Studies on the Function of Glucocorticoid in Mouse Mammary Epithelial Cell Differentiation in Vitro

Bovine mammary epithelial cells can grow and express milk protein synthesis genes at reduced fetal bovine serum concentration

Milk proteins produced by lactating cells isolated from bovine mammary tissue can offer a sustainable solution to the high protein demand of a global growing population. Serum is commonly added to culture systems to provide compounds necessary for optimal growth and function of the cells. However, in a cellular agricultural context, its usage is desired to be decreased. This study aims at examining the minimum level of fetal bovine serum (FBS) required for the growth and functionality of bovine mammary epithelial cells (MECs). The cells were isolated from dairy cows in early and mid-lactation and cultured in reduced concentrations of FBS (10%, 5%, 1.25%, and 0%). Real-time cell analysis showed a significant effect of lactation stage on growth rate and 5% FBS resulted in similar growth rate as 10% while 0% resulted in the lowest. The effect of reducing FBS on cell functionality was examined by studying the expressions of selected marker genes involved in milk protein and fat synthesis, following differentiation. The gene expressions were not affected by the level of FBS. A reduction of FBS in the culture system of MEC, at least down to 5%, does not assert any negative effect on the growth and expression levels of studied genes. As the first attempt in developing an in-vitro model for milk component production using MEC, our results demonstrate the potential of MEC to endure FBS-reduced conditions.

Rapid Communication: Prolactin and hydrocortisone impact TNFα-mediated mitogen-activated protein kinase signaling and inflammation of bovine mammary epithelial (MAC-T) cells

The objective of this study was to evaluate the effects of the hormones prolactin (PRL) and hydrocortisone (HC) on bovine mammary alveolar (MAC-T) cells mitogen-activated protein kinase (MAPK) inflammatory signaling and inflammatory gene expression. MAC-T cells were cultured in the presence (+PRL +HC; Dulbecco's modified Eagle's medium [DMEM] 10% fetal bovine serum, 10 µg/mL of insulin, 100 IU/mL penicillin, 100 µg/mL streptomycin, 1 µg/mL ovine PRL, 0.5 µg/mL HC, and 10 m sodium acetate) or the absence (-PRL -HC; DMEM 10% fetal bovine serum, 10 µg/mL insulin, 100 IU/mL penicillin , and 100 µg/mL streptomycin) of PRL and HC, and MAPK (extracellular signal-regulated kinase [ERK], c-Jun N-terminal kinase [JNK], and p38) phosphorylation and inflammatory gene expression were examined in response to tumor necrosis factor α (TNFα). Statistical analysis was assessed using 1-way ANOVA, and Tukey's post hoc analysis was used to assess statistical significance when ≤ 0.05. MAC-T cells cultured in +PRL +HC and -PRL -HC were co-stimulated with increasing concentrations of TNFα (0, 10, 30, 100, 300, and 1,000 p). Cell lysates were harvested 15 min after TNFα stimulation and assessed for MAPK phosphorylation using immunoblotting. c-Jun N-terminal kinase and p38 phosphorylation increased in a dose-dependent manner and was greater in cells cultured in -PRL -HC. MAC-T cells cultured in +PRL +HC and -PRL -HC were next stimulated with TNFα (300 p), and lysates were harvested over time (0, 15, 30, 60, 120, and 180 min) after TNFα stimulation. c-Jun N-terminal kinase and p38 phosphorylation was transiently increased in MAC-T cells stimulated with TNFα; however, JNK and p38 signaling was greater in MAC-T cells cultured in -PRL -HC. We next examined inflammatory gene expression in MAC-T cells cultured in +PRL +HC and -PRL -HC. Cells were co-stimulated with (300 p) or without TNFα. Ribonucleic acid was isolated 1 h after TNFα stimulation, and a PCR array was performed to examine the expression of 83 inflammatory genes. Gene expression was increased in MAC-T cells in response to TNFα. Consistent with enhanced MAPK signaling, inflammatory gene expression was increased in MAC-T cells cultured in -PRL -HC. Real-time quantitative PCR of 6 target genes was used to validate the PCR array findings. Collectively, our data demonstrate that -PRL -HC MAC-T cells are more responsive to TNFα stimuli. These findings suggest that cell culture conditions (e.g., treatment with hormones) greatly impact cellular response and should be considered prior to experimental design and hypothesis testing.

Antagonistic regulation of tight junction dynamics by glucocorticoids and transforming growth factor-beta in mouse mammary epithelial cells

The synthetic glucocorticoid, dexamethasone, stimulated the transepithelial electrical resistance and suppressed the DNA synthesis of 31EG4 nontransformed mouse mammary epithelial cells. The addition of transforming growth factor-beta 1 (TGF-beta) to mammary cells simultaneously with or up to 24 h after dexamethasone treatment prevented the steroid induction of transepithelial electrical resistance and stimulated the incorporation of [3H]thymidine. However, the TGF-beta inhibition of tight junction formation did not require de novo DNA synthesis. Confocal microscopy revealed that the organized immunostaining pattern of the tight junction protein, ZO-1, and F-actin at the cell periphery was disrupted by TGF-beta, resulting in disorganized and diffuse staining patterns throughout the cell. Western blot analysis demonstrated that TGF-beta did not alter the protein levels of ZO-1. In contrast to cells not treated or pretreated with steroid for up to 24 h, TGF-beta had no effect on cells pretreated with dexamethasone for 48 h. Transfection of chimeric reporter genes containing promoters responsive to either glucocorticoid or TGF-beta demonstrated that the mutual antagonism of tight junction dynamics by dexamethasone and TGF-beta occurs in the presence of intact signaling pathways. Taken together, our results establish for the first time that glucocorticoids and TGF-beta can antagonistically regulate tight junction formation in a nontransformed mammary cell line.

Transforming growth factor-alpha abrogates glucocorticoid-stimulated tight junction formation and growth suppression in rat mammary epithelial tumor cells

The glucocorticoid and transforming growth factor-alpha (TGF-alpha) regulation of growth and cell-cell contact was investigated in the Con8 mammary epithelial tumor cell line derived from a 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma. In Con8 cell monolayers cultured on permeable filter supports, the synthetic glucocorticoid, dexamethasone, coordinately suppressed [3H]thymidine incorporation, stimulated monolayer transepithelial electrical resistance (TER), and decreased the paracellular leakage of [3H]inulin or [14C]mannitol across the monolayer. These processes dose dependently correlated with glucocorticoid receptor occupancy and function. Constitutive production of TGF-alpha in transfected cells or exogenous treatment with TGF-alpha prevented the glucocorticoid growth suppression response and disrupted tight junction formation without affecting glucocorticoid responsiveness. Treatment with hydroxyurea or araC demonstrated that de novo DNA synthesis is not a requirement for the growth factor disruption of tight junctions. Immunofluorescence analysis revealed that the ZO-1 tight junction protein is localized exclusively at the cell periphery in dexamethasone-treated cells and that TGF-alpha caused-ZO-1 to relocalize from the cell periphery back to a cytoplasmic compartment. Taken together, our results demonstrate that glucocorticoids can coordinately regulate growth inhibition and cell-cell contact of mammary tumor cells and that TGF-alpha, can override both effects of glucocorticoids. These results have uncovered a novel functional "cross-talk" between glucocorticoids and TGF-alpha which potentially regulates the proliferation and differentiation of mammary epithelial cells.

Glucocorticoid and polyamine involvement in zinc uptake by COMMA-1D mammary epithelial cells

The objective was to determine if a mammary cell line shows glucocorticoid stimulation of Zn uptake, and to determine whether polyamines mediate this stimulation. 65Zn uptake by COMMA-1D mouse mammary epithelial cells over a 24-h period increased significantly in cells administered 10(-7) or 10(-6) M hydrocortisone. Incorporation of 65Zn over a 1-h period was not hydrocortisone-responsive, suggesting that these incubation times represent uptake into different pools. The rate of entry into the cells over a 15-min period was significantly increased by supplementing cells with hydrocortisone with or without prolactin. Initially, cells grown in lactogenic hormone-supplemented media (10(-6) M hydrocortisone + 5 micrograms/mL ovine prolactin) had up to 65% greater 65Zn uptake over 24 h than cells in nonsupplemented growth media. 65Zn uptake from hormone media with the spermidine synthesis inhibitor methylglyoxal-bis-(guanylhydrazone) (MGBG, 10(-5)M) added was less than from growth media. Exogenous spermidine (10(-6)-10(-3)M) added to the MGBG + hormone media increased 65Zn uptake. Difluoromethylornithine (DFMO), an inhibitor of spermidine synthesis that blocks ornithine decarboxylase, caused a slight dose-dependent decrease in 65Zn uptake over the range 10(-6)-5 x 10(-3)M (p < 0.002) and tended to decrease 65Zn-uptake in lactogenic hormone-stimulated cells with 8 h of incubation, but not at other times. These data show that Zn uptake in mammary epithelial cells can be hormonally mediated by glucocorticoids and suggest that polyamines may be intracellular mediators of this effect.

Effects of estrogen-depletion on rat casein gene expression

Mammary tissue from rats that had been ovariectomized and adrenalectomized 4 weeks previously was compared to that from intact rats in terms of epithelial content and hormone-responsiveness in vitro. The endocrinectomy resulted in about a 30% enlargement of the gland, but led to a loss of only about 12% of the epithelium. This estrogen-depleted epithelium was able to acquire full responsiveness in vitro to insulin in terms of the accumulation of alpha-aminoisobutyric acid, and induction of glucose-6-phosphate and gluconate-6-phosphate dehydrogenases. It was also fully responsive to cortisol in relation to the induction of NADH-cytochrome C reductase, and to prolactin in terms of total RNA synthesis. However, estrogen-depletion led to an 82% loss in the ability of a unit amount of the epithelium to synthesize casein in response to these 3 hormones, and to a similar loss in relation to the accumulation of 25K casein mRNA. Estrogen administration in vivo could prevent and reverse the casein lesion. The disparity between constitutive and casein hormone-responsiveness in the absence of estrogen is discussed in relation to cell commitment.

Glucocorticoid regulation of mouse mammary tumor virus gene expression

Glucocorticoid hormones act rapidly and specifically to stimulate the synthesis of mouse mammary tumor virus RNA in a variety of mouse mammary tumor cells and infected heterologous cells. The increase in viral RNA production appears to be mediated by receptor proteins and requires the presence of basal levels of viral RNA. Infection of heterologous cells with MMTV may alter host cell responses to glucocorticoids; in addition, production of unintegrated viral DNA in these cells has provided reagents required for studying the structure and function of the viral DNA itself. The advent of new techniques for genetic manipulation of eukaryotic cells and for isolation of large amounts of specific DNA sequences should now permit detailed analyses of steroid hormone action in this system.

Regulation of mouse mammary tumor virus gene expression by glucocorticoid hormones

Several laboratories have documented that glucocorticoid hormones markedly stimulate the expression of mouse mammary tumor virus genes in a variety of mouse mammary tumor cells and in infected heterologous cells. The effect of the hormone appears to be a rapid and specific augmentation of the synthesis of viral RNA, mediated by interaction with glucocorticoid receptor proteins. The availability of virus-specific reagents and recent developments in the molecular biology of RNA tumor viruses now permit a highly refined analysis of hormonal regulation in this experimental system.

Lipoprotein lipase of cultured mesenchymal rat heart cells. III. Effect of glucocorticoids and insulin on enzyme formation

Lipoprotein lipase activity was studied in mesenchymal cells isolated from rat hearts and cultured for up to 8 days. The enzyme activity increased markedly between day 3 and 5 while the subsequent increase was less pronounced. Addition of hydrocortisone to complete culture medium resulted in an increase in lipoprotein lipase activity at all stages of culture. Lipoprotein lipase activity did not increase after addition of insulin to the complete culture medium. In the presence of serum-poor medium between day 3 and 6, the increase in lipoprotein lipase activity was much lower than in the presence of complete culture medium. Addition of hydrocortisone and insulin to the serum-poor medium resulted in a significant rise in lipoprotein lipase activity while less consistent effects were obtained after addition of each hormone alone. Transfer of cells to serum-poor medium between day 6 and 7 of culture caused a fall in enzyme activity. Addition of hydrocortisone alone and with insulin restored enzyme activity to control values. No effect on lipoprotein lipase was seen with estradiol, growth hormone, or glucagon when added to serum-containing medium, or serum-poor medium. These results indicate that the lipoprotein lipase of heart is controlled by glucocorticoids and that this control might require the presence of insulin for optimal expression.

Relationship between polyamine contents and protease activity in the rat submaxillary gland

The effect of polyamines on the protease activity in the submaxillary gland of castrated rats has been investigated in vivo. The protease activity, which is increased by testosterone, is also increased to a lesser degree by the subcutaneous administration of spermidine. The administration of putrescine was less effective than that of spermidine. The increase of polyamine contents in the submaxillary gland of the castrated rats administered either testosterone or spermidine was nearly parallel to the increase of the enzymatic activity. The administration of methylglyoxal bis(guanylhydrazone), a potent inhibitor of spermidine synthesis, with testosterone inhibited slightly the increase of the protease activity by testosterone, while the administration of the inhibitor with spermidine had essentially no effect on the increase of the enzymatic activity by spermidine. The administration of testosteorne also caused a slight increase of S-adenosyl-L-menthionine decarboxylase activity. These results suggest that spermidine synthesis may be necessary for the stimulation by testosterone of protease synthesis in the rat submaxillary gland.

Hydrocortisone enhancement of insulin's action on macromolecular synthesis in MCF-7 cells

In MCF-7 human breast cancer cells, insulin stimulated the rate of [3H]uridine incorporation into RNA, [3H]thymidine incorporation into DNA, and [3H]leucine incorporation into protein. In addition, hydrocortisone appeared to augment the effect of insulin, by further increasing the rate of [3H]uridine incorporation into RNA and [3H]thymidine incorporation into DNA. A significant increase in the total amount of DNA and protein was present in cultures treated with insulin compared to untreated controls. Hydrocortisone was shown to augment the insulin effect on total protein accumulation and total RNA accumulation in MCF-7 cells.

Regulation of enzyme turnover during tissue differentiation. Studies on 6-phosphogluconate dehydrogenase in rabbit mammary gland in organ culture

(1) Explants of mammary gland from mid-pregnant rabbits were cultured in Medium 199 in the presence or absence of insulin, prolactin and cortisol. (2) Antiserum to 6-phosphogluconate dehydrogenase was raised in sheep and used to titrate the amount of enzyme activity present in explant extracts. Changes in enzyme activity were found to be due to corresponding changes in amount of the enzyme. The greatest increases in the amount of the enzyme were only brought about by culture of explants in the presence of hormones (insulin, prolactin and cortisol) in Medium 199 which contained glucose. (3) The increases in the amount of the enzyme were similar in explants cultured with hormones in Medium 199 which contained 1.39 mM, 5.55 mM or 55.5 mM glucose. (4) When explants were cultured with hormones in Medium 199 which contained glucose (5.55 mM) for 24 h and then cultured with hormones in Medium 199 which contained glycerol (10.9 mM), a decrease in the amount of the enzyme occurred. In contrast, the culture of explants with hormones in Medium 199 which contained glycerol (10.9 mM) for 24 h followed by transfer of the explants to medium which contained glucose (5.55 mM) resulted in an increase in the amount of the enzyme to reach values which were not different from those found in explants cultured throughout with hormones in Medium 199 which contained glucose.