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PubMed2007

Role of human leucocyte antigen DQ in the presentation of T cell epitopes in the major cow's milk allergen alphas1-casein.

BACKGROUND: Little is known about the association between human leucocyte antigen (HLA) and cow's milk allergy (CMA). The aim of the present study was to determine the HLA restriction of T cell clones (TCCs) specific to alphas1-casein, the most abundant milk protein, and to study possible HLA class II allele associations with CMA. METHODS: alphas1-Casein-specific TCCs were derived from 6 children with CMA, 9 atopic children without CMA and 5 non-atopic children. T cell epitope specificity was defined by stimulation with overlapping peptides, spanning the alphas1-casein molecule. HLA restriction was determined in proliferation assays using antibodies blocking either HLA-DP, HLA-DQ or HLA-DR. HLA genotyping was performed in 32 subjects with CMA, 23 atopic and 22 non-atopic individuals. RESULTS: Ten TCCs were restricted to HLA-DQ, 6 TCCs to HLA-DR and 4 TCCs to HLA-DP. The sequence in alphas1-casein that was most immunogenic to T cells from children with CMA contained T cell epitopes restricted to DQB1*0201, DPB1*0401 and DRB1*1501. The DQB1*0501 allele frequency was lower in children with CMA than in non-atopic children, but this difference could not be confirmed in an additional group of subjects with and without CMA. CONCLUSIONS: HLA-DQ plays a substantial role in the presentation of T cell epitopes in alphas1-casein. However, HLA class II allele frequencies do not show major differences between cow's milk allergic, atopic and non-atopic subjects. T cell epitopes in the most immunogenic region are presented by various abundantly present HLA genotypes. Therefore, this sequence may be a suitable target for peptide immunotherapy.

Adolescent↗
PubMed1983

Serum lipids, lipoprotein composition and liver cholesterol in genetically obese Zucker rats fed semipurified diets containing either casein or soy protein.

The effect of semipurified diets containing either casein or soy protein on serum lipids, lipoprotein composition and liver cholesterol was studied in genetically obese Zucker rats. The ingestion of a cholesterol-enriched semipurified diet containing casein resulted in elevated levels of serum cholesterol and phospholipids compared to the feeding of a soy protein diet. No differences in serum triglycerides were observed. Differences in serum cholesterol and phospholipids were mainly reflected in the very low density lipoproteins and low density lipoproteins and to a minor extent in the high density lipoproteins. Liver cholesterol paralleled the levels of cholesterol in the serum, the rats fed casein exhibited markedly higher levels of liver cholesterol than those fed soy protein. Furthermore, the rats fed casein also had enlarged livers. Thus, this study clearly shows the differential cholesterolemic effect of dietary casein and soy protein in genetically obese Zucker rats.

Animal Feed↗
PubMed1990

Intermediate density lipoprotein-apolipoprotein B turnover in rabbits fed semipurified diets containing casein or soy protein.

The aim of this study was to investigate the underlying causes of elevated levels of intermediate density lipoprotein (IDL) in rabbits fed casein compared to soy protein in a cholesterol-free, semipurified diet. Kinetic studies were carried out in which homologous, radiolabelled IDL was injected into casein- and soy protein-fed animals after a period of 7 months on diet. Total plasma cholesterol and IDL cholesterol and protein were significantly higher in animals fed casein compared to those fed soy protein. The fractional catabolic rate of IDL-apolipoprotein B was significantly lower in casein-fed animals but the difference in mean values for the production rate did not reach statistical significance. The effect of feeding casein on IDL can be attributed to its reduced efficiency of removal from the plasma.

Animals↗
PubMed1995

Anticariogenicity of calcium phosphate complexes of tryptic casein phosphopeptides in the rat.

Casein phosphopeptides (CPP) stabilize calcium phosphate through the formation of casein-phosphopeptide amorphous calcium-phosphate complexes (CPP-CP). The ability of CPP-CP to reduce caries activity was investigated by use of specific-pathogen-free rats inoculated with Streptococcus sobrinus. The animals consumed a defined cariogenic diet free of dairy products. Solutions (100 microL) of the CPP-CP (0.1, 0.2, 0.5, 1.0% w/v) were applied to the animals' molar teeth twice daily. Other groups of animals received solutions containing 500 ppm F, the non-phosphorylated peptides of a casein tryptic digest (0.5% w/v), or the calcium-phosphate complex of a synthetic octapeptide, Ac-Glu-Ser(P)-Ile-Ser(P)-Ser(P)-Ser(P)-Glu-Glu-NHMe, corresponding to the common sequence in the CPP. The CPP-CP significantly reduced caries activity in a dose-response fashion, with 1.0% CPP-CP producing 55% and 46% reductions in smooth surface and fissure caries activity, respectively, being similar to that of 500 ppm F. The anticariogenic effects of CPP-CP and fluoride were additive, since animals receiving 0.5% CPP-CP plus 500 ppm F had significantly lower caries activity than those animals receiving either CPP-CP or fluoride alone. The tryptic digest of casein with the phosphopeptides selectively removed showed no anticariogenic activity. The synthetic octapeptide-calcium phosphate complex significantly reduced caries activity, confirming that this calcium-phosphate-stabilizing portion of the casein phospho-peptides is associated with anticariogenicity. The CPP-CP did not significantly affect the level of S. sobrinus in fissure plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMedDate not supplied

Comparative analysis on the structural features of the 5' flanking region of kappa-casein genes from six different species.

Kappa-casein plays an essential role in the formation, stabilisation and aggregation of milk micelles. Control of kappa-casein expression reflects this essential role, although an understanding of the mechanisms involved lags behind that of the other milk protein genes. We determined the 5'-flanking sequences for the murine, rabbit and human kappa-casein genes and compared them to the published ruminant sequences. The most conserved region was not the proximal promoter region but an approximately 400 bp long region centred 800 bp upstream of the TATA box. This region contained two highly conserved MGF/STAT5 sites with common spacing relative to each other. In this region, six conserved short stretches of similarity were also found which did not correspond to known transcription factor consensus sites. On the contrary to ruminant and human 5' regulatory sequences, the rabbit and murine 5'-flanking regions did not harbour any kind of repetitive elements. We generated a phylogenetic tree of the six species based on multiple alignment of the kappa-casein sequences. This study identified conserved candidate transcriptional regulatory elements within the kappa-casein gene promoter.

5' Flanking Region↗
PubMed2002

Identification of protein tyrosine phosphatase 1B and casein as substrates for 124-v-Mos.

BACKGROUND: The mos proto-oncogene encodes a cytoplasmic serine/threonine-specific protein kinase with crucial function during meiotic cell division in vertebrates. Based on oncogenic amino acid substitutions the viral derivative, 124-v-Mos, displays constitutive protein kinase activity and functions independent of unknown upstream effectors of mos protein kinase. We have utilized this property of 124-v-Mos and screened for novel mos substrates in immunocomplex kinase assays in vitro. RESULTS: We generated recombinant 124-v-Mos using the baculovirus expression system in Spodoptera frugiperda cells and demonstrated constitutive kinase activity by the ability of 124-v-Mos to auto-phosphorylate and to phosphorylate vimentin, a known substrate of c-Mos. Using this approach we analyzed a panel of acidic and basic substrates in immunocomplex protein kinase assays and identified novel in vitro substrates for 124-v-Mos, the protein tyrosine phosphatase 1B (PTP1B), alpha-casein and beta-casein. We controlled mos-specific phosphorylation of PTP1B and casein in comparative assays using a synthetic kinase-inactive 124-v-Mos mutant and further, tryptic digests of mos-phosphorylated beta-casein identified a phosphopeptide specifically targeted by wild-type 124-v-Mos. Two-dimensional phosphoamino acid analyses showed that 124-v-mos targets serine and threonine residues for phosphorylation in casein at a 1:1 ratio but auto-phosphorylation occurs predominantly on serine residues. CONCLUSION: The mos substrates identified in this study represent a basis to approach the identification of the mos-consensus phosphorylation motif, important for the development of specific inhibitors of the Mos protein kinase.

Animals↗
PubMed1983

Thyroid hormone increases type I adenosine 3', 5'-monophosphate-dependent protein kinase and casein kinase activities in rat liver cytosol: analysis of protein kinases by polyacrylamide disc gel electrophoresis.

We investigated the action of thyroid hormone on each protein kinase in rat liver cytosol. Kinases were analyzed by polyacrylamide disc gel electrophoresis and isoelectric focusing in polyacrylamide gel. Polyacrylamide disc gel electrophoresis separated cAMP-dependent protein kinase type I (Rf = 0.35), type II (Rf = 0.44), their catalytic subunit (Rf = 0.26), and cAMP-independent protein kinase (Rf = 0.50). Casein kinase was detected at Rf = 0.37. In addition to the catalytic subunit with Rf = 0.26, another catalytic subunit was found at Rf = 0.44 when the cytosol was preincubated with cAMP. The administration of T3 (20 micrograms/100 g BW for 3 days) to hypothyroid rats increased enzyme activities of type I holoenzyme and casein kinase by 48%. Free catalytic subunit, separated from holoenzyme, had the same level of enzyme activity in both groups, suggesting greater endogenous dissociation of type I holoenzyme in hypothyroid rats. When heat-inactivated rat liver cytosol was used as substrate in the assay of protein kinase activity, the peak enzyme active in phosphorylating the cytosol corresponded to the casein kinase peak. Our data indicate that casein kinase is the main enzyme that mediates phosphorylation of endogenous proteins in rat liver cytosol, and that T3 treatment increases the activity of casein kinase and of type I cAMP-dependent protein kinase.

Animals↗
PubMed1986

Bifunctional activity of epidermal growth factor on alpha- and kappa-casein gene expression in rodent mammary glands in vitro.

Explants from mammary glands of virgin rats and pregnant rats and mice were cultured under serum-free conditions in the presence of various combinations of the hormones insulin (I), aldosterone (A), corticosterone (C), PRL, and epidermal growth factor (EGF). Bifunctional activity of EGF was found on expression of the alpha- and kappa-casein genes. In the presence of I, A, and C, EGF increased the level of alpha-casein mRNA in pregnant mouse mammary gland explants, but not in rats. kappa-Casein mRNA sequences in mouse mammary gland explants were also significantly increased by EGF in the presence of I, A, and C, but in rat mammary gland explants, the increase was less. In contrast, in the presence of I, A, C, and PRL, EGF inhibited the induction of both alpha- and kappa-casein mRNA sequences in tissue from rats and mice. This bifunctionality of EGF in terminal differentiation of the rodent mammary gland was also reflected in the levels of synthesis of total casein and alpha-lactalbumin.

Aldosterone↗
PubMed2006

Increased plasma homocysteine concentration in rats from a low casein diet.

Rats were fed on a 10% casein (10C) diet, 30% casein (30C) diet, 10C+0.5% methionine diet, or 30C+0.5% methionine diet for 14 d to investigate the relationship between the dietary protein level and plasma homocysteine concentration. The plasma homocysteine concentration was significantly higher in the rats fed on the 10C diet than in the rats fed on the 30C diet, and this phenomenon persisted even under the condition of methionine supplementation. The activity of hepatic cystathionine beta-synthase (CBS) was significantly lower in the rats fed on the 10% casein diets than in the rats fed on the 30% casein diets, irrespective of methionine supplementation. This is the first demonstration of a low-protein diet increasing the plasma homocysteine concentration in experimental animals. It is suggested that the decreased CBS activity might be associated, at least in part, with the hyperhomocysteinemia caused by the low-casein diet.

Animals↗
PubMed2001

Effects of bovine beta-casein (1-28) and its chemically synthesized partial fragments on proliferative responses and immunoglobulin production in mouse spleen cell cultures.

Effects of bovine beta-casein (1-28) having a phosphoserine-rich region (Glu14-SerP-Leu-SerP-SerP-SerP-Glu-Glu21) and its chemically synthesized partial fragments on proliferation of lymphocytes and immunoglobulin production were investigated in mouse spleen cell cultures. The parent fragment 1-28 and all fragments containing SerP-Leu-SerP and/or SerP-SerP-SerP had a significant mitogenic effect, stimulated proliferation of lymphocytes induced by lipopolysaccharide, phytohemagglutinin, or concanavalin A, and increased immunoglobulin (IgG + IgM + IgA) or IgA levels in the cell cultures. In contrast, dephosphorylated beta-casein (14-21) and SerP-SerP amide had hardly any immunoregulatory activity. On the other hand, SerP-Leu-SerP amide reacted little with antibodies specific to bovine beta-casein (1-28), but beta-casein (14-21), and SerP-SerP-SerP amide obviously reacted with the antibody. These results confirm that the immunoregulatory activity of casein phosphopeptides is attributable to SerP-X-SerP, which may well be available as a non-allergic food ingredient having an adjuvant activity for mucosal IgA responses.

Adjuvants, Immunologic↗
PubMed2006

Analysis of tissue-specific expression of human type II collagen cDNA driven by different sizes of the upstream region of the beta-casein promoter.

To investigate the ability of 1.8 kb or 3.1 kb bovine beta-casein promoter sequences for the expression regulation of transgene in vivo, transgenic mice were produced with human type II collagen gene fused to 1.8 kb and 3.1 kb of bovine beta-casein promoter by DNA microinjection. Five and three transgenic founder mice were produced using transgene constructs with 1.8 kb and 3.1 kb of bovine beta-casein promoters respectively. Founder mice were outbred with the wild type to produce F1 and F2 progenies. Total RNAs were extracted from four tissues (mammary gland, liver, kidney, and muscle) of female F1 transgenic mice of each transgenic line following parturition. RT-PCR and Northern blot analysis revealed that the expression level of transgene was variable among the transgenic lines, but transgenic mice containing 1.8 kb of promoter sequences exhibited more leaky expression of transgene in other tissues compared to those with 3.1 kb promoter. Moreover, Western blot analysis of transgenic mouse milk showed that human type II collagen proteins secreted into the milk of lactating transgenic mice contained 1.8 kb and 3.1 kb of bovine beta-casein promoter. These results suggest that promoter sequences of 3.1 kb bovine beta-casein gene can be used for induction of mammary gland-specific expression of transgenes in transgenic animals.

Animals↗
PubMed1994

Human alpha S1-casein like protein: purification and N-terminal sequence determination.

Casein components of human milk are generally reported to belong to the beta- and kappa-groups. In this research human casein fraction was obtained from pooled mature milk, either by ultracentrifugation or by acid precipitation. In both cases a minor component with a slightly higher mobility in SDS-PAGE than beta-casein was identified. The protein was purified to homogeneity, the N-terminal sequence of the first 14 amino acid residues of this new human casein subunit shows a high degree of homology with the alpha s1-casein sequences from other species.

Amino Acid Sequence↗
PubMed1980

Utilization of casein or isolated soybean protein supplemented with amino acids and glucose or lactose by neonatal piglets reared artificially.

Forty-five neonatal pigs were used to compare the utilization of casein plus L-tryptophan (Try) and L-arginine (Arg) and of isolated soybean protein (ISP) plus DL--methionine (Met), L-lysine (Lys) and Try, with either glucose or lactose used as the carbohydrate source, from 1 to 29 days of age. A reference diet containing dried skim milk and soybean meal proteins was utilized. No interaction (P greater than .05) occurred between protein and carbohydrate sources. The diets containing lactose or glucose produced similar pig perforamnce, nutrient digestibility and serum levels of glucose, protein and urea nitrogen from 1 to 29 days of age. However, pigs fed the diet containing casein had higher (P less than .05) average daily gain and higher gain to feed ratios from 1 to 15 days of age than did pigs fed the diet containing ISP, while both groups were similar in performance from 15 to 29 days of age. Ether extract, crude protein, energy, ash and dry matter digestibilities and serum levels of protein were greater (P less than .05) for pigs fed the diets containing casein than for those fed the diets containing ISP. Nitrogen free extract digestibility and serum glucose and urea nitrogen were similar for pigs fed the diets containing casein or ISP. The diets that the pigs received from 1 to 29 days of age did not influence their subsequent nursery performance from 29 to 64 days of age, when all groups were fed the same diet. These results indicate that casein plus Try and Arg was superior to isolated soybean protein plus Met, Lys and Try as a source of protein for the baby pig from 1 to 15 days of age, while both protein sources produced similar perforamnce from 15 to 29 days of age.

Animal Nutritional Physiological Phenomena↗
PubMed1996

Characterization and partial purification of microsomal casein kinase II from osteoblast-like cells: an enzyme that phosphorylates osteopontin and phosphophoryn.

Microsomal casein kinase II (mCKII) is a membrane-bound enzyme present in the microsomal fractions of ROS 17/2.8 osteoblast-like cells. It phosphorylates acidic matrix phosphoproteins such as phosphophoryn and osteopontin. Addition of 1.0% Nonidet P-40 facilitates extraction of the optimum amount of detergent-solubilized and -activated enzyme from microsomal fractions. mCKII was partially purified over 3000-fold by sequential chromatography over DEAE-cellulose and heparin-agarose. SDS-polyacrylamide gels, showed that mCKII contained 43 kDa and 31 kDa polypeptides, corresponding to the alpha- and beta-subunits of the enzyme, respectively. The alpha subunit was identified by anti-CKII antiserum and the beta subunit, by its ability to undergo autophosphorylation. The enzyme was inhibited by 50% with 0.4 micrograms/ml heparin and stimulated by 100% with 1.0 mM spermine when casein was used as a substrate. The phosphorylation of phosphophoryn was reduced to 50% by 0.8 micrograms/ml heparin, but was increased to 2-2.5 fold by 5 to 15 mM spermine, which may be due to substrate-directed effects. Kinetic analysis showed that the apparent Km values for phosphophoryn (0.39 microM) and for osteopontin (2.1 microM) were lower than that for casein (21.3 microM). Vmax values of phosphophoryn and osteopontin were 2.2-fold and 4.6-fold higher than that of casein. Using the ratio Vmax/Km as a measure of kinetic specificity, osteopontin and phosphophoryn appear to be the more specific substrates than casein for mCKII. Thus, both proteins can be considered as physiological substrates for mCKII.

Animals↗
PubMed2000

Autocrine insulin-like growth factor II inhibits beta-casein mRNA expression in a mammary cell line.

A hallmark of mammary cell differentiation is the induction of beta-casein mRNA expression. A mouse mammary epithelial cell line (COMMA-1D) was treated with insulin, hydrocortisone (HC), and prolactin (Prl) at concentrations (50, 500, and 20 ng/ml, respectively) that resulted in less than half-maximal beta-casein mRNA expression. The cells secreted insulin-like growth factor (IGF)-II (106 pg/ml per 24 h) in the condition media under these conditions. Replacement of insulin with rhIGF-II (150 ng/ml) resulted in significantly less beta-casein mRNA expression. Long-Arg IGF-I (50 ng/ml) was similar to insulin in terms of its ability to induce differentiation, but its activity differed from that of insulin in that it also induced cell proliferation. When the two receptor-specific IGF-II analogs, Arg54,55IGF-II and Leu27IGF-II, were used in studies, only at high concentrations (150 ng/ml) was either analog capable of stimulating any beta-casein mRNA expression. When autocrine IGF-II was immuno-neutralized or bound by the addition of rhIGF binding protein-3 (IGFBP-3)beta-casein mRNA expression was enhanced seven-fold and three-fold, respectively. Exogenous application of IGF-II to counteract the IGF-II mAb stimulation resulted in increased cellular growth and reduced differentiation. We conclude that autocrine IGF-II inhibits mammary cell differentiation and that the blockage of autocrine IGF-II benefits mammary cell differentiation.

Animals↗
PubMed2000

The two-stage coagulation of milk proteins in the minimum of the heat coagulation time-pH profile of milk: effect of casein micelle size.

Milks with casein micelles larger or smaller than control milk were prepared by differential centrifugation. The heat stability of these modified milks increased markedly throughout the pH range 6.4 to 7.1 with decreasing casein micelle size. Within the region of the minimum in the heat coagulation time-pH profile, the control milk coagulated by a two-stage process, but the modified milks, because of their narrower casein micelle size distribution, coagulated by a single-stage process at the pH of minimum stability. The content of kappa-CN and protein hydration increased as the size of the casein micelles decreased, and the level of glycosylation of kappa-CN and protein surface hydrophobicity increased as a function of micelle size. The effect of casein micelle size on the heat stability of milk is likely to be related to changes in the above physico-chemical properties.

Animals↗
PubMed2002

Micellar casein gelation at high sucrose content.

This article investigates the effect of sucrose addition on the formation of casein gels by acidification and/or renneting of pure micellar casein. Gelation kinetics and gel properties were followed by rheological methods, and microscopy and syneresis measurements were used to obtain a more complete characterization of the structures formed. Sucrose content has been identified as a key parameter for controlling the kinetics of aggregation and the strength of the final gels. Results have shown that the effect of sucrose on gelation can vary such that effects can be completely reversed depending on the gelation route used. During acid gelation, addition of up to 30% (wt/wt) sucrose causes gels to form more rapidly and at higher pH values, and to have higher viscoelastic moduli and a more homogeneous microstructure than those without sucrose. By contrast, gels formed by renneting in the presence of sucrose are weaker and have longer gelation times. It is proposed that sucrose reduces solvent quality and causes the collapse of the "hairy" kappa-casein brush on the surface of the casein micelles. This may explain why sucrose increases the possibility of gel formation during acidification and reduces the degree of kappa-casein hydrolysis during renneting.

Caseins↗
PubMed2006

Immunogenicity of kappa-casein and glycomacropeptide.

Glycomacropeptide (GMP), arising from the cleavage of kappa-casein by chymosin or pepsin, has been correlated with a wide variety of biological activities including immunosuppression capacity, inhibition of pathogen invasion, and induction of satiety. Due to the interest in exploiting such potential of GMP, we aimed at characterizing the immunogenic properties of GMP as an indication of its potential allergenicity. Immunogenicity of kappa-casein and GMP were investigated using 2 animal models based on different routes of immunization: 1) mice immunized intraperitoneally or subcutaneously with either kappa-casein, polymerized GMP, GMP coupled to the immunogenic carrier ovalbumin, or GMP alone; 2) mice coadministered kappa-casein or GMP and cholera toxin. The specific antibody response to GMP was evaluated as well as the antigen-specific T-cell response. The results demonstrated that immunization or feeding with kappa-casein induced GMP-specific antibodies, whereas GMP per se lacked immunogenicity independently of the mode of presentation. The size of the presented form of GMP did not influence its immunogenicity. Because the results showed that GMP did not induce a specific T-cell response, we postulate that GMP lacks the ability to stimulate antigen-specific T cells.

Animals↗