Regulation of protein-synthesis elongation-factor-2 kinase by cAMP in adipocytes.
Treatment of primary rat epididymal adipocytes or 3T3-L1 adipocytes with various agents which increase cAMP led to the phosphorylation of eukaryotic translation elongation factor-2 (eEF-2). The increase in eEF-2 phosphorylation was a consequence of the activation of eEF-2 kinase (eEF-2K), which is a Ca2+/calmodulin-dependent kinase. eEF-2K was shown to be essentially inactive at less than 0.1 microM free Ca2+ when measured in cell-free extracts. Treatment of adipocytes with isoproterenol induced Ca2+-independent eEF-2K activity, and an 8-10-fold activation of eEF-2K was observed at Ca2+ concentrations of less than 0.1 microM. Increased cAMP in 3T3-L1 adipocytes led to the inhibition of total protein synthesis and decreased the rate of polypeptide-chain elongation. We also show that the phosphorylation of eEF-2 and the activity of eEF-2K are insulin-regulated in adipocytes. These results demonstrate a novel mechanism for the control of protein synthesis by hormones which act by increasing cytoplasmic cAMP.
Diggle
T A
TA
Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, U.K. tad3@le.ac.uk
Redpath
N T
NT
Heesom
K J
KJ
Denton
R M
RM
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D054736:Elongation Factor 2 Kinase; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D010441:Peptide Chain Elongation, Translational; D010766:Phosphorylation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
D007328:Insulin; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D000242:Cyclic AMP; C517691:Eef2k protein, rat; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517690:Eef2k protein, mouse; D054736:Elongation Factor 2 Kinase; D002118:Calcium