Effects of contraction and insulin on protein synthesis, AMP-activated protein kinase and phosphorylation state of translation factors in rat skeletal muscle.
In rat epitrochlearis skeletal muscle, contraction inhibited the basal and insulin-stimulated rates of protein synthesis by 75 and 70%, respectively, while increasing adenosine monophosphate-activated protein kinase (AMPK) activity. Insulin, on the other hand, stimulated protein synthesis (by 30%) and increased p70 ribosomal protein S6 kinase (p70S6K) Thr389, 40S ribosomal protein S6 (rpS6) Ser235/236, rpS6 Ser240/244 and eukaryotic initiation factor-4E-binding protein-1 (4E-BP1) Thr37/46 phosphorylation over basal values. Electrical stimulation had no effect on mammalian target of rapamycin complex 1 (mTORC1) signalling, as reflected by the lack of reduction in basal levels of p70S6K, rpS6 Ser235/236, rpS6 Ser240/244 and 4E-BP1 phosphorylation, but did antagonize mTORC1 signalling after stimulation of the pathway by insulin. Eukaryotic elongation factor-2 (eEF2) Thr56 phosphorylation increased rapidly on electrical stimulation reaching a maximum at 1 min, whereas AMPK Thr172 phosphorylation slowly increased to reach threefold after 30 min. Eukaryotic elongation factor-2 kinase (eEF2K) was not activated after 30 min of contraction when AMPK was activated. This could not be explained by the expression of a tissue-specific isoform of eEF2K in skeletal muscle lacking the Ser398 AMPK phosphorylation site. Therefore, in this skeletal muscle system, the contraction-induced inhibition of protein synthesis could not be attributed to a reduction in mTORC1 signalling but could be due to an increase in eEF2 phosphorylation independent of AMPK activation.
Miranda
Lisa
L
Hormone and Metabolic Research Unit, de Duve Institute, Université catholique de Louvain, Avenue Hippocrate, 75, 1200 Brussels, Belgium.
Horman
Sandrine
S
De Potter
Isabelle
I
Hue
Louis
L
Jensen
Jørgen
J
Rider
Mark H
MH
D055372:AMP-Activated Protein Kinases; D000818:Animals; D015153:Blotting, Western; D004558:Electric Stimulation; D039642:Eukaryotic Initiation Factors / Q000502:physiology*; D005091:Exons / Q000235:genetics; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009097:Multienzyme Complexes / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology
C519510:Crtc1 protein, rat; D039642:Eukaryotic Initiation Factors; D007004:Hypoglycemic Agents; D007328:Insulin; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D014157:Transcription Factors; D012313:RNA; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D055372:AMP-Activated Protein Kinases