scholarly journals Effects of starvation, diabetes and acute insulin treatment on the regulation of polypeptide-chain initiation in rat skeletal muscle

1984 ◽  
Vol 223 (3) ◽  
pp. 687-696 ◽  
Author(s):  
C S Harmon ◽  
C G Proud ◽  
V M Pain
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Polypeptide Chain ◽  
Ribosomal Subunit ◽  
Diabetic Rats ◽  
Initiation Factor ◽  
Chain Initiation ◽  
Low Concentrations ◽  
40S Ribosomal Subunit

The rate of protein synthesis in skeletal muscle is greatly decreased in response to diabetes and starvation. Analysis of polyribosome profiles indicates that polypeptide-chain initiation is impaired under these conditions. To identify the step in initiation that is affected, we assayed the incorporation of [35S]methionyl-tRNAfMet into [35S]methionyl-tRNAfMet . 40S-ribosomal-subunit initiation complexes in cell-free extracts based on postmitochondrial supernatants prepared from gastrocnemius muscle. Extracts from either starved or diabetic rats were 30-40% less active in forming these complexes compared with those derived from fed or insulin-maintained controls respectively. This change could be reversed by treatment of either starved or diabetic rats with insulin in vivo 30 min before death. Formation of 40S initiation complexes by extracts from either fed or starved rats could be stimulated by the addition of exogenous purified initiation factor eIF-2, but extracts from starved or diabetic rats were more sensitive than controls to stimulation by low concentrations of the factor. These results provide evidence for the acute regulation by insulin of protein synthesis in skeletal muscle at the level of polypeptide-chain initiation, and suggest that in this tissue, as in certain other eukaryotic systems, control of initiation appears to be mediated by changes in the activity of initiation factor eIF-2.

Regulation of eukaryotic initiation factor-2B activity in muscle of diabetic rats

1993 ◽  
Vol 264 (1) ◽  
pp. E101-E108 ◽  
Author(s):  
A. M. Karinch ◽  
S. R. Kimball ◽  
T. C. Vary ◽  
L. S. Jefferson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Casein Kinase Ii ◽  
Diabetic Rats ◽  
Casein Kinase ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Fast Twitch

Peptide-chain initiation is inhibited in fast-twitch skeletal muscle, but not heart, of diabetic rats. We have investigated mechanisms that might maintain eukaryotic initiation factor (eIF)-2B activity, preventing loss of efficiency of protein synthesis in heart of diabetic rats but not in fast-twitch skeletal muscle. There was no change in the amount or phosphorylation state of eIF-2 in skeletal or cardiac muscle during diabetes. In contrast, eIF-2B activity was decreased in fast-twitch but not slow-twitch muscle from diabetic animals. NADP+ inhibited partially purified eIF-2B in vitro, but addition of equimolar NADPH reversed the inhibition. The NADPH-to-NADP+ ratio was unchanged in fast-twitch muscle after induction of diabetes but was increased in heart of diabetic rats, suggesting that NADPH also prevents inhibition of eIF-2B in vivo. The activity of casein kinase II, which can phosphorylate and activate eIF-2B in vitro, was significantly lower in extracts of fast-twitch, but not cardiac muscle, of diabetic rats compared with controls. The results presented here demonstrate that changes in eIF-2 alpha phosphorylation are not responsible for the effect of diabetes on eIF-2B activity in fast-twitch skeletal muscle. Modulation of casein kinase II activity may be a factor in the regulation of protein synthesis in muscle during acute diabetes. The activity of eIF-2B in heart might be maintained by the increased NADPH/NADP+.

Regulation of protein synthesis after acute resistance exercise in diabetic rats

1999 ◽  
Vol 276 (4) ◽  
pp. E721-E727 ◽  
Author(s):  
Peter A. Farrell ◽  
Mark J. Fedele ◽  
Thomas C. Vary ◽  
Scot R. Kimball ◽  
Charles H. Lang ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Resistance Exercise ◽  
Diabetic Rats ◽  
Initiation Factor ◽  
Moderate Intensity ◽  
Sprague Dawley ◽  
Partial Pancreatectomy ◽  
Igf I ◽  
Arterial Plasma

These studies determined whether insulin-like growth factor-I (IGF-I) involvement in exercise-stimulated anabolic processes becomes more evident during hypoinsulinemia. Male Sprague-Dawley rats ( n = 6–12/group) were made diabetic (blood glucose ≅ 300 mg/dl) by partial pancreatectomy (PPX) or remained nondiabetic (glucose ≅ 144 mg/dl). Rats performed acute resistance exercise by repetitive standing on the hindlimbs with weighted backpacks (ex), or they remained sedentary (sed). Resistance exercise caused increases in rates of protein synthesis (nmol Phe incorporated ⋅ g muscle−1 ⋅ h−1, measured for gastrocnemius muscle in vivo 16 h after exercise) for both nondiabetic [sed = 154 ± 6 (SE) vs. ex = 189 ± 7] and diabetic rats (PPXsed = 152 ± 11 vs. PPXex = 202 ± 14, P < 0.05). Arterial plasma insulin concentrations in diabetic rats, ≅180 pM, were less than one-half those found in nondiabetic rats, ≅444 pM, ( P < 0.05). The activity of eukaryotic initiation factor 2B (eIF2B; pmol GDP exchanged/min) was higher ( P < 0.05) in ex rats (sed = 0.028 ± 0.006 vs. ex = 0.053 ± 0.015; PPXsed = 0.033 ± 0.013 vs. PPXex = 0.047 ± 0.009) regardless of diabetic status. Plasma IGF-I concentrations were higher in ex compared with sed diabetic rats ( P < 0.05). In contrast, plasma IGF-I was not different in nondiabetic ex or sed rats. Muscle IGF-I (ng/g wet wt) was similar in ex and sed nondiabetic rats, but in diabetic rats was 2- to 3-fold higher in ex ( P < 0.05) than in sed rats. In conclusion, moderate hypoinsulinemia that is sufficient to alter glucose homeostasis does not inhibit an increase in rates of protein synthesis after acute moderate-intensity resistance exercise. This preserved response may be due to a compensatory increase in muscle IGF-I content and a maintained ability to activate eIF2B.

Complex of 40S Ribosomal Subunit with Initiation Factor eIF-3

1982 ◽  
Vol 40 ◽  
pp. 162-163
Author(s):  
M. Boublik ◽  
W. Hellmann ◽  
F. Jenkins ◽  
T. Staehelin ◽  
H. Trachsel
Keyword(s):  
Polypeptide Chain ◽  
Ribosomal Subunit ◽  
High Resolution Electron Microscopy ◽  
Initiation Factor ◽  
40S Ribosomal Subunit ◽  
Resolution Electron ◽  
Intracellular Organelles ◽  
Protein Synthesis Initiation ◽  
Function Relationship ◽  
Relationship Of

Ribosomes are intracellular organelles present in all organisms as an integral part of their protein-synthesizing system. Biochemical evidence suggests that ribosomes are engaged in all phases of protein synthesis - initiation, elongation, and termination of a polypeptide chain. However, the mechanism of ribosomal involvement in any of these steps has yet to be established. At present, the most direct approach to the studies of structure-function relationship of ribosomes is by high resolution electron microscopy.

Acute attenuation of translation initiation and protein synthesis by glucocorticoids in skeletal muscle

2000 ◽  
Vol 278 (1) ◽  
pp. E76-E82 ◽  
Author(s):  
O. Jameel Shah ◽  
Scot R. Kimball ◽  
Leonard S. Jefferson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Intraperitoneal Administration ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Nucleotide Exchange ◽  
Α Subunit ◽  
Initiation Factors

Glucocorticoids are diabetogenic factors that not only antagonize the action of insulin in target tissues but also render these tissues catabolic. Therefore, in rats, we endeavored to characterize the effects in skeletal muscle of glucocorticoids on translation initiation, a regulated process that, in part, governs overall protein synthesis through the modulated activities of eukaryotic initiation factors (eIFs). Four hours after intraperitoneal administration of dexamethasone (100 μg/100 g body wt), protein synthesis in skeletal muscle was reduced to 59% of the value recorded in untreated control animals. Furthermore, translation initiation factor eIF4E preferred association with its endogenous inhibitor 4E-BP1 rather than eIF4G. Dexamethasone treatment resulted in dephosphorylation of both 4E-BP1 and the 40S ribosomal protein S6 kinase concomitant with enhanced phosphorylation of eIF4E. Moreover, the guanine nucleotide exchange activity of eIF2B was unaffected as was phosphorylation of the α-subunit of eIF2. Hence glucocorticoids negatively modulate the activation of a subset of the protein synthetic machinery, thereby contributing to the catabolic properties of this class of hormones in vivo.

Phosphorylation of eukaryotic initiation factor eIF2Bε in skeletal muscle during sepsis

2002 ◽  
Vol 283 (5) ◽  
pp. E1032-E1039 ◽  
Author(s):  
Thomas C. Vary ◽  
Gina Deiter ◽  
Scot R. Kimball
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Glycogen Synthase ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Sterile Inflammation ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Skeletal Muscle Protein

We reported that the inhibition of protein synthesis in skeletal muscle during sepsis correlated with reduced eukaryotic initiation factor eIF2B activity. The present studies define changes in eIF2Bε phosphorylation in gastrocnemius of septic animals. eIF2B kinase activity was significantly elevated 175% by sepsis compared with sterile inflammation, whereas eIF2B phosphatase activity was unaffected. Phosphorylation of eIF2Bε-Ser535 was significantly augmented over 2-fold and 2.5-fold after 3 and 5 days and returned to control values after 10 days of sepsis. Phosphorylation of glycogen synthase kinase-3 (GSK-3), a potential upstream kinase responsible for the elevated phosphorylation of eIF2Bε, was significantly reduced over 36 and 41% after 3 and 5 days and returned to control values after 10 days of sepsis. The phosphorylation of PKB, a kinase thought to directly phosphorylate and inactivate GSK-3, was significantly reduced ∼50% on day 3, but not on days 5 or 10, postinfection compared with controls. Treatment of septic rats with TNF-binding protein prevented the sepsis-induced changes in eIF2Bε and GSK-3 phosphorylation, implicating TNF in mediating the effects of sepsis. Thus increased phosphorylation of eIF2Bε via activation of GSK-3 is an important mechanism to account for the inhibition of skeletal muscle protein synthesis during sepsis. Furthermore, the study presents the first demonstration of changes in eIF2Bε phosphorylation in vivo.

Aminoacylation of initiator methionyl-tRNA(i) under conditions inhibitory to initiation of protein synthesis

1993 ◽  
Vol 264 (2) ◽  
pp. E257-E263 ◽  
Author(s):  
K. M. Ojamaa ◽  
S. R. Kimball ◽  
L. S. Jefferson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Rat Liver ◽  
Diabetic Rats ◽  
Peptide Chain ◽  
Perfused Rat Liver ◽  
Chain Initiation ◽  
Total Rna ◽  
Tissue Content ◽  
Total Tissue

Inhibition of protein synthesis in perfused rat liver deprived of either methionine or tryptophan results from a defect in peptide-chain initiation. Similarly, the decreased rate of protein synthesis in liver from rats deprived of food for 24 h and in skeletal muscle after 2 days of diabetes results from a defect in initiation. In the present study, the tissue content of tRNA(iMet) and its level of aminoacylation were measured in these conditions to determine whether methionyl-tRNA(iMet) formation is a mechanism involved in the regulation of initiation. The extent of aminoacylation of tRNA(iMet) in livers perfused with supplemented medium or medium deficient in either methionine or tryptophan was 64 +/- 2, 61 +/- 3, and 66 +/- 2% of the total accepting activity, respectively. The total tissue content of tRNA(iMet), expressed as a percentage of total RNA, was 1.7 +/- 0.1, 1.6 +/- 0.1, and 1.6 +/- 0.1 for the three conditions, respectively. In livers from starved rats, the extent of aminoacylation of tRNA(iMet) was 80 +/- 7% and the total tissue content of tRNA(iMet) was 1.9 +/- 0.1% compared with control values of 82 +/- 6 and 2.0 +/- 0.1%, respectively. In skeletal muscle from diabetic rats, the extent of aminoacylation of tRNA(iMet) was 79 +/- 4% and the total tissue content of tRNA(iMet) was 2.0 +/- 0.3% compared with values of 79 +/- 5 and 2.0 +/- 0.2% for control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Binding and translation of turnip-yellow-mosaic-virus ribonucleic acid by skeletal-muscle ribosomes from normal and diabetic rats

1970 ◽  
Vol 117 (5) ◽  
pp. 899-905 ◽  
Author(s):  
F. S. Rolleston ◽  
I. G. Wool ◽  
T. E. Martin
Keyword(s):  
Skeletal Muscle ◽  
Mosaic Virus ◽  
Equilibrium Constants ◽  
Ribosomal Subunit ◽  
Diabetic Rats ◽  
Yellow Mosaic Virus ◽  
Turnip Yellow Mosaic Virus ◽  
Binding Reaction ◽  
Virus Rna ◽  
40S Ribosomal Subunit

Ribosomes from skeletal muscle of diabetic rats were less active than normal ribosomes in protein synthesis directed by turnip-yellow-mosaic-virus RNA. The proportion of ribosomes from muscle of diabetic rats capable of binding turnip-yellow-mosaic-virus RNA was greater than normal, but there was no difference in the equilibrium constants for the binding reaction. The turnip-yellow-mosaic-virus RNA was bound preferentially to the small (40S) ribosomal subunit, whereas the decrease due to diabetes in its translation was associated with the large (60S) subunit. Thus the diminished capacity of ribosomes from muscle of diabetic rats to translate turnip-yellow-mosaic-virus RNA was not the result of decreased binding of the template.

Sign in / Sign up

Export Citation Format

Share Document