Casein maps: effect of ethanol, pH, temperature, and CaCl2 on the particle size of reconstituted casein micelles

Although conditions favoring casein micelle aggregation are well known, factors promoting the dissociation of the casein micelle are not fully understood. It was our objective to investigate the ethanol-induced dissociation of micellar casein as affected by temperature and a wide range of pH, along with the concentrations of calcium and casein. Two different concentrations of casein micelles were dispersed in imidazole buffer with 0 to 80% ethanol (vol/vol) and 2 and 10mM calcium. Apparent micelle size was determined by dynamic light scattering at 5, 30, and 60°C. In the absence of ethanol, casein precipitation occurred at pH 4.6 in imidazole buffer. Ten to forty percent ethanol promoted casein aggregation (>1,000 nm) and higher temperature (30 and 60°C) enhanced this effect. Higher ethanol concentrations at 50 to 80% induced the dissociation (<40 nm) of the casein micelle upon acidification (pH <5) and alkalization (pH>8) in imidazole buffer. In addition, higher concentrations of casein (0.25mg/mL) and calcium (20mM) caused the formation of larger aggregates (>1,000 nm) in the presence of ethanol when comparing with the initial lower concentrations of casein (0.1mg/mL) and calcium (2mM). Casein micelle dissociation can be achieved near the isoelectric pH by modifying the solvent composition and temperature.

Purification, characterization, and milk coagulating properties of ginger proteases

Ginger proteases are used as milk coagulants in making a Chinese traditional milk product (Jiangzhinai or Jiangzhuangnai), suggesting their potential as a source of rennet substitute that might be applicable in the modern dairy industry. In this study, ginger proteases were extracted from fresh ginger rhizome by using phosphate buffer and subsequently purified by ion exchange chromatography. Ginger proteases, all with a molecular weight around 31 kDa, were found to exist in 3 forms with isoelectric point values around 5.58, 5.40, and 5.22, respectively. These enzymes had very similar biochemical behavior, exhibiting optimal proteolytic activity from 40 to 60 °C and maximum milk clotting activity at 70 °C. They were capable of hydrolyzing isolated α(S1)-, β-, and κ-casein, of which α(S1)-casein was most susceptible to the enzyme; κ-casein was hydrolyzed with a higher specificity than α(S1)- and β-casein. In addition, the ginger proteases exhibited a similar affinity for κ-casein and higher specificity with increasing temperature. Gel electrophoresis and mass spectra indicated that Ala90-Glu91 and His102-Leu103 of κ-casein were the preferred target bonds of ginger proteases. The milk clotting activity, affinity, and specificity toward κ-casein showed that ginger protease is a promising rennet-like protease that could be used in manufacturing cheese and oriental-style dairy foods.

Effect of calcium concentration on the structure of casein micelles in thin films

The structure of thin casein films prepared with spin-coating is investigated as a function of the calcium concentration. Grazing incidence small-angle x-ray scattering and atomic force microscopy are used to probe the micelle structure. For comparison, the corresponding casein solutions are investigated with dynamic light-scattering experiments. In the thin films with added calcium three types of casein structures, aggregates, micelles, and mini-micelles, are observed in coexistence with atomic force microscopy and grazing incidence small-angle x-ray scattering. With increasing calcium concentration, the size of the aggregates strongly increases, while the size of micelles slightly decreases and the size of the mini-micelles increases. This effect is explained in the framework of the particle-stabilizing properties of the hairy layer of kappa-casein surrounding the casein micelles.

Disruption and reassociation of casein micelles during high pressure treatment: influence of whey proteins

In the study presented in this article, the influence of added α-lactalbumin and β-lactoglobulin on the changes that occur in casein micelles at 250 and 300 MPa were investigated by in-situ measurement of light transmission. Light transmission of a serum protein-free casein micelle suspension initially increased with increasing treatment time, indicating disruption of micelles, but prolonged holding of micelles at high pressure partially reversed HP-induced increases in light transmission, suggesting reformation of micellar particles of colloidal dimensions. The presence of α-la and/or β-lg did not influence the rate and extent of micellar disruption and the rate and extent of reformation of casein particles. These data indicate that reformation of casein particles during prolonged HP treatment occurs as a result of a solvent-mediated association of the micellar fragments. During the final stages of reformation, κ-casein, with or without denatured whey proteins attached, associates on the surface of the reformed particle to provide steric stabilisation.

Effect of minerals on casein micelle stability of cows' milk

The effects of minerals on casein micelle stability of individual cows' milk, throughout a complete lactation, were investigated. Calcium and calcium ions, magnesium, phosphorus, sodium, potassium and citrate contents were analysed, together with the following physical properties of milk; pH, ethanol stability, rennet clotting time and coagulum firmness. There was an inverse non-linear relationship between free calcium ion concentration and ethanol stability (ES; r=0.84). Rennet coagulation time showed a weaker relationship with free calcium ion concentration (r=0.44) but a stronger relationship with pH (r=0.66). In addition, samples containing higher amounts of free calcium ions produced a firmer gel. Citrate in natural samples acts as a stabilizing factor, as it slightly improves milk stability. Potassium, on the other hand, exhibited a negative correlation, but only with rennet clotting time (r=-0.52). Throughout lactation the average values were; free Ca2+ concentration 1.88 mM, pH 6.63, ES 83.2% and clotting time 13.6 min. The equilibrium relationship between pH and free Ca2+ concentration was investigated by adjusting milk pH from 5.9 to 7.1, using acid and alkali. There was a good inverse linear relationship between pH and log (free Ca2+) for individual milk samples, with a gradient of -0.62 and a standard deviation of 0.042.

Rac1 links integrin-mediated adhesion to the control of lactational differentiation in mammary epithelia

The expression of tissue-specific genes during mammary gland differentiation relies on the coincidence of two distinct signaling events: the continued engagement of β1 integrins with the extracellular matrix (ECM) and a hormonal stimulus from prolactin (Prl). How the integrin and Prl receptor (PrlR) systems integrate to regulate milk protein gene synthesis is unknown. In this study, we identify Rac1 as a key link. Dominant-negative Rac1 prevents Prl-induced synthesis of the milk protein β-casein in primary mammary epithelial cells cultured as three-dimensional acini on basement membrane. Conversely, activated Rac1 rescues the defective β-casein synthesis that occurs under conditions not normally permissive for mammary differentiation, either in β1 integrin–null cells or in wild-type cells cultured on collagen. Rac1 is required downstream of integrins for activation of the PrlR/Stat5 signaling cascade. Cdc42 is also necessary for milk protein synthesis but functions via a distinct mechanism to Rac1. This study identifies the integration of signals provided by ECM and hormones as a novel role for Rho family guanosine triphosphatases.

Biological properties of the venom from the scorpionfish (Scorpaena plumieri) and purification of a gelatinolytic protease

In this work we describe some biological properties and a partial biochemical characterization of the Scorpanea plumieri crude venom. The fresh venom induced a decrease in blood pressure, cardiac and respiratory frequency, and exhibited hemorrhagic, hemolytic and proteolytic activities. The LD(50) (i.v. mouse) was 0.28 mg/kg. The pharmacological activities were found to be very unstable and this fact could be associated with proteolytic activity. Enzymes which hydrolyze casein and gelatin were found in this venom. A gelatinolytic protease (Sp-GP) was purified to homogeneity from S. plumieri venom through a combination of three chromatographic steps: gel filtration on Sephacryl S-200; ion exchange on DEAE-cellulose and reverse-phase/HPLC on a Vydac C4 column. The purified protease was approximately 2% of the whole protein in the soluble crude venom. The molecular mass of the Sp-GP scorpionfish gelatinase estimated by SDS-PAGE was around 80,000 Da under reducing conditions and 72,000 Da under non-reducing conditions. Attempts to determine the N-terminal sequence by automatic Edman degradation were unsuccessful, probably due to blockage of the N-terminal group. Gelatinolytic activity was optimal at pH 7-8. This is the first report of the isolation and characterization of a scorpionfish venom protease.

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.

The Alcohol-Induced Conformational Changes in Casein Micelles: A New Challenge for the Purification of Colostrinin

Recent advances in protein separation technology have allowed for the isolation of whey proteins and peptides of significant biological importance. In this study, we report a novel method for isolation and purification of the neuroprotective proline-rich polypeptides, also known as Colostrinin (CLN). Although CLN was first isolated from ovine colostrum and characterized as a complex of small molecular peptides, its constituents are present also in other mammal colostrums. The previous purification protocols are very tedious, time consuming, and, due to the diverse characteristics of colostrum, also very difficult to validate. Thus, the aim of this study was to develop a simple protocol with a maximum recovery rate for CLN peptides. Here we demonstrate the two-step extraction/purification method that consists of methanol extraction and ammonium sulfate precipitation as the general principles. When compared with the original material, CLN obtained by this method shows (1) similar pattern of peptides in SDS PAGE, (2) identical amino acid analysis, characterized by high content of proline (22%), a high proportion of nonpolar amino acids, a low percentage of glycine, alanine, arginine, histidine, and no tryptophan, methionine, and cysteine residues, (3) similar pattern of HPLC profiles, and (4) its ability to induce IFN gamma and TNF alpha. More importantly, the protocol for the production of high-quality CLN can be accomplished in less than a 48 h timeframe. In addition, avoidance of excessively harsh conditions preserves the structure and biological activity of the peptides.

Resolution of isoforms of mutalysin II, the metalloproteinase from bushmaster snake venom

Mutalysin II, a zinc endopeptidase possessing direct-acting fibrinolytic activity has been previously purified from bushmaster (Lachesis muta muta) snake venom. We now report a method to isolate two isoforms of natural mutalysin II (mut IIa and mut IIb) using chromatographies on Sephacryl S-200, CM Sepharose CL 6B and Sephadex G-50. The two proteins are monomeric non-glycosylated proteinases with similar molecular masses of 23 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tryptic peptide mapping of the two native enzymes suggested a large degree of structural similarity. Both isoforms showed high similarity in all enzymatic properties using fibrinogen, fibrin and dimethylcasein as substrates. Thus, the specific fibrinolytic activity was estimated as 12+/-1.04 and 11.5+/-1.02 U/microg for mut IIa and mut IIb, respectively. The antigenic cross-reactivity of both isoforms was examined using rabbit hyperimmune serum or immunoglobulin G anti-mut IIa assays on immunodiffusion microscope slides, indirect enzyme-linked immunoabsorbent assay and western blots. From these experiments it was concluded that the two metalloproteinases mut IIa and mut IIb share identical antigenic structures. Since the stability of mutalysin II is dependent upon the presence of zinc, we examined the EDTA sensitivity of the isoforms of mutalysin II. Thus, the IC(50) values (concentration of EDTA to produce 50% inhibition of dimethylcasein hydrolysis) for mut IIa is 180 microM and 165 microM for mut IIb.

The use of lithium chloride to study human milk micelles

Various methods have been used to study the dissociation of milk micelles in attempts to determine their structure and the interactions that stabilize them. These include the addition of urea, cooling to alter hydrophobic bonding, the addition of EDTA to sequester calcium, and changes in pH to alter molecular charge. For this study, the mild chaotropic agent LiCl was added to human milk micelles, and measurements were made on the relative percentages of the six different phosphorylation levels of beta-casein (CN) at various LiCl concentrations for different lengths of time and at different temperatures. Added LiCl had little effect at 37 degrees C but caused maximal dissociation, mainly of the beta-CN species with higher phosphorylation levels, at 23 degrees C and 4 degrees C between 1 and 2 M concentration. Comparison was made with 2-M additions of NaCl, MgCl2, and KCl at 4 degrees C, with LiCl showing the only appreciable change. The results suggest that Li+ may displace Ca2+ in protein-Ca2+-protein or protein-colloidal calcium phos+ phate-protein salt bridges and that the nonphosphorylated form of human beta-CN may change its conformation and mode of interaction upon phosphorylation. Lithium chloride may be useful to study the dissociation of the different CN in bovine milk micelles.

Signal transducers and activators of transcription as downstream targets of nongenomic estrogen receptor actions

17Beta-estradiol-activated estrogen receptor alpha (ERalpha) and beta (ERbeta) are able to induce transcriptional activation of signal transducer and activator of transcription (Stat)-regulated promoters via cytoplasmic signal transduction pathways. Stat5 and Stat3 are required for promoter induction, which correlates with cytoplasmic sublocalization of ERs and is independent of intact coactivator binding sites and DNA-binding domains. In endothelial cells, Stat5 and Stat3 are rapidly phosphorylated on both tyrosine and serine residues in response to 17beta-estradiol, and nuclear translocation is subsequently induced. 17Beta-estradiol-induced transactivation of a Stat-regulated promoter requires at least three different signal transduction pathways, including MAPK, Src-kinase, and phosphatidylinositol-3-kinase activities. In conclusion, this work identifies a novel pathway involving an agonist-bound ER-activated phosphorylation cascade, resulting in nuclear transcriptional activation of target transcription factors. These findings reveal novel targets for the development of drugs that modulate a nongenomic-to-genomic ER-dependent mechanism.

Effects of structural rearrangements on the rheology of rennet-induced casein particle gels

During ageing of casein or skim milk gels, structural changes take place that affect gel parameters, such as pore size and storage modulus. These changes can be explained in terms of rearrangements of the gel network at various length scales. In this paper, rheological experiments on rennet-induced casein gels and a general model on rearrangements are presented. The results of experiments (e.g. microscopy, permeametry) and computer simulations, the model, and recent literature on casein gels and other types of particle gels are compared to each other. Experiments presented include measurements of storage and loss moduli and maximum linear strain of the casein gels. Parameters varied were pH (5.3 and 6.65) and temperature (25 and 30 degrees C). In addition, the casein volume fraction (5-9 vol.%) was varied, which enables application of fractal scaling models. For rennet-induced casein gels, it is demonstrated that at the lower pH, all types of rearrangements proceed significantly faster. The rearrangements include: an increase in the size of compact building blocks; partial disappearance of fractal structure; and the formation of straightened strands, some of which eventually break. All of these rearrangements seem to be a consequence of particle fusion. There are indications of universality of the relation between particle fusion and gel syneresis for gels composed of viscoelastic particles.

Caseinolytic activity of fruit extract from Opuntia ficus-indica on bovine, caprine, and ovine sodium caseinates

The rates and extents of hydrolysis of alpha(S)- and beta-caseins from bovine, caprine, and ovine sodium caseinates produced by an enzymatic extract of the fruit of Opuntia ficus-indica, (L.) Miller were evaluated and compared with those produced by a commercial animal rennet. A mechanistic model based on a pseudo-first-order enzymatic reaction, in the presence of first-order deactivation of the enzyme, was postulated and successfully fitted to the experimental data. The animal rennet exhibited higher enzymatic efficiency than the fruit extract, irrespective of the source (i.e., bovine, caprine, or ovine) and the type (i.e., alpha(S)- or beta-casein) of substrate. The enzymatic efficiency (k(cat)/K(m)) for alpha(S)-casein ranged from 72 to 220 and from 43 to 65 L g(-1) h(-1), and for beta-casein from 242 to 742 and from 55 to 164 L g(-1) h(-1), for the animal rennet and the enzymatic extract of O. ficus-indica, respectively. Finally, it was observed that beta-casein from caprine and ovine caseinates was degraded by O. ficus-indica faster than its alpha(S) counterpart, but the reverse was observed for bovine caseinate.

Influence of milk-clotting enzyme concentration on the alphas1-casein hydrolysis during soft cheeses ripening

We studied the influence of the dose of milk-clotting enzyme on alphas1-CN degradation, soluble nitrogen production, and sensory profile for an Argentinean soft cheese: Cremoso Argentino. Five different types of cheeses were produced: 1) control cheeses with normal technology, 2) cheeses with inactivated milk-clotting enzyme, 3) cheeses with inactivated milk-clotting enzyme, without starter (acidified with glucono delta lactone), 4) cheeses with a half dose of milk-clotting enzyme, and 5) cheeses with a double dose of milk-clotting enzyme. Proteolysis was assessed by isoelectric focusing electrophoresis of the insoluble fraction at pH 4.6, followed by densitometric quantification. Soluble nitrogen at pH 4.6, expressed as a percentage of total nitrogen and defined as ripening index was also performed. A sensorial panel evaluated the cheeses at the end of ripening. The hydrolysis level of alphas1-CN depended on the milk-clotting enzyme dose used in cheese making. Cheeses without active coagulant did not show degradation at the end of ripening, while cheeses with half and whole doses showed proportional degradations to coagulant dose. Cheese with a double dose of coagulant did not show higher alphas1-CN hydrolysis than normal cheese. No difference was found between cheeses with and without microbiological starter, indicating that the selected culture, composed of thermophilic strains, was unable to attack the whole casein. A high linear correlation was found between ripening index and the relation Sensorial characteristics of cheeses agree with objective analysis. Cheeses without active coagulant were hard and crumbly, while cheeses with normal dose were soft and creamy.

[The production of antihypertensive peptides in beta-casein proteolysis]

Antihypertensive peptides were obtained after the proteolysis of beta-casein by starter cells Lactococcus lactis ssp. lactis and lactococci with pepsin or fromase. The peptides have shown the effect as inhibitors of angiotensin-converting enzyme. The strongest action the peptide obtained after the proteolysis of beta-casein by synergic action of lactococci with pepsin has shown. It demonstrates a capability of formation of such peptides directly in milk products during their making and maturation under the action of proteolytic system of lactic acid bacteria and milk clothing proteases.

Mineral and casein equilibria in milk: effects of added salts and calcium-chelating agents

We have investigated the effects of adding a range of mineral salts and calcium-chelating agents on the distribution of casein and minerals between the non-pelleted and pelleted phases of milk obtained upon centrifugation at 78000 g for 90 min. Adding CaCl2 or mixtures of NaH2PO4 and Na2HPO4 to reconstituted skim milk (90 g milk solids/kg) at pH 6.65 increased both pelleted casein and pelleted calcium phosphate. Opposite effects were obtained by adding citrate or EDTA. The change in pelleted calcium phosphate was not simply related to casein release from the micelle. Upon adding 5 mmol EDTA/kg milk, 20% of the pelleted Ca, 22% of the pelleted phosphate and 5% of the micellar casein were removed. Increasing the concentration of EDTA to 10 mmol/kg milk decreased the pelleted Ca by 44% and the pelleted phosphate by 46%, and caused 30% of the micellar casein to be released. The effects of adding phosphate, citrate or EDTA at pH 6.65, followed by the addition of CaCl2, demonstrated the reversibility of the dissolution and formation of the micellar calcium phosphate. There were limits to this reversibility that were related to the amount of colloidal calcium phosphate removed from the casein micelles. Adding CaCl2 to milk containing > or = 20 mmol EDTA or > or = 30 mmol citrate/kg milk did not result in complete reformation of casein micelles. Light-scattering experiments confirmed that the dissolution of moderate amounts of colloidal calcium phosphate had little effect on micellar size and were reversible, while the dissolution of larger amounts of colloidal calcium phosphate resulted in large reductions in micellar size and was irreversible.

Action of cardosin A from Cynara humilis on ovine and caprine caseinates

In the Iberian Peninsula, the proteinases present in the flowers of members of the Cynara genus, C. cardunculus, C. humilis and C. scolymus, have for many years been successfully used in the manufacture of traditional cheeses from ovine and/or caprine milk on individual farms (Vieira de Sá & Barbosa, 1972; Trujillo et al. 1994). In Portugal, C. cardunculus is the species most frequently employed. Although commercial thistle was tentatively assumed to be pure in taxonomic terms, accurate analyses have shown that the flowers of C. cardunculus are often mixed with flowers of C. humilis (Pires et al. 1994). The clotting activity of C. humilis is due to an aspartic proteinase, currently designated cardosin A and similar to another enzyme obtained from C. cardunculus. This enzyme is similar in specificity and activity to chymosin (Pires et al. 1994).

The action of cardosin A from C. cardunculus upon ovine and caprine caseins has been reported recently (Ramalho-Santos et al. 1996; Simo4es, 1998; Sousa & Malcata, 1998), but as yet there is no information on the proteolytic activity of the proteinase from C. humilis upon caseins from milks other than bovine. Caseins from small ruminants' milks are the usual substrates of cardosin during milk coagulation and cheese ripening, and sodium caseinate represents an intermediate system between isolated caseins and the cheese matrix that is free from interference by fat. Thus ovine and caprine caseinates may be useful substrates for investigating the proteolytic activity of cardosin.

The aim of the present study was to compare the action of pure cardosin A, obtained from C. humilis, on caprine and ovine caseinates, and to assess the in vitro contribution of this enzyme to the overall proteolytic action of thistle rennet.

Glucosamine sulfate modulates dysregulated activities of human osteoarthritic chondrocytes in vitro

OBJECTIVE

The efficacy of glucosamine sulfate (GS) in the symptomatic treatment of patients with osteoarthritis (OA) is suggested to be mediated by still unknown effects on the altered OA cartilage.

DESIGN

Using human OA chondrocytes in culture, the effects of GS on protein synthesis, caseinase, collagenase, phospholipase A2 (PLA2) and protein kinase C (PKC) activities as well as production of nitric oxide and cyclic AMP were studied in both cells and culture medium.

RESULTS

GS significantly reduced PLA2 activity, and more modestly collagenase activity, in the OA chondrocytes in a dose-dependent manner. By contrast, PLA2 and collagenase activity of the culture medium was not modified. No effects on caseinase activity was seen. GS significantly and dose-dependently increased protein synthesis. GS did not modify nitric oxide and cAMP production but significantly increased PKC production.

CONCLUSION

GS modified cultured OA chondrocyte metabolism by acting on PKC, cellular PLA2, protein synthesis and possibly collagenase activation. Extrapolation of the effect to the in-vivo situation remains hypothetical but they might represent some possible mechanisms of action of the drug in human.

Citrate inhibition of snake venom proteases

Thirty snake venoms had a citrate content of 2.3 to 12.9%, dry basis, by an aconitase isocitric dehydrogenase coupled enzyme assay. This is a venom concentration range of approximately 30 to 150 mM citrate assuming 25% venom solids content. Inhibition of snake venom protease activity by the addition of exogenous citrate was obtained using azure blue hide powder and azocasein as substrates. Protease inhibitions of 7.5% for Crotalus atrox venom to 78% for Bothrops picadoi venom were observed with citrate. Complete inhibition of snake venom protease activity by citrate was not observed. Bothrops asper (Pacifico) venom showed a 41% protease inhibition by citrate with azocasein as the substrate and 46% inhibition of Bothrops asper (Alantico) venom protease with azure blue hide power as a substrate. Trypsin was not inhibited in this system. Citrate may inhibit some venom protease activity by forming a complex with the zinc of zinc-dependent enzymes. reserved.

Prolactin-inducible enhancer activity of the first intron of the bovine beta-casein gene

We have analyzed the regulatory roles of the first intron (intron-1) of the bovine beta-casein gene in the bovine beta-casein/CAT expression system using a mouse mammary epithelial cell line, HC11. After a combined treatment of HC11 cells with insulin, dexamethasone and prolactin, the induced expression of p beta c1.8/+ICAT vector including 2 kb intron-1 and 1.8 kb promoter was greatly increased to 23.5 folds, while that of p beta ca.8CAT basic vector with 1.8 kb promoter only, was 6.5. A classical enhancer activity was shown in the 2 kb intron fragment from the experiment in which the orientation and the position of the intron-1 on the vectors were changed. The enhancer activity was largely dependent on the lactogenic hormones, especially prolactin. A stepwise reduction of the inducibility in the 5' to 3' deletion analysis of the intron-1 indicates the existence of several functional elements in the region. In particular, an internal fragment (+1071 to +1490) was important for the prolactin-dependent enhancing activity of the intron-1. These results suggest that several elements in the intron-1 of the bovine beta-casein gene cooperatively interact not only with each other but also with its promoter for hormonal induction.

Dominant negative variants of the SHP-2 tyrosine phosphatase inhibit prolactin activation of Jak2 (janus kinase 2) and induction of Stat5 (signal transducer and activator of transcription 5)-dependent transcription

PRL plays a central role in the regulation of milk protein gene expression in mammary epithelial cells and in the growth and differentiation of lymphocytes. It confers its activity through binding to a specific transmembrane, class I hematopoietic receptor. Ligand binding leads to receptor dimerization and activation of the tyrosine kinase Jak (janus kinase) 2, associated with the membrane-proximal, intracellular domain of the receptor. Jak2 phosphorylates and activates Stat5, a member of the Stat (signal transducers and activators of transcription) family. PRL receptor also activates SHP-2, a cytosolic tyrosine phosphatase. We investigated the connection between these two signaling events and derived a dominant negative mutant of SHP-2 comprising the two SH2 domains [SHP-2(SH2)2]. An analogous variant of the SHP-1 phosphatase [SHP-1(SH2)2] was used as a control. The dominant negative mutant of SHP-2 was found to inhibit the induction of tyrosine phosphorylation and DNA-binding activity of m-Stat5a, m-Stat5b, and the carboxyl-terminal deletion variant m-Stat5adelta749, as well as the transactivation potential of m-Stat5a and m-Stat5b. The dominant negative mutant SHP-1(SH2)2 had no effect. The kinase activity of Jak2 is also dependent on a functional SHP-2 phosphatase. We propose that SHP-2 relieves an inhibitory tyrosine phosphorylation event in Jak2 required for Jak2 activity, Stat5 phosphorylation, and transcriptional induction.

Pretreatment with glucocorticoid is essential for lactogenic induction of the bovine beta-casein/CAT expression in HC11 cells

Hormonal regulation of the bovine beta-casein gene expression was studied in a murine mammary epithelial HC11 cells and compared with that of the rat beta-casein gene expression. CAT expression vectors driven by their promoter sequences were transfected into HC11 cells. Stable transfectents were treated with lactogenic hormones, dexamethasone and prolactin for 2 days in confluent cultures. While the lactogenic hormones synergistically induced a strong activation of the rat beta-casein/CAT expression, neither a single or combined treatment of dexamethasone and prolactin induced the bovine beta-casein/CAT expression. To test a sequential treatment effect of lactogenic hormones on the bovine beta-casein/CAT expression, cells were first treated with either dexamethasone or prolactin for various days and then subjected to the second treatment with both hormones for 2 days. Only dexamethasone-, but not prolactin-pretreated cells showed a strong lactogenic induction. Moreover, the fold induction of dexamethasone-pretreated cells increased gradually as a function of duration of dexamethasone pretreatment. A series of the bovine beta-casein/CAT constructs with different length of the bovine beta-casein 5' flanking region ranged from 0.3 kb to about 15 kb was analyzed in 12-days dexamethasone-pretreated cultures. CAT expression was increased even in 0.3 kb-containing construct, but prominent induction was seen in more than 1.8 kb-containing constructs. Therefore, it could be concluded that a long-term dexamethasone pretreatment is essential for lactogenic induction of the bovine beta-casein expression and the 0.3 kb proximal promoter region is important, but more distal promoter element(s) is necessary for mediating the coordinated action of lactogenic hormones to the bovine beta-casein expression.

Effect of gamma-interferon on binding of gliadin and other food peptides to the human intestinal cell line HT-29

gamma-Interferon is one of the main cytokines released during activation of intestinal lymphocytes in coeliac patients. The question has never been addressed whether gamma-interferon influences binding of gliadin and other food peptides to human enterocytes. Therefore, the human intestinal epithelial cell line HT-29 was cultured with gliadin, casein, beta-lactoglobulin and ovalbumin, with or without gamma-interferon, and peptide binding to cells was determined by flow cytometry and fluorescence microscopy. gamma-Interferon stimulated gliadin binding by a factor of 4. Binding was saturable with half maximal binding at 0.15 mg/ml. For maximal binding, an incubation of at least 24 h was necessary. gamma-Interferon increased binding of beta-lactoglobulin and casein, too, but inhibited that of ovalbumin. Binding of gliadin was inhibited by the other peptides. Under the conditions of ongoing mucosal inflammatory reactions and release of gamma-interferon, enhanced binding may trigger intestinal lymphocytes, increase secretion of cytokines and thus induce a vicious circle.

Role of the O-phosphoserine clusters in the interaction of the bovine milk alpha s1-, beta-, kappa-caseins and the PP3 component with immobilized iron (III) ions

alpha s1- and beta-Caseins have a sequence cluster -Ser(P)-Ser(P)-Ser(P)-Glu-Glu- which is not present in kappa-casein and the whey PP3 component. The affinity of these phosphoproteins for the iron(III)-iminodiacetic acid (IDA) complex immobilized on Sepharose was studied as a function of pH, urea concentration, calcium ion concentration, enzymatic dephosphorylation and temperature. The affinity of the three polyphosphorylated proteins (alpha s1- and beta-caseins, PP3) was similar. The sequence cluster was not a specific recognition pattern of the iron(III) ion. These three proteins presented a site of high affinity and a site of weak affinity. kappa-Casein, which had only one Ser(P) residue, presented only the site of weak affinity. Their primary site which was absent after dephosphorylation or calcium ion addition required the presence of at least two Ser(P) residues close in space. Their secondary site was sensitive to the presence of urea. It was sensitive to pH variation for PP3 and kappa-casein. The study of the affinity of a few free amino acids towards iron(III)-IDA showed that the secondary site involved tryptophan and tyrosine residues for alpha s1- and beta-caseins, histidine residues for PP3 and cysteine residues for kappa-casein.

Heregulin induces in vivo proliferation and differentiation of mammary epithelium into secretory lobuloalveoli

Mammary gland development and differentiation is mediated through the combined activities of systemic hormones and locally synthesized growth factors. To determine the in vivo response of mammary epithelium to heregulin (HRG), we implanted Elvax pellets containing HRG alpha or HRG beta within the mammary glands of prepubescent female mice in the presence or absence of exogenous estradiol and progesterone (E/ P). Mice treated in the same way with transforming growth factor alpha (TGF-alpha) were included as a positive control. Each growth factor treatment induced epithelial ductal branching in the presence or absence of E/P. In the absence of E/P, HRG beta did not effect terminal end bud formation, mammary epitheilum branching, or ductal migration. In contrast, TGF-alpha and HRG alpha induced ductal branching and HRG alpha induced ductal migration in the absence of E/P. The overall mammary response to growth factors was potentiated by the concomitant presence of E/P. In every case, the in vivo mammary epithelial responses to HRG alpha were more robust than TGF-alpha. Limited lobuloalveolar development was also observed in growth factor-treated mammary glands when E/P was present. Histological examination of growth factor-induced lobuloalveoli revealed secretory products within the lumen of HRG alpha and HRG beta lobuloalveoli. TGF-alpha-induced lobuloalveoli lacked similar secretory products.

Evaluation of digestive proteinases from the Antarctic krill Euphasia superba as potential chemonucleolytic agents. In vitro and in vivo studies

Chemonucleolysis is a therapeutic procedure whereby a degradative enzyme is injected intradiscally to reduce disc height/width by depolymerisation of extracellular matrix components. This process is considered to diminish disc pressure on inflamed nerve roots, resulting in the alleviation of sciatic pain. In the present study two krill (Euphasia superba) enzyme preparations, a proteinase and an esterase preparation, were evaluated for their potential as chemonucleolytic agents. Initially, their ability to degrade several protein (azocoll, casein, proteoglycans, PGs) and peptide (CBZ-arg-4-nitroanilide, CBZ-lys-thiobenzyl ester) substrates was assessed in vitro. The krill proteinase preparation rapidly converted azocoll, casein and PGs to small peptides. Furthermore, when this degradative enzyme preparation was evaluated in vivo, a relatively low intradiscal dose (0.54 mg/disc) was found to reduce intervertebral disc widths in beagles to 48% +/- 10.5% (mean +/- SEM) of their pre-injection values within 2 weeks of administration. Moreover, the discs injected with this proteinase had reconstituted up to 80% +/- 9% (mean +/- SEM) of their pre-injection widths at the termination of the experiment (32 weeks). These data suggest that the krill protease preparation has potential as a chemonucleolytic agent which would allow disc matrix reconstitution. Conversely, the krill esterase preparation also degraded PGs, but into relatively large fragments. This limited digestion of PGs indicates that the krill esterase would be a less effective chemonucleolytic agent than the corresponding proteinase.

Characterization of human kappa-casein purified by FPLC

Because previous purification procedures for human kappa-casein may have caused the loss of some carbohydrate, relatively gentle methods were used. The protein was isolated by a four-step procedure which included isoelectric precipitation of whole casein, gel chromatography on Sephadex G-200 in the presence of SDS, removal of the SDS with Extracti-Gel D, and FPLC chromatography on Mono Q with buffers containing 6 M urea. The purified protein was nearly identical in amino acid composition to that found earlier by amino acid analysis and peptide sequencing and a molar extinction coefficient of 11.2 +/- 0.1 was determined on the basis of amino acid analysis with a norleucine internal standard. Hydrolysis, acylation, and methylsilylation of the carbohydrate, followed by gas chromatographic analysis on a fused silica column, yielded approximately 5% fucose, 17% galactose, 18% N-acetylglucosamine, 8% N-acetylgalactosamine and 7% sialic acid, totaling almost 55% by weight. The percentages from two different donors were almost the same. About 1 mole phosphorus per mole of kappa-casein was also detected. Using low-speed sedimentation equilibrium methods, a molecular weight of only 33,400 was obtained for human kappa-casein, suggesting carbohydrate lability. Human beta-casein with four phosphoryls was stabilized against precipitation by 10 mM Ca+2 ions at a level greater than 95% when the molar ratio of kappa/beta exceeded 0.15.

Growth is compromised in rats fed ozone-treated casein

Modified casein containing few phenylalanine residues and no other aromatic amino acid residues was obtained by ozonolysis of casein. Although 68% of phenylalanine was decomposed by ozonolysis of casein, ozonolysis caused alterations beyond the destruction of aromatic amino acid residues. Nearly the same degree of decomposition of amino acid residues was observed in casein ozonated after predigestion by pepsin. Rats were fed diets containing 8% casein supplemented with methionine and aspartic acid (8C-AA), 8% ozonated casein supplemented with methionine and free amino acids lost by ozonolysis (8OC-AA), 8% casein ozonated after predigestion by pepsin supplemented with methionine and free amino acids lost during preparation (8POC-AA) or 7.6% amino acid mixture. The growth of rats fed the 8OC-AA diet was significantly lower than that of those fed 8C-AA or 7.6AA diets. The growth of rats fed the 8POC-AA diet was comparable to growth of those fed 8OC-AA. The biological values of the 8OC-AA and 8POC-AA were comparable to that of 8C-AA, but true digestibility of 8OC-AA was significantly lower than that of 8C-AA. True digestibility 8POC-AA was significantly improved relative to 8OC-AA, but the growth of rats fed 8POC-AA was not improved relative to that of those fed 8OC-AA. Kidney and cecum weights of rats fed 8OC-AA and 8POC-AA were significantly heavier than those of the 8C-AA-fed group, although histopathological examination of kidneys showed no deterioration compared to that of the 8C-AA-fed group.(ABSTRACT TRUNCATED AT 250 WORDS)

A polylysine-induced aggregation of substrate accompanies the stimulation of casein kinase II by polylysine

Casein kinase II (CK-II) activation by polylysine parallels an aggregation of substrates promoted by the polycation. CK-II is known to be stimulated by basic polypeptides and polyamines. The mechanism by which this stimulation takes place, however, is not yet fully understood. Here we show that, in the usual CK-II assay, polylysine induces the aggregation of casein. This aggregation has been monitored by turbidimetry, electron microscopy and gel filtration. The polylysine-concentration-dependence of the casein aggregation parallels the polylysine-concentration-dependence of the enzyme stimulation. In the presence of polylysine the enzyme is incorporated into the casein aggregates promoted by the polycation, thus supporting the view that this substrate aggregation is directly related to the mechanism of CK-II stimulation. Preliminary results show that a similar parallelism occurs with other natural substrates of the enzyme. The physiological meaning of this substrate aggregation, and its possible relation to other polylysine-stimulated enzymes and polylysine-aggregated proteins, are discussed.

Specificity of a cell-envelope-located proteinase (PIII-type) from Lactococcus lactis subsp. cremoris AM1 in its action on bovine ?-casein

The action of the cell-envelope proteinase (PIII-type) from Lactococcus lactis ssp. cremoris AM1 on bovine beta-casein was studied. The results were compared with those obtained earlier with (PI-type) proteinases from the cell envelope of other L. lactis strains. From a 4-h digest (pH 6.2; 15 degrees C) of beta-casein made with the PIII-type proteinase, 24 peptides were isolated and purified by selective precipitation followed by semi-preparative reversed-phase HPLC. Altogether, these peptides accounted for the preferential splitting of 16 peptide bonds in beta-casein by the PIII-type proteinase. In nine cases the primary cleavage site (P1-P'1) was a Glx-X or X-Glx peptide bond. In ten cases at least one large hydrophobic residue (Met, Leu, Tyr, Phe) formed part of the cleavable bond. The P2-P3 and/or P'2-P'3 regions of the substrate consisted of hydrophobic and/or negatively charged side chains or of side chains potentially involved in hydrogen bonds. Nine of the peptide bonds split were reported previously to be also susceptible to cleavage by PI-type proteinases, although the kinetics may be different. The PIII-type proteinase shows a broader specificity in its initial cleavage of beta-casein than does the PI-type.