Effects of contraction and insulin on protein synthesis, AMP-activated protein kinase and phosphorylation state of translation factors in rat skeletal muscle

Pflugers Arch. 2008 Mar;455(6):1129-40. doi: 10.1007/s00424-007-0368-2. Epub 2007 Oct 24.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases
  • Animals
  • Blotting, Western
  • Electric Stimulation
  • Eukaryotic Initiation Factors / physiology*
  • Exons / genetics
  • Hypoglycemic Agents / pharmacology*
  • Insulin / pharmacology*
  • Male
  • Multienzyme Complexes / physiology*
  • Muscle Contraction / physiology*
  • Muscle Proteins / biosynthesis*
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / physiology*
  • Phosphorylation
  • Protein Biosynthesis / physiology
  • Protein Serine-Threonine Kinases / physiology*
  • RNA / biosynthesis
  • RNA / genetics
  • Rats
  • Rats, Wistar
  • Receptor Cross-Talk / drug effects
  • Receptor Cross-Talk / physiology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Transcription Factors / physiology

Substances

  • Crtc1 protein, rat
  • Eukaryotic Initiation Factors
  • Hypoglycemic Agents
  • Insulin
  • Multienzyme Complexes
  • Muscle Proteins
  • Transcription Factors
  • RNA
  • Protein Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases, 70-kDa
  • AMP-Activated Protein Kinases