Responses of mammary cells to hormones

The Divergent Effects of Ovarian Steroid Hormones in the MCF-7 Model for Luminal A Breast Cancer: Mechanistic Leads for Therapy

The growth modulating effects of the ovarian steroid hormones 17β-estradiol (E₂) and progesterone (PRG) on endocrine-responsive target tissues are well established. In hormone-receptor-positive breast cancer, E₂ functions as a potent growth promoter, while the function of PRG is less defined. In the hormone-receptor-positive Luminal A and Luminal B molecular subtypes of clinical breast cancer, conventional endocrine therapy predominantly targets estrogen receptor function and estrogen biosynthesis and/or growth factor receptors. These therapeutic options are associated with systemic toxicity, acquired tumor resistance, and the emergence of drug-resistant cancer stem cells, facilitating the progression of therapy-resistant disease. The limitations of targeted endocrine therapy emphasize the identification of nontoxic testable alternatives. In the human breast, carcinoma-derived hormone-receptor-positive MCF-7 model treatment with E₂ within the physiological concentration range of 1 nM to 20 nM induces progressive growth, upregulated cell cycle progression, and downregulated cellular apoptosis. In contrast, treatment with PRG at the equimolar concentration range exhibits dose-dependent growth inhibition, downregulated cell-cycle progression, and upregulated cellular apoptosis. Nontoxic nutritional herbs at their respective maximum cytostatic concentrations (IC₉₀) effectively increase the E₂ metabolite ratio in favor of the anti-proliferative metabolite. The long-term exposure to the selective estrogen-receptor modulator tamoxifen selects a drug-resistant phenotype, exhibiting increased expressions of stem cell markers. The present review discusses the published evidence relevant to hormone metabolism, growth modulation by hormone metabolites, drug-resistant stem cells, and growth-inhibitory efficacy of nutritional herbs. Collectively, this evidence provides proof of the concept for future research directions that are focused on novel therapeutic options for endocrine therapy-resistant breast cancer that may operate via E₂- and/or PRG-mediated growth regulation.

Estrogen Receptors and Post-Receptor Markers in Human Breast Cancer: A Reappraisal

Several major defects in the estrogen receptor pathway have been evidenced in most human breast cancers by an immunofluorescence tracing of estradiol receptor complexes at the single cell level. Endogenous peroxidase seems a reliable postreceptor marker for estrogen-sensitive breast cancer cells. Since almost all human breast cancers appear to include both hormone-sensitive and autonomous cell populations, a combined use of endocrine and cytotoxic regimens is urged. The hormonal regulation of tumor growth parameters could be exploited in order to achieve a maximum recruitment of synchronized tumor cells at risk to chemotherapy.

Preparation of EpH4 and 3T3L1 cells aggregates incorporating gelatin hydrogel microspheres for a cell condition improvement

The objective of this study is to prepare three dimensional (3D) of mouse mammary epithelial EpH4 and mouse preadipocyte 3T3L1 cells in the presence of gelatin hydrogel microspheres (GM) and evaluate the effect of GM presence on the survival and functions of cells in the 3D cell aggregates. Gelatin was dehydrothermally crosslinked at 140 °C for 48 h in a water-in-oil emulsion state to obtain the GM with average diameters of 50 and 200 μm, followed by treatment with fibronectin (FN). EpH4 and/or 3T3L1 cells were cultured with or without the FN-treated GM in round U-bottom wells of 96-multiwell culture plates which had been coated with poly (vinyl alcohol) (PVA) to allow the cells to form their aggregates. On the other hand, EpH4 cells were precultured with the FN-treated GM, and then continued to culture with 3T3L1 cells in the same condition described above. The EpH4 cells attached onto the GM in the cell number dependent manner, irrespective of their size. When 3T3L1 cells were incubated with the original and GM-preincubated EpH4 cells in the presence of both the FN-treated GM, the number of alive cells in the aggregates was significantly high compared with that for the absence of FN-treated GM. In addition, higher β-casein expression level of EpH4 cells in EpH4/3T3L1 cells aggregates in the presence of FN-treated GM was observed than that of cells in the absence of FN-treated GM. Laminin secretion was also promoted for the cells aggregates cultured with FN-treated GM. It is concluded that the presence of FN-treated GM in the EpH4/3T3L1 cells aggregates gave a better condition to cells, resulting in an enhanced generation of β-casein from EpH4 cells in the aggregates.

Polymorphisms of catechol estrogens metabolism pathway genes and breast cancer risk in Mexican women

Breast cancer is associated to estrogen exposure. Allelic variants involved in estrogen metabolism might change the risk of developing this neoplasia. We examined the potential association of breast cancer risk in Mexican women with the polymorphisms CYP1A1 rs1048943, CYP1B1 rs1056836, COMT rs4680, GSTP1 rs1695, GSTT1 null and GSTM1 null which are involved in estrogen metabolism pathway. This study included 150 cases and 150 controls. A significant association was observed between, CYP1A1 rs1048943 (OR = 1.95, C.I. 1.13-3.36) and GSTP1 rs1695 (OR = 2.39, C.I. 1.24-4.24) polymorphisms with the risk of breast cancer. This risk was increased when the women were stratified according to their menopausal status. The results show that breast cancer risk significantly increases in women with 3-6 risk polymorphisms (OR = 3.75, C.I. 1.44-9.74).

Estrogen-induced reactive oxygen species-mediated signalings contribute to breast cancer

Elevated lifetime estrogen exposure is a major risk factor for breast cancer. Recent advances in the understanding of breast carcinogenesis clearly indicate that induction of estrogen receptor (ER) mediated signaling is not sufficient for the development of breast cancer. The underlying mechanisms of breast susceptibility to estrogen's carcinogenic effect remain elusive. Physiologically achievable concentrations of estrogen or estrogen metabolites have been shown to generate reactive oxygen species (ROS). Recent data implicated that these ROS induced DNA synthesis, increased phosphorylation of kinases, and activated transcription factors, e.g., AP-1, NRF1, E2F, NF-kB and CREB of non-genomic pathways which are responsive to both oxidants and estrogen. Estrogen-induced ROS by increasing genomic instability and by transducing signal through influencing redox sensitive transcription factors play important role (s) in cell transformation, cell cycle, migration and invasion of the breast cancer. The present review discusses emerging data in support of the role of estrogen induced ROS-mediated signaling pathways which may contribute in the development of breast cancer. It is envisioned that estrogen induced ROS mediated signaling is a key complementary mechanism that drives the carcinogenesis process. ROS mediated signaling however occurs in the context of other estrogen induced processes such as ER-mediated signaling and estrogen reactive metabolite-associated genotoxicity. Importantly, estrogen-induced ROS can function as independent reversible modifiers of phosphatases and activate kinases to trigger the transcription factors of downstream target genes which participate in cancer progression.

Tissue engineering for conjunctival reconstruction: established methods and future outlooks

Reconstruction of the conjunctiva is an essential part of ocular surface regeneration, especially if an extensive area or the whole ocular surface is affected, such as in patients with ocular cicatricial pemphigoid, Stevens-Johnson syndrome, toxic epidermal necrolysis, or chemical/thermal burns. In these situations, corneal reconstruction almost inevitably fails unless the conjunctival surface is first repaired and a deep fornix is restored. The growing field of tissue engineering and advances in stem cell research offer promising new alternatives for these challenges. This article reviews the present approaches for reconstruction of the conjunctival surface, considering the established strategies and new potential methodologies.

Chemomodulatory influence of Ferula asafoetida on mammary epithelial differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea-induced mammary carcinogenesis in rats

The present study was conducted to ascertain the modulatory influences of Ferula asafoetida L. (asafoetida, flavoring agent) on the mammary epithelial tissue differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in Sprague-Dawley rats. Feeding with two doses of asafoetida (1.25 and 2.5% w/w in diet) showed a remarkable increase in the development and differentiation of ducts/ductules (p < 0.01-0.005), lobules (p < 0.005) and a decrease in terminal end buds (p < 0.05-0.005) as compared to both normal and MNU-treated control animals. To assess the biochemical parameters, effect of asafoetida on drug-metabolizing enzymes was evaluated in the liver of rats. Asafoetida treatment significantly reduced (p < 0.05) the levels of cytochrome P450 and b5. There was an enhancement in the activities of glutathione S-transferase (p < 0.05-0.005), DT-diaphorase (p < 0.05-0.01), superoxide dismutase (p < 0.01-0.005) and catalase (p < 0.05-0.005) and in the level of reduced glutathione (p < 0.05-0.005), followed by asafoetida treatment. Also, asafoetida significantly restored the level of antioxidant system, depleted by MNU-treatment. The strengthening of antioxidant system by the lower and higher doses of asafoetida in the presence and absence of MNU was further substantiated by a significant inhibition (p < 0.005) in lipid peroxidation as measured by thiobarbituric acid-reactive substances (TBARS) in the liver of rat. Further, in long-term animal studies, where MNU was used to induce mammary carcinogenesis, asafoetida treatment resulted in a significant reduction in the multiplicity (p < 0.001) and size of palpable mammary tumors (p < 0.005-0.001) and a delay in mean latency period of tumor appearance (p < 0.005). Together, these findings indicate the chemopreventive potential of asafoetida against MNU-induced mammary carcinogenesis. Thus, asafoetida needs further investigation with regard to identification and characterization of its active principle(s) and mechanism of action, for this compound to be developed as a potential chemopreventive agent for human cancers.

Distribution of casein-like proteins in various organs of rat

Casein-like proteins were detected in various organs of rat by use of a specific antiserum raised against rat milk caseins. The antiserum specifically recognized alpha 1-, alpha 2-, beta-, and gamma-caseins in rat milk by Western blot analysis, whereas no immunoreactive band was observed in sera of rat and fetal bovine and in bovine caseins. Immunohistochemical studies of this antiserum on formalin-fixed mammary glands showed that immunoreactive caseins were localized to the apical portion of the cytoplasm in lactating mammary epithelial cells and in the luminal secretion, which indicates a directional secretion of caseins to the lumen by the mammary epithelial cells. With this antiserum, immunoreactive substances were detected in various organs, including the pancreatic ducts and islets of Langerhans, the secretory ducts of salivary glands, zona fasciculata cells and ganglion cells of adrenal gland, distal tubules and convoluted collecting tubules of kidney, epithelial cells of bronchioles and large pneumocytes of the lung, hair follicles, sebaceous glands, and the prickle cell layer of skin, uterine glands and epithelium of the endometrium, hepatic bile ducts, and brain. In Western blot analysis, major immunoreactive substances in the above organ extracts showed a similarity in molecular weight to alpha 2-casein of rat milk. Skin was the only tissue that expressed both alpha 2- and beta-caseins. There were no other immunoreactive bands with similarity to beta- and gamma-caseins in the other organ extracts, but higher molecular weight immunoreactive bands (> 100 kD) were detected in some organ extracts, such as salivary gland, kidney, liver, lung, and uterus. These findings suggest that the alpha 2-casein-like substance is localized not only in the mammary gland but also in a variety of organs and may play an important role as a functional molecule in those organs.

A mammary epithelial cell line is transiently stimulated towards milk lipid synthesis by lactogenic treatments

A subcloned mouse mammary epithelial cell line (COMMA-D/MME) was cultured on Engelbreth-Holm-Swarm (EHS) tumor cell matrix with lactogenic hormones (insulin, cortisol, prolactin) to stimulate differentiation and challenged with growth factors to interpret the relationship between the signals for growth and differentiation. After 21 days of pretreatment to promote differentiation, cells were capable of growth, but were always less responsive than cells that did not receive lactogenic pretreatment. Although the cells failed to express beta-casein mRNA, droplets of neutral lipids were present in the cell cytoplasm regardless of treatment. Lactogenic hormones induced the appearance of larger droplets that occurred in intracytoplasmic lumens and lipid synthesis rates were initially increased. However, the glycerol incorporation pattern of these lipids only reached 53% of the changes expected for lactating tissue. Furthermore, because secretion of the lipid was inhibited, the accumulation eventually inhibited synthetic capacity. The cellular expression of acetyl Co-A carboxylase message was increased by growth, but not by lactogenic treatments. It is concluded that the COMMA-D/MME are capable of partial and transient differentiation to synthesize milk lipids, but are inhibited by the accumulation of material due to inability to secrete.

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.

The role of estrogen in mammary carcinogenesis

The in vivo and in vitro studies conducted to examine whether E2 functions as an initiator or a promoter in mammary carcinogenesis can be summarized as follows: (1) Clinical and animal studies in vivo have shown a positive correlation of up-regulation of E2 C16 alpha-hydroxylation with either the presence of or the risk for breast cancer, suggesting that this metabolic alteration may represent an early-occurring event in the multistep process of tumorigenesis. (2) The mammary tissue, target for carcinogenesis, exhibits cancer risk-dependent alteration in E2 metabolism in the rodent and human mammary explant culture model, indicating that E2 metabolites may directly influence the mammary epithelium. (3) The 16 alpha-hydroxylated metabolite of E2, 16 alpha-OHE1, induces genotoxic DNA damage and aberrant hyperproliferation similar to that induced by chemical carcinogens in the rodent cell culture model. In preinitiated or fully transformed rodent or human cells, 16 alpha-OHE1 promotes the expression of transformed phenotype. (4) The initiator-mediated perturbation of E2 C16 alpha-hydroxylation in rodent and human mammary explant cultures is modulated by naturally occurring dietary constituents that are known to modulate rodent mammary tumorigenesis. (5) The observed effect of E2 on mammary tumorigenesis may be due in part to the generation of 16 alpha-OHE1, which functions as a weak initiator or a potent promoter of tumorigenic transformation in mammary epithelial cells. (6) The reaction of 16 alpha-OHE1 with the transcription factor ER is unique in that it can be irreversible and leads to aberrant gene expression.

Modulatory influence of oral contraceptives on mammary growth pattern of normal and ovariectomised mice

The present study reports the modulatory influence of oral contraceptive formulations, Ovral (0.05 mg ethinylestradiol plus 0.5 mg norgestrel per pill), Noracycline (0.05 mg ethinylestradiol plus 0.1 mg lynestrenol per pill), Pearl (0.03 mg ethinylestradiol plus 0.30 mg norgestrel) and Centchroman (30 mg), on the growth and developmental pattern of murine mammary epithelium in normal as well as ovariectomised mice. Oral treatments of ovariectomised mice for 15 days with doses D1 (1/5th of a pill) and D2 (1/10th of a pill) of Ovral, Noracycline and Pearl enhanced the diameter of the terminal end buds (TEBS) and lateral buds (LBS) significantly. The increase in the diameters of TEBS and LBS on treatment with similar doses of Centchroman were not much significant. Hence, it may be concluded from the present study that the growth and development pattern of mammary epithelium can be modulated by treatment with oral contraceptives Oral, Noracycline, Pearl and Centchroman which is indicated by the increase in the diameters of TEBS and LBS.

The effect of lactogenic hormones on protein synthesis and amino acid uptake in rat mammary acinar cell culture at various physiological stages

1. The activities of protein synthesis and amino acid uptake at various physiological stages were determined by the incorporation of radioactive materials ([3H]-lysine, [14C]-cycloleucine) in rat mammary epithelial cell cultures. The activity of protein synthesis and amino acid uptake was higher in early lactation than in virgin, pregnant and late lactation stages. 2. Lactogenic hormones (prolactin, hydrocortisone and insulin) treatment related with mammary growth and differentiation increased the activities of protein synthesis and amino acid uptake. But increase of these activities was different at each physiological stage. 3. The effect of prolactin and hydrocortisone on the activities were greater in virgin, pregnant and late lactation than in early lactation. And effect of insulin was greater in pregnant and early lactation than in virgin and weanling.

Persistent estrogen responsiveness of ras oncogene-transformed mouse mammary epithelial cells

Ovarian steroids are associated with the proliferation of normal as well as tumorigenically transformed mammary epithelial cells. The experiments performed in this study were designed to establish that (1) tumorigenic transformation induced by the ras oncogene is associated with alterations in estradiol biotransformation, (2) altered endocrine responsiveness persists in the fully transformed tumor cell phenotype and (3) specific perturbations induced by the ras oncogene can be experimentally downregulated. The ras transfectant pH06T and the tumor-derived T1/Pr1 cells exhibited 3- and 43-fold increases, respectively, in C-16 alpha hydroxylation of estradiol relative to the parental mouse mammary epithelial cells (P less than 0.0001). At the cellular level, this alteration corresponded with approximately 90-fold increase in the anchorage-independent growth of T1/Pr1 cells (P less than 0.0001). Estrogen responsiveness of T1/Pr1 cells was demonstrated by their suppression of growth in phenol red-free and/or tamoxifen-supplemented medium and by the reversal of antiproliferative effect of tamoxifen by phenol red and estradiol. Indole-3-carbinol, a naturally occurring tumor suppressive agent, was able to upregulate C-2 hydroxylation at the expense of C-16 alpha hydroxylation of estradiol. Treatment of T1/Pr1 cells with indole-3-carbinol resulted in a substantial decrease in anchorage-independent growth.

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.

Biotransformation of estradiol by explant culture of human mammary tissue

In vivo experiments on strains of mice that differ in the risk of developing mammary cancer have demonstrated a correlation between the extent of 16 alpha-hydroxylation of estradiol and incidence of mammary cancer. The ability of human mammary terminal duct lobular unit (TDLU), the site of neoplastic transformation, to metabolize estradiol or to accumulate estradiol metabolites has not been unequivocally established. Using a newly developed human mammary TDLU explant culture system and a radiometric assay for estradiol metabolism, we compared the site-specific metabolism of estradiol by the 17-oxidation, 2-hydroxylation, and 16 alpha-hydroxylation pathways in noninvolved human mammary tissue. The relative extent of estradiol 16 alpha-hydroxylation was found to be increased in TDLU from patients in the luteal phase of the menstrual cycle in relation to either those from patients in the follicular phase or from postmenopausal subjects. This study demonstrates that TDLU can metabolize estradiol extrahepatically and that 16 alpha-hydroxylation in the target tissue is dependent on the phase of the menstrual cycle. Furthermore, the specific, risk-related increase in 16 alpha-hydroxylation suggests that intrinsic metabolic ability of the target tissue leading to the formation of 16 alpha-hydroxyestrone from estradiol may be a determinant in, or a marker for, the relative risk of developing mammary cancer.

Effect of DMBA on the expression of prolactin receptors and IGF1 genes in rat mammary gland

Prolactin receptor and IGF1 gene expression were measured in mammary glands from Sprague-Dawley rats at different times (10, 30; and 58 d) after administration of a single dose of 15 mg dimethylbenz(a)-anthracene (DMBA) per os at 55 d of age, and in DMBA-induced mammary tumors appearing in these rats at approximately 2 months after DMBA administration; The relative gene expression of prolactin receptor and insulin-like growth factor (IGF1) mRNAs was measured by hybridization to Northern blots prepared from pools of tissue. The probes used were 32P-labelled cDNAs specific to the extracellular domain of the receptor (E probe), common to all forms, and a probe specific to the intracellular position of the long form of the receptor (I probe), a human IGF1 probe, and chicken beta-actin probe, to correct for loss of tissue and different metabolic activity of the tissues. Hybridization with the prolactin receptor probes revealed bands at 2.5, 3; and 5.5 kb hybridizing with the long form of the receptor and a more intense band at 1.8 kb that corresponded to the short form of the receptor. There were no changes in the relative expression of prolactin receptor mRNAs in the mammary gland of control (oil-treated) or DMBA-treated rats, although there was a gradual diminution of expression with increasing age of the animals. In contrast, in DMBA-induced mammary tumors, there was a marked increase in the relative expression of prolactin receptor mRNAs with, however, no modification in the relative proportion of short and long forms.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro biotransformation of estradiol by explant cultures of murine mammary tissues

In vivo experiments have demonstrated a correlation between the extent of 16 alpha-hydroxylation of estradiol and incidence of mammary cancer. The ability of mammary ductal epithelium (MDE), the site for neoplastic transformation, to metabolize estradiol or to accumulate estradiol metabolites has not been unequivocally established. Using a newly developed mammary explant culture system and a radiometric assay, we have compared the site-specific metabolism of estradiol (E2) by the C-17-oxidation and C-16 alpha-hydroxylation pathways in mouse tissues that differ in relative risk for mammary cancer. A comparison between MDE (target tissue) and liver (nontarget tissue) from NFS (low risk) and C3H/ouj (high risk) mice revealed that: a) increase in C-17-oxidation was similar in MDE and liver from the two strains, and b) while C-16 alpha-hydroxylation was similar in liver from the two strains (p = 0.5, n.s.), it was increased 4-fold in the MDE from the high risk C3H/ouj strain relative to that from the low risk NFS strain (p = 0.001). Furthermore, in vivo administration of progesterone resulted in modulation of cell proliferation as well as of E2 metabolism in mammary explant cultures. The effect of progesterone depended upon the presence of the MtV-2 proviral gene. This study demonstrates that mammary explants can extrahepatically metabolize estradiol. The specific risk-related increase in C-16 alpha-hydroxylation suggests that intrinsic metabolic ability of the target tissue leading to the formation of 16 alpha-hydroxyestrone from estradiol may be a determinant in the relative risk for developing mammary cancer.

Turnover of epidermal growth factor binding sites in mouse mammary epithelial cells

An in vitro method of studying epidermal growth factor (EGF) receptors in mouse mammary epithelial cells in serum-free collagen gel culture has been developed. Binding of EGF averaged 108 +/- 19 fmol/mg DNA in cells isolated from freshly dissociated virgin mammary tissue. Initial binding values were maintained in cells cultured in the presence of 0.1 ng/ml EGF, but decreased in either 0 ng/ml or 10 ng/ml EGF. Addition of either chloroquine (100 microM) or ammonium chloride (10 mM) to the culture medium increased receptor levels 10-fold. Cycloheximide (0.1 microgram/ml), ouabain (3 mM), and actinomycin D (5 x 10(-2) micrograms/ml) each decreased receptor levels, in some cases by as much as 80%. Both methylamine (10 mM) and dinitrophenol (0.1 mM) had no significant effect. These studies suggest that the net level of EGF receptors in these target cells is the result of an equilibrium between synthesis and degradation. The difference between the effects of the compounds tested on either receptor degradation or synthesis in comparison to cell growth, may be indicative that receptor degradation is not linked to cell proliferation.

Ha-ras and c-myc oncogene expression interferes with morphological and functional differentiation of mammary epithelial cells in single and double transgenic mice

We studied the effects of the tissue-specific and lactogenic hormone-dependent expression of the recombinant whey acidic protein (Wap)-ras and Wap-myc oncogenes on the differentiation of the mammary epithelium in transgenic mice. The histological appearance of mammary glands in pregnant, lactating, and postlactational animals and their ability to express milk protein genes were analyzed. Activated Ha-ras expression caused a decrease of milk protein synthesis during the lactation period. The formation of glandular epithelium and the postlactational regression of epithelial cells were not affected. c-myc expression impaired the development of the glandular epithelium, and milk protein synthesis was decreased strongly. Epithelial cell proliferation continued during lactation and postlactationally. Coexpression of both oncogenes in double transgenic mice synergistically affected differentiation and resulted in a high number of neoplastic foci. Palpable tumors were observed only after a latency of 3-4 months. Tumor cells utilize the Wap promoter hormone independently, express increased levels of Wap-ras and induce adjacent stromal cells to produce tenascin.

Structure and expression of the guinea-pig alpha-lactalbumin gene

The entire guinea-pig alpha-lactalbumin gene was isolated from a genomic DNA library constructed in the bacteriophage lambda L47. The complete nucleotide sequence of the gene and its immediate 5' and 3' flanking sequences were determined and compared with those of the human and rat alpha-lactalbumin genes. This demonstrates that the size, organization and sequence of the exons is highly conserved between species, and reveals the presence of the highly conserved potential regulatory 'milk box' consensus sequence [RGAAGRAAA(N)TGGACAGAAATCAA(CG)TTTCTA] between positions -140 and -110 relative to the transcriptional start point. A guinea-pig LINE repeat sequence was also present in the 5' flanking region between positions -520 and -1195. Transfection of the alpha-lactalbumin gene cloned in a bovine papilloma virus vector into the mouse C127 and human MCF-7 mammary tumour cell-lines gave rise to stable but seemingly constitutive expression of alpha-lactalbumin. Expression was from the correct transcriptional start point, resulting in the accumulation of correctly processed mRNA and the secretion of alpha-lactalbumin into the culture medium.

A novel system for mammary epithelial cell culture

A method is described for the isolation and density gradient enrichment of mammary epithelial fragments from pregnant, nonlactating bovine tissue. Immunocytochemical analysis prior to and following culture revealed specific staining with antibodies to keratin, indicating that these cells are epithelial in nature. Fragments enriched for epithelium could be stored in liquid nitrogen for extended periods prior to culture. When cast within a three-dimensional matrix of collagen gel, the mammary fragments grew as branching, duct-like structures and displayed a 4-fold increase in cell number during 10 to 12 d of culture.

The gene for human alpha-lactalbumin is assigned to chromosome 12q13

A cDNA clone complementary to the mRNA encoding human alpha-lactalbumin (ALA) has been used as a probe in the analysis of DNA from panels of rodent/human somatic cell hybrids. The presence of the ALA gene correlates with the presence of chromosome 12. In situ hybridization localizes the ALA gene to 12q13.

Organization and sequence of the human alpha-lactalbumin gene

A recombinant bacteriophage containing the entire alpha-lactalbumin gene was isolated from a human genomic library constructed in bacteriophage lambda L47. Within this recombinant the 2.5 kb alpha-lactalbumin gene is flanked by about 5 kb of sequence on either side. The complete nucleotide sequence of the gene and its immediate flanking sequences were determined and compared with those of the rat alpha-lactalbumin gene. These studies showed that the size, organization and sequence of the exons have been highly conserved, whereas the introns have diverged considerably. In particular, the first intron of the human gene was found to contain an Alu repetitive sequence not present in the rat. A high degree of homology (67%) was also observed in the 5' flanking regions, extending as far as 655 nucleotide residues upstream of the transcriptional initiation site. Comparison of the 5' flanking sequences of these two alpha-lactalbumin genes with those of five casein genes has revealed the presence of a highly conserved region [consensus sequence: RGAAGRAAA(N)TGGACAGAAATCAA(CG)TTTCTA], extending from position -140 to -110 in all seven sequences examined, suggesting a possible regulatory role in the hormonal control or tissue-specific expression of milk protein genes in the mammary gland.

Milk protein expression and ductal morphogenesis in the mammary gland in vitro: hormone-dependent and -independent phases of adipocyte-mammary epithelial cell interaction

Epithelial cell differentiation frequently occurs in situ in conjunction with supporting mesenchyme or connective tissue. In embryonic development the importance of the supporting mesenchyme for cytodifferentiation and morphogenesis has been demonstrated in several epithelial tissues, but the importance of epithelial-connective tissue interactions is less well studied in adult epithelial organs. We have investigated the interaction of adult mammary epithelial cells with adipocytes, which compose the normal supporting connective tissue in the mammary gland. Mammary epithelial cells from mice in various physiological states were cultured on cellular substrates of adipocytes formed from cells of the 3T3-L1 preadipocyte cell line. We found that there were two distinct phases to the interaction of epithelial cells with adipocytes. Cytodifferentiation of the epithelial cells and milk protein production were dependent on lactogenic hormones (insulin, hydrocortisone, and prolactin), whereas ductal morphogenesis was lactogenic hormone independent. When cultured on preadipocytes or adipocytes, mammary epithelial cells from never pregnant, pregnant, lactating, and involuting mice responded to lactogenic hormones rapidly by producing and secreting large amounts of alpha-, beta-, and gamma-casein and alpha-lactalbumin. This response was seen in individual as well as in clusters of epithelial cells, but was not seen if the same cells were cultured on tissue culture dishes without adipocytes, on fibroblasts (human newborn foreskin fibroblasts) or in the presence of adipocytes but in the absence of lactogenic hormones. Continued incubation of mammary epithelial cells on adipocytes in the presence or absence of lactogenic hormones resulted in the formation of a branching ductal system. Mammary epithelial cells in ducts that formed in the absence of lactogenic hormones produced no casein, but rapidly synthesized casein when subsequently exposed to these hormones. Ultrastructural studies revealed that the formation of a basement membrane occurs only in co-cultures of mammary epithelium with adipocytes or preadipocytes. Ultrastructural changes associated with secretion occurred only in the presence of lactogenic hormones. We propose that growth and formation of a ductal system in vitro can occur in the absence of lactogenic hormones, but that certain environment-associated events must occur if the epithelium is to become responsive to lactogenic hormones and undergo the cytodifferentiation associated with lactation.

Steroid hormone receptor regulation by various hormonal factors during mammary development and growth in the normal mouse

The studies described herein are focused on the nature and regulation of estrogen receptors in normal mammary tissue, with the rationale that manipulation of these receptors is the sole basis for endocrine therapy of human breast cancer. Various features of this complex system have been uncovered by our studies. The presence of different forms of cytosol estrogen receptor, fluctuating in unison with glandular stimulation, results in differential responsiveness of the cells. Tissue that is relatively estrogen-starved presents its receptors in a form that avidly attract the limited available ligands and can hastily put them to use in the nucleus. In contrast, the receptor system in the highly stimulated state displays a sort of refractoriness to estrogen, being relatively sluggish in its responsiveness. Once formed, however, these latter complexes are probably far more effective in terms of eliciting estrogenic responses, since they have an enhanced affinity for DNA and a prolonged half-life. (Table; see text) Prolactin is clearly a very important mediator of the action of estrogen on the mammary gland estrogen receptors, presenting a tissue-specific difference in comparison with the regulation of the uterine estrogen-receptor system. An odd finding was that prolactin inhibits nuclear retention of the estrogen receptor (and probably the progesterone receptor), an effect that is counterproductive to its very strong positive action on the level of intracellular receptor. Perhaps prolactin is the gross effector of receptor fluctuation, allowing estrogen the privilege of dictating the degree of receptor function; indeed our data on the dose-responsiveness of estrogen action and the effects of bromocriptine indicate that a portion of the estrogenic stimulation is not mediated by prolactin. An interesting sidelight of these studies was the finding that high levels of bromocriptine, pharmacologic in terms of prolactin suppression, exhibited an inhibitory effect on nuclear retention of estrogen receptors that was independent of, and did not prevent subsequent elicitation of, the action of prolactin on the receptors. The role of prolactin in tumorigenesis is well established in experimental animals, but its role in the human disease is not clear. Although prolactin receptors have been measured in human breast cancer, there does not appear to be any distinguishable correlation with the presence of estrogen or progesterone receptors. While it is a bit premature to draw conclusions, initial trials of bromocriptine usage have not been supportive of beneficial effects of such treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Glucose 6-phosphatase activity in pregnant and lactating mammary glands of the mouse

Glucose 6-phosphatase activity was studied in the secretory epithelial cell and other cell types composing alveoli of the mammary gland (cytochemical study) and in the whole mammary gland (biochemical study) of pregnant and lactating mice. The reaction product for the enzyme activity was seen in the endoplasmic reticulum and nuclear envelope in secretory epithelial cells from all animals examined (days 7 and 14 of pregnancy, and days 0, 3, 10, and 20 of lactation. The amounts of the reaction product appeared scarce at day 7 of pregnancy, moderate at day 14 of pregnancy and day 0 of lactation, and abundant at days 3 and 10 of lactation. The reaction product, however, became generally scarce at day 20 of lactation. Biochemical activity was relatively low at days 7 and 14 of pregnancy and days 0 and 20 of lactation, while it was high at days 3 and 10 of lactation. The increased activity is probably related to functions of secretory epithelial cells in the lactating gland.

Paracrine regulation of mammary gland growth

The growth and differentiation of the mammary gland is a complex process involving the interactions of various steroid and polypeptide hormones. The mammary growth occurs in a discontinued way during five distinct phases, i.e. fetal, prepubertal, postpubertal, pregnancy, and early lactation periods. The gland expresses its differentiated function by producing milk during the period of lactation. Although the mammary gland has been regarded as one of the well-known target tissues for various types of hormones, evidence has been accumulating in recent years indicating the involvement of other factors and substances in the process of mammary growth and differentiation. In this chapter the importance of the mesenchymal component in mammary epithelial cell growth has been documented. This component, including embryonic mesenchyme and adipocytes in adult tissue, play an essential role by not only serving as a structural entity of the gland but also by producing extracellular matrix substances and various factors that promote the growth, morphologic development and differentiation of mammary epithelium in a paracrine fashion. Other possible paracrine peptide factors for mammary cell growth have been isolated from several other sources including mammary tumors and milk. Thus, it is possible that paracrine growth factors play a role in mammary tumorigenesis. Since most of these factors are present in minute amounts, it is difficult to obtain pure forms of these factors in sufficient amounts for detailed physicochemical characterization. Moreover, further studies are needed to assess the physiological importance of these growth factors, their mode of action, and the mechanism of regulation relating to their production. It is conceivable that some mammary paracrine agents interact with each other or with endocrine agents in promoting the normal and neoplastic growth of mammary cells. Furthermore, the possibility exists that the production and release of paracrine factors are under the endocrine control. In view of the rapid progress and great interest in this area, these questions may be answered before long, along with the discovery of some other new growth regulating agents in this system. Clearly such information is important for understanding the complex process of normal and neoplastic growth of the mammary gland.

Differential response of normal rat mammary epithelial cells to mammogenic hormones and EGF

A simple dissociation procedure and the collagen gel culture system have been utilized to determine the effects of mammogenic hormones and epidermal growth factor (EGF) on the proliferation of normal rat mammary epithelial (RME) cells in serum-free culture. Epithelial fragments, isolated from normal virgin F344 rat mammary glands by enzyme digestion followed by Percoll density gradient centrifugation, were embedded within a rat tail collagen matrix. A three- to four-fold increase in cell number was observed when ovine prolactin (PRL) and progesterone (P) were present in the basal medium during 7 days of culture. Mouse EGF stimulated one cell doubling during the same culture period. Isolated mammary organoids produced a 'stellate' type colony when PRL + P were present in the culture medium. These colonies were composed of small, tightly packed cuboidal cells. The addition of EGF to the basal medium produced a diffuse 'basket' type colony which was composed of large, elongate cells. When the complete hormonal and growth factor combination (PRL + P + EGF) was present, a 'mixed' type colony was observed which contained both the large and small epithelial cell types. Immunocytochemical analysis revealed that both the cuboidal and elongate cells present in the two colony types stained with antibodies to keratin indicating that these cells were epithelial in nature. The small cuboidal cells also expressed thioesterase II and alpha-lactalbumin, both specific for secretory mammary epithelial cells. The large, elongate cell type, however, was positive for actin but did not stain for either secretory epithelial specific marker. The results reported here suggest that normal rat mammary tissue may contain two epithelial populations, one which responds to PRL + P and the other which responds to EGF.

Measurements of chemical carcinogen-induced sister-chromatid exchanges in a whole organ in vitro

Sister-chromatid exchange (SCE) was measured in epithelial cells of mammary organs exposed to 3 different carcinogens in vitro. 7,12-Dimethylbenz[alpha]anthracene (DMBA), N-nitrosodiethylamine (DENA) and N-methyl-N-nitrosourea (MNU) are capable of inducing a significant enhancement of SCE over the basal level in the mammary cells. Analysis of SCE caused by the mutagenic and/or carcinogenic agents in the organ culture presents the advantages that: (1) the culture procedure does not require enzymatic dissociation of the tissue and (2) the medium does not need to be supplemented with serum or exogenous mitogenic agents thereby minimizing the basal level of SCE. Moreover, the assay does not require utilization of exogenous microsomal enzymes needed for activation of certain carcinogenic chemicals. SCE measurements in the organ culture system also should provide clues about the mechanism of action of the chemopreventive agents, particularly the antioxidants, which are under investigation for their possible influence on the processes of neoplastic transformation.

Cell-cell interactions promote mammary epithelial cell differentiation

Mammary epithelium differentiates in a stromal milieu of adipocytes and fibroblasts. To investigate cell-cell interactions that may influence mammary epithelial cell differentiation, we developed a co-culture system of murine mammary epithelium and adipocytes and other fibroblasts. Insofar as caseins are specific molecular markers of mammary epithelial differentiation, rat anti-mouse casein monoclonal antibodies were raised against the three major mouse casein components to study this interaction. Mammary epithelium from mid-pregnant mice was plated on confluent irradiated monolayers of 3T3-L1 cells, a subclone of the Swiss 3T3 cell line that differentiates into adipocytes in monolayer culture and other cell monolayers (3T3-C2 cells, Swiss 3T3 cells, and human foreskin fibroblasts). Casein was synthesized by mammary epithelium only in the presence of co-cultured cells and the lactogenic hormone combination of insulin, hydrocortisone, and prolactin. Synthesis and accumulation of alpha-, beta-, and gamma-mouse casein within the epithelium was shown by immunohistochemical staining of cultured cells with anti-casein monoclonal antibodies, and the specificity of the immunohistochemical reaction was demonstrated using immunoblots. A competitive immunoassay was used to measure the amount of casein secreted into the culture medium. In a 24-h period, mammary epithelium co-cultured with 3T3-L1 cells secreted 12-20 micrograms beta-casein per culture dish. There was evidence of specificity in the cell-cell interaction that mediates hormone-dependent casein synthesis. Swiss 3T3 cells, newborn foreskin fibroblasts, substrate-attached material ("extracellular matrix"), and tissue culture plastic did not support casein synthesis, whereas monolayers of 3T3-L1 and 3T3-C2 cells, a subclone of Swiss 3T3 cells that does not undergo adipocyte differentiation, did. We conclude that interaction between mammary epithelium and other specific nonepithelial cells markedly influences the acquisition of hormone sensitivity of the epithelium and hormone-dependent differentiation.

Expression of keratins and other cytoskeletal proteins in mouse mammary epithelium during the normal developmental cycle and primary culture

Mammary epithelium is composed of ductal, alveolar, and myoepithelial cells, and undergoes dramatic responses in growth, differentiation, and function to hormonal stimuli during the four stages of the mammary developmental cycle represented in virgin, pregnant, lactating, and involuting animals. To determine if progression of the epithelium through the cycle is accompanied by changes in cytoskeletal composition, particularly the keratins, the polypeptides in cytoskeletal extracts from BALB/c mouse mammary tissues were analyzed by one- and two-dimensional gel electrophoresis combined with immunoblots using polyclonal and monoclonal antikeratin antibodies. The major polypeptides in cytoskeletal fractions enriched in intermediate filaments included seven acidic and three basic components ranging in molecular weight from 40,000 to 90,000. Two major polypeptides of Mr 50,000 and 40,000, along with two minor components of Mr 57,000 and 55,000 were identified as keratins. The polypeptide profiles of mammary glands from virgin, pregnant, lactating, and involuting mice were very similar, indicating a remarkable stability of cytoskeletal composition during hormonal shifts and periods of minimal or maximal cell growth and differentiated function. The data also suggest that ductal and alveolar cells express the same set of cytoskeletal polypeptides, including keratins. Mammary cells grown in primary culture exhibited a loss or reduction in most of the basic polypeptides, a large increase in an acidic Mr 55,000 keratin, and the appearance of a prominent acidic polypeptide of Mr 46,000. The latter results demonstrate that keratin expression in mouse mammary epithelial cells is subject to regulation by certain environmental factors.

Prolactin binding in normal human minor salivary gland tissue: an immunohistochemical study

The breast and salivary gland exhibit some similarities in the biochemical and cellular spheres. There are also some tumors that are common to both organs. The protein hormone prolactin seems to play a role in the health and disease of the mammary gland, and an investigation was launched to see if this hormone exhibited any binding activity in normal human minor salivary gland. With the use of immunohistochemical methods, dose-dependent staining for prolactin binding was demonstrated in the striated and collecting ducts in four of six specimens of normal human minor salivary gland (two males and two females). The hormone concentrations used ranged from 6.25 ng/ml to 500 ng/ml of highly purified rat prolactin. A review of known functions of prolactin in man and other animals is presented, and it was concluded that normal human minor salivary gland tissue possesses binding sites for prolactin, which suggests that prolactin may play a role in the metabolic functioning of the salivary duct cells.

Variation of DNA polymerase activities and DNA synthesis in mouse mammary gland during pregnancy and early lactation

The rate of DNA synthesis and the activity of DNA polymerases and thymidine kinase were measured during the endocrine-regulated cellular growth and differentiation of mouse mammary gland. Using specific assays, the activity of the DNA polymerases, alpha, beta and gamma, was determined in tissue extracts of mammary glands of mice at various stages of pregnancy and early lactation. In addition, extracts of the mammary tissue of virgin, mid-pregnant and early lactating mice were fractionated on sucrose density gradients, and the activity of DNA polymerase alpha and beta was assayed in the gradient fractions. It was demonstrated that the activity of DNA polymerase alpha varied considerably during pregnancy and after parturition, showing peaks on day 12 of pregnancy and days 3-4 of lactation. In pregnancy, there was an apparently parallel correlation between the amount of DNA-polymerase-alpha activity and the rate at which the cells incorporated labelled thymidine into DNA, but the relationship was less clearly expressed during early lactation. The activity of the DNA polymerases, beta and gamma, as well as that of thymidine kinase showed little variation during these periods. Thus, in the developing mammary gland, no correlation was found between DNA synthesis and the activity of the DNA polymerases, beta and gamma, or thymidine kinase.

Evidence for physiological function of epidermal growth factor: pregestational sialoadenectomy of mice decreases milk production and increases offspring mortality during lactation period

Female virgin mice, whose submandibular glands were removed, underwent normal pregnancy and delivery. During the nursing period, however, a substantial number of pups born to and nursed by sialoadenectomized mothers died within 5 days of birth, whereas this did not occur among pups born to normal mothers. Cross-foster nursing experiments indicated that the cause of death of pups was to be found in sialoadenectomized mothers, not in the pups. The capacity of the sialoadenectomized mothers to nurse pups was much less than that of normal mothers, as shown by experiments involving alterations in the number of pups nursed by both sialoadenectomized and normal mothers. The mammary gland of lactating sialoadenectomized mice was smaller in size and produced less milk compared with that of normal mice. No apparent qualitative difference in milk proteins was found in the milk produced by the two groups of mothers. The decreased growth of the mammary gland of sialoadenectomized mice was also manifested during the second half of pregnancy, and mammary explants from those mice synthesized less casein in response to lactogenic stimuli, insulin, cortisol, and prolactin, in an organ culture system, when compared with mammary explants from normal pregnant mice. When epidermal growth factor, a polypeptide hormone that is synthesized and secreted by the submandibular gland, was injected daily at a dose of 5 micrograms into sialoadenectomized pregnant mice, the survival rate of the pups nursed by their mothers increased to the value obtained with normal mothers. The results were discussed in terms of a possible role of the submandibular gland and epidermal growth factor in the development of the mammary gland.

Guinea-pig casein A cDNA. Nucleotide sequence analysis and comparison of the deduced protein sequence with that of bovine alphas2 casein

The nucleotide sequence (1036 bases) of guinea-pig casein A mRNA has been determined. Two cDNA recombinant plasmids contained a total of 993 base pairs, including part of the 5' noncoding region, and the complete coding and 3' noncoding region. The remaining 5' noncoding sequence was obtained by primer extension. The deduced 223-amino-acid-coding sequence of guinea-pig pre-casein A exhibited 30% homology with bovine alpha s2 casein, the most striking similarities being in the locations of potential phosphorylation sites.

The study of differentiative potential of the lactating mouse mammary gland in organ culture

The organ culture of the mammary gland of lactating mice was used to examine the response of the differentiated gland to lactogenic stimuli, insulin, cortisol, and prolactin. Time course studies showed that casein synthesis in cultured tissue decreased rapidly during the first 2 d despite the presence of the three hormones, but on the 3rd d tissue cultured with either insulin and prolactin or all three hormones regained the ability to synthesize milk proteins, casein, and alpha-lactalbumin: a greater increase occurred in the three hormone system. The delayed addition of prolactin on Day 2 to the culture system containing insulin and cortisol also stimulated casein synthesis. The addition of cytarabine, which inhibited insulin-dependent cell proliferation in cultured explants, did not block the rebound of milk protein synthesis. These results indicate that in the presence of insulin, cortisol, and prolactin mammary epithelial cells in culture first lose and then regain the ability of synthesizing milk protein without requiring the formation of new daughter cells.

Characterization of a sheep pituitary-derived growth factor for rat and human mammary tumor cells

A growth factor for rat and human mammary tumor cells (MTGF-Pit) was isolated from lyophilized powders of whole sheep pituitaries by a rapid four-step procedure utilizing acetic acid extraction, heating at 93 degrees C, and sequential chromatography in 0.10 M acetic acid on sulphopropyl Sephadex and Sephadex G-50. From 10 g of pituitary powder, 8-10-mg amounts of MTGF-Pit were isolated. By 8 M urea, 0.1% SDS-12.5% polyacrylamide gel electrophoresis analysis followed by Coomassie blue staining, this preparation was shown to be one major stained band. When assayed for growth effects on cells maintained in serum-free medium, 5.1-19.2 nM MTGF-Pit half replaced the growth of MTW9/PL rat and MCF-7 and T-47D human mammary tumor cells in response to 2% to 10% serum. MTGF-Pit shows mitogenic activity toward normal human diploid fibroblasts only at concentrations in excess of 2.5 X 10(-4) M, while rat fibroblasts are unresponsive even at this high concentration. From data available, we conclude that a mitogenic activity for epithelial-type mammary cells has been isolated, and this growth factor appears to be a previously undetected acid- and heat-stable activity that is highly abundant (estimated at 0.16% or more of the total dry weight of the pituitary powder). The isolated ovine MTGF-Pit (3,900 +/- 200 daltons) does not share the molecular weight of native prolactin (24,000 daltons), "cleaved" prolactin (16,000 daltons), or growth hormone (22,000 daltons), and by all tests applied cannot be replaced with other known hormones and purified growth factors. We conclude a potent new mammary tumor cell mitogenic activity has been identified from sheep pituitaries.

Response of end bud cells from immature rat mammary gland to hormones when cultured in collagen gel

End buds from 4- to 5-week-old rat mammary glands were isolated and cultured within a rat tail tendon collagen gel matrix. Media containing equine serum or porcine serum and cholera toxin promoted growth, but not the production of casein or thioesterase II, nor did they induce a state of differentiation as assessed by cell ultrastructure. Medium supplemented with only 5% porcine serum, insulin and cholera toxin did not support growth or differentiation. However, when prolactin, estradiol, progesterone and hydrocortisone were added to this medium, growth was stimulated greatly and a differentiated state was induced as assessed by the production of casein and thioesterase and by the appearance of a highly secretory ultrastructure.

Induction of differentiation in a rat mammary epithelial stem cell line by dimethyl sulphoxide and mammotrophic hormones

Rama 25 is a clonal epithelial cell line derived from a dimethylbenzanthracene-induced rat mammary adenocarcinoma. In the presence of the mammotrophic hormones, insulin, hydrocortisone, estrogen and prolactin, Rama 25 produces small amounts of casein and forms domes at a low rate. The rates of both these processes can be greatly increased by the addition of dimethyl sulphoxide or hexamethylenebisacetamide which are also known to induce the differentiation of Friend erythroleukemia cells. Other compounds which stimulate the differentiation of Rama 25 cells include linoleic acid and 6-thioguanine. The intracellular pathways triggering changes in the two markers of differentiation are partially separable using different combinations of hormones, prolactin and hydrocortisone being the most important for the production of casein and the formation of domes respectively. The kinetics of differentiation, as judged by the appearance of these two markers, are characterised by two phases, a fixed period of 8 h (lag phase), the length of which is independent of the dimethyl sulphoxide concentration and a second phase where their rates are dependent on the concentration of dimethyl sulphoxide. Rama 25 cells do not become committed to differentiate during this lag phase but increasing numbers of cells do so after this period. We suggest that the differentiation processes occur in two stages. The first stage, involving the inducer, commits Rama 25 cells to a new differentiated state. The second stage, involving the hormones, modulates the expression of different markers of this state. Both casein production and dome formation can be blocked by inhibitors of DNA synthesis and show reciprocal changes with the rates of cellular DNA synthesis. Thus, in its hormonal and DNA synthetic requirements for differentiation, Rama 25 cells appear to resemble some of the mammary epithelial cells of mature virgin rats.

Comparison of the growth of normal and neoplastic mouse mammary cells on plastic, on collagen gels and in collagen gels

The growth of normal and neoplastic mouse mammary cells was compared in primary cultures on plastic, on rat tail collagen gels and in rat tail collagen gels. Cells on plastic grew for the first few days, then stopped with only a 1- to 3-fold increase in cell number after 2 weeks in culture. Cells grown on or in collagen gels grew continuously over the 2-week culture period with up to 10-fold increase in cell number for cultures on collagen gels and a 20-fold increase for cells embedded in collagen gels. The difference in growth rates between cells grown in collagen gel and those grown on collagen gels was due, in part, to the three-dimensional growth of the colonies in collagen gel their two-dimensional growth on collagen gel. Cells grown on and in collagen gel can produce an electron-dense basal lamina-like structure which is associated with collagen IV and laminin as judged by immunofluorescence. Cells grown on plastic do not form this structure. Cis-OH-proline blocks the production of collagen and inhibits the growth of the cultured cells indicating collagen production to be involved in growth. Rat tail collagen gels are a superior substratum for the growth of mouse mammary cells and this may be related to the cells' ability to form a collagen IV-containing basal lamina-like structure.

Fluctuations in DNA synthesis by mammary tissue from the pregnant hamster, rat and three strains of mice

1. DNA synthesis was determined at midnight and noon in mammary tissue from 13-day pregnant mice (C3H, C57B110 and BALB/c) and 14-day pregnant golden hamsters and Sprague-Dawley rats. 2. Mammary tissue from the hamster and the three mouse strains had elevated DNA synthesis at midnight compared with noon. 3. In contrast, DNA synthesis in mammary tissue from the rat was not different at these two time periods.