Myocardial ischemia and increased heart work modulate the phosphorylation state of eukaryotic elongation factor-2.
Protein synthesis, in particular peptide chain elongation, is an energy-consuming biosynthetic process. AMP-activated protein kinase (AMPK) is a key regulatory enzyme involved in cellular energy homeostasis. Therefore, we tested the hypothesis that, as in liver, it could mediate the inhibition of protein synthesis by oxygen deprivation in heart by modulating the phosphorylation of eukaryotic elongation factor-2 (eEF2), which becomes inactive in its phosphorylated form. In anoxic cardiomyocytes, AMPK activation was associated with an inhibition of protein synthesis and an increase in phosphorylation of eEF2. Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), did not mimic the effect of oxygen deprivation to inhibit protein synthesis in cardiomyocytes or lead to eEF2 phosphorylation in perfused hearts, suggesting that AMPK activation did not inhibit mTOR/p70 ribosomal protein S6 kinase (p70S6K) signaling. Human recombinant eEF2 kinase (eEF2K) was phosphorylated by AMPK in a time- and AMP-dependent fashion, and phosphorylation led to eEF2K activation, similar to that observed in extracts from ischemic hearts. In contrast, increasing the workload resulted in a dephosphorylation of eEF2, which was rapamycin-insensitive, thus excluding a role for mTOR in this effect. eEF2K activity was unchanged by increasing the workload, suggesting that the decrease in eEF2 phosphorylation could result from the activation of an eEF2 phosphatase.
Horman
Sandrine
S
Hormone and Metabolic Research Unit, Christian de Duve Institute of Cellular Pathology, University of Louvain Medical School, Avenue Hippocrate 75, ICP-UCL 7529, B-1200 Brussels, Belgium.
Beauloye
Christophe
C
Vertommen
Didier
D
Vanoverschelde
Jean-Louis
JL
Hue
Louis
L
Rider
Mark H
MH
D055372:AMP-Activated Protein Kinases; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D054736:Elongation Factor 2 Kinase; D006334:Heart Function Tests; D000860:Hypoxia / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009097:Multienzyme Complexes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D017202:Myocardial Ischemia / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects; D010100:Oxygen / Q000494:pharmacology; D020652:Peptide Elongation Factor 2 / Q000378:metabolism*; D010477:Perfusion; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D058570:TOR Serine-Threonine Kinases
D009097:Multienzyme Complexes; D020652:Peptide Elongation Factor 2; D011494:Protein Kinases; C546842:MTOR protein, human; C546845:mTOR protein, rat; C517689:EEF2K protein, human; C517691:Eef2k protein, rat; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D054736:Elongation Factor 2 Kinase; D055372:AMP-Activated Protein Kinases; D010100:Oxygen