TNF-alpha increases protein content in C2C12 and primary myotubes by enhancing protein translation via the TNF-R1, PI3K, and MEK

Am J Physiol Endocrinol Metab. 2008 Feb;294(2):E241-50. doi: 10.1152/ajpendo.00129.2007. Epub 2007 Oct 30.


Recent evidence supports that TNF-alpha, long considered a catabolic factor, may also have a physiological function in skeletal muscle. The catabolic view, mainly based on correlative studies in human and in vivo animal models, was challenged by experiments with myoblasts, in which TNF-alpha induced differentiation. The biological effects of TNF-alpha in differentiated muscle, however, remain poorly understood. In the present study, we tested whether TNF-alpha has growth-promoting effects in myotubes, and we characterized the mechanisms leading to these effects. Treatment of C(2)C(12) myotubes with TNF-alpha for 24 h increased protein synthesis (PS) and enhanced cellular dehydrogenase activity by 22 and 26%, respectively, without changing cell numbers. These effects were confirmed in myotubes differentiated from primary rat myoblasts. TNF-alpha activated two signaling cascades: 1) ERK1/2 and its target eIF4E and 2) Akt and its downstream effectors GSK-3, p70(S6K), and 4E-BP1. TNF-alpha-induced phosphorylation of Akt, and ERK1/2 was inhibited by an antibody against TNF-alpha receptor 1 (TNF-R1). PD-98059 pretreatment abolished TNF-alpha-induced phosphorylation of ERK1/2 and eIF4E, whereas PS was only partially inhibited. LY-294002 completely abolished TNF-alpha-induced stimulation of PS as well as phosphorylation of Akt and its downstream targets GSK-3, p70(S6K), and 4E-BP1. Rapamycin inhibited TNF-alpha-induced phosphorylation of the mTOR C1 target p70(S6K) without altering TNF-alpha-induced PS and 4E-BP1 phosphorylation. In conclusion, our results provide evidence that TNF-alpha enhances PS in myotubes and that this is based on enhanced protein translation mediated by the TNF-R1 and PI3K-Akt and MEK-ERK signaling cascades.

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Line
  • Cell Survival / drug effects
  • Mice
  • Mitochondria, Muscle / drug effects
  • Mitochondria, Muscle / enzymology
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / physiology*
  • Muscle Fibers, Skeletal / drug effects
  • Muscle Fibers, Skeletal / metabolism*
  • Muscle Proteins / biosynthesis*
  • Oncogene Protein v-akt / metabolism
  • Oxidoreductases / metabolism
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / physiology*
  • Phosphorylation
  • Protein Biosynthesis / drug effects
  • Receptors, Tumor Necrosis Factor, Type I / genetics
  • Receptors, Tumor Necrosis Factor, Type I / physiology*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / drug effects
  • Tumor Necrosis Factor-alpha / pharmacology*


  • Muscle Proteins
  • Receptors, Tumor Necrosis Factor, Type I
  • Tumor Necrosis Factor-alpha
  • Oxidoreductases
  • Phosphatidylinositol 3-Kinases
  • Oncogene Protein v-akt
  • Mitogen-Activated Protein Kinases