lobuloalveolar development and express milk proteins in a hormone dependent manner, and, following hormonal withdrawal, undergo involution. Moreover, transformation of the MEC is readily accomplished. Culture of isolated MEC organoids within an EHS-derived reconstituted basement membrane permits extensive proliferation, branching end bud and alveolar morphogenesis, and accumulation of milk protein and lipid in a physiologically relevant hormone- and growth factor-dependent manner. This model can thus be utilized to investigate the mechanism by which various modulators exert their direct effects on the epithelium. Finally, in view of compelling evidence for stromal-epithelial interactions during normal mammary gland development, and potentially also during the development of malignancy, models in which MEC can be cocultured with enriched populations of stroma offer considerable potential as a tool to understand the nature and mechanisms of the interactions that occur during the various developmental states, and how such interactions may go awry during carcinogenesis.

Extracellular matrix signaling from the cellular membrane skeleton to the nuclear skeleton: a model of gene regulation

It is well established that cells must interact with their microenvironment and that such interaction is crucial for coordinated function and homeostasis. However, how cells receive and integrate external signals leading to gene regulation is far from understood. It is now appreciated that two classes of cooperative signals are implicated: a soluble class including hormones and growth factors and a class of insoluble signals emanating from the extracellular matrix (ECM) directly through contact with the cell surface. Using 3-dimensional culture systems and transgenic mice, we have been able to identify some of the elements of this ECM-signaling pathway responsible for gene regulation in rodent mammary gland differentiation and involution. Our major observations are 1) the requirement for a laminin-rich basement membrane; 2) the existence of a cooperative signaling pathway between basement membrane and the lactogenic hormone prolactin (PRL);3) the importance of beta 1-integrins and bHLH transcription factor(s) and the presence of DNA response elements (exemplified by BCE-1, located on a milk protein gene, beta-casein); and 4) the induction of mammary epithelial cell programmed cell death following degradation of basement membrane. We hypothesize that this cooperative signaling between ECM and PRL may be achieved through integrin- and laminin-directed restructuring of the cytoskeleton leading to profound changes in nuclear architecture and transcription factor localization. We postulate that the latter changes allow the prolactin signal to activate transcription of the beta-casein gene. To further understand the molecular mechanisms underlying ECM and hormonal cooperative signaling, we are currently investigating ECM regulation of a "solid-state" signaling pathway including ECM fiber proteins, plasma membrane receptors, cytoskeleton, nuclear matrix and chromatin. We further postulate that disruption of such a pathway may be implicated in cell disorders including transformation and carcinogenesis.

A hierarchy of ECM-mediated signalling regulates tissue-specific gene expression

A dynamic and reciprocal flow of information between cells and the extracellular matrix contributes significantly to the regulation of form and function in developing systems. Signals generated by the extracellular matrix do not act in isolation. Instead, they are processed within the context of global signalling hierarchies whose constituent inputs and outputs are constantly modulated by all the factors present in the cell's surrounding microenvironment. This is particularly evident in the mammary gland, where the construction and subsequent destruction of such a hierarchy regulates changes in tissue-specific gene expression, morphogenesis and apoptosis during each developmental cycle of pregnancy, lactation and involution.

Mammary epithelial cells undergo secretory differentiation in cycling virgins but require pregnancy for the establishment of terminal differentiation

Postnatal development of the mammary gland begins during puberty with ductal proliferation and is completed at delivery with the appearance of secretory alveolar structures. Using endogenous milk protein genes and a WAP-lacZ reporter transgene, we show that the differentiation of alveolar cells is initiated in virgin mice in estrus in a limited number of cells. With the onset of pregnancy, the number of expressing cells and the cellular expression levels increase until full activity is reached at lactation. Milk protein genes are activated in a defined temporal sequence. WDNM1 and beta-casein are expressed early in pregnancy and increase during alveolar proliferation. WAP (whey acidic protein) and alpha-lactalbumin are expressed later near the end of gestation, which is characterized by terminal differentiation of the mammary secretory phenotype. By in situ hybridization, we have established evidence for asynchrony in milk protein gene expression among alveolar cells showing large variations in the intensity of hybridization among adjacent cells. The asynchrony of maturation of epithelial cells within a given alveolus suggests that the genetic program leading to terminal differentiation is subject to local modulation. It is likely that these signals are manifest through various pathways including growth factors, the extracellular matrix or gene products specific to terminal differentiation such as WAP. We extended our analyses to WAP/WAP transgenic mice in which WAP is synthesized precociously and functional differentiation of alveolar cells is impaired. We found an altered expression pattern of milk protein genes, with a strong reduction of alpha-lactalbumin RNA. We conclude that the early production of WAP in WAP/WAP mammary glands disrupts the timing of gene activation leading to a premature termination of the differentiative program.

Dynamic reciprocity revisited: a continuous, bidirectional flow of information between cells and the extracellular matrix regulates mammary epithelial cell function

Interactions between cells and the extracellular matrix (ECM) generate two classes of signals, mechanical and biochemical. In the case of the mammary epithelial cell, both are required to initiate ECM-dependent expression of the abundant milk protein beta-casein. Mechanical signals induce a cellular rounding, while functional biochemical signals are associated with an increase in tyrosine phosphorylation. These individual components are part of a complex signalling hierarchy that leads to the emergence of the fully functional lactational phenotype. Interestingly, both the assembly and disassembly of this hierarchy, which occur cyclically in vivo, are constantly modulated by dynamic and reciprocal interactions that take place within a functional unit composed of both the cell and the ECM.

Position-independent expression of whey acidic protein transgenes

The expression of a 3-kilobase genomic rat whey acidic protein (WAP) clone (-949/+2020) in transgenic mice has been demonstrated previously to be copy number-dependent and independent of the site of integration (Dale, T., Krnacik, M. J., Schmidhauser, C., Yang, C. Q.-L., Bissell, M. J., and Rosen, J. M. (1992) Mol. Cell. Biol. 12, 905-914). The present study demonstrated that position-independent expression of the rat WAP -949/+2020 transgene was dependent on transgene spacing. Position-independent expression also was inhibited by an internal replacement of 49 base pair within the conserved GC-rich 3'-untranslated region (3'-UTR) with an identically sized nonspecific DNA sequence. Using electrophoretic mobility shift assays, nuclear factors isolated from mouse and human cells were shown to associate specifically with the rWAP 3'-UTR DNA, but not with the 3'-UTR containing the internal replacement or specific point mutations. Since a single copy of the 3'-UTR inserted 5' of the promoter could not rescue the 3'-UTR deletion, the 3'-UTR element does not appear to be functioning as either a classic enhancer or insulator element. However, the level of expression of rWAP transgenes was correlated with transgene association with the chromosomal scaffold in vivo.

Extracellular matrix regulates whey acidic protein gene expression by suppression of TGF-alpha in mouse mammary epithelial cells: studies in culture and in transgenic mice

Whey acidic protein (WAP) is an abundant rodent milk protein. Its expression in mouse mammary epithelial cell cultures was previously found to require the formation of an extracellular matrix (ECM)-induced three-dimensional alveolar structure. In the absence of such structures, cells were shown to secrete diffusible factors leading to suppression of WAP expression. We demonstrate here that (a) TGF-alpha production and secretion by mammary cells is downregulated by the basement membrane-dependent alveolar structure, and (b) compared with beta-casein, WAP expression is preferentially inhibited both in culture and in transgenic mice when TGF-alpha is added or overexpressed. Thus, (c) the enhanced TGF-alpha production when cells are not in three-dimensional structures largely accounts for the WAP-inhibitory activity found in the conditioned medium. Since this activity can be abolished by incubating the conditioned medium with a function blocking antibody to TGF-alpha. The data suggest that ECM upregulates WAP by downregulating TGF-alpha production. We also propose that changes in TGF-alpha activity during mouse gestation and lactation could contribute to the pattern of temporal expression of WAP in the gland. These results provide a clear example of cooperation among lactogenic hormones, ECM, and locally acting growth factors in regulation of tissue-specific gene expression.

Cellular growth and survival are mediated by beta 1 integrins in normal human breast epithelium but not in breast carcinoma

We previously established a rapid three-dimensional assay for discrimination of normal and malignant human breast epithelial cells using a laminin-rich reconstituted basement membrane. In this assay, normal epithelial cells differentiate into well-organized acinar structures whereas tumor cells fail to recapitulate this process and produce large, disordered colonies. The data suggest that breast acinar morphogenesis and differentiation is regulated by cell-extra-cellular matrix (ECM) interactions and that these interactions are altered in malignancy. Here, we investigated the role of ECM receptors (integrins) in these processes and report on the expression and function of potential laminin receptors in normal and tumorigenic breast epithelial cells. Immunocytochemical analysis showed that normal and carcinoma cells in a three-dimensional substratum express profiles of integrins similar to normal and malignant breast tissues in situ. Normal cells express alpha 1, alpha 2, alpha 3, alpha 6, beta 1 and beta 4 integrin subunits, whereas breast carcinoma cells show variable losses, disordered expression, or downregulation of these subunits. Function-blocking experiments using inhibitory anti-integrin subunit antibodies showed a > 5-fold inhibition of the formation of acinar structures by normal cells in the presence of either anti-beta 1 or anti-alpha 3 antibodies, whereas anti-alpha 2 or -alpha 6 had little or no effect. In experiments where collagen type I gels were used instead of basement membrane, acinar morphogenesis was blocked by anti-beta 1 and -alpha 2 antibodies but not by anti-alpha 3. These data suggest a specificity of integrin utilization dependent on the ECM ligands encountered by the cell. The interruption of normal acinar morphogenesis by anti-integrin antibodies was associated with an inhibition of cell growth and induction of apoptosis. Function-blocking antibodies had no inhibitory effect on the rate of tumor cell growth, survival or capacity to form colonies. Thus under our culture conditions breast acinar formation is at least a two-step process involving beta 1-integrin-dependent cellular growth followed by polarization of the cells into organized structures. The regulation of this pathway appears to be impaired or lost in the tumor cells, suggesting that tumor colony formation occurs by independent mechanisms and that loss of proper integrin-mediated cell-ECM interaction may be critical to breast tumor formation.

Nuclear factor I and mammary gland factor (STAT5) play a critical role in regulating rat whey acidic protein gene expression in transgenic mice

The rat whey acidic protein (WAP) gene contains a mammary gland-specific and hormonally regulated DNase I-hypersensitive site 830 to 720 bp 5' to the site of transcription initiation. We have reported previously that nuclear factor I (NFI) binding at a palindromic site and binding at a half-site are the major DNA-protein interactions detected within this tissue-specific nuclease-hypersensitive region. We now show that point mutations introduced into these NFI-binding sites dramatically affect WAP gene expression in transgenic mice. Transgene expression was totally abrogated when the palindromic NFI site or both binding sites were mutated, suggesting that NFI is a key regulator of WAP gene expression. In addition, a recognition site for mammary gland factor (STAT5), which mediates prolactin induction of milk protein gene expression, was also identified immediately proximal to the NFI-binding sites. Mutation of this site reduced transgene expression by approximately 90% per gene copy, but did not alter tissue specificity. These results suggest that regulation of WAP gene expression is determined by the cooperative interactions among several enhancers that constitute a composite response element.

Extracellular matrix induces hormone responsiveness and differentiation in RUCA-I rat endometrial adenocarcinoma cells

We recently described the establishment and the characterization of two rat endometrial adenocarcinoma cell lines which we called RUCA-I and RUCA-II. Despite fairly high estrogen receptor levels neither cell line responded to estradiol in conventional cell culture conditions on plastic and in the presence of serum. A limited hormonal response to the antiestrogen tamoxifen was detectable in RUCA-I but not in RUCA-II cells. To advance our cell culture conditions we plated RUCA-I cells on a layer of reconstituted basement membrane (Harbor Matrix) in the presence of a serum-free defined medium. These cell culture conditions induced hormone responsiveness of RUCA-I cells and permitted a stimulation of proliferation by estradiol. Further, two estradiol-induced secretory proteins with an apparent molecular weight of 115 kD and 60 kD could be identified by SDS-gelelectrophoresis if analyzed under reducing conditions. These proteins migrated as a single band in a non-reducing electrophoresis gel and were identified as components of the complement C3 system. Additionally, our results suggest that the effects of extracellular matrix and hormones on the expression of these proteins are additive. We conclude that processes of functional differentiation are most likely to occur in this in vitro model, particularly since the expression of components of the complement C3 system was under estrogenic control. Complement C3 proteins represent major estradiol-inducible secretory protein of the immature rat uterus in vivo. Culturing RUCA-I cells on top of a layer of reconstituted basement membrane provides a novel tool to study the importance of the extracellular environment on the hormone-induced gene expression in endometrial carcinogenesis in vitro.

Alterations in gene expression associated with changes in the state of endothelial differentiation

The endothelium maintains a developmental plasticity which allows rapid phenotypic change in response to extracellular signals during normal processes, such as corpus luteum formation and wound healing, and in pathologic processes, such as tumor angiogenesis. Endothelial cells (EC) in culture have been very useful for investigating various aspects of endothelial growth and behavior. In spite of documented similarities between EC in vitro and the endothelium in vivo, many characteristics of the vessel endothelium are lost when the cells are placed into culture. We have undertaken to identify differences in gene expression between differentiated vessel endothelium and dedifferentiated EC. We utilized a new technique called differential display which compares polymerase chain reaction (PCR)-amplified mRNA from two (or more) cell populations. Endothelium scraped directly from freshly obtained aortas, and demonstrated to be free of contaminants, were used as the source of differentiated RNA, whereas proliferating, primary explanted EC grown for five days in the presence of basic fibroblast growth factor (bFGF) provided a pool of 'dedifferentiated' RNA. Using differential display, we have observed numerous reproducible differences in gene expression. To confirm that the expression differences visualized by differential display represented actual differences in gene expression, we isolated vessel-specific and culture-specific cDNA tags for additional analysis. Three cDNA tags specific to vessel endothelium were cloned and sequenced, and compared to nucleotide and protein databases. Two of the clones (A1 and 2.5) displayed no significant sequence similarity, whereas a third clone (A2) is nearly identical to a human expressed sequence tag (EST) and has significant sequence similarities to a plant and Xenopus ubiquitin-like protein. Northern and/or in situ hybridization analysis of the A1 and A2 genes confirmed their restricted expression to the vessel endothelium. The expression of A1 by the endothelium in vivo is not simply a function of growth state, as cultured cells did not express A1 even when grown to postconfluence. One other cDNA fragment, selected as a culture-induced gene, was identified by sequence analysis as the bovine homologue of laminin B1, and Northern analysis confirmed that expression was induced upon culturing of EC. Use of differential display to study endothelial gene expression will allow us to investigate the molecular mechanisms that underlie initiation and maintenance of endothelial differentiation.

Tenascin-C inhibits extracellular matrix-dependent gene expression in mammary epithelial cells. Localization of active regions using recombinant tenascin fragments

The physiological role of tenascin in vivo has remained obscure. Although tenascin is regulated in a stage and tissue-dependent manner, knock-out mice appear normal. When tenascin expression was examined in the normal adult mouse mammary gland, little or none was present during lactation, when epithelial cells actively synthesize and secrete milk proteins in an extracellular matrix/lactogenic hormone-dependent manner. In contrast, tenascin was prominently expressed during involution, a stage characterized by the degradation of the extracellular matrix and the subsequent loss of milk production. Studies with mammary cell lines indicated that tenascin expression was high on plastic, but was suppressed in the presence of the laminin-rich, Engelbreth-Holm-Swarm (EHS) tumour biomatrix. When exogenous tenascin was added together with EHS to mammary epithelial cells, beta-casein protein synthesis and steady-state mRNA levels were inhibited in a concentration-dependent manner. Moreover, this inhibition by tenascin could be segregated from its effects on cell morphology. Using two beta-casein promoter constructs attached to the chloramphenicol acetyltransferase reporter gene we showed that tenascin selectively suppressed extracellular matrix/prolactin-dependent transcription of the beta-casein gene in three-dimensional cultures. Finally, we mapped the active regions within the fibronectin type III repeat region of the tenascin molecule that are capable of inhibiting beta-casein protein synthesis. Our data are consistent with a model where both the loss of a laminin-rich basement membrane by extracellular matrix-degrading enzymes and the induction of tenascin contribute to the loss of tissue-specific gene expression and thus the involuting process.

Extracellular matrix-dependent tissue-specific gene expression in mammary epithelial cells requires both physical and biochemical signal transduction

Extracellular matrix (ECM) profoundly influences the growth and differentiation of the mammary gland epithelium, both in culture and in vivo. Utilizing a clonal population of mouse mammary epithelial cells that absolutely requires an exogenous ECM for function, we developed a rapid assay to study signal transduction by ECM. Two components of the cellular response to a basement membrane overlay that result in the expression of the milk protein beta-casein were defined. The first component of this response involves a rounding and clustering of the cells that can be physically mimicked by plating the cells on a nonadhesive substratum. The second component is biochemical in nature, and it is associated with beta 1 integrin clustering and increased tyrosine phosphorylation. The second component is initiated in a morphology-independent manner, but the proper translation of this biochemical signal into a functional response requires cell rounding and cell clustering. Thus, physical and biochemical signal transduction events contribute to the ECM-dependent regulation of tissue-specific gene expression in mouse mammary epithelial cells.

Negative regulatory element in the mammary specific whey acidic protein promoter

Expression of the whey acidic protein (WAP) gene is tightly regulated in a tissue and developmental stage specific manner, in that the WAP gene is exclusively expressed in the mammary gland during pregnancy and lactation. Using both deletion and competition analyses, evidence is provided for the existence of a negative regulatory element (NRE) in the WAP promoter located between -413 and -93 with respect to the WAP transcriptional initiation site. This NRE dramatically decreases transcription from linked heterologous promoter-reporter gene constructs. The activity of NRE requires WAP promoter sequences that are 230 bp apart since subfragments of the NRE fail to inhibit transcription of adjoining reporter genes. Nuclear extracts from different cell types, in which the WAP gene is not active, contain a protein or complex that specifically interacts with the entire NRE but not with subfragments of it. The contact points between this protein (NRE binding factor [NBF]) and the NRE element have been partially determined. Mutation of the implicated nucleotides severely reduces the ability of NBF to bind, and such mutated promoter fragments fail to alleviate transcriptional repression in competition experiments. This suggests that NBF binding to the NRE is at least in part responsible for the negative regulation of the WAP promoter. Since NBF is not detectable in the lactating mammary gland, where the WAP gene is expressed, we speculate that it may be a determinant of the expression spectrum of the WAP gene.

Transcriptional activation by viral enhancers: critical dependence on extracellular matrix-cell interactions in mammary epithelial cells

Extracellular matrix (ECM)-cell interactions are essential for the regulation of many genes in differentiated cell types. A number of expression vectors that work well in cells cultured on tissue-culture plastic appear to be inactive or sporadically active in vivo. We reasoned that these responses also may be influenced by the ECM. We therefore examined three commonly used viral enhancers and found that they all responded either positively or negatively to the presence of exogenous ECM. Using mouse mammary epithelial cells, we found that a mouse mammary tumor virus enhancer linked to its own promoter or to a truncated (and by itself inactive) beta-casein promoter drove transcription efficiently only when the cells were in contact with an ECM (more than a 100-fold induction over tissue-culture plastic). Similarly, the cytomegalovirus enhancer was more active in cells in contact with ECM. In contrast, the simian virus 40 enhancer, linked to the beta-casein promoter, was 12-fold more active in cells on tissue-culture plastic. This activity was strongly reduced when the cells interacted with ECM. Thus, we conclude that different enhancers can respond to ECM by either activating or suppressing transcription. This observation has important implications for understanding the mechanisms of promoter action and for designing expression systems for use in gene therapy.

High level production of human growth hormone in the milk of transgenic mice: the upstream region of the rabbit whey acidic protein (WAP) gene targets transgene expression to the mammary gland

The 5' flanking region (6.3 kb) of the rabbit WAP (rWAP) gene possesses important regulatory elements. This region was linked to the human growth hormone (hGH) structural gene in order to target transgene expression to the mammary gland. Thirteen lines of transgenic mice were produced. Milk could be collected from six lines of transgenic mice. In five of them, hGH was present in the milk at high concentrations ranging from 4 to 22 mg ml-1. hGH produced by the mammary gland comigrated with hGH of human origin. It was biologically active, and through its prolactin-like activity induced lactogenesis when introduced into mammary culture media. Two of these mouse lines were studied further. hGH mRNA was only detected in the mammary gland during lactation. In the seven other transgenic lines, hGH was present in the blood of cyclic females. The prolactin-like effect of hGH in these mice probably induced female sterility, and milk could therefore not be obtained. In two lines studied in more detail, the mammary gland was the main organ producing hGH, even in cyclic mice. Low ectopic expression was detected in other organs which varied from one line to the other. This was probably due to the influence on the transgene of the site of integration into the mouse genome. In the 13 lines studied, high mammary-specific hGH expression was not correlated to the transgene copy number. The rWAP-hGH construct thus did not behave as an independent unit of transcription. However, it can be concluded that the 6.3 kb flanking region of the rWAP gene contains regulatory elements responsible for the strong mammary-specific expression of hGH transgene, and that it is a good candidate to control high levels of foreign protein gene expression in the mammary gland of lactating transgenic animals.

Extracellular matrix-dependent differentiation of rabbit tracheal epithelial cells in primary culture

The differentiation of tracheal epithelial cells in primary culture was investigated according to the nature of the extracellular matrix used. Cultures obtained by the explant technique were realized on a type I collagen substratum either as a thin, dried coating or as a thick, hydrated gel supplemented with culture medium and serum. These two types of substratum induced distinct cell morphology and cytokeratin expression in the explant derived cells. Where cells are less proliferating (from Day 7 to 10 of culture), differentiation was evaluated by morphologic ultrastructural observations, immunocytochemical detection of cytokeratins, and determination of cytokeratin pattern by biochemical analysis. The epithelium obtained on gel was multilayered, with small, round basal cells under large, flattened upper cells. The determination of the keratin pattern expressed by cells grown on gel revealed an expression of keratin 13, already considered as a specific marker of squamous metaplasia, that diminished with retinoic acid treatment. Present results demonstrated by confocal microscopy that K13-positive cells were large upper cells with a dense keratin network, whereas lower cells were positively stained with a specific monoclonal antibody to basal cells (KB37). Moreover, keratin neosynthesis analysis pointed out a higher expression of K6, a marker of hyperproliferation, on gel than on coating. All these data suggest a differentiation of rabbit tracheal epithelial cells grown on gel toward squamous metaplasia. By contrast, the epithelium observed on coating is nearly a monolayer of very large and spread out cells. No K13-positive cells were observed, but an increase in the synthesis of simple epithelium marker (K18) was detected. These two substrata, similar in composition and different in structure, induce separate differentiation and appear as good tools to explore the mechanisms of differentiation of epithelial tracheal cells.

Production of interleukin-6 and interleukin-8 by human mammary gland epithelial cells

The production of transforming growth factor-beta 2 (TGF-beta 2), interleukin-1 beta (IL-1 beta), IL-6, IL-8, and tumor necrosis factor-alpha (TNF-alpha) by spontaneously immortalized human mammary gland epithelial cells of non-malignant origin and the effect of prolactin upon the production of those cytokines were investigated. Cells were cultured on plastic with epithelial growth factor, insulin, and hydrocortisone. Cytokines were quantified by enzyme-immunoassays. The cells produced IL-6 and IL-8, but no detectable TGF-beta 2, IL-1 beta, or TNF-alpha. Although prolactin enhanced the uptake of [3H]thymidine, it did not alter the production of cytokines/interleukins. Because of the marked production of IL-8 by mammary epithelium and a past report of TGF activity in human milk, those agents were quantified in human milk. The mean +/- S.D. concentrations of IL-8 and TGF-beta 2 in human milk obtained in the first 3 days of lactation were 3684 +/- 2910 and 130 +/- 108 pg/ml, respectively. Thus, IL-8 and TGF-beta 2 are normal constituents in human milk, and human mammary gland epithelium may be responsible for producing some of the IL-6 and IL-8 in human milk.

Morphological and functional differentiation of cryopreserved lactating bovine mammary cells cultured on floating collagen gels

Cryopreserved bovine mammary epithelial cells prepared from lactating mammary tissue synthesize and secrete the milk proteins alpha s1-casein, lactoferrin (Lf), and alpha-lactalbumin during in vitro culture on collagen gels in serum-free medium. Each milk protein is differently regulated by detachment and thickness of the collagen substratum, fetal calf serum, and prolactin in the medium. Collagen detachment did not modulate lactoferrin secretion but strongly induced casein secretion, with detachment on day 6 (after formation of cell sheets) inducing casein secretion to 3 micrograms/ml medium, which was 2-3-fold higher than for cells on collagen detached on day 2 (prior to cell spreading to form sheets), and ten-fold higher than for cells grown on collagen not detached. Alpha-lactalbumin secretion was also induced, but only to low levels, in cells grown on detached but not on attached collagen. Cells grown on thin collagen gels secreted lower levels of lactoferrin and casein compared to cells on thick collagen. Lactoferrin but not casein secretion was increased in cells grown in the presence of fetal calf serum. Casein but not lactoferrin secretion was completely dependent on prolactin. Cells grown serum-free on collagen gels detached on day 6 of culture showed a polarized epithelial cell layer with high differentiation evidenced by the apical microvilli, tight junctions, and fat droplets surrounded by casein-containing secretory vesicles. An underlying layer of myoepithelial-like cells was also evident. These studies show for cryopreserved primary bovine mammary cells prepared from lactating mammary tissue the induction of highly differentiated and polarized cell morphology and ultrastructure with concomitant induction of the secretion of casein, lactoferrin, and alpha-lactalbumin in vitro, and that the non-coordinate regulation of milk protein secretion by substratum, prolactin, and serum likely involves alternate routing and control of secretion pathways for casein and lactoferrin.

Structure and function of milk protein genes

Interspecies comparisons of cDNA and mosaic milk protein genes have confirmed their high rate of evolution, but the overall gene organization has been conserved. The three Ca-sensitive casein genes, which share common motifs in the promoter region and contain similar sequences that encode signal peptide and multiple phosphorylation sites, probably derived from a common ancestor. alpha s1- and alpha s2-casein genes, divided into many small exons, undergo complex splicing, and the deleted caseins arise from exon skipping. The four bovine casein genes are clustered on 200 kb of chromosome 6. alpha-Lactalbumin and beta-lactoglobulin pseudogenes occur in ruminants. Study of the expression of native and modified milk protein genes in mammary cell lines and transgenic animals and DNA footprinting have shown the occurrence of important regulatory motifs in the proximal 5' flanking region, including one recognized by a specific mammary nuclear factor. Good stage- and tissue-specific expression has been obtained in transgenic animals with milk protein genes having less than a 3-kb 5' flanking region. Better knowledge of both the structure and function of milk protein genes, which has already allowed the use of powerful techniques for the rapid identification of alleles, offers the potential for the genetic modification of milk composition.

Extracellular matrix regulates expression of the TGF-beta 1 gene

Transforming growth factor-beta (TGF-beta) is a potent regulator of cell proliferation and modulates the interactions of cells with their extracellular matrix (ECM), in part by inducing the synthesis of various ECM proteins. Three different isoforms of TGF-beta are synthesized in a defined pattern in specific cell populations in vivo. In the specific case of TGF-beta 1, this well-defined and limited expression stands in sharp contrast to its synthesis by virtually all cells in culture. Using mammary epithelial cells as a model system, we evaluated the substratum dependence of the expression of TGF-beta 1. The level of TGF-beta 1 expression is high in cells on plastic, but is strongly downregulated when cells are cultured on a reconstituted basement membrane matrix. In contrast, TGF-beta 2 mRNA levels in cells on either substratum remain unchanged. Using the chloramphenicol acetyl transferase gene as reporter gene under the control of the TGF-beta 1 promoter, we show that transcription from this promoter is suppressed when the cells are in contact with either endogenously synthesized or exogenously administered basement membrane. TGF-beta 1 promoter activity is strongly induced by the absence of basement membrane, i.e., by direct contact of the cells with plastic. This modulation of transcription from the TGF-beta 1 promoter occurs in the absence of lactogenic hormones which allow full differentiation. Our results thus indicate that basement membrane is an important regulator of TGF-beta 1 synthesis, and explain why most cells in culture on plastic express TGF-beta 1 in contrast with the more restricted TGF-beta 1 synthesis in vivo. We propose that there is a feedback loop whereby TGF-beta 1-induced synthesis of basement membrane components is repressed once a functional basement membrane is present. Finally, these results together with our current knowledge of regulation of TGF-beta 1 and TGF-beta 2 synthesis, suggest that, in vivo, TGF-beta 1 may play a major role in regulating the ECM synthesis and the cell-ECM interactions, whereas TGF-beta 2 may be more important in morphogenetic processes.

Hormonal induction of functional differentiation and mammary-derived growth inhibitor expression in cultured mouse mammary gland explants

A method for the cultivation of organ explants from abdominal mammary glands of virgin mice has been established. In a serum-free medium containing aldosterone, prolactin, insulin, and cortisol (APIH medium) mammary gland development was documented by lobuloalveolar morphogenesis. The hormonal requirements for in vitro expression of beta-casein and of the mammary-derived growth inhibitor (MDGI) were tested. To this end, a full length cDNA coding for mouse MDGI was prepared displaying strong homologies to a mouse heart fatty acid binding protein, which is also expressed in the mammary gland. MDGI and beta-casein transcripts were found to be absent in the mammary tissue from primed virgin mice, and were induced upon culture of mammary explants in the APIH medium. An immunohistochemical analysis with specific antibodies against MDGI and casein revealed a different pattern of expression for the two proteins. In the APIH medium, MDGI was expressed mainly in differentiating alveolar cells of the lobuloalveolar structures, whereas beta-casein was present in both ductules and alveoli. The relationship between functional differentiation and MDGI expression was further studied in explants from glands of late-pregnant mice. At this stage of development, MDGI is found both in ducts and in alveoli. If explants were cultured with epidermal growth factor (EGF) and insulin, the lobuloalveolar structure was still present, whereas MDGI disappeared. Reinduction of MDGI expression was achieved by subsequent PIH treatment. Independent on developmental stage, EGF strongly inhibits MDGI mRNA expression. It is concluded that MDGI-expression is associated with functional differentiation in the normal gland.

Coordinated expression of extracellular matrix-degrading proteinases and their inhibitors regulates mammary epithelial function during involution

Extracellular matrix (ECM) plays an important role in the maintenance of mammary epithelial differentiation in culture. We asked whether changes in mouse mammary specific function in vivo correlate with changes in the ECM. We showed, using expression of beta-casein as a marker, that the temporal expression of ECM-degrading proteinases and their inhibitors during lactation and involution are inversely related to functional differentiation. After a lactation period of 9 d, mammary epithelial cells maintained beta-casein expression up to 5 d of involution. Two metalloproteinases, 72-kD gelatinase (and its 62-kD active form), and stromelysin, and a serine proteinase tissue plasminogen activator were detected by day four of involution, and maintained expression until at least day 10. The expression of their inhibitors, the tissue inhibitor of metalloproteinases (TIMP) and plasminogen activator inhibitor-1, preceded the onset of ECM-degrading proteinase expression and was detected by day two of involution, and showed a sharp peak of expression centered on days 4-6 of involution. When involution was accelerated by decreasing lactation to 2 d, there was an accelerated loss of beta-casein expression evident by day four and a shift in expression of ECM-remodeling proteinases and inhibitors to a focus at 2-4 d of involution. To further extend the correlation between mammary-specific function and ECM remodeling we initiated involution by sealing just one gland in an otherwise hormonally sufficient lactating animal. Alveoli in the sealed gland contained casein for at least 7 d after sealing, and closely resembled those in a lactating gland. The relative expression of TIMP in the sealed gland increased, whereas the expression of stromelysin was much lower than that of a hormone-depleted involuting gland, indicating that the higher the ratio of TIMP to ECM-degrading proteinases the slower the process of involution. To test directly the functional role of ECM-degrading proteinases in the loss of tissue-specific function we artificially perturbed the ECM-degrading proteinase-inhibitor ratio in a normally involuting gland by maintaining high concentrations of TIMP protein with the use of surgically implanted slow-release pellets. In a concentration-dependent fashion, involuting mammary glands that received TIMP implants maintained high levels of casein and delayed alveolar regression. These data suggest that the balance of ECM-degrading proteinases and their inhibitors regulates the organization of the basement membrane and the tissue-specific function of the mammary gland.(ABSTRACT TRUNCATED AT 400 WORDS)

The influence of type I collagen on the growth and differentiation of the human colonic adenocarcinoma cell line HT-29 in vitro

HT-29 Human colonic adenocarcinoma cells when grown on a plastic substratum were anaplastic in appearance and failed to express any morphological or biochemical features that were characteristic of intestinal differentiation. Growth of HT-29 cells subcutaneously in the flank of immune deprived mice gave rise to morphologically heterogeneous tumors which were poorly differentiated but contained approximately 11% of cells with an intestinal phenotype: these showed features typical of cell polarization with well-developed microvilli, tight junctional complexes and desmosomes between adjacent cells. The transfer of cells from plastic onto either a fixed (designated 'non-released') or floating (designated 'released') type I collagen gel induced some morphological features typical of intestinal differentiation; for example goblet-like cells were observed after 9 days, but biochemical markers of differentiation were expressed only modestly. The continued subculture of HT-29 cells on collagen type I gels, which were either attached to the plastic or floating in the medium, induced some morphological features of intestinal differentiation and changes in the activity of brush border-associated enzymes. Alkaline phosphatase activity was enhanced from 1.3 x 10(-3) mumoles/mg/min for cells cultured on plastic substrata to 2.1 x 10(-3) mumoles/mg/min when gels were non-released, and 2.9 x 10(-3) mumoles/mg/min when gels were released after 12 days of culture. This was confirmed by electron microscopical visualization of alkaline phosphatase activity. Elevated levels of aminopeptidase activity were also observed on day 12 (plastic = 26 milliunits/mg; non-released gel = 41 milliunits/mg; released gel = 36 milliunits/mg). Similarly, changes occurred in the secretion of carcinoembryonic antigen from 0.96 x 10(-2) micrograms/mg/48 hours by cells cultured on plastic to 2.3 x 10(-2) micrograms/mg/48 hours by cells cultured on floating collagen gels. The effects of permitting HT-29 cells to undergo polarization were tested by culture on inert filter inserts: morphological features of intestinal differentiation were observed although this did not occur until after 21 days. These studies show that optimization of the growth conditions of anaplastic cells in vitro may provide cultures more representative of the tumor in vivo. This model system may be useful for cell biological and pharmacological studies of colon carcinoma.

A 17.6 kbp region located upstream of the rabbit WAP gene directs high level expression of a functional human protein variant in transgenic mouse milk

We have investigated whether DNA regions present in the rabbit whey acidic protein (WAP) promoter/5' flanking sequence could potentially confer, in vivo, high level expression of reporter genes. Transgenic mice were generated expressing a variant of human alpha 1-antitrypsin, which has inhibitory activity against plasma kallikrein under the control of a 17.6 kbp DNA fragment located upstream of the rabbit WAP gene. Up to 10 mg/ml of active and correctly processed recombinant protein were detected in mouse milk, thus suggesting that the far upstream DNA sequences from the rabbit WAP gene might be useful for engineering efficient protein production in the mammary glands of transgenic animals.

Mammary epithelial reorganization on extracellular matrix is mediated by cell surface galactosyltransferase

When plated at appropriate densities in serum-free media, the COMMA-D mammary epithelial cell line rapidly reorganizes into multicellular spheres on the basement membrane matrix derived from Engelbreth-Holm-Swarm murine tumor. Using time-lapse video-microscopy, four stages of reorganization were discerned during the first 24 h of culture. In the first few hours, cells attached to the matrix, elongated, migrated, and formed chains. In the next 6 h, chains of cells linked together in anastomosing networks. In the period between 8 and 18 h postplating, the networks contracted, resulting in dense cords radiating from central aggregates. During the final 6 h, the cords were drawn into the aggregates, which condensed further into spheres. The events occurring during mammary epithelial cell reorganization on the matrix were shown to be mediated by cell surface beta-1,4-galactosyltransferase (GalTase), a receptor that binds N-acetylglucosamine residues on glycosylated proteins. GalTase activity was evident at the surface of cells cultured on reconstituted matrix for 3 h but was absent from cells on glass. The protein alpha-lactalbumin (alpha-LA) inhibits the association of GalTase with N-acetylglucosamine. alpha-LA present from the beginning of culture on reconstituted matrix had no effect on cell attachment but caused concentration-dependent inhibition of the first two steps of reorganization, i.e., cell elongation and network formation, which then interfered with subsequent events. These observations were replicated using polyclonal antibodies to GalTase. Reorganization was impaired when alpha-LA was added during the first two stages but no effect was observed when it was added during the last two stages. Cells cultured on plastic, which lack surface GalTase activity, were unperturbed by incubation with alpha-LA. Thus certain events (cell elongation and network elaboration) during mammary epithelial cell reorganization on reconstituted matrix are GalTase dependent, while others (attachment, network contraction, and compaction) are not. The functional and temporal specificity of GalTase involvement indicates that GalTase mediates cell-matrix, but not cell-cell, interactions during epithelial morphogenetic events in culture.

High-level expression of the rat whey acidic protein gene is mediated by elements in the promoter and 3' untranslated region

The high-level expression of the rat whey acidic protein (WAP) gene in transgenic mice depends on the interaction of 5'-flanking promoter sequences and intragenic sequences. Constructs containing 949 bp of promoter sequences and only 70 bp of 3'-flanking DNA were expressed at uniformly high levels, comparable to or higher than that of the endogenous gene. Although this WAP transgene was developmentally regulated, it was expressed earlier during pregnancy than was the endogenous WAP gene. Replacement of 3' sequences, including the WAP poly(A) addition site, with simian virus 40 late poly(A) sequences resulted in an approximately 20-fold reduction in the expression of WAP mRNA in the mammary gland during lactation. Nevertheless, position-independent expression of the transgene was still observed. Further deletion of 91 bp of conserved WAP 3' untranslated region (UTR) led to integration site-dependent expression. Position independence was restored following reinsertion of the WAP 3' UTR into the deleted construct at the same location, but only when the insertion was in the sense orientation. The marked differences observed between the expression levels of the 3'-end deletion constructs in transgenic mice were not seen in transfected CID 9 mammary epithelial cells. In these cells, expression of the endogenous WAP gene was dependent on the interaction of these cells with a complex extracellular matrix. In contrast, the transfected WAP constructs were not dependent on extracellular matrix for expression. Thus, both the abnormal expression of WAP in cells cultured on plastic and the precocious developmental expression of WAP in transgenic mice may reflect the absence of a negative control element(s) within these recombinant constructs.

High-level expression of the rat whey acidic protein gene is mediated by elements in the promoter and 3' untranslated region

The high-level expression of the rat whey acidic protein (WAP) gene in transgenic mice depends on the interaction of 5'-flanking promoter sequences and intragenic sequences. Constructs containing 949 bp of promoter sequences and only 70 bp of 3'-flanking DNA were expressed at uniformly high levels, comparable to or higher than that of the endogenous gene. Although this WAP transgene was developmentally regulated, it was expressed earlier during pregnancy than was the endogenous WAP gene. Replacement of 3' sequences, including the WAP poly(A) addition site, with simian virus 40 late poly(A) sequences resulted in an approximately 20-fold reduction in the expression of WAP mRNA in the mammary gland during lactation. Nevertheless, position-independent expression of the transgene was still observed. Further deletion of 91 bp of conserved WAP 3' untranslated region (UTR) led to integration site-dependent expression. Position independence was restored following reinsertion of the WAP 3' UTR into the deleted construct at the same location, but only when the insertion was in the sense orientation. The marked differences observed between the expression levels of the 3'-end deletion constructs in transgenic mice were not seen in transfected CID 9 mammary epithelial cells. In these cells, expression of the endogenous WAP gene was dependent on the interaction of these cells with a complex extracellular matrix. In contrast, the transfected WAP constructs were not dependent on extracellular matrix for expression. Thus, both the abnormal expression of WAP in cells cultured on plastic and the precocious developmental expression of WAP in transgenic mice may reflect the absence of a negative control element(s) within these recombinant constructs.

Serial cultivation of epithelial cells from human and macaque salivary glands

To study the regulation of human salivary-type gene expression we developed cell culture systems to support the growth and serial cultivation of salivary gland epithelial and fibroblastic cell types. We have established 22 independent salivary gland epithelial cell strains from parotid or submandibular glands of human or macaque origin. Nineteen strains were derived from normal tissues and three from human parotid gland tumors. Both the normal and the tumor-derived salivary gland epithelial cells could be serially cultivated with the aid of a 3T3 fibroblast feeder layer in a mixture of Ham's F12 and Dulbecco's modified Eagle's media supplemented with fetal bovine serum, calcium, cholera toxin, hydrocortisone, insulin, and epidermal growth factor. Salivary gland epithelial cells cultured under these conditions conditioned to express the genes for at least two acinar-cell-specific markers at early passages. Amylase enzyme activity was detected in conditioned media from cultured rhesus parotid epithelial cells as late as Passage 5. Proline-rich-protein-specific RNAs were detected in primary cultures of both rhesus and human parotid epithelial cells. Neither amylase enzyme activity nor PRP-specific RNAs were detected in fibroblasts isolated from the same tissues. In addition, salivary gland epithelial cells cultured under our conditions retain the capacity to undergo dramatic morphologic changes in response to different substrata. The cultured salivary gland epithelial cells we have established will be important tools for the study of salivary gland differentiation and the tissue-specific regulation of salivary-type gene expression.

Control of mammary epithelial differentiation: basement membrane induces tissue-specific gene expression in the absence of cell-cell interaction and morphological polarity

Functional differentiation in mammary epithelia requires specific hormones and local environmental signals. The latter are provided both by extracellular matrix and by communication with adjacent cells, their action being intricately connected in what appears to be a cascade of events leading to milk production. To distinguish between the influence of basement membrane and that of cell-cell contact in this process, we developed a novel suspension culture assay in which mammary epithelial cells were embedded inside physiological substrata. Single cells, separated from each other, were able to assimilate information from a laminin-rich basement membrane substratum and were induced to express beta-casein. In contrast, a stromal environment of collagen I was not sufficient to induce milk synthesis unless accompanied by cell-cell contact. The expression of milk proteins did not depend on morphological polarity since E-cadherin and alpha 6 integrin were distributed evenly around the surface of single cells. In medium containing 5 microM Ca2+, cell-cell interactions were impaired in small clusters and E-cadherin was not detected at the cell surface, yet many cells were still able to produce beta-casein. Within the basement membrane substratum, signal transfer appeared to be mediated through integrins since a function-blocking anti-integrin antibody severely diminished the ability of suspension-cultured cells to synthesize beta-casein. These results provide evidence for a central role of basement membrane in the induction of tissue-specific gene expression.

Rabbit whey acidic protein concentration in milk, serum, mammary gland extract, and culture medium

Rabbit whey acidic protein has been purified from whey using an AcA54 column. The purified whey acidic protein had an amino acid composition in agreement with the previously defined cDNA sequence. An antibody against whey acidic protein was raised in guinea pig. This antibody did not crossreact with mouse or cow milk or with rabbit alpha s1-casein and beta-casein. Whey acidic protein concentration was measured in rabbit milk using the antibody with a radioimmunoassay. The concentration of whey acidic protein in rabbit milk was 15 mg/ml, whereas the concentrations of alpha s1-casein and beta-casein were 16 and 45 mg/ml, respectively. The concentration of the three proteins was also evaluated in culture medium of rabbit primary mammary cells. The three proteins were induced by prolactin alone. Glucocorticoids amplified the prolactin effect on whey acidic protein more intensively than on caseins. The three proteins were present in mammary extract from virgin rabbit. The concentration of these proteins was lower at d 8 and 14 of pregnancy, and it was very high at d 25 of pregnancy. Whey acidic protein was undetectable in blood of virgin, weaned, and midpregnant females and of males. Whey acidic protein was present in blood of lactating rabbits, but alpha s1-casein and beta-casein were not detectably present in rabbit blood at the examined physiological states.

Hormone responsive elements within the upstream sequences of the rabbit whey acidic protein (WAP) gene direct chloramphenicol acetyl transferase (CAT) reporter gene expression in transfected rabbit mammary cells

Whey acidic protein gene transcription is induced in the mammary gland under the influence of lactogenic hormones: prolactin, insulin and cortisol. The rabbit WAP gene has already been isolated and sequenced in a previous work. In the present study, we have evaluated the role of the 5' flanking region of the rabbit WAP gene in the transcriptional regulation of the WAP gene by using a reporter CAT gene. Chimeric genes containing the upstream region of the WAP gene have been linked to the bacterial CAT gene and transfected into rabbit primary mammary cells. The results reported here show that two regions carrying important regulatory elements of the rabbit WAP gene are located between -6300 and -3000 bp, and between -3000 and -1800 bp upstream from the WAP transcription start point, respectively. The contribute to the high level of expression of the rabbit WAP gene in the mammary cell.

Establishment and characterization of bovine mammary epithelial cell lines

One bovine mammary epithelial cell clone, designated PS-BME-Cl, and two bovine mammary epithelial cell lines, designated PS-BME-L6 and PS-BME-L7, were derived from mammary tissue of a pregnant (270 day) Holstein cow. The cells exhibit the distinctive morphologic characteristics of mammary epithelial cells and express the milk fat globule membrane protein, PAS-III. They form domes when cultured on plastic substrata and acinilike aggregates when cultured on a collagen matrix. These cells are capable of synthesizing and secreting alpha-lactalbumin and alpha-s1-casein when cultured on a collagen matrix in the presence of insulin, cortisol, and prolactin. The cells have a near-normal diploid number and do not grow in suspension culture. When transplanted to the cleared mammary fat pads of female athymic nude mice, the cells readily proliferate forming noninvasive palpable spherical cellular masses within 8 wk after inoculation. The cells may become a useful tool to study the regulation of ruminant mammary epithelial cell growth and differentiation.

Protein synthesis is required for the initiation of dendritic growth in embryonic rat sympathetic neurons in vitro

We have utilized an experimental paradigm which allows the manipulation of dendritic growth in sympathetic neurons in culture to examine the effects of inhibitors of protein synthesis and RNA synthesis on the development of dendrites. Embryonic rat sympathetic neurons extend only axons when they are grown in serum-free medium on a polylysine substrate. The addition of an extract of basement membrane proteins (BME) to this culture system elicits dendritic growth within 48 h. Both cycloheximide and actinomycin-D inhibited BME-induced dendritic growth in greater than 80% of the neuronal population and reduced the number of dendrites extended by greater than or equal to 97%. In contrast, cycloheximide was found to have minimal effects on axonal growth in short-term (less than or equal to 18 h) cultures as measured with respect to the percentage of the population with axons and the number of axons per neuron. However, this inhibitor did significantly reduce (84%) the length of the axonal plexus extended. These results indicate that dendritic and axonal growth in sympathetic neurons are differentially dependent on protein synthesis such that the formation of dendrites requires protein synthesis whereas the initiation, but not the elongation, of axons is relatively independent of protein synthesis.

Proteinases of the mammary gland: developmental regulation in vivo and vectorial secretion in culture

The extracellular matrix (ECM) is an important regulator of mammary epithelial cell function both in vivo and in culture. Substantial remodeling of ECM accompanies the structural changes in the mammary gland during gestation, lactation and involution. However, little is known about the nature of the enzymes and the processes involved. We have characterized and studied the regulation of cell-associated and secreted mammary gland proteinases active at neutral pH that may be involved in degradation of the ECM during the different stages of mammary development. Mammary tissue extracts from virgin and pregnant CD-1 mice resolved by zymography contained three major proteinases of 60K (K = 10(3) Mr), 68K and 70K that degraded denatured collagen. These three gelatinases were completely inhibited by the tissue inhibitor of metalloproteinases. Proteolytic activity was lowest during lactation especially for the 60K gelatinase which was shown to be the activated form of the 68K gelatinase. The activated 60K form decreased prior to parturition but increased markedly after the first two days of involution. An additional gelatin-degrading proteinase of 130K was expressed during the first three days of involution and differed from the other gelatinases by its lack of inhibition by the tissue inhibitor of metalloproteinases. The activity of the casein-degrading proteinases was lowest during lactation. Three caseinolytic activities were detected in mammary tissue extracts. A novel 26K cell-associated caseinase--a serine arginine-esterase--was modulated at different stages of mammary development. The other caseinases, at 92K and a larger than 100K, were not developmentally regulated. To find out which cell type produced the proteinases in the mammary gland, we isolated and cultured mouse mammary epithelial cells. Cells cultured on different substrata produced the full spectrum of gelatinases and caseinases seen in the whole gland thus implicating the epithelial cells as a major source of these enzymes. Analysis of proteinases secreted by cells grown on a reconstituted basement membrane showed that gelatinases were secreted preferentially in the direction of the basement membrane. The temporal pattern of expression of these proteinases and the basal secretion of gelatinases by epithelial cells suggest their involvement in the remodelling of the extracellular matrix during the different stages of mammary development and thus modulation of mammary cell function.

Animal cell shape changes and gene expression

Cell shape and cell contacts are determined by transmembrane receptor-mediated associations of the cytoskeleton with specific extracellular matrix proteins and with ligands on the surface of adjacent cells. The cytoplasmic domains of these microfilament-membrane associations at the adherens junction sites, also localize a variety of regulatory molecules involved in signal transduction and gene regulation. The stimulation of cells with soluble polypeptide factors leads to rapid changes in cell shape and microfilament component organization. In addition, this stimulation also activates the phosphoinositide signaling pathway. Recently, a linkage between actin-binding proteins and the phosphoinositide signaling pathway, was discovered. It is suggested that by the association with the second messenger system, and/or by controlling the localization of regulatory molecules, the cytoskeleton may regulate gene expression.

An upstream regulatory region mediates high-level, tissue-specific expression of the human alpha 1(I) collagen gene in transgenic mice

Studies in vitro have not adequately resolved the role of intronic and upstream elements in regulating expression of the alpha 1(I) collagen gene. To address this issue, we generated 12 separate lines of transgenic mice with alpha 1(I) collagen-human growth hormone (hGH) constructs containing different amounts of 5'-flanking sequence, with or without most of the first intron. Transgenes driven by 2.3 kb of alpha 1(I) 5'-flanking sequence, whether or not they contained the first intron, were expressed at a high level and in a tissue-specific manner in seven out of seven independent lines of transgenic mice. In most tissues, the transgene was expressed at levels approaching that of the endogenous alpha 1(I) gene and was regulated identically with the endogenous gene as animals aged. However, in lung, expression of the transgene was anomalously high, and in muscle, expression was lower than that of the endogenous gene, suggesting that in these tissues other regions of the gene may participate in directing appropriate expression. Five lines of mice were generated containing transgenes driven by 0.44 kb of alpha 1(I) 5'-flanking sequence (with or without the first intron), and expression was detected in four out of five of these lines. The level of expression of the 0.44-kb constructs in the major collagen-producing tissues was 15- to 500-fold lower than that observed with the longer 2.3-kb promoter. While transgenes containing the 0.44-kb promoter and the first intron retained a modest degree of tissue-specific expression, those without the first intron lacked tissue specificity and were poorly expressed in all tissues except lung. These results contribute to our understanding of the role of the first intron in regulating alpha1(I) gene expression and identify a region, upstream of the basal alpha1(I) promotor, which is necessary for full tissue-specific, developmentally regulated expression of the alpha1(I) collagen gene.

Transgenic mice carrying the guinea-pig alpha-lactalbumin gene transcribe milk protein genes in their sebaceous glands during lactation

We have generated transgenic mice carrying the entire guinea-pig alpha-lactalbumin gene. Lactating transgenic mice expressed high levels of correctly initiated and processed guinea-pig alpha-lactalbumin mRNA in the secretory epithelium of their mammary glands, and secreted guinea-pig alpha-lactalbumin in their milk. Transcripts were detectable after 7 days of pregnancy, indicating that the transgene was under correct hormonal control. Whereas no or negligible transcription was detectable in all other tissues tested, high levels of transcripts were found in the skin of lactating transgenic mice. Guinea-pig alpha-lactalbumin protein was undetectable in the skin, however. In situ hybridization analysis showed that expression was localized to the undifferentiated cells in the basal layer of the sebaceous glands. Further studies revealed high levels of endogenous beta-casein mRNA in normal lactating mouse skin, demonstrating that the transcription of milk protein genes in lactating mouse skin is a normal event, and is not peculiar to the transgene. This surprising finding highlights the developmental relationship of the mammary gland to other specialized structures of the skin, supports a role for epithelial-extracellular matrix interactions in the regulation of milk protein gene expression in vivo, and identifies the skin as a particularly accessible model system in which to study the regulation of milk protein gene expression. In addition, the guinea-pig alpha-lactalbumin gene will be a source of regulatory sequences with which to direct heterologous gene expression to the sebaceous glands of transgenic mice.

An upstream regulatory region mediates high-level, tissue-specific expression of the human alpha 1(I) collagen gene in transgenic mice

Studies in vitro have not adequately resolved the role of intronic and upstream elements in regulating expression of the alpha 1(I) collagen gene. To address this issue, we generated 12 separate lines of transgenic mice with alpha 1(I) collagen-human growth hormone (hGH) constructs containing different amounts of 5'-flanking sequence, with or without most of the first intron. Transgenes driven by 2.3 kb of alpha 1(I) 5'-flanking sequence, whether or not they contained the first intron, were expressed at a high level and in a tissue-specific manner in seven out of seven independent lines of transgenic mice. In most tissues, the transgene was expressed at levels approaching that of the endogenous alpha 1(I) gene and was regulated identically with the endogenous gene as animals aged. However, in lung, expression of the transgene was anomalously high, and in muscle, expression was lower than that of the endogenous gene, suggesting that in these tissues other regions of the gene may participate in directing appropriate expression. Five lines of mice were generated containing transgenes driven by 0.44 kb of alpha 1(I) 5'-flanking sequence (with or without the first intron), and expression was detected in four out of five of these lines. The level of expression of the 0.44-kb constructs in the major collagen-producing tissues was 15- to 500-fold lower than that observed with the longer 2.3-kb promoter. While transgenes containing the 0.44-kb promoter and the first intron retained a modest degree of tissue-specific expression, those without the first intron lacked tissue specificity and were poorly expressed in all tissues except lung. These results contribute to our understanding of the role of the first intron in regulating alpha1(I) gene expression and identify a region, upstream of the basal alpha1(I) promotor, which is necessary for full tissue-specific, developmentally regulated expression of the alpha1(I) collagen gene.