Activation of AMP-activated protein kinase leads to the phosphorylation of elongation factor 2 and an inhibition of protein synthesis.
Protein synthesis, in particular peptide-chain elongation, consumes cellular energy. Anoxia activates AMP-activated protein kinase (AMPK, see ), resulting in the inhibition of biosynthetic pathways to conserve ATP. In anoxic rat hepatocytes or in hepatocytes treated with 5-aminoimidazole-4-carboxamide (AICA) riboside, AMPK was activated and protein synthesis was inhibited. The inhibition of protein synthesis could not be explained by changes in the phosphorylation states of initiation factor 4E binding protein-1 (4E-BP1) or eukaryotic initiation factor 2alpha (eIF2alpha). However, the phosphorylation state of eukaryotic elongation factor 2 (eEF2) was increased in anoxic and AICA riboside-treated hepatocytes and in AICA riboside-treated CHO-K1 cells, and eEF2 phosphorylation is known to inhibit its activity. Incubation of CHO-K1 cells with increasing concentrations of 2-deoxyglucose suggested that the mammalian target of the rapamycin (mTOR) signaling pathway did not play a major role in controlling the level of eEF2 phosphorylation in response to mild ATP depletion. In HEK293 cells, transfection of a dominant-negative AMPK construct abolished the oligomycin-induced inhibition of protein synthesis and eEF2 phosphorylation. Lastly, eEF2 kinase, the kinase that phosphorylates eEF2, was activated in anoxic or AICA riboside-treated hepatocytes. Therefore, the activation of eEF2 kinase by AMPK, resulting in the phosphorylation and inactivation of eEF2, provides a novel mechanism for the inhibition of protein synthesis.
Horman
Sandrine
S
Hormone and Metabolic Research Unit, Christian de Duve International Institute of Cellular Pathology and Université Catholique de Louvain, Avenue Hippocrate, 75, B-1200, Brussels, Belgium.
Browne
Gareth
G
Krause
Ulrike
U
Patel
Jigna
J
Vertommen
Didier
D
Bertrand
Luc
L
Lavoinne
Alain
A
Hue
Louis
L
Proud
Christopher
C
Rider
Mark
M
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D015687:Cell Hypoxia; D002460:Cell Line; D003847:Deoxyglucose / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000502:physiology; D006801:Humans; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D009840:Oligomycins / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010441:Peptide Chain Elongation, Translational; D020652:Peptide Elongation Factor 2 / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012263:Ribonucleosides / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases
D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009840:Oligomycins; D020652:Peptide Elongation Factor 2; D012263:Ribonucleosides; D000620:Aminoimidazole Carboxamide; C011651:acadesine; D003847:Deoxyglucose; D011494:Protein Kinases; C546842:MTOR protein, human; C546845:mTOR protein, rat; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D010100:Oxygen