Difference between mammary epithelial cells from mature virgin and primiparous mice.
Mammary epithelial cells from mature virgin mice are similar to those from primiparous mice in several respects. However, there is one known difference. The cells from the mature virgin must traverse the cell cycle in order to become competent to make casein and enzymatically active alpha-lactalbumin in vitro; those from the primiparous animal can make these proteins without first traversing the cycle. In this regard, cells from human placental lactogen- and prolactin-treated mature virgins are, after involution, similar to those from primiparous mice. The developemental block in the cells from the mature virgin, imposed by preventing cell cycle traversal, has been partially delineated. It does not appear to reside at the levels of ultrastructural maturation or the formation of casein messenger RNA. Rather, the lesion is postranscriptional and may be at the level of translation, or posttranslational modification, or both. (+info)
Receptor clearance obscures the magnitude of granulocyte-macrophage colony-stimulating factor responses in mice to endotoxin or local infections.
Marrow cells from mice lacking high-affinity receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF; betac-/- mice) were shown to bind and internalize much less GM-CSF than cells from normal (betac+/+) mice. betac-/- mice were used to determine the effect of negligible receptor-mediated clearance on detectible GM-CSF responses to the intravenous injection of endotoxin or the intraperitoneal injection of casein plus microorganisms. Unlike the minor serum GM-CSF responses to endotoxin seen in betac+/+ mice, serum GM-CSF levels rose 30-fold to 9 ng/mL in betac-/- mice even though loss of GM-CSF in the urine was greater than in betac+/+ mice. Organs from betac-/- and betac+/+ mice had a similar capacity to produce GM-CSF in vitro, as did peritoneal cells from both types of mice when challenged in vitro by casein. However, when casein was injected intraperitoneally, betac-/- mice developed higher and more sustained levels of GM-CSF than did betac+/+ mice. The data indicated that receptor-dependent removal of GM-CSF masks the magnitude of GM-CSF responses to endotoxin and local infections. Because of this phenomenon, serum GM-CSF concentrations can be a misleading index of the occurrence or nonoccurrence of GM-CSF responses to infections. (+info)
Enhanced mitochondrial biogenesis is associated with increased expression of the mitochondrial ATP-dependent Lon protease.
Rats bearing the Zajdela hepatoma tumor and T3-treated hypothyroid rats were used to study the role of protein degradation in the process of mitochondrial biogenesis. It was shown that the activity, protein and mRNA levels of the ATP-dependent Lon protease increased in rapidly growing Zajdela hepatoma cells. The increase in the rate of mitochondrial biogenesis by thyroid hormone was similarly accompanied by enhanced expression of the Lon protease. The results imply that mitochondrial biogenesis in mammalian cells is, at least partially, regulated by the matrix Lon protease. (+info)
Met-HGF/SF mediates growth arrest and differentiation in T47D breast cancer cells.
Hepatocyte growth factor/scatter factor (HGF/SF) is a pluripotent growth factor that exerts mitogenic, motogenic, and morphogenic effects. To elucidate the cellular mechanisms underlying the pluripotent function of this growth factor, T47D human breast cancer cells were transfected with human hgf/sf. The hgf/sf-positive clones exhibited different levels of biologically functional HGF/SF expression and up-regulation of endogenous Met (HGF/SF receptor) expression. In addition, a constitutive phosphorylation of the receptor on tyrosine residues was detected, establishing a Met-HGF/SF autocrine loop. The autocrine activation of Met caused marked inhibition in cell growth accompanied by cell accumulation at G0/G1. These cells underwent terminal cell differentiation as determined by morphological changes, synthesis of milk proteins such as beta-casein and alpha-lactalbumin, and production of lipid vesicles. Our results demonstrate that Met-HGF/SF, an oncogenic signal transduction pathway, is capable of inducing growth arrest and differentiation in certain breast cancer cells and, thus, may have potential as therapeutic and/or prognostic tools in breast cancer treatment. (+info)
Lipoprotein(a) and dietary proteins: casein lowers lipoprotein(a) concentrations as compared with soy protein.
BACKGROUND: Substitution of soy protein for casein in the diet decreases LDL cholesterol and increases HDL cholesterol. How the 2 proteins affect lipoprotein(a) [Lp(a)], an independent risk factor for coronary artery disease, is unknown. OBJECTIVE: We compared the effects of dietary soy protein and casein on plasma Lp(a) concentrations. DESIGN: Nine normolipidemic men were studied initially while consuming their habitual, self-selected diets, and then, in a crossover design, while consuming 2 liquid-formula diets containing either casein or soy protein. The dietary periods lasted 45 d (n = 7) or 33 d (n = 2). Fasting total cholesterol, LDL-cholesterol, HDL-cholesterol, triacylglycerol, and Lp(a) concentrations were measured throughout. RESULTS: After 30 d of each diet, the mean concentration of Lp(a) was not significantly different after the soy-protein and self-selected diets. However, Lp(a) decreased by an average of 50% (P < 0.001) after the casein diet as compared with concentrations after both the soy-protein and self-selected diets. Two weeks after subjects switched from the self-selected to the soy-protein diet, Lp(a) increased by 20% (P = 0.065), but subsequently decreased to baseline. In contrast, the switch to the casein diet did not cause an increase in Lp(a), but instead a continuing decrease in mean concentrations to 65% below baseline (P < 0.0002). Total cholesterol, LDL cholesterol, and HDL cholesterol were significantly lower > or =30 d after both the casein and soy-protein diets than after the self-selected diet (P < 0.001). HDL cholesterol was 11% higher after the soy-protein diet than after the casein diet (P < 0.002), but LDL cholesterol, total cholesterol, and triacylglycerol were not significantly different after the casein and soy-protein diets. CONCLUSION: These findings indicate that soy protein may have an Lp(a)-raising effect, potentially detrimental to its use in antiatherogenic diets. (+info)
The adsorption-induced secondary structure of beta-casein and of distinct parts of its sequence in relation to foam and emulsion properties.
Changes in the secondary structure upon adsorption of beta-casein (betaCN) and of distinct parts of its sequence were investigated by far-ultraviolet circular dichroism in order to find suggested relationships with foam and emulsion-forming and -stabilising properties of the same protein/peptides. A teflon/water interface was used as a model system for foam and emulsion interfaces. The maximum surface loads of beta-casein and its derived peptides were investigated. The main secondary structure element of all samples in solution was the unordered random coil, but upon adsorption ordered structure, especially alpha-helix, was induced. At lower pH more ordered structure was induced, just as at lower ionic strength. Apparently, both hydrophobic and hydrophilic groups influence the change of secondary structure induced at a hydrophobic interface. The results suggest that the hydrophobic C-terminal half of betaCN accounted for the high maximum surface load on teflon, while the N-terminal half of betaCN seemed to be responsible for the secondary structure induction upon adsorption. A relation between the maximum surface load and the foam-stabilising properties was found, but an influence of the secondary structure properties on the foam and emulsion-forming and -stabilising properties was not observed. (+info)
Guinea-pig milk-protein synthesis. Isolation and characterization of messenger ribonucleic acids from lactating mammary gland and identification of caseins and pre-alpha-lactalbumin as translation products in heterologous cell-free systems.
1. The major milk proteins synthesized by the lactating mammary gland of the guinea pig were identified and designated as caseins A, B and C and alpha-lactalbumin, with estimated mol.wts. of 28000, 25500, 20500 and 14500 respectively. 2. Antisera to the total casein fraction and to alpha-lactalbumin were prepared from rabbits. The milk proteins were also iodinated with either 131I or 125I. 3. A poly(A)-rich RNA fraction was isolated from lactating guinea-pig mammary glands. Isolation was by affinity chromatography on oligo(dT)-cellulose. 4. Examination of this RNA fraction by electrophoresis on polyacrylamide gels containing formamide indicated three major species 1, 2 and 3, with estimated wol.wts. of 5.4 X 10(5) and 3.3 X 10(5), and the apparent absence of rRNA species. 5. The poly(A)-rich RNA stimulated protein synthesis in heterologous cell-free systems based on wheat germ, Krebs II ascites-tumour cells, and the latter supplemented with an initiation factor-3 fraction from rabbit reticulocyte ribosomes. 6. Between 80 and 90% of the protein synthesis directed by the mRNA was for milk proteins. 7. Analysis of the proteins immunoprecipitated by the alpha-lactalbumin antiserum showed in the wheat-germ system that the product was a protein with a molecular weight greater than that of alpha-lactalbumin, whereas in the ascites-tumour-cell systems both this protein and alpha-lactalbumin were found. When the larger protein was treated with CNBr and the resulting peptides were examined, it was shown that the extra peptide was at the N-terminus. This and other evidence is adduced for the initial translation product of alpha-lactalbumin being a precursor with an addition of about ten amino acids at the N-terminus. 8. Similar analysis of the casein immlnospecific proteins produced under the direction of mRNA indicated that the products had a molecular weight that was apparently a littel smaller than that of the caseins synthesized in vivo. This was not consistent with higher-molecular weight casein precursors. 9. Possible explanations for the results obtained are discussed, especially in terms of the physiological significance of the pre-alpha-lactalbumin as a secretory protein. (+info)
Colchicine inhibition of the first phase of amyloid synthesis in experimental animals.
Colchicine was found to inhibit the first phase of casein-induced synthesis of murine amyloid. When mice were treated with colchicine during the first 7 days of an amyloid induction regimen or when colchicine was given to the donor mice in a transfer model, the amyloidogenic stimulus of casein was blocked completely. Amyloid synthesis was however, not interrupted by the administration of colchicine during the last 7 days of the casein regimen nor by colchicine treatment of recipient mice in a transfer model. (+info)