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PubMed2005

Oct-1 counteracts autoinhibition of Runx2 DNA binding to form a novel Runx2/Oct-1 complex on the promoter of the mammary gland-specific gene beta-casein.

The transcription factor Runx2 is essential for the expression of a number of bone-specific genes and is primarily considered a master regulator of bone development. Runx2 is also expressed in mammary epithelial cells, but its role in the mammary gland has not been established. Here we show that Runx2 forms a novel complex with the ubiquitous transcription factor Oct-1 to regulate the expression of the mammary gland-specific gene beta-casein. The Runx2/Oct-1 complex forms on a Runx/octamer element which is highly conserved in casein promoters. Chromatin immunoprecipitation, RNA interference, promoter mutagenesis, and transient expression analyses were used to demonstrate that the Runx2/Oct-1 complex contributes to the transcriptional regulation of the beta-casein gene. Analysis of the complex revealed autoinhibitory domains for DNA binding in both the N-terminal and the C-terminal regions of Runx2. Oct-1 stimulates the recruitment of Runx2 to the beta-casein promoter by interacting with the C-terminal region of Runx2, suggesting that Oct-1 stimulates Runx2 recruitment by relieving the autoinhibition of Runx2 DNA binding. These findings demonstrate that Runx2 collaborates with Oct-1 and contributes to the expression of a mammary gland-specific gene.

Animals↗
PubMed2004

Optimization of casein-based semisynthetic medium for growing of toxigenic Corinebacterium diphtheriae in a fermenter.

Diphtheria toxin is produced by growing Corinebacterium diphtheriae either in a semisynthetic casein-based medium or in the Pope-Lingood meat extract based medium. The World Health Organization advises the use of the semisynthetic one, as it has important advantages. Data on the composition of casein-based media and their ability to support high toxin production are not freely available. Important factors affecting toxin production during C. diphtheriae cultivation are the pH of the culture medium and the concentration of casein hydrolysate and of Fe2+. We established that the optimal pH for toxin production is 7.2. The highest yield of toxin was obtained using a casein hydrolysate concentration of 35.0 g/L and a Fe2+ concentration of 0.05-0.41 microg/mL. Under these conditions, diphtheria toxin with higher purity and yield compared with the batches obtained using the meat-based medium of Pope-Lingood was produced.

Caseins↗
PubMed1995

Isolation and characterization of a new bradykinin potentiating octapeptide from gamma-casein.

Peptides that display bradykinin-potentiating activity have been obtained from a number of distinct sources, such as snake venoms, fibrinogen, and casein. This paper describes the isolation and sequencing of a novel bradykinin-potentiating peptide, generated by tryptic hydrolysis of the gamma-casein chain. No homology was found to other known vasoactive or vasopotentiating peptides. The octapeptide Tyr-Pro-Val-Gln-Pro-Phe-Thr-Glu, corresponding to the gamma-casein(114-121) sequence, was isolated from the tryptic hydrolysis of gamma-casein and also synthesized by solid-phase peptide synthesis. Both natural and synthetic peptides had the same retention time in HPLC and displayed a selective potentiating activity on isolated guinea-pig ileum for bradykinin and Lys-bradykinin but were not able to potentiate the effects of Met-Lys-bradykinin, Ile-Ser-bradykinin, angiotensin II, acetylcholine, or histamine. Intravenous injections of bradykinin and of bradykinin-potentiating octapeptide produced a persistent hypotension in conscious rats, a pattern that was not obtained when the octapeptide was replaced by captopril. This bradykinin-potentiating octapeptide is a strong competitive inhibitor of endo-oligopeptidase A (EC 3.4.24.15, formerly EC 3.4.22.19), but it has low inhibitory potency towards angiotensin-converting enzyme (EC 3.4.15.1). Thus, our results suggest that other peptidases in addition to angiotensin-converting enzyme, such as endo-oligopeptidase A, may contribute to the reduction of the effective concentration of bradykinin in the circulation.

Amino Acid Sequence↗
PubMed1994

Progesterone and EGF inhibit mouse mammary gland prolactin receptor and beta-casein gene expression.

Regulation of mouse mammary gland long-form prolactin receptor (PRL-RL) mRNA levels by progesterone and epidermal growth factor (EGF) and the relationship between PRL-RL and beta-casein gene expression were examined in vivo and in vitro. PRL-RL and beta-casein mRNA levels increased approximately 6- and 15-fold from the pregnant to the lactating period, respectively, when normalized to the level of beta-actin mRNA. Ovariectomy of pregnant mice rapidly reduced the serum concentration of progesterone and increased the level of PRL-RL and beta-casein mRNAs approximately three- and fourfold compared with sham-operated animals 24 h after the operation. Injection of progesterone, but not estrogen, inhibited the increase in both mRNA levels. PRL-RL and beta-casein mRNA levels in cultured mammary epithelium increased in response to insulin, hydrocortisone, and prolactin, whereas progesterone or EGF caused inhibition. The combination of EGF and progesterone produced a greater inhibition than either hormone alone. These results indicate that both progesterone and EGF serve as negative regulators of lactogenesis.

Animals↗
PubMed2002

Soy protein, casein, and zein regulate histidase gene expression by modulating serum glucagon.

Glucagon has been postulated as an important physiological regulator of histidase (Hal) gene expression; however, it has not been demonstrated whether serum glucagon concentration is associated with the type and amount of protein ingested. The purpose of the present work was to study the association between hepatic Hal activity and mRNA concentration in rats fed 18 or 50% casein, isolated soy protein, or zein diets in a restricted schedule of 6 h for 10 days, and plasma glucagon and insulin concentrations. On day 10, five rats of each group were killed at 0900 (fasting), and then five rats were killed after being given the experimental diet for 1 h (1000). Rats fed 50% casein or soy diets showed higher Hal activity than the other groups studied. Rats fed 50% zein diets had higher Hal activity than rats fed 18% casein, soy, or zein diets, but lower activity than rats fed 50% casein or soy diets. Hal mRNA concentration followed a similar pattern. Hal activity showed a significant association with serum concentrations of glucagon. Serum glucagon concentration was significantly correlated with protein intake. Thus the type and amount of protein consumed affect Hal activity and expression through changes in serum glucagon concentrations.

Amino Acids↗
PubMedDate not supplied

The effects of milk and kappa-casein on salivary pellicle formed on hydroxyapatite discs in situ.

The effects of milk and kappa-casein rinses on the salivary pellicle formed on hydroxyapatite discs carried in the mouth were studied. SDS-PAGE analyses revealed an increase in the number of proteins deposited onto the discs carried after the water and milk rinses only. Scanning electron microscopy studies revealed the deposition of an amorphous material, small, micelle-like structures, cocci and rods on discs carried in the mouth after the water rinse. Large, micelle-like structures were seen on discs carried in the mouth after the milk and kappa-casein rinses; bacteria were not seen. Glucosyltransferase (Gtf) activity on discs carried in the mouth after the milk and kappa-casein rinses were 45+/-5 and 67+/-2% lower than the activity of Gtf on discs carried in the mouth after a water rinse, respectively. These data suggest that milk and kappa-casein may influence pellicle formation in vivo.

Animals↗
PubMed1982

Comparative effects of soy and casein protein on plasma cholesterol concentrations.

The effects of soy and casein protein on cholesterol metabolism were determined under normocholesterolemic and hypercholesterolemic conditions in male Wistar rats and in Swiss White mice. Hypercholesterolemia was induced by feeding cholesterol and cholic acid in the diet for a period of 2 weeks. Our results demonstrate that there are significant species differences. The hypercholesterolemic effect of exogenous cholesterol was more pronounced in the mouse than in the rat. The rats fed the basal (no cholesterol, no cholic acid) semisynthetic diet containing either soy or casein had plasma cholesterol concentrations similar to those observed in chow-fed controls. However, plasma cholesterol concentrations in the mice fed the basal semisynthetic diet containing either of the two proteins were significantly elevated compared to the control mice fed commercial chow. Rat data demonstrate that the hypercholesterolemia induced by exogenous cholesterol administration is of a lesser magnitude in the presence of soy compared to casein as a dietary protein source. The mice data show that the concentrations of hepatic and biliary cholesterol and plasma triglycerides and in response to exogenous cholesterol are significantly lower in the soy protein diet compared to the casein protein diet.

Animals↗
PubMed1984

Influence of dietary casein or soy protein on serum lipids and lipoproteins of monkeys (Macaca fascicularis).

In order to learn whether a complete exchange of dietary soy protein for casein causes a change of serum lipid levels in primates, 8 Macaca fascicularis monkeys were fed a semi-purified ration; its basic composition was similar to diets consumed in Western Europe. In a crossover experiment, casein was exchanged for a soy protein isolate and vice versa. Plasma and lipoprotein cholesterol and triglyceride levels were determined following a 3-week dietary regimen. There was no significant difference of total serum cholesterol levels between the soy protein and casein periods (4.6 vs. 4.7 mmol/l). However, high-density lipoprotein (HDL) cholesterol levels were significantly higher (1.6 vs. 1.2 mmol/l, p less than 0.01) and very-low-density lipoprotein (VLDL) cholesterol levels were significantly lower (0.39 vs. 0.55 mmol/l, p less than 0.01) following the soy protein diet. There was no distinct change in total or lipoprotein triglyceride levels following exchange of the dietary protein. It is concluded that in nonhuman primates a complete exchange of soy protein for casein produces changes of HDL, but not of total or low-density lipoprotein (LDL) cholesterol.

Animals↗
PubMed1995

The effect of milk and kappa casein on streptococcal glucosyltransferase.

Many dietary components such as carbohydrates, lipids and proteins may be incorporated into the salivary pellicle and thus may affect glucosyltransferase (GTF) activity on pellicle surfaces. The effect of milk on streptococcal GTF activity was determined. Milk, when coated onto buffer-coated hydroxyapatite or saliva-coated hydroxyapatite (sHA), reduced the subsequent adsorption of GTF onto the surfaces. Milk also reduced the expression of enzymatic activity of GTF adsorbed onto sHA. kappa-Casein, when present on the surface of sHA, reduced the adsorption of GTF activity onto sHA, resulting in reduced glucan formation. alpha-Casein had no effect on the adsorption of GTF onto sHA or on subsequent glucan formation. Both milk and kappa-casein reduced activity of the enzyme in solution. The presence of milk and kappa-casein fractions on the surface of sHA and in solution with GTF can clearly modulate glucan formation in vitro.

Adult↗
PubMed1988

Cobalt-dependent protein phosphatases from human cord blood erythrocytes. II. Further characterization of E2 casein phosphatase.

Of three casein phosphatases isolated from the cytosol of human cord blood erythrocytes two were cobalt-dependent, E2 and E3. In the presence of CoCl2, E2 activity was the most prominent. In addition to casein, E2 dephosphorylated phosvitin and p-nitrophenyl phosphate (p-NPP) with pH optima at 6.8-7.2 for proteins and 9.0 for p-NPP. The native enzyme had a molecular weight of 104,000 daltons after AcA-44 Ultrogel filtration. According to SDS/PAGE it consisted of two subunits, 78,000 and 15,000 daltons. The 104,000-dalton form exhibited Michaelis-Menten kinetics and had the greatest affinity for casein between protein substrates tested. Ethanol denaturated the enzyme by 80%. Optimal activation of E2 phosphatase was achieved with 5 mmol/l CoCl2 which did not affect the catalytic properties of the enzyme but did affect the rate of 'E-S' complex formation. Inorganic pyrophosphate was not inhibitory for the 104,000-dalton enzyme. Judging by all these properties the natural substrate for E2 casein phosphatase could be P-pyruvate kinase.

Caseins↗
PubMed2006

Selenised casein protects against AOM-induced colon tumors in Sprague Dawley rats.

Selenium (Se) has been shown to be protective against cancers in animal models at concentrations exceeding those considered essential for normal nutritional requirements. Organic forms of Se provided as dairy proteins were obtained from cows fed diets supplemented with yeast Se. The casein extracted from milk was found to contain approximately half the Se of the Se-enriched milk. This casein was included in a semi-purified AIN rodent diet so as to provide 1 ppm Se and 25% protein and was compared with AIN diets containing no added Se (control, 0.05 ppm), 1 ppm and 4 ppm Se as selenised yeast (Sel-Plex) Their influence on colon tumor expression was examined in rats induced with azoxymethane, the diets being introduced post-induction. The selenised casein diet at this concentration was effective in reducing colon tumor incidence (by 29%) and burden (decreased 52%, P < 0.05) relative to the control in rats 26 wk post-induction. Selenised yeast, when added at similar (1 ppm) and increased Se concentration (4 ppm), did not influence significantly colon tumor expression. However, in a second study, with Se yeast providing Se at 1 ppm, 4 ppm, and 8 ppm throughout the experiment, a significant reduction in tumors was observed with 8 ppm Se (colon tumor incidence was 15% lower and colon tumor burden was 35% lower, P < 0.05). However this was associated with a significantly lower body weight in the rats (down 10.5%, P < 0.05) indicating a possible disturbance with normal energy intake or metabolism. The form in which Se is presented in the diet may influence significantly its bioavailability and/or anticancer potential at given concentrations within a safe range. The efficacy of selenised casein and indeed other potential dietary sources deserve further investigation with regard to their ability to prevent colon tumors at concentrations considered safe in the diet.

Animals↗
PubMed1983

Deoxyribonucleic acid synthesis-dependent casein gene expression: species differences.

Mammary gland explants from mature virgin mice, rats, and rabbits exhibit an increased rate of both DNA and casein syntheses when cultured in the presence of specific combinations of insulin, hydrocortisone, and PRL. If cytosine arabinoside, a potent inhibitor of DNA synthesis, is added to the culture medium, casein synthesis is inhibited in explants from mice but not in those from rats or rabbits. This inhibition is at the level of accumulation of casein mRNA; an 89% reduction of stimulated levels was observed. The nature of this block was investigated further by examining the general response of mature virgin mouse mammary explants to hydrocortisone and PRL, hormones considered essential for casein gene expression in this species. Cytosine arabinoside did not prevent an increment in either hydrocortisone-induced NADH-cytochrome c-reductase or PRL-induced total RNA synthesis. Previous work has shown that certain insulin-induced responses are also unaffected. Taken collectively, these results suggest that the lesion induced by cytosine arabinoside inhibition of DNA synthesis is distal to the receptor for one or more of these hormones. The necessity for coupling DNA synthesis with overt differentiation in the mature virgin mouse, but not in the rat or rabbit, is one of numerous examples of species variation in regard to the interaction of hormones with the mammary gland.

Animals↗
PubMed1983

Extracellular calcium ion concentration required for prolactin to express its actions on casein, ribonucleic acid, and lipid biosynthesis in mouse mammary gland explants.

The depletion of extracellular calcium ions by EGTA abolishes the PRL stimulation of [14C]acetate incorporation into lipids in mouse mammary gland explants. This abolition is reversed by the addition of calcium, but not magnesium. The chelation of calcium ions was similarly shown in earlier studies to abolish PRL's actions on RNA and casein synthesis. When the actions of PRL on lipid, RNA, and casein biosynthesis were tested when the extracellular calcium ion concentration was varied, it was observed that 5-10 microM calcium was required for PRL to manifest its actions. The calcium ionophore A23187 was unable, however, to mimic the PRL stimulation of lipid, RNA, or casein synthesis. Trifluoperazine, an inhibitor of calmodulin action had no effect on the PRL-induced synthesis of lipids, RNA, or casein, except at pharmacological levels.

Acetates↗
PubMed1987

Comparison of the roles of insulin and insulin-like growth factor I in casein gene expression and in the development of alpha-lactalbumin and glucose transport activities in the mouse mammary epithelial cell.

The concentration-activity profiles for insulin and insulin-like growth factor I (IGF-I; in the presence of and insulin-like growth factor I (IGF-I; in the presence of hydrocortisone and PRL) have been compared in terms of the accumulation of beta-casein mRNA, total casein synthesis, and alpha-lactalbumin and basal carrier-mediated glucose transport activities in mammary epithelial cells from midpregnant mice. For the accumulation of the casein mRNA and the induction of casein synthesis and alpha-lactalbumin activity, the insulin ED50 is 1-2 ng/ml, while that for IGF-I is 10- to 20-fold greater. The effects of insulin and IGF-I are not additive in these instances. For the induction of basal carrier-mediated glucose transport, the insulin ED50 is 8 ng/ml, and that for IGF-I is 16 ng/ml. Either factor can induce transport activity up to the level present in the cells from 2-day lactating mice. In this instance the effects are additive; insulin and IGF-I together can induce the transport up to the 10-day lactating level.

3-O-Methylglucose↗
PubMed2004

Insulin and prolactin synergistically stimulate beta-casein messenger ribonucleic acid translation by cytoplasmic polyadenylation.

Previous studies have shown that the synthesis and stability of milk protein mRNAs are regulated by lactogenic hormones. We demonstrate here in cultured mouse mammary epithelial cells (CID 9) that insulin plus prolactin also synergistically increases the rate of milk protein mRNA translation. Insulin alone stimulates synthesis of both milk and nonmilk proteins, whereas prolactin alone has no effect, but insulin plus prolactin selectively stimulate synthesis of milk proteins more than insulin alone. The increase in beta-casein mRNA translation is also reflected in a shift to larger polysomes, indicating an effect on translational initiation. Inhibitors of the phosphatidylinositol 3-kinase, mammalian target of rapamycin, and MAPK pathways block insulin-stimulated total protein and beta-casein synthesis but not the synergistic stimulation. Conversely, cordycepin abolishes synergistic stimulation of protein synthesis without affecting insulin-stimulated translation. The poly(A) tract of beta-casein mRNA progressively increases from approximately 20 to about 200 A residues over 30 min of treatment with insulin plus prolactin. The 3'-untranslated region of beta-casein mRNA containing an unaltered cytoplasmic polyadenylation element is sufficient for the translational enhancement and mRNA-specific polyadenylation, based on transient transfection of cells with a reporter construct. Insulin and prolactin stimulate cytoplasmic polyadenylation element binding protein phosphorylation with no increase of cytoplasmic poly(A) polymerase activity.

3' Untranslated Regions↗
PubMed1988

A transfected alpha-casein minigene bypasses posttranscriptional control by hormones, but retains cell-substratum regulation in mammary epithelial cells.

DNA-mediated gene transfection using an alpha-casein minigene cloned into a bovine papilloma virus (BPV)-based neomycin-selectable expression vector has been employed to study the mechanisms by which hormonal and cell-substratum interactions regulate milk protein gene expression. Permanently transformed clones and pooled populations of normal midpregnant mouse mammary epithelial cells (COMMA-D) containing the minigene express an authentic rat alpha-casein mRNA, as well as a series of larger cytoplasmic RNA transcripts. These transcripts are correctly initiated and spliced; however, a large proportion also contain additional sequences at the 3'-end. Constitutive expression of the minigene in the absence of PRL and glucocorticoids in COMMA-D cells grown on floating type I collagen gels is observed. Thus, the minigene-BPV construct apparently overrides the normal posttranscriptional regulatory mechanisms which are responsible for the expression of unstable casein gene transcripts in the absence of PRL and glucocorticoids. In contrast, this minigene-BPV construct is regulated appropriately by cell-substratum interactions in pooled transfectants. Minigene expression is undetectable when pooled transfectants are plated on a plastic substratum, and readily detectable when cells are grown on floating type I collagen gels. Thus, hormones and cell-substratum interactions may regulate different steps in the same differentiation pathway leading to increased casein gene expression.

Animals↗
PubMed1990

Transcriptional analysis of the mouse beta-casein gene.

These studies were designed to further elucidate the relative contributions of transcriptional and posttranscriptional mechanisms involved in beta-casein gene regulation in the mammary epithelial cell line designated COMMA-D and a clonal subline desginated HC-11. Primary transcripts were mapped under various hormonal and substratum conditions using the technique of nuclear run-on transcription and single stranded sense and antisense probes spanning the beta-casein gene. In the presence of insulin alone very little sense transcription is detectable, but antisense transcription is observed, which originates at least 150 basepairs upstream of the normal start site of transcription and is present regardless of hormonal, cell substratum, cell type, or gene activity. Antisense transcription is also detectable in the 3' end of the gene. Insulin, glucocorticoids, and PRL are all necessary for a maximal increase in transcription. A 2- to 4-fold increase in transcriptional activity is observed in the presence of insulin and PRL compared to insulin alone, and this is accompanied by a 125-fold increase in the level of beta-casein mRNA. All three hormones act synergistically to induce a 10-fold increase in transcriptional activity, but the transcriptional increase across the gene is not equimolar. The 5' half of the gene is transcribed at a level that is 2- to 10-fold lower than that of the 3' half of the gene. These studies reveal a significant transcriptional component to beta-casein gene regulation which was not heretofore detected using double stranded cDNA probes representative of only the 3' half of the gene.

Animals↗
PubMed2000

Appearance of extracellular glutathione peroxidase (eGPx) in the ascite fluid of casein-elicited rats.

Glutathione peroxidase (GPx) activity was detected in the ascite fluid of rats injected intraperitoneally with 2.5% heat-denatured casein solution. Activity in the ascite fluid increased with time after the injection of casein, and reached a maximum at 24 h. The active component was concentrated with successive 35% ammonium sulfate precipitation and Activated Thiol-Sepharose 4B column chromatography from the ascite fluid of rats at 24 h after the injection of casein. No N-terminal amino acid of the protein corresponding to GPx was detected by automatic amino acid sequence analysis following separation with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and transfer to a polyvinyl difluoride (PVDF) membrane. Following BrCN treatment of the protein, the N-terminal amino acid sequences of two 14 and 2.6 kDa peptide fragments were found to be S-G-T-I-Y-E-Y-G-A-L and K-I-H-D-I-R-W-N-F-E, respectively. The former and the latter fragments corresponded to sequences beginning at the 37th and 176th amino acid residues of rat extracellular GPx (eGPx), respectively. The exclusive presence of eGPx in the ascite fluid of rats elicited by casein was confirmed immunologically by ELISA, immuno-precipitation and Western blotting assays. No other GPx isozymes such as cytosolic GPx (cGPx), phospholipid hydroperoxide GPx (PHGPx) or intestinal GPx (iGPx) were detected. eGPx activity and protein were also detected in the pleuritic fluid of rats following injection of 2% carrageenan. These findings indicate that eGPx appears at various sites of acute inflammation in rats. This pattern is due to leakage from circulation as a result of the increased capillary permeability at inflammation sites elicited by chemotactic factors.

Animals↗