Expression of kappa-casein in normal and neoplastic rat mammary gland is under the control of prolactin

Investigating the genetic polymorphism of sheep milk proteins: a useful tool for dairy production

Sheep is the second most important dairy species after cow worldwide, and especially in the Mediterranean and Middle East regions. In some countries, the difficult environmental conditions require a peculiar adaptation and, in these contexts, sheep are able to provide higher quality protein than cattle. In the least-developed countries, the amount of dairy sheep and ovine milk production is progressively increasing. In order to improve dairy productions, in particular those with local connotations, it is necessary to obtain in-depth information regarding milk quality and rheological properties. The genetic polymorphisms of milk proteins are often associated with quantitative and qualitative parameters in milk and are potential candidate markers that should be included in breeding strategies similar to those already available for cattle. Due to the current and growing interest in this topic and considering the large amount of new information, the aim of this study was to review the literature on sheep milk protein polymorphisms with a particular emphasis on recent findings in order to give scientists useful support. Moreover, the effects of different protein variants on milk yield and composition are discussed.

An isolated tumor perfusion model in mice

The role of stromal cells in the tumor microenvironment has been extensively characterized. We and others have shown that stromal cells may participate in several steps of the metastatic cascade. This protocol describes an isolated tumor perfusion model that enables studies of cancer and stromal cell shedding. It could also be used to study the effects of therapies interfering with the shedding of tumor cells or fragments, circulating (stem) cells or biomarkers. Primary tumors are grown in a microenvironment in which stromal cells express GFP ubiquitously. Tumors are implanted orthotopically or can be implanted ectopically. As a result, all tumor-associated stromal cells express GFP. This technique can be used to detect and study the role of stromal cells in tumor fragments within the circulation in mice. Studying the role of stromal cells in circulating tumor fragments using this model may take 2-10 weeks, depending on the growth rate of the primary tumor.

Cloning and sequencing of the porcine kappa-casein cDNA

cDNA clones encoding porcine kappa-casein were isolated and sequenced. The porcine kappa-casein cDNA is 851 bp in length and encodes a preprotein of 188 amino acids.

Comparative aspects of milk caseins

The caseins comprise the major protein component of milk of most mammals and are secreted as micelles that also carry high concentrations of calcium. They are phosphoproteins that represent the products of four genes, equivalent to those that encode the bovine alpha s1, alpha s2, beta, and kappa-caseins. There is considerable variation in the relative proportions of the particular caseins across species. The primary sequences of the alpha s1, alpha s2, and beta-caseins also show considerable species variation consistent with rapidly evolving genes that are proposed to have a common precursor. In contrast, the kappa-caseins exhibit features that demonstrate a separate origin and function where they are proposed to stabilise the micelle structure. This review focuses on comparative aspects of the caseins across a number of species for which information is now available.

Structure of the human kappa-casein gene

The human kappa-casein-encoding gene, Kca, was cloned and sequenced. The structural gene consists of five exons ranging from 33 to 496 nucleotides (nt) separated by introns ranging from 1146 to 2942 nt, and extends over 8821 nt. All intron/exon splice junctions conform to the GT/AG rule. The gene organization is similar to that of the bovine gene. The 5'-flanking region contains an A + T-rich sequence; TTTAATT, close to where the TATA motif is found in most other genes, a CAAT box, and an AP-1 consensus sequence. In addition, one Alu repetitive element was found in the second intron.

A change in soybean agglutinin binding patterns of bovine milk fat globule membrane glycoproteins during early lactation

Milk fat globule membrane (MFGM) glycoproteins were prepared from bovine milk at different stages of early lactation. Western blot analyses using several lectins revealed that reactivity of MFGM glycoproteins, especially 47K and 80K bands, to soybean agglutinin (SBA) remarkably increased during the lactation, while no change was observed for Ricinus communis agglutinin-I (RCA-I) binding. Sialidase treatment of MFGM glycoproteins revealed that the number of SBA-positive bands and the amount of SBA-positive oligosaccharides in these bands are increased during the lactation. Since SBA binds N-acetylgalactosamine terminated oligosaccharides, the results indicated that N-acetylgalactosaminylation of bovine MFGM glycoproteins is stimulated during the lactation.

The multimeric structure and disulfide-bonding pattern of bovine kappa-casein

Bovine kappa-casein was analyzed by SDS/PAGE, MS and amino acid sequence analysis in order to determine its multimeric composition and disulfide-bonding pattern. SDS/PAGE revealed that kappa-casein in the native state can range in size from a monomer to a multimeric structure larger than a decamer. Three types of interchain disulfide linkage, Cys11-Cys11, Cys11-Cys88 and Cys88-Cys88, were all assigned in multimers purified from [14C]carboxymethylated and untreated bulk milk, as well as a milk sample from a kappa-casein-variant-B homozygote Co20. These results indicate that multimerization occurs in a random or at present unpredictable disulfide-bonding pattern regardless of the size of the multimer or the genotype.

Caseins of various origins and biologically active casein peptides and oligosaccharides: structural and physiological aspects

The first part of the present review is focused on structural aspects concerning the so far studied casein fractions of various origins: they are compared to the four classical major bovine caseins (alpha s1-, alpha s2-, beta- and kappa). The calcium-sensitive casein fractions are always phosphorylated whereas kappa-caseins are glycosylated. The study of the casein genes showed that the calcium-sensitive caseins diverged from a common ancestral gene and during the evolution, intergenic and intragenic duplications occurred. The considerable conservation of the phosphorylation sites emphasizes the importance of phosphorylated residues for the function of caseins, i.e. the formation of micelles and the binding of Ca2+. In kappa-caseins all the prosthetic sugar groups are linked by O-glycosidic linkages: their number varies from 0 to 5 in bovine kappa-casein and up to 10 in human kappa-casein. The structures of the known kappa-casein carbohydrate moieties are described. Finally the milk clotting process (interaction kappa-casein/chymosin) is compared to the blood clotting process (interaction fibrinogen/thrombin): a large number of similarities could be noted between both clotting phenomena. The second part of the review is devoted to the study of short casein peptides endowed with various biological activities. Some of them behaved as immunomodulators or casomorphins or angiotensin I converting enzyme inhibitors; others demonstrated an effect on platelet functions. A 'strategic zone' containing immunostimulating and opioid peptides could be located in cow and human beta-caseins. Furthermore bitter peptides, emulsifying peptides, calcium absorption enhancing peptides, chymosin-inhibiting peptides, have also been described and several further properties have been attributed to the kappa-caseinoglycopeptide; two tetrasaccharides isolated from the latter possess blood group activities. In conclusion caseins, the main milk proteins, should not only be considered as a nutriment but as a possible source of biologically active components. If, in the future, some of the discussed active peptides cannot be characterized in vivo, they can all, nevertheless, be synthesized and used either as food additives or in pharmacology.

Isolation and characterization of the bovine kappa-casein gene

1. The bovine kappa-casein gene has been isolated as a series of overlapping lambda clones and shown to consist of five exons distributed over a total length of approximately 13 kb. Most of the mature protein-coding sequence is contained in a single large exon. 2. Approximately 65% of the gene has been sequenced together with portions of the 5'- and 3'-flanking sequences. The immediate 5'-flanking sequence contains several motifs which are characteristic of upstream regions including a TATA box, a CAAT box, a sequence similar to that recognized by transcription factor AP-1 and a purine-rich sequence resembling that found upstream in all other lactoprotein genes. Other possible regulatory sequences are found upstream of exon 4. 3. The organization of the kappa-casein gene, together with its upstream sequence, confirms previous conclusions that it is unrelated to the calcium-sensitive-casein gene family to which it is linked. Evidence is presented which supports a previous suggestion that kappa-casein and the fibrinogens are evolutionarily related. 4. Intron sequences contain several examples of the A family of the artiodactyl Alu-like repeated sequences, together with a single example of a C-family sequence. The remainders of the introns of the kappa-casein gene, compared with the repeat elements and exons, are A + T-rich. 5. Among the lambda clones isolated, representatives were found of the A and B genetic variants which can be distinguished by restriction-enzyme analysis. Several other examples of polymorphisms in the non-coding region were found.

Rubella virus replication: effect of interferons and actinomycin D

The effect of alpha and gamma interferon (IFN alpha, IFN gamma) and actinomycin D on the expression of wild type rubella virus in African green monkey kidney cells (Vero 76) was studied. Viral protein synthesis in the infected cells was significantly reduced upon treatment of the cells with IFN alpha or IFN gamma, which is accompanied by the reduction in the level of both the (+) stranded and the (-) stranded viral RNAs. The residual rubella viral RNA from interferon-treated cells, however, was structurally intact as judged by Northern blot analysis and in vitro translation. These results suggest that the effect of IFN alpha and IFN gamma on rubella viral protein synthesis is both at the transcriptional and the translational level. The effect of actinomycin D on rubella virus replication was found to be time-dependent. It is much more pronounced during the eclipse phase of the viral growth (first 4 h) than after 8 h at which time actinomycin D had lesser effect. A similar effect on rubella virus replication was observed when alpha-amanitin was used instead of actinomycin D. These results were taken to indicate that during the viral infection, host cell DNA directs the synthesis of a cellular factor(s) which is essential for the viral replication. When the synthesis of this cellular factor(s) is terminated at an early stage of viral infection by actinomycin D or by alpha-amanitin, viral replication is impaired.

Construction and identification of recombinant plasmids carrying cDNAs coding for ovine alpha S1-, alpha S2-, beta-, kappa-casein and beta-lactoglobulin. Nucleotide sequence of alpha S1-casein cDNA

An ovine mammary cDNA library has been constructed from total poly(A)+ RNA isolated from the mammary gland of a lactating ewe, using a classical procedure. Blunt-ended double-stranded cDNAs prepared with reverse transcriptase and nuclease S1 were tailed with dCTP, inserted into the dGMP-tailed PstI site of plasmid pBR322 and cloned in E. coli. Five series of homologous clones representing abundant messenger RNAs (strong hybridization with a single-stranded cDNA probe generated from total poly(A)+ RNA) were selected using each time a different predominant cloned ds-cDNA as probe, then identified by positive hybridization-translation of the cognate mRNA and subsequent immunoprecipitation and electrophoresis of the protein. The lengths of alpha s1-, alpha s2-, beta-, kappa-casein and beta-lactoglobulin mRNAs are in the range of 1.2, 1.1, 1.25, 1.0 and 0.85 kb, respectively, as determined by Northern blotting analysis. Five homologous mRNAs of similar sizes were identified in the porcine species by dot blot hybridization and Northern analyses. The nucleotide sequence of alpha s1-casein mRNA was determined by sequencing, according to Maxam and Gilbert, both a 1080 bp long cloned ds-cDNA and a ss-cDNA (268 nucleotides) generated by 5' extension of a 5' terminal truncated radiolabeled fragment (83 bp) of the relevant ds-cDNA, used as primer for reverse transcription. The 3' non coding region (431 nucleotides, excluding the poly(A) tail) represents 70% of the length of the coding region (618 nucleotides) flanked by a 61 nucleotide 5' region. Comparison of sequences of ovine and bovine, rat and guinea-pig alpha s1-casein mRNAs has revealed a greater homology in the 3' and especially 5' non coding regions. In the reading frame, the conserved regions are essentially those corresponding to the signal peptide and phosphopeptide domains. The derived 206 amino acid sequence of ovine pre-alpha s1-casein differs from that of its bovine counterpart (genetic variant B) by 24 amino acid substitutions and a deletion of 8 amino acid residues occurring in the polypeptide chain of the mature protein. Such a variation (84% homology only) in two phylogenetically closely related species indicates a high rate of evolution of alpha s1-casein.

Molecular cloning of mouse mammary gland kappa-casein: comparison with rat kappa-casein and rat and human gamma-fibrinogen

A cDNA clone for kappa-casein mRNA from the lactating mouse mammary gland was isolated and its nucleotide sequence determined. Analysis of the deduced amino acid sequence revealed a precursor protein with a 21-amino-acid signal sequence and a mature protein of 160 amino acids, the mature mouse protein being 3 amino acids longer than the rat kappa-casein. Northern blot analysis of the lactating rat and mouse mammary gland showed a specific mRNA for rat kappa-casein and two distinct mRNAs for mouse kappa-casein. This result is explained by the presence of two putative polyadenylation sites in mouse kappa-casein cDNA, whereas rat kappa-casein cDNA has only one polyadenylation site. Comparison of the nucleotide sequence and of the deduced amino acid sequence of kappa-casein from mouse with that of the rat showed 85% homology between the two sequences. However, when amino acid sequences of kappa-casein from rat and mouse were compared with ovine kappa-casein, only a 45% homology was observed. Amino acid sequences of kappa-casein from rat, mouse, and sheep were 36.53% homologous with rat and human gamma-fibrinogen. The extent of homology was similar (32%) when nucleotide sequences of corresponding cDNAs were compared. The stretches of homology existing at different regions between the two proteins were more confined toward the amino-terminal half of gamma-fibrinogen. However, when nucleotide sequences were compared, mouse kappa-casein cDNA showed homology only with the second half of the rat gamma-fibrinogen cDNA, i.e., between nucleotides 661-1135. The homology with the human gamma-fibrinogen cDNA spanned over two regions, one between nucleotides 1-328 and the second between nucleotides 591-726.(ABSTRACT TRUNCATED AT 250 WORDS)