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PubMed1986

A complex noncoordinate regulation of alpha-lactalbumin and 25 K beta-casein by corticosterone, prolactin, and insulin in long term cultures of normal rat mammary cells.

The concentrations of PRL, corticosterone, and insulin required by long term cultures of normal rat mammary cells to produce alpha-lactalbumin (alpha LA) and the 25,000 mol wt beta-casein were evaluated with a variety of hormone ratios and concentrations. For these studies a double antibody RIA for beta-casein capable of measuring 0.5 ng beta-casein/100 microliter growth media was developed and used along with our previously reported RIA for alpha LA. PRL was active at physiological levels (0.05-0.15 micrograms/ml) and quantitatively stimulated beta-casein more than alpha LA, whereas physiological levels of corticosterone (0.05-0.15 micrograms/ml) quantitatively stimulated alpha LA more than beta-casein. The concentration of corticosterone greatly altered the magnitude of the cells' response to insulin and PRL for alpha LA output by cells from either virginal or midpregnant rats. Insulin also enhanced production of these milk proteins, but very little effect was measured in the physiological range. alpha LA was increased more by insulin than by PRL, and beta-casein was enhanced more by insulin than by corticosterone. Cells from midpregnant rats required less insulin to stimulate beta-casein production than to stimulate alpha LA. Cells from virginal rats required a supraphysiological insulin level to stimulate both beta-casein and alpha LA under these conditions. These cells generally require 5-6 weeks to achieve a steady-state rate of milk protein output. The complexities of our observations help explain some of the conflicting reports in the literature concerning which hormone is of prime importance for quantitatively increasing the synthesis of a particular milk protein, particularly since high hormone levels are often employed and time in culture varies considerably among reports. We conclude that lower levels of all these hormones can and should be used in vitro. Our messenger RNA (mRNA) studies using cloned complementary DNA probes for two rat casein mRNAs show that cells grown for 2 months with hormones contain significant amounts of both alpha- and beta-casein mRNAs. Simultaneous quantification of beta-casein mRNA levels and rates of beta-casein protein production in these long term cell cultures indicated that a substantial portion of their beta-casein protein production is regulated by the amount of its mRNA. This could be controlled by mRNA synthesis and/or mRNA degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Transcriptional regulation of the beta-casein gene by cytokines: cross-talk between STAT5 and other signaling molecules.

The beta-casein promoter has been widely used to monitor the activation of STAT (signal transducer and activator of transcription)5 since STAT5 was originally found as a mediator of PRL-inducible beta-casein expression. However, not only is expression of the beta-casein gene regulated by STAT5 but it is also affected by other molecules such as glucocorticoid and Ras. In this report, we describe the transcriptional regulation of the beta-casein gene by cytokines in T cells. We have found that the beta-casein gene is expressed in a cytotoxic T cell line, CTLL-2, in response to interleukin-2 (IL-2), which activates STAT5. While IL-4 does not activate STAT5, it induces expression of STAT5-regulated genes in CTLL-2, i.e. beta-casein, a cytokine-inducible SH2-containing protein (CIS), and oncostatin M (OSM), suggesting that STAT6 activated by IL-4 substitutes for the function of STAT5 in T cells. IL-2-induced beta-casein expression was enhanced by dexamethasone, and this synergistic effect of Dexamethasone requires the sequence between -155 and -193 in the beta-casein promoter. Coincidentally, a deletion of this region enhanced the IL-2-induced expression of beta-casein. Expression of an active form of Ras, Ras(G12V), suppressed the IL-2-induced beta-casein and OSM gene expression, and the negative effect of Ras is mediated by the region between -105 and -193 in the beta-casein promoter. In apparent contradiction, expression of a dominant negative form of Ras, RasN17, also inhibited IL-2-induced activation of the promoter containing the minimal beta-casein STAT5 element as well as the promoters of CIS and OSM. In addition, Ras(G12V) complemented signaling by an erythropoietin receptor mutant defective in Ras activation and augmented the activation of the beta-casein promoter by the mutant erythropoietin receptor signaling, suggesting a possible role of Ras in Stat5-mediated gene expression. These results collectively reveal a complex interaction of STAT5 with other signaling pathways and illustrate that regulation of gene expression requires integration of opposing signals.

Animals↗
PubMed1995

A protein less sensitive to trypsin, guanidinated casein, is a potent stimulator of exocrine pancreas in rats.

Previously, we have shown that, in rats that have had bile-pancreatic juice (BPJ) diverted from the proximal small intestine for 7 days, the exocrine pancreatic secretion was enhanced after they were fed a casein, fat-free diet. This demonstrates that the pancreatic secretion is stimulated by dietary protein with a pancreatic protease-independent pathway. To examine the chemical structure of casein responsible for the enhancement of pancreatic secretion, we prepared chemically modified casein in which lysine residues were guanidinated. Secretion of protein, amylase, and chymotrypsin in the chronic BPJ-diverted rat was increased much more after the rats were fed a diet containing guanidinated casein (250 g/kg diet) than after they were fed a diet containing intact casein (250 g/kg diet). In normal rats whose diverted BPJ was returned to the duodenum, the increases in the pancreatic secretion after consuming the guanidinated casein diet were comparable to those after consuming the intact casein diet. In vitro digestibility of guanidinated casein by trypsin and chymotrypsin was much lower than that of intact casein. Also, guanidinated casein inhibited tryptic hydrolysis of benzoyl-L-arginine p-nitroanilide to a lesser extent than did intact casein as determined by an in vitro assay. These results demonstrate that guanidinated casein is less sensitive to trypsin than is intact casein and that the structure that is sensitive to trypsin is not involved in the stimulation of pancreatic secretion in diverted rats. The results evidence that masking luminal trypsin activity does not predominantly contribute to the enhancement of pancreatic secretion in 7-day BPJ-diverted rats. Also, in normal rats, the luminal protease-independent mechanism may play a role partly in increasing the pancreatic secretion by dietary protein.

Amylases↗
PubMed1981

Further purification and characterization of casein kinases from human erythrocyte hemolysate. Effect of Triton X-100.

Two cyclic AMP-independent casein kinases can be isolated from human erythrocyte hemolysate, one of which (referred to as 'casein kinase S') phosphorylates only serine residues of whole commercial casein, while the other (referred to as 'casein kinase TS') phosphorylates both serine and threonine residues of the same substrate. Moreover, the casein kinase S, unlike casein kinase TS, is able to phosphorylate the erythrocyte membrane proteins. The present paper deals with the further characterization of casein kinase S, freed from histone kinase activity by DEAE and subsequent phosphocellulose chromatography of the crude hemolysate in the presence of 0.2% Triton X-100. In particular, cytosol casein kinase S exhibits some physico-chemical and catalytic properties identical to those of the membrane-bound casein kinase, solubilised and purified as previously described. Both casein kinases display the same chromatographic behaviour, the same Sepharose elution volume, the same optimal pH range, the same Km for casein and ATP, the same response to NaCl, MgCl2 and CaCl2, and the same ability to phosphorylate serine but not threonine residues of beta-casein.

Calcium Chloride↗
PubMed2002

A multi-centre, blinded international trial of the effect of A(1) and A(2) beta-casein variants on diabetes incidence in two rodent models of spontaneous Type I diabetes.

AIMS/HYPOTHESIS: The diabetes-inducing potential of cows' milk is still debated and there is no consensus on the diabetogenicity of individual milk proteins. A(1)-beta-casein has been associated with increased diabetes frequency in ecological studies and in NOD mice. Our aim was to ascertain whether A(1)-beta-casein was more diabetogenic than A(2) and to test the diabetogenicity of a milk-free diet in animals representing different forms of spontaneous Type I (insulin-dependent) diabetes mellitus. METHODS: Defined diets were coded and shipped to laboratories in New Zealand (NOD/NZ), Canada (BB) and the UK (NOD/Ba). Base diets were Pregestimil (PG) and ProSobee (PS). Purified fractions of whole casein (WC), A(1)or A(2)-beta-casein were added at 10%. A milk-free, wheat-predominant, NTP-2000 diet was the control. Animals were fed from weaning up to 150 or 250 days, and insulitis, diabetes frequency and expression of pancreatic cytokines were assessed. RESULTS: Diabetes incidence was highest in three locations in animals fed NTP-2000. PG and PS diets were protective except for NOD/Ba mice fed PG+WC where incidence was similar to NTP-2000. A(1) and A(2) diets were protective in both models, but A(1) beta-casein was slightly more diabetogenic in PS-fed BB rats. The New Zealand study was confounded by an infection. CONCLUSION/INTERPRETATION: A milk-free, wheat-predominant diet was highly diabetogenic in three widely separate locations in both animal models. A previous result that A(1) beta-casein was more diabetogenic than A(2) beta-casein in NOD mice was not confirmed; both beta-casein variants were protective in BB rats and NOD mice. Whole Casein promoted diabetes in NOD/Ba but protected BB showing that unique diabetes haplotypes react differently to dietary proteins. A(1)- was more diabetogenic than A(2)-beta-casein only in PS-fed BB rats. Neither the analysis of insulitis nor of pancreatic cytokine gene expression showed a difference between A(1) or A(2) beta-casein fed animals. Milk caseins are unlikely to be exclusive promoters of Type I diabetes, but could enhance the outcome of diabetes in some cases. Other diet components such as wheat could be more important promoters of Type I diabetes.

Animals↗
PubMed1981

Purification and characterization of four components of rat caseins.

Rat casein components (C1-, C3A-, C3B- and C4-casein) were extensively purified from rat milk, and the properties of these proteins were compared with those of other caseins including rat C2-casein. C1-casein was precipitated by a low concentration of CaCl2 (1.5 mM). Both C3A- and C3B-casein were less sensitive to Ca2+ than were C1- and C2-casein, and the presence of 20 mM CaCl2 was required at 37 degrees C for their precipitation. C4-casein was absolutely insensitive to Ca2+. This protein exhibited the ability to stabilize all of the other rat casein components against Ca2+-dependent precipitation. In addition, C4-casein contained sialic acid, galactose and N-acetylgalactosamine. Therefore, C4-casein appears to be a bovine kappa-casein-like protein.

Amino Acids↗
PubMed1985

Comparative analysis of casein synthesis during mammary cell differentiation in collagen and mammary gland development in vivo.

Substrata upon which epithelial cells are cultured modulate their morphology,growth, and ability to differentiate. Mouse mammary epithelial cells cannot be induced to synthesize caseins, a marker of cell differentiation, when grown on a plastic surface. An analysis was made of the effect of time within a collagen matrix on the ability of normal mammary epithelial cells to be induced to synthesize caseins and that response was compared to mammary gland development in vivo. Primary cultures of mammary cells from unprimed virgin BALB/c mice were embedded in rat-tail collagen gel mixtures and maintained in growth medium. Induction medium containing lactogenic hormones was added at various times. The cells were monitored every 3-7 days over a period of 8 weeks for cell growth, casein synthesis, and ability to grow in vivo in cleared mammary fat pads. Casein accumulation was assayed quantitatively by an ELISA competition assay and qualitatively by the immunoblot procedure using specific antisera prepared against purified mouse caseins. No marked differences in cell numbers and transplantability potential were observed among cells cultured for various times in collagen. Mammary cells grown in collagen for up to 8 weeks retained the capacity to grow in vivo as normal ductal outgrowths. The duration of culture within collagen prior to hormonal stimulation did influence the kinetics of casein synthesis. Cells cultured for 1 week in growth medium did not accumulate detectable levels of casein until after 3 weeks of induction, whereas cells cultured for 2 or 4 weeks responded by accumulating caseins after 2 weeks and 3 days of induction, respectively. While the levels of total caseins that accumulated under optimal conditions of induction in culture approached levels found during lactation in vivo, the relative proportion of specific casein polypeptides synthesized in culture was altered from alpha casein (43K) in favor of the beta casein (30K) species. These results suggest that a period of culture within collagen is required to permit mammary epithelial cells to become responsive for hormone-induced differentiation. It is possible that during growth within the collagen the cells synthesize and deposit extracellular matrix components important in modulating gene expression.

Animals↗
PubMed1984

A comprehensive study of the relationship between size and protein composition in natural bovine casein micelles.

Casein micelles of bovine skimmed milk were fractionated by permeation chromatography on porous glass (CPG-10, 50 nm followed by CPG-10, 300 nm) at 30 degrees C. Micelles were pooled in eight eluant fractions and their size distribution was determined by electron microscopy. The composition of casein in the eight fractions was determined by quantitative hydroxyapatite chromatography. Micelle size decreased progressively with increasing elution volume, and volume-to-surface average diameter ranged from 154 nm in fraction 1 to 62 nm in fraction 8. Concurrently there was a decrease in relative proportions of alpha s- and beta-caseins and a large enrichment of kappa-casein, which changed from 4.1% total casein in fraction 1 to 12.1% total casein in fraction 8. At least half the decrease in alpha s-casein proportions was attributed to the alpha s1-casein component, but the data also suggested a decline in proportions of alpha s2-casein in the smallest micelle fractions. A plot of kappa-casein fractional content versus micelle surface-to-volume ratio gave a straight line (correlation coefficient from linear regression 0.98) from which an average kappa-casein surface coverage of 1.5 m2/mg or 47.3 nm2/molecule was obtained. If a constant surface coverage for kappa-casein is assumed, the parameters of the linear equation predict that micelle voluminosity is inversely related to micelle diameter, being approximately 30% larger in fraction 8 compared to fraction 1.

Animals↗
PubMed1980

Casein micelle size and composition related to the enzymatic coagulation process.

Chymosin (EC 3.4.23.4) and rennet, the latter containing about 85% chymosin and 15% pepsin, have been compared according to their coagulation properties with native micelles of different sizes or monomeric caseins as substrate. The casein micelles were separated on columns of controlled-pore glass (CPG-10/3000), which fractionates particles of up to 300 nm diameter. The results show that the coagulation time varies with the micelle size. The effect, which is more pronounced with chymosin than with rennet, appears to be related to the availability of kappa-casein. Therefore the largest micelles, with a lower kappa-casein content, showed longer coagulation times than medium size micelles. In the region of the smallest micelles this time increases again, probably due to an increased beta-casein content. Addition of monomeric kappa-casein decreased the coagulation time with both rennet and chymosin, but alpha s1-and beta-casein had the opposite effect. When isolated monomeric caseins were treated alone with rennet or chymosin, kappa-casein caused turbidity, but alpha s1-and beta-casein did not. Centrifugation experiments with micelles after monomeric casein addition showed that a limited amount of the added casein was able to join the micelle. This was confirmed by chromatographic studies.

Animals↗
PubMed2002

New chromatographic method for separation and determination of denatured alphaS1-, alphaS2-, beta- and kappa-caseins by hydrophobic interaction chromatography.

Separation and determination of denatured alpha-, beta- and kappa-caseins by hydrophobic interaction chromatography (HIC) was improved by using a TSK-Gel Ether-5PW column (Tosoh Biosep). The method, already proposed and performed by a TSK-Gel Phenyl-5PW column (Tosoh Biosep), is based on fast and easy solubilization of commercial and real samples by 4.0 M guanidine thiocyanate and HIC analysis in the presence of 8.0 M urea in the mobile phase. Employment of the less hydrophobic ether phase had the main advantage of separating casein fractions in less than 22 min and, additionally, of separating a-casein in kappaS1- and alphaS2 -casein fractions. The method has been validated by the analysis of reference skim milk powder (BCR-063R) certified for total nitrogen content. A linear relationship between the concentration of casein and peak area (UV absorbance detector at 280 nm) has been obtained over the concentration range of 0.5-40 microM. The detection limit for alpha-, beta- and kappa-caseins ranged between 0.33 and 0.65 microM. The precision of the method was evaluated, the RSDs for alphaS1-, alphaS2-, beta- and kappa-casein determination ranging between 2.3 and 5.5% for standard solutions and between 4.4 and 6.2% for real sample solutions. The mean value of casein content found in eight aliquots of BCR-063R calculated with respect to the total protein content (estimated on the basis of certified total nitrogen content) was 78.3 +/- 6.1%. Results of linear fitting of standard additions data of alphaS1-, alphaS2-, beta- and kappa-caseins to BCR-063R were compared with linear fitting of alphaS1-, alphaS2-, beta- and kappa-casein calibration data. The method was applied to commercial caseins and to 30 real, raw samples. A statistical comparison was performed between results on quantitation of alpha-, beta- and kappa-caseins obtained by TSK-Gel Ether-5PW and TSK-Gel Phenyl-5PW HIC columns, showing more accurate results for chromatographic analysis performed by the ether column.

Caseins↗
PubMed2002

Structure and regulation of the murine gamma-casein gene.

The murine casein locus consists of five genes, which are coordinately regulated during mammary development. The levels of casein-specific mRNAs in mammary epithelial cells increase during the second half of pregnancy and remain high during lactation. The murine gamma-casein gene, which corresponds to the alphaS2-casein gene in ruminants, was isolated from a mouse bacterial artificial chromosome (BAC) library (strain 129SV). The gene contains 14 exons, which are distributed over 14 kb of DNA sequence. The expression pattern of the murine gamma-casein gene mimics that of the neighbouring beta-casein gene in terms of developmental induction in vivo. In cell culture, both the beta- and gamma-casein promoter are synergistically induced by prolactin and glucocorticoids. Glucocorticoid induction is critically dependent on prolactin-mediated activation of STAT5 in both promoters. Several consensus STAT5 binding sites were identified in the gamma-casein promoter, some of which may have an additive effect on prolactin induction. mRNA levels of gamma- and beta-casein are similar in lactating mammary tissue. However, promoter segments derived from the gamma-casein gene are significantly less active in cell culture than comparable fragments of the beta-casein promoter. Promoter hybrids between the gamma- and beta-casein promoters revealed that the critical sequences which are responsible for the different in vitro activity are located in a short promoter proximal region.

Animals↗
PubMed1975

The participation of methionine and cysteine in the formation of bonds resistant to the action of proteolytic enzymes in heated casein.

1. The influence of temperature, moisture content and the presence of glucose on the level of available methionine and cysteine in casein was studied. 2. Differences between total and available methionine and cysteine contents of heated casein (90 degrees for 24 h) were determined by an in vitro method. The maximum losses in total and available methionine content were 22 and 51% respectively. The losses in total and available cysteine content were 24 and 100% respectively. 3. The results indicated that for heated casein the release of amino acids by proteolytic enzymes was less complete than for native casein. 4. The results of rat growth assays suggested that diets containing oxidized casein are less well utilized by rats than those containing native casein. The decrease in body-weight of rats receiving the diets containing oxidized casein could be counteracted by the addition of methionine and 20 g unoxidized casein/kg diet. 5. There was a lower level of some available amino acids (determined after enzymic hydrolysis using pancreatopeptidase E (EC 3-4-4-7), leucine aminopeptidase (EC 3-4-I-I) and prolidase (EC 3-4-3-7)), including those essential for the rat, in oxidized casein as compared with native casein. 6. Cysteic acid, in oxidized casein, probably makes impossible the utilization of the amino acids in its neighbourhood. 7. From the differences in the available amino acid contents of the native, oxidized and heated casein it was concluded that the oxidation of casein causes the formation of complexes in the polypeptide chain, resistant to enzymic hydrolysis, but to a much lesser extent than does heating.

Amino Acids↗
PubMed1979

Role of mammary casein kinase in the phosphorylation of milk proteins.

Casein kinase from lactating bovine mammary gland catalyses the transfer of the terminal phosphoryl group of ATP to specific serine residues in dephosphorylated caseins. Best substrates for casein kinase are the dephosphorylated proteins (bovine alpha S1- and beta-caseins and pepsin), unphosphorylated human beta-casein and the dephosphorylated peptide (residues 1-25) from bovine beta-casein. Results obtained with bovine and human beta-caseins indicate that the two serines underlined in the cluster Ser-Leu-Ser-Ser-Ser are particularly susceptible to the action of casein kinase. Since a similar sequence is found in dephosphorylated alpha S1-casein, it is probable that serines in this region of alpha S1-casein are also phosphorylated. The results support the concept that certain serines in casein are particularly susceptible to phosphorylation by casein kinase.

Amino Acid Sequence↗
PubMed1979

Stability of buffalo casein micelles.

Buffalo skim-milk is less heat stable than cow skim-milk. Interchanging ultracentrifugal whey (UCW) and milk diffusate with micellar casein caused significant changes in the heat stability of buffalo casein micelles (BCM) and cow casein micelles (CCM). Buffalo UCW dramatically destabilized CCM, whereas buffalo diffusate with CCM exhibited the highest heat stability. Cow kappa-casein stabilizes alphas-casein against precipitation by Ca better than buffalo kappa-casein. About 90% of alphas-casein could be stabilized by kappa:alphas ratios of 0.20 and 0.231 for cow and buffalo, respectively. Sialic acid release from micellar kappa-casein by rennet was higher than from acid kappa-casein in both buffalo and cow caseins, the release being slower in buffalo. The released macropeptide from buffalo kappa-casein was smaller than that from cow kappa-casein as revealed by Sephadex gel filtration. Sub-units of BCM have less sialic acid (1.57 mg/g) than whole micelles (2.70 mg/g). On rennet action, 47% of bound sialic acid was released from sub-units as against 85% from whole micelles. The sub-micelles are less heat stable than whole micelles. Among ions tested, added Ca reduced heat stability more dramatically in whole micelles, whereas added phosphate improved the stability of micelles and, more strikingly, of sub-micelles. Citrate also improved the heat stability of sub-micelles but not of whole micelles.

Animals↗
PubMed2004

Differential allele-specific accumulation of bovine kappa-casein mRNA throughout lactation.

A differential allele-specific accumulation of kappa-casein mRNA that is not linked to the kappa-casein protein variants is described in Holstein cows. Actually, cows genotyped kappa-casein AB were a mixed population. For the first group of kappa-casein AB cows, allele A-specific kappa-casein mRNA contents within mammary epithelial cells were lower than the allele B-specific ones (cows LH), suggesting that the allele A-specific kappa-casein gene was expressed with lower efficiency in mRNA. For the other group of kappa-casein AB cows, allele A- and B-specific kappa-casein mRNA accumulated to a similar level within mammary epithelial cells (cows HH). The objective of this study was to determine whether the accumulation of allele-specific kappa-casein mRNA remained constant throughout lactation for the two groups of cows. Quantitative RT-PCR was used to monitor Holstein cows kappa-casein AB genotyped HH and LH throughout lactation for the proportion of allele B-specific mRNA accumulation relative to the total kappa-casein encoded mRNA within mammary epithelial cells: RNA was extracted from milk somatic cells known to contain a small proportion of mammary epithelial cells. Mean values of allele B-specific mRNA content were 50.6+/-0.5 and 54.0+/-0.9%, for cows HH and cows LH, respectively, and did not vary during lactation (P> 0.10). This suggests that the phenotypic expression of the genetic mutation that causes the differential allele-specific accumulation of kappa-casein mRNA was not affected by physiological and environmental factors, which tend to vary considerably throughout lactation.

Alleles↗
PubMed1976

Isolation and characterization of purified rat casein messenger ribonucleic acids.

Purification of casein messenger ribonucleic acids (mRNAs) from lactating rat mammary gland RNA has been accomplished by a combination of sizing techniques, including Sepharose 4B chromatography and preparative agarose-urea gel electrophoresis, and affinity chromatography of poly(adenylic acid)-containing mRNA on oligo(dT)-cellulose. The separation of the individual casein mRNAs into discrete molecular species free of apparent ribosomal RNA contaminants was facilitated by the use of denaturing conditions either prior to or during each of the fractionation procedures. Two casein mRNA fractions were isolated: (1) a 15S mRNA doublet which directed the synthesis of the two largest rat caseins in the wheat-germ, cell-free, translation assay, and (2) a 12S mRNA which migrated as a single species during agarose-urea gel electrophoresis and directed the in vitro synthesis of the smallest of three rat caseins. These mRNAs had apparent molecular weights of 450 000 +/- 30 000 and 320 000 +/- 25 000 and contained poly(adenylic acid) sequences at their 3' termini ranging from 15 to 150 residues with number average lengths of 42 and 38 adenosines, respectively. The purity of the isolated casein mRNA'S was determined both by agarose-urea gel electrophoresis and by a careful comparison of the total products synthesized in the wheat-germ translation assay with those recognized by a specific casein antibody using an indirect immunoprecipitation technique. The specificity of the indirect immunoassay procedure was demonstrated by the selective displacement by purified rat casein of greater than 95% of the radioactive product synthesized in the cell-free system. Under optimal translation conditions for casein mRNA, at least 90% of the released protein synthesized in response to the 15S casein mRNA was specifically immunoprecipitable, representing a 178-fold purification compared with the initial RNA extract. Using these techniques a comparable purification was also obtained for a 15S mouse casein mRNA fraction. Finally, an analysis by fluorography on 5-20% (w/v) polyacrylamide gradient slab gels of the total proteins synthesized in response to both the 15S and 12S casein mRNAs revealed a close correspondence with those proteins which were specifically immunoprecipitated.

Animals↗
PubMed1976

Studies on the synthesis of casein messenger RNA during pregnancy in the rabbit.

The quantity of casein mRNA in the rabbit mammary gland was assayed during the course of pregnancy, by translation of casein mRNA in a reticulocyte lysate and by hybridization to DNA complementary to purified casein mRNA. Both methods indicated that the major increases in the concentration of casein mRNA in both polysomal and total cellular RNA occurred between the 18th and 25th day of pregnancy. The change in casein mRNA concentration during this period coincided with a sharp rise in casein synthesis in mammary gland explants suggesting that the levels of casein mRNA determine the rate of casein synthesis in the mammary gland. The sensitivity of the hybridization assay made it possible to detect the presence of casein mRNA in virgin animals and during the very early stages of pregnancy. At day 5, casein mRNA was found associated with polysomes indication that there was probably some casein synthesis at this early stage of gestation. These results suggest that the hormones controlling lactogenesis in the rabbit may function by augmenting the rate of casein mRNA synthesis rather that initiating transcription of previously inactive genes.

Animals↗
PubMedDate not supplied

Effect of soy protein added to casein diet on the development of glomerular injury in spontaneous hypercholesterolemic male Imai rats.

BACKGROUND: We have already reported an attenuating effect of a semipurified alcohol extract of soy protein (mainly consisting of isoflavones) on glomerular injury. Therefore, in the present study, we investigated whether soy protein itself has an ability to attenuate glomerular injury when added to casein diet in male Imai rats of a spontaneous focal segmental glomerulosclerosis model. METHOD: Male Imai rats were used and allocated into five groups. Group A of control casein diet (Ca) was fed standard diets containing 24.5% casein as a protein source. Group B of control soy protein diet (SP) was fed soy protein diet containing 24.5% protein that substituted a soy protein isolate for casein. Groups C (Ca-SP10) and D (Ca-SP20) were fed a mixture diet of casein (24.5%) and SP (10%) or SP (20%). Group E (Ca-Ca) was fed high casein diet containing the same quantity in protein content (44.5% casein) as the Ca-SP20 diet. Body weight, urinary protein, serum constituents and systolic blood pressure were investigated every 4 weeks from 12 weeks through 24 weeks of age. At 24 weeks of age, rats were studied morphologically. RESULTS: Animals fed control SP diet showed a significantly greater body growth than animals fed the other 4 test diets. No significant differences were found in body growth among the other 4 groups except for group E, which showed a stunt at the end of the experiment. Control SP diet significantly decreased proteinuria and serum cholesterol and attenuated glomerular injury and glomerular hypertrophy as compared with control casein diet. Added SP failed to attenuate glomerular injury, but when compared with high casein diet (group E), added SP resulted in less proteinuria, less hyperlipidemia, less hypoalbuminemia, less glomerular hypertrophy and less renal histological damage despite the quantity being the same in protein content. CONCLUSION: The present study indicates that soy protein added to conventional casein diet did not have the ability to attenuate glomerular injury, but soy protein is not as harmful as casein as a protein source when added to casein diet in the development of glomerular injury in the rat model of spontaneous focal glomerular sclerosis.

Animals↗