scholarly journals Plasma protein synthesis by isolated rat hepatocytes.

1977 ◽  
Vol 72 (1) ◽  
pp. 11-25 ◽  
Author(s):  
L J Crane ◽  
D L Miller
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Rat Hepatocytes ◽  
Secretory Protein ◽  
Liver Protein ◽  
Albumin Synthesis ◽  
Isolated Rat Hepatocytes ◽  
General Protein Synthesis ◽  
General Protein ◽  
High Level

A system of preparation of rat hepatocytes with extended viability has been developed to study the role of hormones and other plasma components upon secretory protein synthesis. Hepatocytes maintained in minimal essential medium reduced the levels of all amino acids in the medium except the slowly catabolized amino acids leucine, isoleucine, and valine, which steadily increase as the result of catabolism of liver protein. Although the liver cells catabolize 10-15% of their own protein during a 20-h incubation, the cells continue to secrete protein in a linear fashion throughout the period. The effects of insulin, cortisol, and epinephrine on general protein synthesis, and specifically on fibrinogen and albumin synthesis, have been tested on cells from both normal rats and adrenalectomized rats. Cells from normal animals show preinduction of tyrosine amino transferase (TAT), having at the time of isolation a high level of enzyme which shows only an increase of approximately 60% upon incubation with cortisol. In contrast, cells from adrenalectomized animals initially have a low level of enzyme which increases fourfold over a period of 9 h. The effects of both epinephrine and cortisol on protein synthesis are also much larger in cells from adrenalectomized animals. After a delay of several hours, cortisol increases fibrinogen synthesis sharply, so that at the end of the 20-h incubation, cells treated with hormone have secreted nearly 2.5 times as much fibrinogen as control cells. The effect is specific; cortisol stimulates neither albumin secretion nor intracellular protein synthesis. The combination of cortisol and epinephrine strongly depresses albumin synthesis in both types of cells. Insulin enhances albumin and general protein synthesis but has little effect on fibrinogen synthesis.

Effect of amino acid deprivation on initiation of protein synthesis in rat hepatocytes

1989 ◽  
Vol 256 (1) ◽  
pp. C18-C27 ◽  
Author(s):  
W. V. Everson ◽  
K. E. Flaim ◽  
D. M. Susco ◽  
S. R. Kimball ◽  
L. S. Jefferson
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Rat Hepatocytes ◽  
Initiation Factor ◽  
Synthetic Activity ◽  
Perfused Liver ◽  
Amino Acid Deprivation ◽  
Isolated Rat Hepatocytes ◽  
Reticulocyte Lysate

Conditions were defined for maintaining optimal protein synthetic activity in suspensions of freshly isolated rat hepatocytes. Under these conditions, isolated hepatocytes exhibited rates of protein synthesis and levels of polysomal aggregation equivalent to those observed in vivo and in perfused liver. Deprivation of total amino acids or single, essential amino acids resulted in a rapid decrease in the rate of protein synthesis, which was readily reversed by readdition of the deficient amino acid(s). The decrease was accompanied by a disaggregation of polysomes and an inhibition of 43S initiation complex formation, which was indicative of a limitation in the rate of initiation of protein synthesis. Extracts prepared from perfused liver deprived of amino acids were inhibitory to initiation of protein synthesis in reticulocyte lysate. The inhibition in reticulocyte lysate was accompanied by an increase in phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF-2), suggesting activation of an eIF-2 alpha kinase or inhibition of a phosphatase in amino acid-deprived hepatocytes. This suggestion was confirmed by prelabeling hepatocytes with 32Pi before amino acid deprivation. Incorporation of 32Pi into eIF-2 alpha was two- to threefold higher in lysine-deprived cells than in hepatocytes incubated in fully supplemented medium. Overall, the results indicated that an increase in eIF-2 alpha phosphorylation was responsible for the defect in initiation of protein synthesis caused by amino acid deprivation.

scholarly journals Effects of amino acids, ammonia and leupeptin on protein synthesis and degradation in isolated rat hepatocytes

1978 ◽  
Vol 174 (2) ◽  
pp. 469-474 ◽  
Author(s):  
P O Seglen
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Specific Radioactivity ◽  
Rat Hepatocytes ◽  
Amino Acid Mixture ◽  
Acid Mixture ◽  
Isolated Rat Hepatocytes ◽  
Lysosomal Protein ◽  
Isolated Rat

Protein synthesis in isolated rat hepatocytes, as measured by the incorporation of [14C]-valine at constant specific radioactivity, proceeded at a rate of 0.3-0.5%/h in an unsupplemented medium, i.e. only about one-tenth the rate of protein degradation (4%/h). Leupeptin, which inhibits lysosomal protein degradation (previously found to be 75% of the total degradation in hepatocytes), had no effect on protein synthesis, showing that endogenous protein degradation supplied amino acids in excess of the substrate requirements for protein synthesis. The inhibition of protein synthesis by NH4Cl (another inhibitor of lysosomal protein degradation) as well as the stimulation by a physiological amino acid mixture must therefore represent indirect effects, either on general energy metabolism, or on unknown regulatory processes.

scholarly journals Alterations in albumin secretion and total protein synthesis in livers of thyroidectomized rats

1981 ◽  
Vol 198 (2) ◽  
pp. 289-299 ◽  
Author(s):  
D E Peavy ◽  
J M Taylor ◽  
L S Jefferson
Keyword(s):  
Protein Synthesis ◽  
Total Protein ◽  
Rat Hepatocytes ◽  
Secretory Protein ◽  
Secretory Proteins ◽  
Isolated Rat Hepatocytes ◽  
Transit Times ◽  
Free Translation ◽  
Albumin Mrna

Perfused rat livers and isolated rat hepatocytes exhibited a 50% decrease in the secretion of both albumin and total secretory proteins after thyroidectomy. In contrast, synthesis of non-secretory proteins was decreased by only 20% from the rates observed in liver preparations from euthyroid rats. These observations suggested a disproportionate effect of thyroidectomy on the synthesis of secretory proteins compared with non-secretory proteins. Disproportionate decreases in the synthesis of albumin in other endocrine-deficient states such as hypophysectomy and diabetes had previously been shown to be associated with decreases of similar magnitude in the relative abundance of albumin-mRNA sequences. In contrast, thyroidectomy did not affect the activity or amount of albumin mRNA in total liver poly(A)-containing RNA when assayed by cell-free translation and by hybridization with complementary DNA, respectively. Furthermore, labelling experiments in vivo demonstrated that albumin synthesis represented 12.9 +/- 0.5% and 12.4 +/- 0.4% of total protein synthesis in livers of thyroidectomized and euthyroid rats respectively. Therefore the fall in secretion of albumin and total secretory protein after thyroidectomy did not appear to be a reflection of disproportionate decreases in the synthesis of these proteins. Instead, defects in steps involved in the post-synthetic processing and secretion of albumin are suggested. A number of comparisons, including ribosome half-transit times, the size distributions of total and albumin-synthesizing polyribosomes, and the fraction of RNA present as inactive ribosomes, provided evidence that the overall decrease in protein synthesis after thyroidectomy was not due to generalized alterations in translational processes. Instead, the decrease in total protein synthesis appeared to reflect the RNA content of the liver, which fell in proportion to th decrease in protein synthesis.

scholarly journals Induction of carnitine acetyltransferase by clofibrate in rat liver

1981 ◽  
Vol 194 (1) ◽  
pp. 249-255 ◽  
Author(s):  
B Mittal ◽  
C K R Kurup
Keyword(s):  
Protein Synthesis ◽  
Enzyme Activity ◽  
Rat Liver ◽  
Time Lag ◽  
Mitochondrial Protein ◽  
Carnitine Acetyltransferase ◽  
Enzyme Protein ◽  
General Protein Synthesis ◽  
Liver And Kidney ◽  
General Protein

Administration of the anti-hypercholesterolaemic drug clofibrate to the rat increases the activity of carnitine acetyltransferase (acetyl-CoA-carnitine O-acetyltransferase, EC 2.3.1.7) in liver and kidney. The drug-mediated increase in enzyme activity in hepatic mitochondria shows a time lag during which the activity increases in the microsomal and peroxisomal fractions. The enzyme induced in the particulate fractions is identical with one normally present in mitochondria. The increase in enzyme activity is prevented by inhibitors of RNA and general protein synthesis. Mitochondrial protein-synthetic machinery does not appear to be involved in the process. Immunoprecipitation shows increased concentration of the enzyme protein in hepatic mitochondria isolated from drug-treated animals. In these animals, the rate of synthesis of the enzyme is increased 7-fold.

Effect of hyperinsulinemia and hyperaminoacidemia on muscle and liver protein synthesis in lactating goats

1994 ◽  
Vol 267 (6) ◽  
pp. E877-E885 ◽  
Author(s):  
I. Tauveron ◽  
D. Larbaud ◽  
C. Champredon ◽  
E. Debras ◽  
S. Tesseraud ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Skeletal Muscles ◽  
Constant Infusion ◽  
Acid Mixture ◽  
Liver Protein ◽  
Group I ◽  
Lactating Goats ◽  
Group A

The experiment was carried out to clarify the roles of insulin and amino acids on protein synthesis in fed lactating goats (30 days postpartum). Protein synthesis in the liver and various skeletal muscles was assessed after an intravenous injection of a large dose of unlabeled valine containing a tracer dose of L-[2,3,4-3H]valine. The animals were divided into three groups. Group I was infused with insulin (1.7 mumol/min) for 2.5 h under glucose, potassium, and amino acid replacement. Group A was infused with an amino acid mixture to create stable hyperaminoacidemia for 2.5 h. Group C animals were controls. The fractional synthesis rates (FSR) were 31.5 +/- 2.2, 6.5 +/- 0.4, 4.3 +/- 0.8, 4.0 +/- 1.2, 3.9 +/- 1.2, and 3.6 +/- 0.4%/day (SD) in liver, masseter, diaphragm, anconeus, semitendinosus, and longissimus dorsi, respectively, for group C. Neither hyperinsulinemia in group I nor hyperaminoacidemia in group A had not affected by hyperinsulinemia but was stimulated by hyperaminoacidemia (+30%, P < 0.05). In contrast to previous experiments in which a labeled amino acid was constantly infused, this study revealed a stimulating effect of amino acids on protein synthesis in the liver but not in skeletal muscles. As previously observed in studies with the constant-infusion method, insulin had no effect on protein synthesis.

scholarly journals Bmp Induces Osteoblast Differentiation through both Smad4 and mTORC1 Signaling

2016 ◽  
Vol 37 (4) ◽  
Author(s):  
Courtney M. Karner ◽  
Seung-Yon Lee ◽  
Fanxin Long
Keyword(s):  
Protein Synthesis ◽  
Intracellular Signaling ◽  
Osteoblast Differentiation ◽  
De Novo ◽  
Bmp Signaling ◽  
Endoplasmic Reticulum Stress Response ◽  
Versus Protein ◽  
Mtorc1 Signaling ◽  
General Protein Synthesis ◽  
General Protein

ABSTRACT The bone morphogenetic protein (Bmp) family of secreted molecules has been extensively studied in the context of osteoblast differentiation. However, the intracellular signaling cascades that mediate the osteoblastogenic function of Bmp have not been fully elucidated. By profiling mRNA expression in the bone marrow mesenchymal progenitor cell line ST2, we discover that BMP2 induces not only genes commonly associated with ossification and mineralization but also genes important for general protein synthesis. We define the two groups of genes as mineralization related versus protein anabolism signatures of osteoblasts. Although it induces the expression of several Wnt genes, BMP2 activates the osteogenic program largely independently of de novo Wnt secretion. Remarkably, although Smad4 is necessary for the activation of the mineralization-related genes, it is dispensable for BMP2 to induce the protein anabolism signature, which instead critically depends on the transcription factor Atf4. Upstream of Atf4, BMP2 activates mTORC1 to stimulate protein synthesis, resulting in an endoplasmic reticulum stress response mediated by Perk. Thus, Bmp signaling induces osteoblast differentiation through both Smad4- and mTORC1-dependent mechanisms.

Initiation of protein synthesis in a cell-free system prepared from rat hepatocytes

1989 ◽  
Vol 256 (1) ◽  
pp. C28-C34 ◽  
Author(s):  
S. R. Kimball ◽  
W. V. Everson ◽  
K. E. Flaim ◽  
L. S. Jefferson
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Rat Hepatocytes ◽  
Initiation Factor ◽  
Nucleotide Exchange ◽  
Isolated Rat Hepatocytes ◽  
Intact Cells ◽  
Free System ◽  
Cell Free System ◽  
A Cell

A cell-free system, which maintained a linear rate of protein synthesis for up to 20 min of incubation, was prepared from isolated rat hepatocytes. The rate of protein synthesis in the cell-free system was approximately 20% of the rate obtained in isolated hepatocytes or perfused liver. More than 70% of total protein synthesis in the cell-free system was due to reinitiation, as indicated by addition of inhibitors of initiation, i.e., edeine or polyvinyl sulfate. The rate of protein synthesis and formation of 43S initiation complexes in the cell-free system were reduced to 60 and 30% of the control values, respectively, after incubation of hepatocytes in medium deprived of an essential amino acid. Therefore, the cell-free system maintained the defect in initiation induced in the intact cells by amino acid deprivation. The defect in initiation was corrected by addition of either rat liver eukaryotic initiation factor 2 or the guanine nucleotide exchange factor (GEF) to the cell-free system. A role for GEF in the defect in initiation was further implicated by experiments that showed that the activity of the factor was decreased in extracts from livers perfused with medium deficient in amino acids. The cell-free system should provide a valuable tool for investigation of mechanisms involved in the regulation of initiation of protein synthesis.

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