Influence of hormones on lobulo-alveolar differentiation of mouse mammary glands in vitro

Targeting steroid hormone receptors for anti-cancer therapy-A review on small molecules and nanotherapeutic approaches

The steroid hormone receptors (SHRs) among nuclear hormone receptors (NHRs) are steroid ligand-dependent transcription factors that play important roles in the regulation of transcription of genes promoted via hormone responsive elements in our genome. Aberrant expression patterns and context-specific regulation of these receptors in cancer, have been routinely reported by multiple research groups. These gave an window of opportunity to target those receptors in the context of developing novel, targeted anticancer therapeutics. Besides the development of a plethora of SHR-targeting synthetic ligands and the availability of their natural, hormonal ligands, development of many SHR-targeted, anticancer nano-delivery systems and theranostics, especially based on small molecules, have been reported. It is intriguing to realize that these cytoplasmic receptors have become a hot target for cancer selective delivery. This is in spite of the fact that these receptors do not fall in the category of conventional, targetable cell surface bound or transmembrane receptors that enjoy over-expression status. Glucocorticoid receptor (GR) is one such exciting SHR that in spite of it being expressed ubiquitously in all cells, we discovered it to behave differently in cancer cells, thus making it a truly druggable target for treating cancer. This review selectively accumulates the knowledge generated in the field of SHR-targeting as a major focus for cancer treatment with various anticancer small molecules and nanotherapeutics on progesterone receptor, mineralocorticoid receptor, and androgen receptor while selectively emphasizing on GR and estrogen receptor. This review also briefly highlights lipid-modification strategy to convert ligands into SHR-targeted cancer nanotherapeutics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

3D culture assays of murine mammary branching morphogenesis and epithelial invasion

Epithelia are fundamental tissues that line cavities, glands, and outer body surfaces. We use three-dimensional (3D) embedded culture of primary murine mammary epithelial ducts, called "organoids," to recapitulate in days in culture epithelial programs that occur over weeks deep within the body. Modulating the composition of the extracellular matrix (ECM) allows us to model cell- and tissue-level behaviors observed in normal development, such as branching morphogenesis, and in cancer, such as invasion and dissemination. Here, we describe a collection of protocols for 3D culture of mammary organoids in different ECMs and for immunofluorescence staining of 3D culture samples and mammary gland tissue sections. We illustrate expected phenotypic outcomes of each assay and provide troubleshooting tips for commonly encountered technical problems.

Serotonin: a local regulator in the mammary gland epithelium

Serotonin (5-hydroxytryptamine, 5-HT) is a very simple molecule that plays key roles in complex communication mechanisms within the animal body. In the mammary glands, serotonin biosynthesis and secretion are induced in response to dilation of the alveolar spaces. Since its discovery several years ago, mammary 5-HT has been demonstrated to perform two homeostatic functions. First, serotonin regulates lactation and initiates the transition into the earliest phases of involution. Second, serotonin is a local signal that induces parathyroid hormone-related peptide (PTHrP), which allows the mammary gland to drive the mobilization of calcium from the skeleton. These processes use different receptor types, 5-HT7 and 5-HT2, respectively. In this review, we provide synthetic perspectives on the fundamental processes of lactation homeostasis and the adaptation of calcium homeostasis for lactation. We analyze the role of the intrinsic serotonin system in the physiological regulation of the mammary glands. We also consider the importance of the mammary serotonin system in pathologies and therapies associated with lactation and breast cancer.

Practical considerations for long-term time-lapse imaging of epithelial morphogenesis in three-dimensional organotypic cultures

Epithelia are one of the fundamental tissues in the animal body, and there is broad interest in understanding the cellular and molecular basis of their formation, growth, remodeling, and pathologic degeneration. Unfortunately, from an imaging perspective, many epithelial tissues develop deep within the animal and are inaccessible to high-resolution optical imaging with visible wavelengths. To circumvent this problem, researchers have long sought to model epithelial morphogenesis in culture systems. Protocols for culturing whole epithelial organs have existed since the 1950s, but the use of three-dimensional (3D) organotypic cultures of epithelial fragments has advanced dramatically in recent years. There has been a considerable increase in interest in imaging cell behaviors and molecular activities within these cultures. This article discusses the common technical challenges associated with imaging epithelial morphogenesis in 3D cultures and presents a range of specific strategies to address these challenges. Solutions are presented, first conceptually and then at several levels of sophistication and expense. The goal is to help you adapt those specific methods most useful to your own research, in a manner compatible with your needs and budget.

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

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

Susceptibility of rats to mammary gland carcinogenesis by the food-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) varies with age and is associated with the induction of differential gene expression

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine found in cooked meat, induces mammary gland cancer when administered to adolescent female rats (43-day-old). In contrast, mature virgin rats (150-day-old) were resistant to mammary carcinogenesis by PhIP. To explore the possible mechanisms for the age-related differences in susceptibility, PhIP-DNA adduct levels, mutations, and gene expression were examined in glands from 43-day and 150-day-old PhIP-treated rats. In rats of different ages, PhIP-DNA adduct levels detected by the (32)P-post-labeling assay and mutant frequency measured in the lacI reporter gene of Big Blue rats were not statistically different. PhIP-DNA adduct levels, adduct removal, and mutation burden did not appear to account for the variation in carcinogen susceptibility with age. However, cDNA microarray analysis indicated that PhIP treatment differentially altered the profile of gene expression in glands from 43-day-old and 150-day-old rats. In 150-day-old rats, PhIP enhanced the expression of genes associated with differentiation (eg, beta-casein, kappa-casein, whey acidic protein) and induced morphological differentiation. In contrast, in 43-day-old rats, PhIP inhibited the expression of differentiation genes and enhanced cellular proliferation. From 3 hours to 6 weeks after PhIP dosing, the number of clones showing altered expression declined more than 50% in 150-day-old rats but increased fourfold in 43-day-old rats (29 clones versus 194, respectively) suggesting that PhIP induced a cascade of gene expression alterations only in susceptible rats. Genes showing altered expression specifically in 43-day-old rats included the Ras superfamily genes and genes associated with protein synthesis/degradation (lysosomal proteins, heat shock proteins, and proteasomes). The microarray data support the notion that the mechanism of age-dependent susceptibility to mammary gland cancer is largely associated with differential responses in expression of genes involved in cellular differentiation, proliferation, and protein homeostasis.

Morphogenesis of mammary gland development

Development of the mammary gland in females is a dynamic, orchestrated process that occurs throughout postnatal development. Initiated during embryogenesis, epithelial cells advance into the underlying stromal matrix to form a primitive rudimentary structure. With the onset of puberty this anlage then responds to hormonal and local cues to rapidly establish a ductal network. Whereas in mice this network is relatively simple, in humans there is significantly more branching morphogenesis to develop terminal duct lobular unit structures. With the onset of pregnancy and associated changes in the hormonal and local environment, alveolar development progresses to establish a gland that is densely filled with alveolar structures by the end of pregnancy. Concomitantly, mammary epithelial cells within the gland begin to attain their unique ability to synthesize various milk constituents, such that by parturition, functional lactogenesis can be realized.

Effect of exogenous epidermal-like growth factors on mammary gland development and differentiation in the estrogen receptor-alpha knockout (ERKO) mouse

The development of the mouse mammary gland requires the interaction between several different ovarian and pituitary hormones such as estrogen, progesterone and prolactin as well as several locally-derived growth factors in the mammary gland such as epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha), amphiregulin (AR) and heregulin (HRG). The focus of this study was to investigate the degree of mammary growth and differentiation in the adult, virgin mammary gland of wild type (wt) and estrogen receptor knockout (ERKO) females that lack estrogen receptor alpha (ERalpha) after reciprocal transplantation into the cleared mammary fat pad of virgin wt or ERKO mice. In addition, we assessed the local response of ERKO mammary tissue to TGFalpha or HRGbeta1 delivered from slow release-Elvax pellets. Our initial results indicated that when we transplanted virgin wt mammary tissue into ERKO mammary fat pads, mammary morphogenesis failed to occur. However, when transplanted virgin ERKO mammary tissue was transplanted into fat pads of virgin or pregnant wt mice, the development and differentiation of lobuloalveoli was readily observed. In addition, treatment of the virgin ERKO mammary gland with TGFalpha or HRGbeta1 stimulated ducts to undergo localized branching and growth and both growth factors induced secretory differentiation as evidenced by the production of milk proteins, caseins and/or whey acidic protein (WAP). The results from this study imply that in ERKO mammary tissue. ERKO ductal epithelium has the capacity to proliferate and differentiate in response to non-estrogenic, morphogenic stimuli.

Role of the progesterone receptor (PR) in susceptibility of mouse mammary gland to 7,12-dimethylbenz[a]anthracene-induced hormone-independent preneoplastic lesions in vitro

Glands of wild-type (WT) and progesterone receptor knockout (PRKO) mice were exposed to 7,12-dimethylbenz[a]anthracene (DMBA) while cultured in serum-free medium containing insulin, prolactin, aldosterone, and cortisol. Glands of WT but not PRKO mice responded to DMBA with epithelial hyperplasia after 10 days in this medium. After culture without prolactin and adrenocortical hormones for an additional 14 days, hyperplastic lesions were present only in glands of WT mice. We conclude that in the absence of PR, epithelial structures are resistant to the carcinogenic action of DMBA.

The mineralocorticoid receptor may compensate for the loss of the glucocorticoid receptor at specific stages of mammary gland development

To study the role of glucocorticoid receptor (GR) at different stages of mammary gland development, mammary anlage were rescued from GR-/- mice by transplantation into the cleared fat pad of wild-type mice. In virgin mice, GR-/- outgrowths displayed abnormal ductal morphogenesis characterized by distended lumena, multiple layers of luminal epithelial cells in some regions along the ducts, and increased periductal stroma. In contrast, the loss of GR did not result in overt phenotypic changes in mammary gland development during pregnancy, lactation, and involution. Surprisingly, despite the known synergism between glucocorticoids and prolactin in the regulation of milk protein gene expression, whey acidic protein and beta-casein mRNA levels were unaffected in GR-/- transplants as compared with wild-type transplants. That mineralocorticoid receptor (MR) might compensate for the loss of GR was suggested by the detection of MR in the mammary gland at d 1 of lactation. This hypothesis was tested using explant cultures derived from the GR-/- transplants in which the mineralocorticoid fludrocortisone was able to synergistically induce beta-casein gene expression in the presence of prolactin and insulin. These studies suggest that MR may compensate for the absence of GR at some, but not at all stages of mammary gland development.

Glucocorticoids maintain the extracellular matrix of differentiated mammary tissue during explant and whole organ culture

Mouse mammary whole organ culture (WOC) and explant culture of lactating tissue were used to investigate the mechanism by which glucocorticoids maintain secretory epithelium following lobuloalveolar development. The relative number of mammary epithelial cells expressing glucocorticoid receptors did not change with the loss of secretory epithelium during involution as demonstrated with competitive binding assays and immunohistochemistry for the glucocorticoid receptor. Furthermore, glucocorticoids did not inhibit AP-1 binding activity. However, Northern analysis demonstrated that genes associated with the breakdown of the extracellular matrix were not expressed in tissues cultured with glucocorticoids, in contrast to their upregulation during involution of mammary tissue cultured with insulin alone. Tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA expression was lowest in tissue cultured in the presence of glucocorticoids and increased 2.3-, 3.4-, and 9-fold when tissues were involuted in the presence of insulin (Ins) alone, Ins and hydrocortisone (Hyd) with 0. 005 mg/ml, or 0.01 mg/ml collagenase IV, respectively. These data indicate that glucocorticoids maintain mammary differentiation in part by inhibiting the turnover of basement membrane.

The insulin-like growth factors (IGFs) and IGF binding proteins in postnatal development of murine mammary glands

The insulin-like growth factors are mitogens and survival factors for normal mammary epithelial cells in vitro. Data reviewed here demonstrate that mRNAs for IGF-I and IGF-II, the IGF type I receptor and the IGFBPs are expressed locally in mammary tissue during pubertal and pregnancy-induced growth and differentiation of murine mammary glands. IGF-I, IGF-II and the IGF-IR were expressed in terminal end buds (TEBs) in virgin glands during ductal growth. In addition, IGF-II and IGF-IR mRNAs were expressed in ductal and alveolar epithelium in glands throughout postnatal development. Consistent with these results, IGF-I promoted ductal growth and proliferation in mouse mammary glands in organ culture. In addition to endogenous expression of the IGFs and IGF-IR, the IGFBPs showed a varied pattern of expression in mammary tissue during postnatal development. For example, IGFBP-3 and -5 mRNAs were expressed in TEBs and ducts while IGFBP-2 and -4 mRNAs were expressed in stromal cells immediately surrounding the epithelium. These results support a role for the IGFs and IGFBPs as local mediators of postnatal mammary gland growth and differentiation.

Progesterone stimulates DNA synthesis and lobulo-alveolar development in mammary glands in ovariectomized mice

The objective of this study was to determine whether sustained progesterone (P) use in the absence of estrogen could influence mammary development in mice. Three-week-old intact or ovariectomized mice were primed with subcutaneous (s.c.) cholesterol (C), estrogen (E), P, or estrogen and progesterone (E/P) together. Nine days after priming, mammary glands were removed and incubated as a whole organ in media supplemented with various combinations of lactogenic hormones. After 5 days in whole organ culture, glands were removed and end buds, alveolar buds and lobulo-alveoli were quantified. Glands from mice primed with C or E developed significantly less lobulo-alveoli than glands from mice primed with P or E/P. While the development was greater in animals treated with E/P compared to those treated with P, it was clear that P in the absence of E could still induce lobulo-alveolar development. We have shown in this paper that P, in the absence of E, can stimulate cell proliferation during priming. Subsequently, the P primed glands can differentiate in response to lactogenic hormones.

The insulin-like growth factors (IGF) and IGF type I receptor during postnatal growth of the murine mammary gland: sites of messenger ribonucleic acid expression and potential functions

The goals of this study were to determine the cellular sites of insulin-like growth factor (IGF) and IGF type-I receptor (IGF-IR) expression and to begin to elucidate functional roles for the IGFs during postnatal development of the murine mammary gland. Using in situ hybridization analyses, we determined that IGF-I, IGF-II, and IGF-IR messenger RNAs were expressed in the highly proliferative terminal end buds during pubertal ductal growth. Consistent with these data, IGF-I (in combination with mammogenic hormones) promoted ductal growth in pubertal stage mammary glands cultured in vitro. During postpubertal and pregnancy stages, IGF-II and IGF-IR continued to be expressed in ductal epithelium. Expression of IGF-II in ductal and alveolar epithelium correlated with the pattern of rapidly proliferating cells, as determined by incorporation of 5-Bromo-2'-deoxyuridine, suggesting a potential autocrine or paracrine role for IGF-II as a mitogen for ductal epithelial cells. IGF-I expression was reinitiated in mammary epithelium in the differentiated alveoli at the end of pregnancy, suggesting an additional role for this factor in maintenance of the alveoli during lactation. Taken together, these data support an in vivo role for locally-produced IGFs in promoting ductal growth during puberty and suggest that IGF-I and IGF-II may have distinct functions during pregnancy-induced alveolar development.

Progesterone signaling and mammary gland morphogenesis

Progesterone was identified as a mammogenic hormone several years ago but until now its precise role in mammary development has remained obscure. Recently with the generation of several transgenic mouse models and development of reagents for analysis of progesterone receptor expression, the role of progesterone signaling in mammary development is becoming more clear. The most significant observations to emerge from these studies are (1) progesterone receptors (PR) are present in a heterogeneous manner in the epithelial cells and undetectable in the surrounding fat pad; (2) they are essential for lobuloalveolar and not for ductal morphogenesis; (3) progesterone signaling through progesterone receptors, leading to lobuloalveolar development, is initiated in the epithelium and may occur through paracrine mechanisms; and (4) a regulated expression of the two isoforms of progesterone receptor is critical for maintaining appropriate responsiveness to progesterone and hence, epithelial cell replicative homeostasis. These studies also reveal that the consequences of progesterone signaling through progesterone receptor may depend on the cell context, cell-cell and cell-extracellular matrix interactions, the dynamics of PR turnover and the fate of PR positive cells.

Effects of steroid hormone treatment on mammary development in prepubertal heifers

The objective of this study was to determine the effects of steroid hormone implantation in heifer calves on the ability of mammary tissue to develop subsequently in organ culture. Twenty-four calves were paired by date of birth and assigned to groups (eight calves/group). At 4, 7, or 10 mo of age, calves were implanted subcutaneously (s.c.) with pellets containing cholesterol or cholesterol, 17 beta-estradiol, and progesterone for 9 or 18 d. The calves were euthanized and uteri and mammary glands were removed and weighed. Slices of mammary parenchymal tissue were incubated for 5 d at 37 degrees C in a 50% O2, 5% CO2 humidified atmosphere in Waymouth's 752/liter medium supplemented with insulin (5.0 micrograms/ml) or lactogenic hormone complex insulin (5.0 micrograms/ml), aldosterone (0.1 microgram/ml), hydrocortisone (0.1 microgram/ml), and prolactin (1.0 microgram/ml) in the presence or absence of epidermal growth factor (EGF) (0.06 microgram/ml) to promote lobulo-alveolar development. Tissue sections were stained and mounted on slides for morphologic and histologic analysis or prepared to evaluate expression of beta-casein mRNA. There were no morphologic differences in slices from calf mammary tissues despite age, steroid hormone priming, or hormones used in tissue culture. The 4-mo-old calves required steroid priming followed by incubation of the tissue slices with the lactogenic complex with or without epidermal growth factor to induce cytological changes associated with lactogenesis but did not express beta-casein mRNA. At 7 mo of age, steroid hormone priming was not necessary for induction of alveolar formation and secretion. Incubation of the tissue slices from 7-mo-old calves with the lactogenic complex was sufficient to induce alveolar formation and secretion. However, beta-casein mRNA was not expressed. At 10 mo of age, exposure of tissue from calves to the lactogenic hormones caused histologic changes reminiscent of the ability to secrete milk regardless of hormone priming. However, estrogen and progesterone priming was necessary before incubation of the tissue slices with the lactogenic hormones to induce beta-casein mRNA expression. When epidermal growth factor was added to the lactogenic hormone complex, beta-casein mRNA expression decreased. These data support the concept that there is a sequential development of responsiveness of the mammary gland to various hormones. By 10 mo of age, prepubertal heifers reach a stage of maturity where steroid hormone priming followed by incubation of tissue slices with the lactogenic hormones is sufficient to induce both structural and functional differentiation.

Estrogen affects development of alveolar structures in whole-organ culture of mouse mammary glands

In order to determine if estrogen affects lobulo-alveolar development, and to determine if whole organ culture of mouse mammary glands is an appropriate model of estrogen effects on mammary development, mouse mammary glands were cultured in the presence or absence of phenol red and estrogen. Lobulo-alveolar development did not occur in vitro when phenol red was eliminated from culture medium. Lobulo-alveolar development was stimulated by 17 beta-estradiol in a dose dependent manner over a physiological range. These results support the hypothesis that estrogen plays a critical role in alveolar development in the mammary gland. In this report an in vitro model of mammary development is identified in which the effects of estrogen are morphologically described and quantified.

Roles of estrogen and progesterone in normal mammary gland development insights from progesterone receptor null mutant mice and in situ localization of receptor

In contrast to most other organs, the development of normal mammary glands occurs mostly in the postnatal state and in a discontinuous fashion. In all species, the glands are composed of various cell types, and it is the epithelium, embedded in the fatty stroma (commonly known as the "fat pad"), that is targeted for proliferation and differentiation. Hormones, in particular the female sex steroids estrogen and progesterone, are absolutely essential for the proliferation of mammary epithelial cell. However, despite intensive efforts by many laboratories spanning nearly 4 decades, at present, the precise role of these steroids and their relative importance in mammary development remains unclear. This article reviews the general features and the effects of estrogen and progesterone on normal mammary gland development, followed by a discussion of our recent studies, which emphasize the primary importance of progesterone and progesterone receptor for the normal mammary epithelial cell proliferation and differentiation. (c) 1997, Elsevier Science Inc. (Trends Endocrinol Metab 1997;8:34-39).

Involution of the lactating mammary gland is inhibited by the IGF system in a transgenic mouse model

Development of the mammary gland during puberty, pregnancy, and lactation is controlled by steroid and peptide hormones and growth factors. To determine the role of the insulin-like growth factors (IGFs) in this process we developed a transgenic model using the whey acidic protein (WAP) gene to direct expression of rat IGF-I and human IGF binding protein-3 (IGFBP-3) to mammary tissue during late pregnancy and throughout lactation. High levels of expression of transgenic IGF-I and IGFBP-3 were seen in lobular-alveolar cells by in situ hybridization. There was no obvious effect on mammary development during pregnancy and lactation; indeed, mothers were capable of nursing their pups normally and the only structural difference seen in the mammary glands at peak lactation was an overall smaller size of the alveoli. We also evaluated the role of IGF-I and IGFBP-3 in the remodeling of mammary tissue during involution. Compared with control animals, the process of involution was modified in both transgenic lines. The degree of apoptotic cells was lower in the WAP-IGF-I and WAP-BP-3 expressing mice. In addition, there was a more quiescent pattern of involution with residual lobular secretary ability and a muted host inflammatory reaction with fewer lumenal microcalcifications. These results demonstrate that IGF-I and IGFBP-3 may modulate the involutionary process of the lactating mammary gland.

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.

Antiprogestins inhibit growth and stimulate differentiation in the normal mammary gland

Antiprogestins possess a potent antitumor activity in hormone-dependent experimental breast cancer models. Though the underlying mechanism is not clear, induction of functional differentiation seems to be a major event. This study attempts to test directly for antiproliferative and differentiation promoting activities of antiprogestins on the normal mammary gland. To this end, whole organ cultures of mammary glands from estradiol/progesterone-primed virgin mice maintained in a serum-free medium with aldosteron, prolactin, insulin, and hydrocortisone were exposed to the antiprogestin ZK114043. A 4-day treatment of organ cultures led to a strong inhibition of epithelial DNA synthesis. In parallel, ZK114043 caused alveolar cells to acquire a more differentiated phenotype distinguished by secretory active alveoli composed of single cell layers with increased fat droplet accumulation and enhanced expression of the milk proteins beta-casein and whey acidic protein (WAP). Particularly strong effects were found on the expression of mammary-derived growth inhibitor (MDGI). Both half-maximal inhibition of epithelial DNA synthesis and stimulation of MDGI mRNA expression were found at about 5 ng/ml of ZK114043. Presence in the medium of 5 micrograms/ml hydrocortisone rendered antiglucocorticoid effects of ZK114043 highly unlikely. Furthermore, prevention of action of ZK114043 by the progesterone agonist R5020 and ZK114043 stimulated expression of beta-casein and MDGI mRNA in cultured glands of 10-week-old unprimed virgin mice suggest a progesterone receptor-mediated mechanism of antiprogestin action. Two other antiprogestins, Mifepristone and Onapristone, likewise stimulated MDGI expression. The data provide direct evidence that antiprogestins act like a differentiation factor in the normal mammary gland.

Prolactin and epidermal growth factor regulation of the proliferation, morphogenesis, and functional differentiation of normal rat mammary epithelial cells in three dimensional primary culture

The epithelial cell-specific effects of prolactin and epidermal growth factor (EGF) on the development of normal rat mammary epithelial cells (MEC) were evaluated using a three dimensional primary culture model developed in our laboratory. Non-milk-producing MEC were isolated as spherical end bud-like mammary epithelial organoids (MEO) from pubescent virgin female rats. The cultured MEO developed into elaborate multilobular and lobuloductal alveolar organoids composed of cytologically and functionally differentiated MEC. Prolactin (0.01-10 micrograms/ml) and EGF (1-100 ng/ml) were each required for induction of cell growth, extensive alveolar, as well as multilobular branching morphogenesis, and casein accumulation. MEO cultured without prolactin for 14 days remained sensitive to the mitogenic, morphogenic, and lactogenic effects of prolactin upon subsequent exposure. Similarly, cells cultured in the absence of EGF remained sensitive to the mitogenic and lactogenic effects of EGF, but were less responsive to its morphogenic effects when it was added on day 14 of a 21-day culture period. If exposure to prolactin was terminated after the first week, the magnitude of the mitogenic and lactogenic effects, but not the morphogenic response was decreased. Removal of EGF on day 7 also reduced the mitogenic response, but did not have any effect on the magnitude of the lactogenic or morphogenic responses. These studies demonstrate that physiologically relevant development of normal MEC can be induced in culture and that this model system can be used to study the mechanisms by which prolactin and EGF regulate the complex developmental pathways operative in the mammary gland.

Hydrocortisone and progesterone regulation of the proliferation, morphogenesis, and functional differentiation of normal rat mammary epithelial cells in three dimensional primary culture

The mechanisms of action of, and resistance to, the steroidal regulators of normal mammary epithelial and breast cancer cell development are only partially understood. A major obstacle to research progress has been the difficulty in supporting physiologically relevant development of normal mammary epithelial cells (MEC) under defined serum-free conditions. A primary culture system was developed in our laboratory that permits nonfunctional rat MEC to undergo extensive proliferation, functional differentiation, as well as multilobular and lobuloductal branching alveolar morphogenesis. In the studies reported here, the contributions of hydrocortisone and progesterone during the coordinate induction of cellular proliferation, organoid morphogenesis, and functional capacity were assessed. Hydrocortisone (0.1-10 microgram/ml) induced alveolar and multilobular branching morphogenesis, suppressed lobuloductal branching morphogenesis, and enhanced casein accumulation. Hydrocortisone also played a role in maintaining alveolar as well as multilobular branching morphogenesis and casein levels. Progesterone (0.01-1 microgram/ml) induced cellular proliferation as well as multilobular and lobuloductal branching morphogenesis, and suppressed casein accumulation. At a supraphysiological concentration (10 micrograms/ml), progesterone inhibited cell growth, alveolar branching morphogenesis, and casein accumulation. MEC cultured without progesterone for up to 1 week retained the ability to respond when subsequently exposed to this steroid. Reversibility studies suggested that progesterone was required for the induction, but not the maintenance of the mitogenic, morphogenic, and lactogenic effects. This physiologically relevant primary culture system can be used to study the factors that regulate steroid responsiveness as well as the cross-talk between steroid and growth factor receptor signaling pathways in normal MEC and breast cancer cells.

Hormonal induction of alpha-lactalbumin and beta-lactoglobulin in cultured mammary explants from pregnant pigs

Mammary tissue from pigs on days 60, 80, 90, 100 and 100+ (days 106-111) of pregnancy has been cultured in vitro as explants. The total accumulation in tissue and culture medium of the whey proteins alpha-lactalbumin and beta-lactoglobulin has been measured using specific radioimmunoassays. The control, uncultured tissue showed progressive morphological development from sparse, non-secretory epithelial tissue on day 60 to full lobulo-alveolar development with some accumulated secretion from day 100. In uncultured explants beta-lactoglobulin could be detected consistently from day 90 (13 +/- 12 ng/micrograms DNA, n = 4) and alpha-lactalbumin from day 100 (1.3 +/- 0.5 ng/micrograms DNA, n = 11). At all stages of pregnancy, both whey proteins increased markedly during the period of culture (up to 7 d). Stimulation of alpha-lactalbumin appeared to be primarily under prolactin control. Prolactin increased alpha-lactalbumin accumulation to a similar extent alone, or in the presence of insulin and/or corticosterone. The response to prolactin was dose-dependent over the range 0.4-20 nM (10-500 ng/ml). Porcine prolactin was more potent than ovine prolactin. There was no effect of porcine growth hormone and no synergism detected between prolactin and tri-iodothyronine. By contrast, no specific hormonal requirements were established for accumulation of beta-lactoglobulin, which appeared to increase in vitro if tissue remained viable in various combinations of insulin, corticosterone and prolactin. It was not stimulated by growth hormone. There was some indication of a prolactin-sensitive component in longer term cultures after day 4.

Estrogen enhances epidermal growth factor-induced DNA synthesis in mammary epithelial cells

Estradiol (E2) priming (1 nM for 48 h) of normal murine mammary gland epithelial cells significantly increased the response of those cells to epidermal growth factor (EGF)-induced DNA synthesis. The synergism between E2 and EGF was evident in two aspects: After serum-free synchronization for 24 h, more cells entered the S-phase of the cell cycle after E2 priming and when treated with 0.17 nM EGF (13%) than did control cells (1.3%) or cells treated with EGF (4%) or E2 (3.5%) alone; further, the dose of EGF required to elicit maximal response was reduced an order of magnitude in estrogen-primed cells (0.17 nM) compared to controls (1.7 mM). Estrogen alone, however, did not increase DNA synthesis in these cells. Ligand binding studies indicate that these effects of estrogen on proliferating mammary epithelial cells may be explained, at least in part, by a 3.7-fold increase in the number of high affinity EGF-receptors observed in estrogen primed cells (7,300 receptors per cell) compared to estrogen deprived cells (1,960 receptors/cell).

Role of epidermal growth factor and transforming growth factors in mammary development and lactation

Epidermal growth factor, transforming growth factor-alpha, and transforming growth factor-beta 1 are potent effectors of mammary growth that work in concert with endocrine hormones, such as estrogen, progesterone, corticosteroids, and prolactin. Estrogen and progesterone stimulate production of epidermal growth factor or transforming growth factor-alpha to stimulate mammary growth. Epidermal growth factor and prolactin synergize in whole organ culture to cause lobulo-alveolar development and to alter the profile of synthesized milk proteins. Transforming growth factor-beta 1 inhibits mammary development of prepubertal mice. However, once the gland is committed to differentiation, transforming growth factor-beta 1 no longer affects mammary morphogenesis. The role of transforming growth factor-beta 1 in milk protein synthesis is unknown. Transforming growth factor-alpha and -beta 1 mRNA have both been identified in the mammary gland of cows. The gland has epidermal growth factor receptors, and epidermal growth factor or transforming growth factor-alpha can stimulate proliferation of mammary epithelial cells in vitro. The role of transforming growth factor-beta 1 in bovine mammary tissue has not been studied. An understanding of the role of epidermal growth factor, the transforming growth factors, and their interactions with endocrine hormones will lead to a more complete understanding of how mammary development and lactation are regulated.

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.

Lactogenic hormones increase epidermal growth factor messenger RNA content of mouse mammary glands

Epidermal growth factor (EGF) is known to stimulate mammary epithelial proliferation, has been identified in milk and is expressed in lactating mammary epithelia. This study examined hormonal control of EGF mRNA in mammary glands of mice. Prepro-EGF mRNA (4.7 kb) was detected during lactation (and increased significantly during this period), whereas a smaller EGF-like RNA (.5 kb) was at highest levels in mammary glands of virgin and pregnant mice. The 4.7 kb RNA was polyadenylated, whereas .5 kb RNA was not. In mammary gland organ cultures from steroid-primed mice, the combinations of insulin + hydrocortisone and insulin + prolactin + hydrocortisone increased both prepro-EGF and beta-casein mRNA expression. When hydrocortisone was present there was a decrease in mammary gland content of EGF-like RNA (.5 kb band). We conclude that prepro-EGF mRNA expression in mouse mammary tissue is under the control of the lactogenic hormones prolactin and hydrocortisone.

Estrogen-independent growth of mouse vaginal epithelium in organ culture

A serum-free vaginal explant culture system was established to investigate the in vitro effect of estrogen on the growth of mouse vaginal epithelium. Vaginal explants were isolated from 40-day-old, ovariectomized BALB/cCrgl mice and cultured in a basal unsupplemented medium or in basal medium plus various doses of 17 beta-estradiol. Explants were processed for histology at the end of culture periods or were given 4-hour pulses of tritiated thymidine at various times and processed for autoradiography. Vaginal epithelium increased 3- to 5-fold in thickness and 2-fold in the number of epithelial cell layers during 72 hours of culture without estrogen; addition of estrogen did not significantly influence epithelial growth. Keratinization of vaginal epithelium occurred within 48 hours of culture in the absence of estrogen, and again addition of estrogen did not accelerate its appearance. Covering the explants with collagen decreased the estrogen-independent growth of vaginal epithelium. Autoradiography showed that ca. 70-90% of basal epithelial cells entered S phase during the initial 4 hours of culture and that this number declined rapidly after 48 hours to ca. 20%. Addition of 1.8 nM 17 beta-estradiol significantly decreased the labelling index of basal cells at 48 hours, but did not affect the labelling index at 24 and 72 hours. Stromal cells were not labelled at any time. Thus, DNA synthesis, cellular proliferation, and differentiation (keratinization) of vaginal epithelium in organ culture occurred without estrogen and were not stimulated by the addition of estrogen.

Effects of inositol 1,4,5-trisphosphate on calcium release from the endoplasmic reticulum and Golgi apparatus in mouse mammary epithelial cells: a comparison during pregnancy and lactation

It has been established that inositol 1,4,5-trisphosphate(IP3) is responsible for the mobilization of calcium(Ca2+) from intracellular locations in a wide variety of tissues, and that this response triggers the stimulation of several hormones and neurotransmitters. However, these phenomena have yet to be examined in the mammary epithelium. Ca2+ uptake from the medium into the endoplasmic reticulum(ER) and Golgi apparatus in vitro in both pregnant and lactating mouse mammary epithelial cells was studied and a strong Ca2+ release from these organelles into the medium with the use of IP3 was shown. The Ca2+ uptake and its release due to IP3 was also usually greater during pregnancy than lactation.

Developmental regulation of mammary-derived growth inhibitor expression in bovine mammary tissue

The cDNA for a previously described growth inhibitor, designated as mammary-derived growth inhibitor (MDGI) (Grosse, R., and P. Langen. 1989. In Handbook of Experimental Pharmacology. In press) has been cloned from a plasmid library which was derived from terminally differentiated bovine mammary gland. Sequencing of the cDNA showed an open reading frame coding for a protein of 133 amino acids. In six positions differences were found between the sequence determined from the cDNA and that determined previously by amino acid sequence analysis. Northern blot analysis revealed abundant MDGI mRNA in the terminally differentiated mammary gland, whereas in virgin gland, liver or pancreas transcripts were not expressed. By use of in situ hybridization technique transcription of MDGI in the developing bovine mammary gland was analyzed. Increasing amounts of MDGI mRNA were detected in the epithelial cells of embryonic mammary rudiment, in the epithelium of developing lobules and in terminal parts of ducts and lobuloalveolar epithelial cells of differentiated glands. There was a geographical gradient of MDGI mRNA concentration in bovine mammary gland reaching a maximum in the proximal parts of the tissue. An immunohistochemical analysis with different polyclonal and peptide directed antibodies against MDGI confirmed the in situ hybridization data with respect to the tissue-specific and differentiation-dependent MDGI expression in bovine mammary gland. The results suggest a close relationship between MDGI transcription and developmental processes in the normal bovine mammary gland.

Binding and action of glucocorticoids and mineralocorticoids in rabbit mammary gland. Exclusive participation of glucocorticoid type II receptors for stimulation of casein synthesis

In order to ascertain whether the effect of corticoids upon casein synthesis in pregnant rabbit mammary gland culture is due to interactions with classical glucocorticoid or type I (mineralocorticoid) receptors we have demonstrated the existence of both types of receptors in the tissue and have studied the effects of aldosterone and the specific glucocorticoid agonist RU 28362 upon casein synthesis in tissue culture. Both compounds significantly stimulated prolactin-induced casein synthesis. On dose-response studies RU 28362 proved to be as active as dexamethasone, cortisol was active at intermediate concentrations and aldosterone was the least active. The three glucocorticoids were able to stimulate DNA synthesis in the tissue, but aldosterone had no effect. Finally, RU 486, a potent glucocorticoid antagonist, blocked the action of aldosterone and the other corticoids upon casein synthesis, whereas spironolactone, a mineralocorticoid antagonist, was unable to do so. These results demonstrate that the stimulatory effect of corticoids upon casein synthesis in pregnant rabbit mammary tissue culture is mediated through classical (type II) glucocorticoid receptors. Transferrin accumulation in the tissue was not modified by any treatment, indicating that the action of the steroids was specific for casein, and not a general stimulation of protein synthesis.

Hormonally induced elevations of alpha- and beta-casein mRNA levels are blocked by cyclic adenine nucleotide and prostaglandins

Normal mammary gland development during pregnancy follows a coordinated program of morphological development (formation of lobuloalveoli) and biochemical differentiation (casein production). In culture, whole mammary glands of Balb/c mice can be similarly induced by application of a mixture of insulin, prolactin, aldosterone and hydrocortisone (IPAH) for 7 days. Our previous reports have shown that lobuloalveolar development, induced by IPAH, is competitively inhibited by the simultaneous presence of dibutyryl cyclic AMP (Bt2cAMP), prostaglandins (PGs) E1, E2, and B1, and papaverine (pap). However, if this mixture is not added until day 4, lobuloalveolar development is relatively unaffected but casein synthesis is repressed. This report explores the mechanism by which cyclic adenine nucleotides and prostaglandins interfere with the normal developmental pathway. The accumulation of alpha- and beta-casein mRNAs induced by prolactin, hydrocortisone and aldosterone is blocked by the combination of Bt2cAMP, PGs E1, E2, and B1, and pap added to the medium for the final 3 days (days 4-7). Under these conditions the glands retain their lobuloalveoli, and little squamous metaplasia can be discerned. Furthermore, de novo synthesis of both caseins is selectively inhibited, despite the continued presence of casein mRNAs in the glands and normal protein synthesis. In contrast, the synthesis of keratin is stimulated. Incomplete mixtures of Bt2cAMP and pap or the combination of PGs E1, E2, and B1, are only partly effective in preventing the accumulation of casein mRNAs. All three mixtures bring about similar effects on both alpha- and beta-casein mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of novel, stage-specific polypeptides associated with the differentiation of mammary epithelial stem cells to alveolar-like cells in culture

A linear pathway of morphologically intermediate cells has been identified between the cuboidal epithelial stem cells and the doming alveolar-like cultures of the cell line Rat Mammary (Rama) 25 in the order: cuboidal----grey----dark----dark droplet cell----doming cultures. The overall process can be accelerated by dimethyl sulfoxide (DMSO) or retinoic acid (RA) in the presence of mammotrophic hormones. From 400-450 [35S]methionine-labeled polypeptides that are routinely separated by two-dimensional gel electrophoresis approximately only 3% change during this process. As the Rama 25 cultures become confluent, three polypeptides of molecular weights (MW) 35 kD (pl = 7.7), 45 kD (pl = 7.5) and 33 kD (pl = 7.7) increase dramatically in radioactive abundance. These increases correspond to increases in numbers of grey cells for the 35 kD polypeptide, to increases in numbers of dark cells together with increases in peanut lectin-binding-ability for the 45 kD polypeptide, and to increases in the numbers of dark cells and in the numbers of droplet cells for the 33 kD polypeptide. After treatment with DMSO, RA or in spontaneously doming cultures, a second set of four polypeptides of MW 26 kD (pl = 5.9), 27 kD (pl = 6.2), 30 kD (pl = 7.2), and the same 33 kD polypeptide as above increase with the increase in numbers of droplet cells, domes, and increase in casein secretion. A variant of Rama 25, Rama 259, which fails to produce droplet cells, domes, or to secrete casein with DMSO and hormones also shows the same changes in the first set but not in the second set of polypeptides. The elongated, myoepithelial-like cell line derived from Rama 25, Rama 29, which cannot undergo any of the above intercellular conversions, fails to show changes in any of these polypeptides. Major changes in radioactive polypeptides have been confirmed for nonradioactive polypeptides and for polypeptides labeled for 4 hr with [35S]methionine. The synthesis of these novel polypeptides thus marks specific morphological stages of the differentiation of mammary epithelial stem to alveolar-like cells in culture, and as such may mark similar differentiation stages in vivo.

Induction of squamous metaplasia: requirement for cell multiplication, and competition with lobuloalveolar development in cultured mammary glands

Mouse mammary glands were previously shown to undergo either of two courses of development and differentiation in whole organ culture. The combination of insulin, prolactin, aldosterone, and hydrocortisone induces a structural development of lobuloalveoli, followed by casein production. In the second course, the mixture of dibutyryl cyclic AMP, prostaglandins E1, E2 and B1, and papaverine brings about an extensive squamous metaplasia and excessive keratinization. In the present study, the foci of the metaplastic squamous cells appeared to originate from single or very few cells. A preferential stimulation of squamous cell multiplication was involved in the induction process. Twice the relative number of nuclei incorporated 3H-thymidine in the squamous metaplastic cells than in the surrounding cuboidal epithelium, according to autoradiography. The necessity for cell multiplication was indicated by the reversible and complete inhibitions of both the metaplastic squamous development and 3H-thymidine incorporation by 1 mM hydroxyurea in the culture medium. Simultaneous inductions of both courses of development and differentiation revealed a competitive and reciprocal relationship between the two pathways. The concurrent expressions of both courses were considerably less than those achieved when either pathway was induced alone. Only the combination of the three types of inducers of squamous metaplasia was able to compete effectively with the hormonal induction of lobuloalveolar development and differentiation. The findings suggest that individual metaplastic squamous foci may originate as clones of cells by processes that require cell multiplication, rather than through a direct non- replicative conversion of pre-existent cells of the cuboidal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell proliferation and milk protein gene expression in rabbit mammary cell cultures

We analyzed the synthesis of DNA, the rate of cell proliferation, and the expression of milk protein genes in mammary cells grown as primary cultures on or in collagen gels in chemically defined media. We assessed DNA synthesis and cell growth, measured by [(3) H]- thymidine incorporation into acid-insoluble material, DNA content, and cell counts, in a progesterone- and prolactin-containing medium. In some experiments, cultures were pulsed for 1 h with [(3)H]thymidine and dissociated into individual cells which were cytocentrifuged and processed for immunocytochemistry and autoradiography. We analyzed expression of milk protein genes at the transcriptional, translation and posttranslational levels in progesterone-depleted medium in the presence or absence of prolactin. We measured protein secretion by radioimmunoassays with antisera directed against caseins, alpha-lactalbumin and milk transferrin1. We determined protein synthesis by incorporating radio-labeled amino acids into acid-precipitable material and by immunoprecipitating biosynthetically labeled milk proteins. We assessed the accumulation of casein mRNA by hybridizing total cellular RNA extracted from cultured cells with (32)P-labeled casein cDNA probes. On attached collagen gels, the cells synthesized DNA and replicated until they became confluent. The overall protein synthetic activity was low, and no milk proteins were synthesized or secreted even in the presence of prolactin. The block in milk protein gene expression was not restricted to translational or posttranslational events but also included transcription, since no casein mRNA accumulated in these cells. On floating gels, protein synthesis was threefold higher than in cells from attached gels. Overall protein synthesis as well as casein and alpha-lactalbumin synthesis and secretion were prolactin-dependent with maximal stimulation at around 10(-9) M. A marked inhibition occurred at higher hormone concentrations. Casein mRNA accumulated in these cells, provided prolactin was present in the medium. In contrast, these cells did not synthesize DNA, nor did they replicate. In embedding gels, the rate of cell proliferation was exponential over 25 d with a doubling time of approximately 70 h. The overall protein synthesis increase was parallel in time with the increase in cell number. Caseins and alpha-lactalbumin (in contrast to transferrin) were synthesized only in the presence of prolactin. We observed the same hormone dependency as with cells growing on floating gels. The number of casein- and transferring-positive cells was measured after dissociating the cell cultures. At day 12, 60 percent of the total cells stored transferring in small cytoplasmic vesicles, whereas only 25 percent of the cells accumulated casein. Differences in the organization and in the shape of mammary cells depending on cell surface conditions suggest that the geometry of the cells, their interaction with extracellular matrix constituents, and cell-to-cell interactions play a role in the expression of two mammary functions: DNA synthesis and growth, as well as milk protein gene expression.

Enhancement of squamous cell development in cultured skin by cyclic adenine nucleotide and prostaglandins

The present study tests the hypothesis that agents known to elevate the level of intracellular cyclic adenine nucleotide may direct different epithelial cells onto a pathway of epidermoid (squamous) development and differentiation. We report here that the mixture of dibutyryl cyclic AMP (dbcAMP), prostaglandins E1, E2 and B1 (PG E1, E2, B1), and papaverine (pap) enhances the rate of normal squamous cell development in organ-cultured skin of chick embryos. The three components may act synergistically to elevate the level of intracellular cyclic adenine nucleotide. We recently reported that the same group of agents induces abnormal development (squamous metaplasia) and aberrant differentiation (keratin production) in the normally cuboidal epithelium of cultured whole mammary glands of mice [1]. Thus, dbcAMP, PG E1, E2, B1, and pap are effective in enhancing normal squamous cell development and also in inducing squamous metaplasia de novo in the epithelial components of two different organs of embryonic and adult animals of two classes of vertebrates. The combined findings are suggestive that cyclic adenine nucleotide together with the prostaglandins may act generally on diverse types of epithelia to bring about squamous cell development and a differentiation marked by keratin production.

Simultaneous occurrence of pregnancylike lobuloalveolar morphogenesis and casein-gene expression in a culture of the whole mammary gland

Entire second thoracic mammary glands of estrogen- and progesterone-treated immature virgin BALB/c mice were stimulated to pregnancylike lobuloalveolar morphogenesis after 6 days of incubation with insulin (5 micrograms/ml), aldosterone (1 micrograms/ml), growth hormone (5 micrograms/ml), cortisol (5 micrograms/ml), and prolactin (80 ng/ml, present as a contaminant in 5 micrograms/ml growth hormone). The alveolar growth in the glands, as judged by morphological studies, was accompanied by an increase in cell number as a function of incubation time in the hormonal medium. Hybridization of the total RNA from these glands to the casein mRNA specific complementary DNA probe (cDNAcsn) revealed that the level of casein mRNA rises from 0.00012 to 0.005% between 1 and 6 days of incubation. Estimates showed that the concentration of casein mRNA per cell rises 17-fold from 70 molecules on Day 1 to 1200 molecules on Day 6, whereas the number of epithelial cells increases only twofold during the same incubation time. When the growth hormone preparation was totally replaced by 80 ng of prolactin during the 6-day incubation, casein-mRNA levels were found to be 0.0083%. These results demonstrate that a pregnancy-like morphogenesis and concurrent expression of the casein gene in vitro can be achieved in a controlled hormone environment containing high cortisol and low prolactin concentrations. This one-step mammogenesis-lactogenesis culture model should be useful for studying the mechanisms of hormonal regulation of casein-gene expression observed in prepartum mammary gland in vivo.

Human breast epithelium in organ culture: effect of hormones on growth and morphology

Normal breast tissue from a 17-year-old girl was grown in organ culture for 3 weeks. A comparison was made between the effects on the epithelium of a defined culture medium containing various combinations of hormones and serum-supplemented medium that has been used to successfully maintain other human tissues for 4 months routinely, and in some cases for up to 1 year. After culture for 3 weeks the explants were exposed to [3H]thymidine and autoradiographs were prepared and evaluated in order to determine labeling indexes. The only serum-free defined medium that permitted any significant survival or labeling of the cells contained insulin + hydroxycortisone + prolactin. However, serum-supplemented medium along gave an even higher labeling index, and this was elevated more in media containing either progesterone or other combinations of hormones. Our study indicates that normal human breast (removed at the early postovulatory stage of the menstrual cycle) can be maintained in a differentiated state for 12 days in serum-supplemented media. By 2 weeks the cells had begun to migrate onto the surface of the explant. They then began to accumulate tonofilaments so that after 3 weeks in culture nearly all of the cells contained tonofilaments. The one exception was found in breast tissue cultured in the presence of human chorionic gonadotropin, where the cells maintained differentiated characteristics, despite the fact that they contained many lysosomes.

Absolute requirement of glucocorticoid for expression of the casein gene in the presence of prolactin

Second thoracic mammary glands of immature BALB/c female mice were stimulated to pregnancy-like lobuloalveolar (LA) development aftr 6 days of incubation in a corticosteroid-free step I culture medium containing insulin, prolactin, estradiol, progesterone, and growth hormone. A low basal level (0.0009%) of casein mRNA (mRNAcsn) sequences was detectable in the LA glands by a specific cDNA probe. Subsequent incubation of the LA glands for 3 days in medium containing insulin and prolactin or insulin and cortisol failed to elicit mRNAcsn above the basal level, indicating that neither prolactin nor cortisol alone can support casein gene expression. However, an increase in mRNAcsn levels was observed when the 3-day incubation with insulin and cortisol or insulin and prolactin was followed by 3 days of culture in presence of insulin, prolactin, and cortisol. When a 3-day incubation with insulin and prolactin was followed by 3 days in insulin and cortisol medium, mRNAcsn levels in the gland remained similar to the basal level. However, a 20-fold increase in the mRNAcsn levels ensued when the LA glands were sequentially incubated for 3 days in insulin and cortisol and then for another 3 days in insulin and prolactin medium. After a preincubation in insulin and cortisol medium, the LA glands retained residual cortisol during subsequent incubation in insulin and prolactin medium, and the mRNAcsn levels in these glands were related to the level of residual cortisol present. When mRNAcsn and the residual cortisol level reached a minimum, addition of fresh cortisol to the medium caused a 20-fold increase in the mRNAcsn levels. This indicates that cortisol is a limiting factor in insulin and prolactin medium and its presence is absolutely required for casein gene expression.